Additive Manufacturing in Construction (AMC)

This is the Website of the Collaborativ Research Centre CRC / TRR 277 'Additive Manufacturing in Construction' - Welcome!  

https://amc-trr277.de

- PLEASE VISIT OUR NEW WEBSITE -

Current state of research

During intensive testing, optimizing potentials of GRES have been identified to improve the system, to be robust and reliable. Therefore, all zones without material movement (dead zones) have been flagged and are being iteratively removed by adding plastic 3D printed dead zone blockers. Furthermore, a new compression section has been designed to smoothen layer deposition, eliminate dead zones, and enhance print quality (see Fig. 2).

This newly designed section consists of multiple adjustable angled paddles that prevent material to build up inside the compression compartment. To prevent material buildup in the previous conveying section, the top paddles of the compression screw reach into the conveying section to actively extract material. In the sense of basic research, the screw and its housing are exchangeable to optimize the deposition quality via optimized screw geometry.

After analyzing the precision of the volumetric dosing unit, and foreseeing problems concerning consistent material quality by unprecise dosing of the solid, dry materials this system is being substituted. Therefor a gravimetric dosing unit is currently being tested to reach the required metering accuracy of < 1.5%.

With ongoing tests together with working group Gehlen (A03-1) at the AMC Lab in Freising we are actively validating abovementioned optimizations as solutions for the upcoming second prototype (see Fig. 3). This second iteration will be focusing not only on enhancing reliability and automation but also on lightweight construction and compatibility with a portal system to print larger scale elements than possible with the current industrial robot.

Current state of research

The above mentioned surface modification techniques gave promising results, regarding the packing density, the flowability ffC, measured with a ring shear tester as seen in Figure 2, and the compressive strength. To better understand the reasons leading to these improvements, experiments are carried out, taking a deeper look onto the surface properties of the modified powders, e.g. inverse gas chromatography is used to measure the surface energy of the powder. This should give hints on the adhesive forces between single particles.

Furthermore, additional research is needed to investigate, if the higher strength of printed specimen is caused by the higher packing density alone, since other aspects like the hydration of the cement could be a reason for this observation, too.

Current state of research

In addition to the effects on the resulting strand geometry and the buildability of the applied layers, the rheological fresh concrete properties also play an essential role in the integration of reinforcement elements. In contrast to a conventional production of reinforced elements in molds, 3D-printed concrete is not externally compacted after production. Thus, the bond quality to integrated reinforcement elements depends significantly on the rheological fresh concrete properties. For the reinforcement strategy of "interlayer reinforcement bars", where reinforcement bars are placed in the interfaces between deposited layers, Freund & Lowke (2022)1 found that an increasing yield stress of the applied material is accompanied by an increase of voids around the integrated rebars. Here, a direct correlation to the resulting mechanical bond strength was found. Freund & Lowke (2022) systematically increased the yield stress of the applied concrete by adding setaccelerator. The yield stress was determined in-situ using a shotcrete penetrometer, see Figure 2a. The void content could be determined by computed tomography, see Figure 2b. Figure 2c shows the relationship between yield stress and the determined void content in the surroundings of the integrated rebar.

Current state of research

The AM extrusion process combined with lightweight concrete can produce mono-material and multi- functional elements with high thermal performance and low resource consumption. So far, a prototypical wall element with an internal closed cellular structure was designed and manufactured using a simulation- based parametric design process. The theoretical and actual thermal performance of the wall element were evaluated through an analytical approach, 2D and 3D heat flux simulations (see Fig 2), as well as experimental heat flux measurements. 

As a next step, a "breathing murocaust wall" with a further improved effective U-value is being developed. To achieve this, heating and cooling loads are shifted in an integrated closed air channel system using pumping effects driven by thermal buoyancy and controlled by smart thermo-responsive flaps.

Current state of research

In the combined SPI+WAAM process, the main part of the reinforcements produced with WAAM will be encased in concrete. Therefore, a directed and precise cooling of the reinforcing bars is necessary. A robot- guided cooling system is being developed for this purpose while different cooling strategies are compared. One of these cooling strategies is spray water cooling. The experimental setup of a preliminary experiment is shown in Figure 2.

As depicted in Figure 1, truss structures include joining and branching nodes. For the accurate and collision- free manufacturing of these geometric features, special strategies are developed. To avoid collisions between the welding torch and the manufactured structure the ctwd is increased in the area of the nodes. Also, the order of deposition is varied for branching nodes in a specific manner, since the electric arc can be deflected when deposition points are spatially close to each other. This leads to shape deviations if no countermeasures are taken.

A collaboration within the AMC was initiated to look into topology-optimised reinforced concrete structures. The optimised structures may significantly increase the potential for the Additive Manufacturing of reinforced concrete.

AMC Tour First Take - Munich in February

In mid-February, the AMC office had the chance to meet with some of the subprojects based at the TU Munich. Anne Niemann, Jeldrik Mainka and Meike Bährens took the opportunity, away from a formal conference and the time constraints of other meetings, to take a closer look at various projects from Focus Area A and subproject B05 from Focus Area B and to engage in scientific dialogue with the researchers. The office would like to thank all participants for the exciting insights, the smooth organization and the extremely interesting discussions. For a brief overview of the visited subprojects and their research, please see the photo gallery

Principles of Mobile Robotics for Additive Manufacturing in Construction

01.03.2022

Dielemans, Gido; Doctoral researcher,
Technical University of Munich,
Department of Architecture, TT Professorship Digital Fabrication

This research examines the architectural implications of mobile robotics for AM in construction and develops methods for their implementation. The material deposition method of clay and concrete extrusion 3D printing is used to investigate mobile part-based AM strategies, that is, to produce large objects whose size exceeds the static workspace of the robot. By implementing advanced sensor and control solutions, autonomous localization and precise manipulation techniques for mobile AM are explored. In addition, this research aims to provide scalability to AM processes by examining the use of multiple robots to collaborate on single fabrication jobs. The objective of this research is to develop mobile AM technology for its direct implementation on construction sites.

Summary

Two medium scale mobile platforms have been designed and constructed to be capable of omnidirectional ground-based movement using four steerable wheels. The platforms are equipped with a vertical linear axis, on top of which a 6DOF robotic manipulator with a range of 1.3 meters and a payload of 10kg is mounted. For initial case studies, the mobile manipulators are equipped with a clay extrusion 3D printing system, in which a clay cartridge is mounted on the 3rd link of the robot arm and connected to the extruder system mounted as an end effector via a hose. The current setup allows for material extrusion heights of 2.5m (Fig. 1).

For localization and positioning, these mobile systems rely on onboard sensors, where the localization is performed using a two tier strategy. First, global localization is performed through SLAM using a front mounted 3d LiDAR, which provides an accuracy of ±5cm for the pose of the mobile system in the work environment. This degree of accuracy does not suffice for extrusion tasks with a nozzle size of 7mm, and therefore a second tier of localization is adopted. For this, the end-effector is equipped with a 2D profile scanner that can capture the printed geometry and locate the robot in reference to the work piece.

This two tier sensing and part-based fabrication is being explored in a case study for 3d printed clay formworks for1:1 large scale concrete building components, using a mobile robotic system and a print-drive-print approach.

Current state of research

The current project status is researching the additive manufacturing of building components on a 1:1 scale with mobile robot systems using clay extrusion 3D printing. In the experiments currently being conducted, the clay serves as a formwork for the casting of a lightweight concrete, where the clay defines the shape while the concrete applies shape stability and structural properties to the building component (Fig, 2). As the clay and the concrete do not adhere, the clay can be easily removed from the concrete after hardening and reused for a new formwork.

Testing and validating the capabilities of the mobile platform in a print-drive-print approach, clay formworks are constructed in segmented parts from multiple robot locations. This requires a geometry to be segmented into parts that consider physical constraints such as end-effector collisions and the robotic manipulator range, as well as material constraints such as build-up rates and strength evolution over time.

A design-to-fabrication environment has been set up, allowing bi-directional communication with all components of the mobile robot systems and thus to control the manufacturing process directly from the architectural planning software. Manufacturing the formwork from multiple locations requires accurate localization of the robot system in relation to the building component. Within this initial case study, the two-tier localization and positioning system using on-board sensors is being evaluated to ensure accurate mobile manufacturing performance.

Structural Timber by Individual Layer Fabrication (ILF)

04.02.2022

Buschmann, Birger; Doctoral researcher
Technical University of Munich, 
Chair of Timber Structures and Building Construction

The main goal of the project ‘A08 -Structural Timber by Individual Layer Fabrication (ILF)’ is to develop a process to additively manufacture large-scale, wood composite objects with a maximum content of wood material and strength values suited for applications in construction. In the course of the project multiple process variants and material combinations are explored. For this, the necessary machinery is developed in iterative steps and the mechanical properties of the resulting objects as well as the geometric capacity of the processes are investigated. Finally, multiple demonstrators are fabricated for showcase purposes.

Summary

Within A08 the working group Henke is researching the ILF method as a whole and developing a working process chain together with the necessary machinery. The general scheme of the ILF process is displayed in Figure 2 and can be divided into four main steps. A thin layer of wood particles is scattered (a) and bound by selectively dispensing adhesive according to the target geometry of the object (b). After dispensing the adhesive, the wood particle layer is pressed (c). In doing so, the amount of required adhesive is drastically reduced while at the same time the mechanical properties of the wood composite are increased. Finally, the unbound material is removed and the contoured layer of bound material is laminated onto the stack of previously produced layers (d).

For each of these process steps the respective machinery is either developed or acquired and modified if necessary. Sometimes machines from different fields of technology can be adapted to suit the needs of the ILF process. For example, a valve, developed originally for the electronics industry, can be used to very precisely dispense the adhesive in a desired pattern.

With the Manufacturing of various demonstrators (see e.g. Fig 1) knowledge is gained about the intricacies of the ILF process and its practical application. A suitable process parameter framework, geometric limitations and possible improvements are identified.

Current state of research

A first set of design rules, describing which geometries are feasible with the ILF process, was formulated. However, the process is currently still under development. Thus, adaptions will have to be made in the future.

Concerning the last process step (Fig. 2, d), multiple ideas were collected and a manual workflow was created. In the next months a final concept for automating this step will have to be decided upon and the required machinery developed.

Process steps one to three (Fig. 2., a to c) were investigated in depth. The respective machinery was built and multiple materials were tested with promising results. Currently, the next generation of devices for these process steps is being built as part of an integrated process chain. When completed, this new layer printer will enable the fully automatic production of individually contoured layers.

Integration of Additive Manufacturing in the Construction Process

11.02.2022

Placzek, Gerrit; Doctoral researcher
TU Braunschweig, IBB

The integration of additive manufacturing into construction requires an interdisciplinary approach. The different competences of the team - digital fabrication in architecture (Hack), geodesy and photogrammetry (Gerke) and construction management (Schwerdtner) - lead to a research from diverse perspectives on the various scalar levels of construction to be viewed holistically: component, building and industry Scale.

Within Subproject C06, our goal is to create a continuous digital and lean-based process chain from design (using BIM method) to fabrication (using AM method). Based on process models, we develop production systems for the construction industry 4.0.

Summary

Currently, one of the most followed approaches is to produce walls replacing masonry for in-situ constructed single-storey houses (either with straight extruded geometries or with slightly curved freeform). By simply replacing conventional technologies the potential of additive manufacturing will not be fully exploited. Concepts and strategies have to be developed and discussed considering its applicability for individual construction projects. The correspondent research questions address fundamental aspects in the field of construction operations and of project delivery systems in the construction industry. Therefore, it is one of the goals of subproject C06 to analyse different AM methods on a component level in order to develop an adequate value chain on a building scale and evaluate future implications on an industry scale.

Two concepts are predominant in current research “in-situ” and “off-site” production. However, the high procedural flexibility of AM offers a third option: “on-site” production. This concept corresponds to stationary (pre-)manufacturing of components on the construction site.

In order to determine the right concept more knowledge is necessary to create a future value chain. Shotcrete 3D Printing is one AM method that is currently used for off-site production. In our research, we use it as an example to investigate parameters like processing and lead times, material or resource consumptions.

Current state of research

As we pointed out earlier, from a construction management point of view, the role of additive manufacturing methods is still unclear when it comes to the “right” use cases within construction (e. g. house building, bridges or tunnels).

To address this uncertainty, we firstly analysed automated and robotics systems (ARS) used for extrusion-based concrete additive manufacturing as a part of a construction process planning. We identified four main categories (flexibility, mobility, productivity and environment) that could be decision criteria for an appropriate production system. Next, we will try to quantify those criteria by defining relevant parameters for a future comparative analysis.

Secondly, based on the achieved results regarding the investigation of ARS and initially classified production concepts in-situ, on-site and off-site (see previous RSR), we now develop potential production strategies. For example, production strategies within the production concept in-situ vary between “whole structure printing” (using a gantry-system) and “section-by-section printing” (using a smaller robot; fig. 1). Hybrid solutions might be adequate as well depending on the described criteria. Those terms and production strategies are currently under discussion.

Wire and Arc Additive Manufacturing (WAAM) of complex individualized steel components

04.02.2022

Müller, Johanna; doctoral researcher
TU Braunschweig, Institute of Joining and Welding

The aim of TP A07 is the design, the manufacturing and the testing of complex individualized steel components by means of WAAM. That contains the fundamental investigation of design and the design process for WAAM components. For the manufacturing of steel components by WAAM, stable and reliable processes for basic geometries are qualified and based on that, case study demonstrators for the identification of manufacturing restrains are fabricated. Furthermore a novel approach for material and component testing is developed to identify local material and component properties.

Summary

The aim of WG Hensel within the TP A07 is to produce on the one hand force-flow optimized steel nodes and on the other hand anchorage structures for concrete. While the steel node mainly consists of thin shells and voluminous parts, the anchorage structures resemble winded reinforcement bars, where the fabrication strategy follows the dot-by-dot printing method.

For the manufacturing of complex individual steel nodes, the geometry is broken down into the above mentioned basic geometries (bars, shells, volumes). For each basic geometry process qualifications were conducted to identify the effect of welding parameters on the resulting layer height, width and mechanical properties. Within the last reporting period, the process qualification of voluminous parts was completed by comparing three different infill pattern: hachure, meander and spiral.

By combing the basic geometries complex structures can be realized. However, when designing force flow optimized structured, geometric features occur which need to be manufactured. Hence, case study demonstrators were developed to investigate proper manufacturing strategies for those features and to identify manufacturing restrictions which need to be considered in the design process.

For the basic geometry bar, a case study demonstrator was developed and produced which represents the inclination and intersection of three or more bars, see Figure 1.

For thin-walled structures, different case study demonstrators, like overhangs and closed structures with one-sided overhangs were produced. One is depicted in Figure 2. For those closed structures the side with overhang needs to be produced with more layers than the rest of the part, as the building direction is inclined and follows the hypotenuse.

Current state of research

For the comparative study for voluminous parts different infill pattern were investigated: hachure, meander and spiral, compare Figure 3. They were evaluated regarding superelevations, inner defects, hardness and microstructure and residual stresses. Small superelevations are desired since they accumulate with increasing height of the structure, influence the process stability and the predictability of the layer height. Hachure showed the best properties and is furthermore the most suitable pattern with regard to geometrical flexibility.

By the fabrication of case study demonstrators, occurring geometric features of a force flow optimized steel node are represented in smaller parts. For bars this is for example the inclination or intersection of three or more bars, compare Figure 1. Here the key factor is the proper estimation of the resulting layer height and a precise process control.

Another case study demonstrator produced is a closed thin-walled structure with an overhang on one side. The special feature is the diverging number of layers between the 0° inclined part of the structure and the 45° inclined part. While the 0° contains only 23 layers, the 45° part consists of 32 layers to have in the end the same height.

Jointing Principles for Combination of Concrete Elements Produced by Different Additive Manufacturing

28.01.2022

Empelmann, Martin; Project Leader
Lanwer, Jan-Paul; Doctoral Researcher
TU Braunschweig, Institute of Building Materials, Concrete Construction and Fire Safety (iBMB), Division of Concrete Construction

Main goal

The main goal of the C05 project is to investigate the correlation between the execution and manufacturing of joints on the load-bearing behaviour of dry joints in AM concrete elements. Fundamental knowledge will be gained for the design of resource-efficient AM components and their application in construction.

Summary

The first summary report of C05 contained an evaluation strategy to gather, design and select appropriate joint profiles for the connection between elements produced by different additive manufacturing processes. Fig. 1 shows the selected joint profiles for the further investigations.

The joint profiles are manufactured by all available AM processes, i.e. shotcrete, extrusion and particle-bed. Since only particle-bed is able to print the joint profile directly with the specimen, shotcreted and extruded blanks require subtractive post-processing. Two subtractive post-processing techniques (CNC-milling, sawing) are available and should be compared with each other concerning the manufacturing accuracy. Furthermore, the subtractive post-processing is done after three resp. seven days of concrete hardening to find out whether it is possible to accelerate the manufacturing process of AMC components. The first results of the evaluation of the joint quality show, that there are no significant influences of the joint accuracy regardless of whether the subtractive post-processed is done after three or seven days. Once the manufacturing accuracy has been evaluated, the concrete elements are tested under compression loading. On one face of the joint, the strain in horizontal and perpendicular direction is measured with strain gauges. On the other side of the joint a high speed camera records the failure of the specimen. The records of the high speed camera should give hints of the failure mode and the crack propagation near the joint. All tested specimens showed so far that the major failure mode is splitting tensile failure. Furthermore the strain gauges show that there is an influence of the layer-orientation. 

Current state of research

Since the last research report, the selected joint profiles has been manufactured, scanned and tested. The manufacturing was done by shotcrete, extrusion and particle-bed. After the manufacturing, the joint geometries were milled and sawed into the specimens. Afterwards the joint profiles were scanned by an optical laser. The laser scanning was done to evaluate the joint quality. Figure 2 shows how the specimens have been manufactured by subtractive post-processing.

The evaluation shows again that there is no major influence of the joint quality if the subtractive post-processing is done after three or seven days. So it can be concluded that the concrete strength is sufficient for a subtractive post processing after three days.

3D Structural Puzzle – Numerical Multi Scale Shape and Topology Optimisation Methods to Additively Manufacture Optimal Structures from Optimised Pieces

27.01.2022

Dr.-Ing. Reza Najian Asl; Post-Doc Research Associate
TUM, Chair of Structural Analysis

This project deals with structures considered as large 3D puzzles and multi scale optimization aspects. The goal is to create optimized individual structural pieces which are subsequently assembled to form an overall optimal structure. Additive manufacturing is the ideal meaning of greatest potential to combine industrial efficient production with individual design and structural layout. The main research question is to develop numerical, simulation-based optimization methods which allow for the design and creation of large, additively manufactured structures to be carried out as a consistent, holistic procedure. Based on Vertex Morphing for free-form shape optimization, numerical methods for supporting a complete simulation based multi scale optimization tool chain will be developed. It will span from:

• The first tentative form finding of the large, complete structure (large scale).

• Further detailed structural design and optimization (large scale), through the optimal decomposition into structural pieces.

• The optimized design of those pieces considering compensation and residual stresses as consequences of the composition procedure (medium scale).

• As well as specifications and constraints of the printing process (small scale).

The joint potential of simulation, optimization, and additive manufacturing will be exploited for structures of innovative shapes.

Jahresauftakt beim AMC – digitaler Cross Project Workshop

Die Halbzeit der ersten Förderphase des Sonderforschungsbereich Transregio 277 Additive Manufacturing in Construction (AMC) ist erreicht. Ende Januar trafen sich die Wissenschaftler*innen des AMC zum digitalen Jahresauftakt. Nach zwei Jahren Förderung ging es einerseits um genaue Bestandsaufnahmen der Projektverläufe sowie der Promotionsfortschritte der Doktorand*innen und andererseits um Ausblicke in die zweite Förderphase, besonders im Hinblick auf die Entwicklung von weiterführenden Ideen und Inhalten für diese.

Am 24. und 25. Januar stellten die Forschenden ihren jeweiligen, aktuellen Projektstand und die bisher erreichten Zwischenziele vor. „Es war beeindruckend zu sehen, wie tief sich die Wissenschaftlichen Mitarbeiterinnen und Mitarbeiter in ihre Themen eingearbeitet haben. Im Speziellen die Vernetzung der Teilprojekte untereinander, ein wesentlicher Schwerpunkt des gesamten AMC, ist bei den Projektbeteiligten absolut angekommen und wird intensiv umgesetzt“, so Prof. Dr. Kathrin Dörfler, Co-Sprecherin des AMC.

Besonderes Augenmerk wurde diesmal auf die Vision der Forschenden für die zweite Projektphase gelegt. Welcher Fokus soll gesetzt werden? Was sind die spannenden Themen der Zukunft und wie sind diese gerade unter dem Stichwort Nachhaltigkeit umzusetzen? Spannende Diskussionen über Inhalte und weitere Fokussierung des AMC sind daraus entstanden. Sie werden in die Weiterentwicklung des AMC einfließen und vor allem den klimatischen und gesellschaftlichen Entwicklungen, die sowohl hochdynamisch als auch rasant voranschreiten, Rechnung tragen. Der AMC forscht an der Zukunft des Bauens. Besondere Herausforderungen sind das ressourcenschonende und energiesparende Bauen, verbunden mit recycelbaren Bauteilen und formschlüssigem Design. Dieser Mehrklang fungiert als Motor aller Forschenden im AMC.

We're hiring!

We look for a postdoc to join our team and the research associated with the DFG-funded Collaborative Research Center TRR 277 Additive Manufacturing in Construction. 

Post Doctoral Researcher for Digital Building Construction

Laser Powder-Bed Fusion (PBF-LB/M) of Steel Elements for Construction – Basics of Design and Mechanical Resilience

20.01.2022

Diller Johannes; Doctoral researcher, TU Munich, Chair of Metal Structures
Dorina Siebert; Doctoral researcher, TU Munich, Chair of Metal Structures
Wenzler, David; Doctoral researcher, TU Munich, Institute for Machine Tools and Industrial Management
Kolb, Cara; Doctoral researcher, TU Munich, Institute for Machine Tools and Industrial Management

At the halfway point of the first funding period, one of four work packages has already been completed and further important findings have been obtained in the work package on mechanical resilience.  These include, in particular, results on the influence of the cooling rate and heat treatment on strength and residual stresses.

Conventional manufacturing methods like hot rolling of 316L-steel develop a yield strength of 200 to 200 to 220 MP. The high cooling rate (up to 40 K/µs) of PBF-LB/M-manufactured 316L parts results in a fine needle-like microstructure. This fine grain size increases the yield strength up to 650 MPa. However, the high cooling rate during the PBF-LB/M manufacturing process also develops high residual stresses (see Fig. 1).

These residual stresses can be reduced by applying heat treatment.

To investigate the effect of the heat treatment as well as the laser parameters, six specimens were manufactured. Five different laser parameters were used. After the manufacturing of the specimens, two different heat treatment routes were applied to two specimens. One specimen was heat-treated, followed by water quenching. Another specimen (HIP) was hot isostatically pressed, followed by air cooling.

The phase composition, the grain orientation as well as the crystallite sizes are explored by applying x-ray diffraction to the non-heat-treated specimens, as well as to the heat-treated specimens. The range of the 2-Theta angle was set between 15° and 75° for all specimens. To increase the accuracy of the measurements, the irradiation time was set to 20 hours per specimen.

The results show a clear reduction of the residual stresses in the heat-treated specimens. However, a complete equalization of the residual stresses in the heat-treated specimens was not achieved.

Integration of Individualized Prefabricated Fibre Reinforcement in Additive Manufacturing with Concrete

14.01.2022

Gantner, Stefan; Scientific Researcher, TU Braunschweig, Institute of Structural Design (ITE)

Cement-based additive manufacturing techniques need to be enhanced by the ability of integrating reinforcement, in order to fulfil requirements of construction. This project focuses on non-metallic continuous fibre reinforcement, which is not only corrosion resistant but also flexible in handling. Instead of bending and welding, glass or carbon fibre rovings can be processed by winding onto a support structure.

Based on three fundamental AM-principles, namely material jetting and extrusion, as well as particle bed printing, a set of winding concepts for integrating reinforcement has been developed. Within a holistic framework all relevant aspects from fabrication constraints to the scope of applications are considered. The interaction of printing process and reinforcement integration is already playing an important role in the conceptual design. If the reinforcement is integrated into additive manufacturing in a subordinate step, this leads to different shaping possibilities than if a fibre structure is preproduced serving as support for subsequent concreting.

In the first place, the interaction of reinforcement and concrete is a key factor for practical implementation. Currently, testing and development is carried out for the three most promising process combinations: Firstly, Frame Winding and Shotcrete 3D Printing (SC3DP), secondly, Pin Grid Winding and Particle Bed Printing, and thirdly, SC3DP and Core Winding Reinforcement (CWR).

Specific challenges arise and lead to demonstrators with different levels of sophistication. The double curved wall with force-flow oriented post-integration of continuous glass fibres by CWR shown in figure 1 represents the most advanced demonstrator by now. The fully automated fabrication includes shotcrete core printing, individualised fibre application by means of a novel end-effector and concrete cover printing with subsequent surface finishing.

Integrated Additive Manufacturing Processes for Reinforced Shotcrete 3D Printing (SC3DP) Elements with Precise Surface Quality

09.01.2022

Dörrie, Robin; doctoral researcher, Technische Universität Braunschweig, Institute of Structural Design

After validating the concept of force-flow compliant reinforcement for concrete construction elements in the beginning of 2021, different reinforcement strategies and integration methods were investigated. These integration methods are all automated and range from placing prefabricated reinforcement structures to incrementally produce reinforcement during the printing process.

In this period two different concepts were tested. Firstly “concrete supports reinforcement” were a force compliant printed concrete bed is utilized to place flexible/textile reinforcement on top of itself. This way the reinforcement is shaped according to the tensional trajectories already and can be sprayed over. Secondly the concept of “reinforcement supports concrete” was investigated. Here a prefabricated structure is used to support the concrete during application and encase the reinforcement structure.

Demonstrators were manufactured for both concrete using Carbon Mesh as textile reinforcement for the first concept and a prefabricated Wire Arc Additive Manufacturing (WAAM) structure for the second concept. These novel techniques show the opportunities of the SC3DP Process and will be further developed in this upcoming year. 

Post-Doctoral Researcher for Digital Building Construction

We look for a postdoc to join our team and the research associated with the DFG-funded Collaborative Research Center TRR 277 Additive Manufacturing in Construction. The position is to start in March 2022, or upon agreement.

Process Control and Adaptive Path Planning for Additive Manufacturing Processes Based on Industrial Robots with an Extended Degree of Freedom

20.12.2021

Lachmayer, Lukas, Doctoral researcher
Leibniz Universität Hannover, Institute of Assembly Technology (match)

In terms of sustainability, additive manufacturing processes represent an advanced method to preserve non-renewable resources. Especially in the construction industry, utilizing such production technics enables dispensing formwork elements and realizing topology optimized designs. However, the latter aspect, in particular, requires manufacturing processes with extensive freedom in terms of component design. In this regard, shotcrete 3D printing (SC3DP) offers a free orientation of the material application due to the spray process, as shown in Fig. 1.

A decisive challenge in manufacturing based on SC3DP is the time-dependent flow behavior of the fresh concrete and the associated unstable behavior of the application process. E.g., suppose the material application height does not match the planned values due to environmental influences. In that case, the distance between the printing nozzle and the applied material, increases steadily. Such behavior leads to widening of the deposited strand geometry and reduction of the height, further expanding the spray distance and destabilizing the production process.

We could overcome this instability with motion control, which we proved in the experimental production of wall segments. For this purpose, we mount a laser scanner on the nozzle, as shown in Fig. 1. The system is continuously measuring the distance to the applied material. In case of deviations from a predefined target distance, the feed rate of the robot or the nozzle is adjusted so that more or less material is applied.

Extrusion of Near-Nozzle Mixed Concrete – Individually Graded in Density and in Rate of 3D Fibre Reinforcement

17.12.2021

Hechtl, Christian, TP editor
Matthäus, Carla, TP editor
Dr.-Ing. Kränkel, Thomas, Project Leader
Prof. Dr.-Ing. Gehlen, Christoph, Project Leader
All: TUM, Chair of Materials Science and Testing

The goal of project A03 is to design a new extrusion method for graded concrete. In contrast to conventional concrete extrusion the Gradation-ready Extrusion System (GrES) produces fresh concrete from raw components – both dry and liquid – just before deposing the fresh material. This system has many advantages over the conventional approach. Figure 1 shows a rendering of the GrES.

One of the essential advantages is the opportunity to immediately adjust the material properties during the printing process (gradation). This way, it is possible to switch between lightweight concrete with high thermal insulation properties and high-strength concrete allowing high load transfer. The combination of different materials during 3D-printing enables multifunctionality of additively manufactured objects. In addition to gradation of the concrete, the range of applications can be extended even further by integrating reinforcement. This can be done in the form of steel fibers or, as shown in Fig. 1, via insertion of steel rebars into the already printed layers by a second robot. Lastly, by using the GrES the conflict between pumpability and buildability is diminished so that the focus of material development can be on good buildability and fast printing. The green strength of the fresh material is significantly increased, as the requirements for workability of the material are simplified with the short conveying distance.

Bridging Scales – From Geometric Part Details to Construction Elements

10.12.2021

Oztoprak, Oguz; Doctoral researcher
Rank, Ernst; Project Leader
Kollmannsberger, Stefan; Project Leader
all: TUM, Chair of Computational Modeling and Simulation

Quality assurance is important for Additive Manufacturing in Construction (AMC) like in any other production technology. Two paths are imaginable: a) to carry out physical experiments i.e. to produce a part and to measure its properties after production or b) to reliably predict the performance of a part or a structure using computational analysis before production. While the second option is much cheaper, leads to faster design cycles, and has become a standard procedure in many industries, this is not the case for parts produced by additive manufacturing in civil engineering. A missing link is the validation of the applied models and the computed results (often also called virtual experiments) against physical experiments.

To close this research gap, C01 is conducting virtual experiments to mirror in-situ measurements on a closed-cellular wall element produced by C03 and thereby to validate the computational methods. The predictive model shall then be used by C01 and C03 to improve the thermal performance of wall elements through virtual experiments.

Additive Manufacturing is able to directly produce geometrically and topologically demanding designs. However, this freedom of design is highly challenging for current computational methods. One bottleneck is the flawless transition from a geometric model to a fully three-dimensional virtual experiment. To this end, C01 further develops the Finite Cell Method as it allows for a smooth transition of practically any geometric model to analysis. It achieves this transition by avoiding the generation of boundary conforming Finite Element meshes. Instead, it embeds the geometrical model into a simply shaped background mesh. Figure 1 shows the computational setup exemplarily for the investigated wall element.

Particle-Bed 3D Printing by Selective Cement Paste Intrusion (SPI) - Particle Surface Functionalisation, Particle Synthesis and Integration of WAAM Reinforcement

03.12.2021

Straßer, Alexander, TP editor
Matthäus, Carla, TP editor
Kränkel, Thomas, TP editor
Gehlen, Christoph, PL
all: TUM, Chair of Materials Science and Testing

The goal of A02 is the implementation of reinforcement with Wire and Arc Additive Manufacturing (WAAM) in concrete elements produced by Selective Paste Intrusion (SPI). Since the cement paste is applied to the aggregates and must penetrate the cavities between the aggregates only driven by gravity, consistent and suitable rheological properties of the cement paste are essential for a high layer bonding and a good print quality. The welding process with WAAM generates high temperatures – - more than 1500 °C at the welding point. Therefore, initial investigations have already been performed with cement paste regarding the rheological changes under the influence of temperature. A summary can be found in the short report A02-1 dated 09.04.2021.

The next step towards practical application is to perform tests on the SPI printer. The following steps have to be taken for this:

• Setup of the SPI printer (conversion of the SCA printer to the SPI printer).

• Investigations for optimal settings and parameters for high print quality (scattering roller, feed, spacing, offsets, and cement paste formulation)

• Investigations on the printer for different cooling strategies, e.g., increasing the z-distance between particle bed and printing nozzles

• Investigations and prints with functionalized aggregates and verification of print quality (e.g., print image, geometry, and strength)

• Investigations of the print quality with external temperature loads

• Integration of the welding process into the SPI printer

Integrating Digital Design and Additive Manufacturing through BIM-Based Decision Support and Digital Twin

29.11.2021

Borrmann, André; Project leader
Slepicka, Martin; Researcher
all: Technical University of Munich, Chair of Computational Modeling and Simulation

Digital Manufacturing methods, such as Additive Manufacturing (AM), offer more geometrical freedom than conventional methods as well as function integration into the components, however, more complex data preparation is required, especially if multi-axis robots are involved in the manufacturing process. If the AM machine system is able to rotate the print head freely, not only position information needs to be described but also the orientation at each position.

In the Fabrication Information Modeling (FIM) method, which is implemented by this project, the position and orientation of a robot system is described with two mutually referenced objects (shared parameter space). Additionally these objects can be used as a “container” to hold sensor data that is collected during the manufacturing process.

Modelling and Simulation of Shotcrete 3D Printing (SC3DP) Based on a Massively Parallel Multi-Phase, Multi-Component Coupled LBM-DEM Approach

26.11.2021

Kutscher, Konstantin; PostDoc Researcher
Geier, Martin; Project leader
Krafczyk, Manfred; Project leader
all: TU Braunschweig, IRMB

In this project we develop a phase field model for the simulation of the shotcrete printing process. As this process involves a mixture of liquid cement and air, the model needs to support a large density ratio between the phases. Conservative momentum-based formalism tends to become unstable under these conditions such that a non-conservative velocity[1]based formalism is chosen in this project. The velocity[1]based formalism avoids the problems arising from large gradients in the conserved quantities (i.e. momentum) at the cost of additional correction terms which are expensive to compute. Here we were able to obtain some of the required gradient operators from an evaluation of the non-equilibrium second order cumulants which are already computed in the lattice Boltzmann method and hence come at essentially zero additional cost. A benchmark simulation with a falling droplet shows identical behavior to the method in which all correction terms are acquired from expensive finite differences.

Particle-bed 3D printing by selective cement activation: Particle surface functionalization, particle bed compaction and reinforcement

19.11.2021 

Herding, Friedrich; Researcher
Mai, Inka; Leading researcher
Lowke, Dirk; Project leader
All: TU Braunschweig, Institute of Building Materials and Concrete Construction and Fire Safety (iBMB)

The main objective of our research is to understand the material-process-interactions in particle bed 3D printing by Selective Cement Activation in order to produce concrete elements with high mechanical performance and geometric precision, see Figure 1. However, to fully utilize the potential of additively manufactured elements, reinforcement integration is crucial. Therefore, we are investigating the implementation of various reinforcement strategies, which differ in integration and reinforcement type. Recent small scale experiments show promising results for the integration of fibre rods into the printed specimens. Next steps are an upscaling of the experimental setup and the usage of free formed reinforcement-layouts.

Jointing Principles for Combination of Concrete Elements Produced by Different Additive Manufacturing Processes

12.11.2021 

Baghdadi, Abtin; Post-Doc Researcher, Institut fürTragwerksentwurf (ITE)

C05's main target is investigating and developing the robotic-milling approaches to manufacturing dry concrete connections. Furthermore, the structural performance of each evaluated connection regarding the shear and axial loads are supposed to be studied.In the evaluations, the performance of dry connections produced by different additively manufactured materials (A01-A04), the effect of the printing layers and post-tensioning loads will be studied. 

After general preparations and developing the robotic approach, the axial and shear capacities will be experimental and numerical evaluated in working packages two and three. Then the final demonstrator, which in principle is a hollow segmental precast concrete beam (bridge), based on the developed robotic milling/sawing technique and the evaluated dry connections, will be designed and produced. 

Particle-bed 3D printing by Selective Cement Paste Intrusion: Particle Surface Functionalisation, Particle Synthesis and Integration of WAAM Reinforcement

15.10.2021 

Hamilton, Leigh Duncan; Researcher
Breitung-Faes, Sandra; Leading Researcher
Kwade, Arno; PL
All: TU Braunschweig, Institute for Particle Technology (iPAT)

The main goal of our research at A02 is the implementation of Wire and Arc Additive Manufacturing (WAAM) as a means of simultaneously printing the reinforcement during the concrete 3D-printing method selective paste intrusion (SPI).

The combination of SPI and WAAM is accompanied by obstacles that must be overcome in order to ensure the collaborated functionality. One major challenge occurs from the propagated thermal load of WAAM (approx. 1600 °C), which has negative effects on the paste rheology and resulting concrete strength. Therefore, the overall goal is to minimise heat propagation into the particle bed [1].

Substantially, the project partners from TU Munich are investigating process parameters and additional cooling strategies for SPI and WAAM, whereas iPAT is conducting a closer inspection into developing tailored particles. On the one hand, an optimal combination of particle size distribution and morphology of the aggregate (sand) particles as well as cement paste are to be found to support the process. On the other hand, the effect of certain additives on both components in order to withstand the remaining thermal load and/or compensate for water loss will be studied.

Considering the latter, a new approach was tested, whereby water can be stored in a coarse dry aggregate bulk of material without negatively influencing the properties of the bulk material. These properties, e.g. flowability, are influenced by the inter-particle forces and mainly determine the quality of the particle bed build by a doctor blade. Subsequently, the particle bed properties correlate with the product properties like strength or porosity. The additive at hand is commonly known as dry water, which consists of water droplets with a silica coating, and thus, is capable of storing up to 98 wt.% of water. In fact, dry water appears as a free-flowing powder, as depicted in Figure 1.

Integration of Individualized Prefabricated Fibre Reinforcement in Additive Manufacturing with Concrete

15.10.2021 

Rothe, Tom; Doctoral researcher, TU Braunschweig, Institute for Mechanics and Adaptronics (IMA)

The aim of this project is to develop a machine and a process for the production of textile-based prefabricated reinforcements and strategies for their integration into additive manufacturing with concrete. These reinforcements are produced by a dynamic winding machine and will be used in a robotic winding process. In the dynamic winding machine an in-situ fibre preparation is done initially. Following this, the used rovings are formed to a strand, which is further used as main core of the reinforcement. Additionally, a helix surface structuring is applied by wrapping a secondary yarn around the main core. 

The shown winding machine in Fig. 1 contains several optimizations and additions in comparison to the first prototype to overcome constraints and problems, which occurred while the intense usage. Because of a new mounting system the resin impregnation bath is more stable and changing it during the usage is easier. Another main improvement is the active pulling of the main core. By this, the helix winding can directly be linked to the pulling speed and a more precise thread pitch is achieved. In addition to this, the tension unit does furthermore serves as storage unit. The position of the dancer is detected by a sensor and the pulling speed is adjusted to it. This flattens the acceleration and deceleration by the robotic winding and a smoother pulling occurs, which decreases the maximum pulling forces in the system.

First experiments with the optimized machine show, that reinforcements with a thickness between 1mm and up to 8mm with a regular thread pitch are producible. Furthermore, first tensile tests for reinforcement bars have been done.

To increase the process quality and to be able to produce thicker reinforcements, a new winding machine is currently developed. In addition, further mechanical tests of the reinforcement are planned.

Laser Powder-Bed Fusion (PBF-LB/M) of Steel Elements for Construction – Basics of Design and Mechanical Resilience

08.10.2021 

Wenzler, David; Doctoral researcher, Technical University of Munich, Institute for Machine Tools and Industrial Management
Diller, Johannes; Doctoral researcher, Technical University of Munich, Chair of Metal Structures
Siebert, Dorina; Doctoral researcher, Technical University of Munich, Chair of Metal Structures

The projects A06 and A07 combined their expertise to perform a fundamental experiment on the combina-tion of the powder bed fusion of metals using a laser beam (PBF-LB/M) and the wire and arc additive manufacturing (WAAM). This strategy aims to bring together the advantages of both processes while the weaknesses are compensated (Fig. 1).

In the experiment, a wall was produced by PBF-LB/M, and subsequently, a second wall was added on top by WAAM. Tensile specimens were machined, and specimens for metallurgy were extracted out of the wall. The metallurgical analysis of the fusion zone showed adequate bonding, as no hot cracks or porosity were visible. However, the subgrain size differed significantly.

Due to the different cooling rates, the subgrain sizes of the PBF-LB/M manufactured part were notably smaller compared to the WAAM manufactured part of the wall. This is illustrated in Fig. 2. In future investigations, tensile tests will be conducted with strain-field measurements to analyze the plasticity behavior in the fusion zone between the two walls.

Integrated Additive Manufacturing Processes for Reinforced Shotcrete 3D Printing (SC3DP) Elements with Precise Surface Quality

01.10.2021 

David, Martin; Doctoral Researcher, TU Braunschweig, Institute for Machine Tools and Production Technology (IWF)

The research in TP-A04 is focused on the Shotcrete 3D Printing (SC3DP) process with regard to process strategies, materials, tools and methods concerning improved process control, reinforcement integration, surface quality and process automation. 

For the automation of the whole process chain different end-effectors have to be developed. Especially since the first results of manually integrated rebars showed promising results, an end effector for the automated insertion has been developed (Fig 1).

To achieve a controlled movement, the rotation of the rebar and the vertical movement of the insertion have to be synchronized. While a stepper motor (3) is rotating a pneumatic centric gripper (6), the vertical movement is achieved by a 5-axis-kinematic. Due to a limitless rotation of the gripper a slip-ring (4) is needed to transmit the pressured air, energy and signals for the gripper and the sensors (5). 

First tests showed promising results in the automated insertion of short rebars. For the presented end effector, further modules such as a magazine and a feeding mechanism are under development.

Structural Timber by Individual Layer Fabrication (ILF)

17.09.2021 

Bunzel, Frauke; Project leader
Asshoff, Carsten; Doctoral researcher
Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut WKI

The new additive manufacture process ‘individual layer fabrication (ILF)’ extends other additive manufacturing processes with wood by one that is intended to be applicable for structural timber. The focus is also on significantly reducing the amount of required adhesive. The individual process steps consisting of the scattering of wood chips, application of adhesive with a valve and subsequent mechanical pressing with and without heat input must be developed individually and coordinated with each other.

On the material side, the need for research focuses on the appropriate selection of wood chips in terms of morphology. They must be long enough to produce sufficient strength. On the other hand, wood chips that are too long reduce contour accuracy and can make automated processing difficult.

The adhesive must be selected accordingly so that the viscosity and surface tension are as low as possible. These properties should enable the adhesive applied onto the wood chips from above to penetrate into deeper layers. Due to the better flow behavior, the local adhesive content can be reduced. However, this must work in a controlled manner to maintain contour accuracy. To ensure the required strength and compatibility of the adhesive to the wood chips, the initial focus is on the use of already established adhesives from the wood-based materials industry.

For the repeatable and automatable application of the adhesive from above onto the wood chips, experiments with a spray-valves are investigated. By atomizing the adhesive with air, the local adhesive content should be reduced.

Process Control and Adaptive Path Planning for Additive Manufacturing Processes Based on Industrial Robots with an Extended Degree of Freedom

08.09.2021 

Ekanayaka, Virama; Doctoral researcher, TU Braunschweig, Institute of Machine Tools and Production Technology (IWF)

The integration of robot-guided additive manufacturing in the construction industry increases the degree of automation and can thus lead to an increased productivity and increased component quality. In shotcrete 3D printing (SC3DP), reproducible manufacturing results and ensuring component qualities are a major challenge, as the properties of shotcrete depend on many different parameters (e.g. temperature, pressure, water-cement ratio, hardening accelerator).

The goal of this research project is to develop a reproducible, robot-guided shotcrete process based on multi-model adaptive path planning for the production of high-quality large and complex components. The core of this multi-model based path planning is the combination of geometric data and a physical material model into an application process model. 

Within the scope of this research, a MATLAB framework is created which enables the coupling of the path planning to a novel process based Finite Element model. The geometrical relations for deriving the mesh geometry from the printing path is shown in Figure 1.

The deformations predicted in the FEA simulation will be used in a feedback loop to adjust the printing parameters to minimize the deviation between the target geometry and printed geometry and ensure better component quality, reduced test effort, and fewer buildability failures. 

For the initial offline approach to select the appropriate process parameters, data from FEA simulations would be sufficient. However to adjust the process parameters in real time utilizing scan data during the printing process, much faster computation will be required. This can be realized through the implementation of surrogate models as a replacement for FEA simulations.

Integration of Additive Manufacturing in the Construction Process

08.09.2021 

Mawas, Karam; Doctoral researcher, TU Braunschweig, Institute of Geodesy and Photogrammetry (IGP)
Gerke, Markus; Project leader, TU Braunschweig, Institute of Geodesy and Photogrammetry (IGP)
Maboudi, Mehdi; Associated scientist, TU Braunschweig, Institute of Geodesy and Photogrammetry (IGP)
Riedel, Björn; Associated scientist, TU Braunschweig, Institute of Geodesy and Photogrammetry (IGP)

Quality inspection is the step where the printed object is being checked with its digital twin under the predefined tolerances of the project. This step has to be done instantaneously and in particular during the printing phase. In the printing lab DBFL there are two robots one for deposing the material (printing robots) and one for subtracting the material out from the printed object (mill robot). Each robot has its coordinate system and has no awareness of its surrounding – the DBFL itself.

To minimize the time needed for scanning the printed object and all scans should be in one coordinate system. One solution is to mount the scanner on one of the two robots as is shown in Fig.1. Thus, the scanner can be driven to the aimed position through the robot. Furthermore, to align the different scanning stations, the transformation between the different coordinate systems has to be solved as well.

In this context we conclude that we have three different coordinate systems in the DBFL: i) Mill robot, ii) Printing robot, and iii) the DBFL system. These transformations have to be computed. Also, the position of the scanner can be obtained from the robot, once the transformation between the different scanner positions has been solved. The data acquisition can be done faster than the normal procedure and quality inspection can proceed immediately after the acquisition as a cloud to model (C2M) algorithm, M3C2 algorithm, or any different algorithm.

Wire and Arc Additive Manufacturing (WAAM) of complex individualized steel components

27.08.2021 

Müller, Christoph; doctoral researcher, Braunschweig, Institute for Structural Design (ITE)

The attempt to generate a geometry via a self-organising system differs fundamentally from the usual application of FEA for topology optimisation as a design step for additively manufactured components. 

The concept of self-organising systems is based on the individual participants in the system and their behaviour among each other. Most readers should be familiar with this behaviour from nature in the form of birds or flocks of fish. The basic behaviour is of a simple nature while the generated geometry is subject to complex questions. 

Forschung, Familie und Austausch – AMC Cross Project Workshop - Herbstmeeting

Im frisch renovierten Audimax der TU Braunschweig fand das diesjährige Herbstquartalsmeeting des Sonderforschungsbereich / Transregio TRR 277 als hybrid kombinierte On- und Offline Veranstaltung statt. 80 Forschende aus den Teilprojekten trafen sich vom 11.10. bis 13.10.2021, um sich einerseits in projektübergreifenden Workshops auszutauschen und andererseits ihre Beziehungen zueinander zu intensivieren. Begrüßt wurden die Forschenden von TRR 277 Sprecher Prof. Dr.-Ing. Harald Kloft, im Anschluss seiner Einführung übergab dieser das Wort an Dr.-Ing. Christina Radlbeck und M.Sc. David Briels. Die Vortragenden beschäftigten sich mit den Herausforderungen von Elternschaft und Forschungsarbeit und wie diese erfolgreich bewältigt werden können. Ein wesentliches Anliegen für den TRR 277 ist es, die nötigen Rahmenbedingungen für das Gelingen dieser beiden Faktoren zu bieten.

Im Anschluss an den viel beachteten Vortrag stellten Prof. Dr. sc. ETH Kathrin Dörfler, Junior Prof. Dr. sc. ETH Norman Hack und Dr.-Ing. Klaudius Henke ihr Workshop Konzept vor. Ziel des zweitägigen Workshops war eine kreative Ideensammlung zum übergeordneten Thema Zentraldemonstrator. Neben den Workshops führte der TRR 277 seine Jahreshauptversammlung durch. Hier wurde Prof. Dr. sc. ETH Kathrin Dörfler zur neuen Co-Sprecherin des Projekts gewählt. Am letzten Tag des Quartalsmeeting war es für alle Interessierte möglich, sich die unterschiedlichen Institute und Laboratorien die am TRR 277 mitwirken und an der TU Braunschweig angesiedelt sind, anzuschauen. In Form einer technical tour und in Kleingruppen führten Forschende ihre Kolleg*innen durch die jeweiligen Räumlichkeiten.

Als Fazit der Veranstaltung möchte wir unseren Sprecher Harald Kloft zitieren: „Solche Veranstaltungen sind das Lebenselixier. Die Kultur des Zusammenarbeitens kommt nur durch den persönlichen Austausch zustande.“

Artikel

TOPIC: "Potential and Challenges of Shotcrete 3D Printing (SC3DP) Within the Building Construction Process" and reflects joint work within C06

WHEN: 1^th of October 2021

SPEAKER: Markus Gerke

For further information please visit: https://www.iros2021roboticfabrication.ch/

TOPIC: Intersectional and Resilient: New Forms of Automation for Architecture

WHEN: 4^th of October 2021

SPEAKER: Mollie Claypool

Only accessible to network partners

For further information please visit AdvanceAEC​​​​​​​

Extrusion of Near-Nozzle Mixed Concrete – Individually Graded in Density and in Rate of 3D Fibre Reinforcement

20.08.2021 

Dahlenburg, Maximilian; TP editor, TUM, Chair of Materials Handling, Material Flow, Logistics
Tan, Yuan; TP editor, TUM, Chair of Materials Handling, Material Flow, Logistics
Prof. Dr.-Ing. Fottner, Johannes; Project Leader, TUM, Chair of Materials Handling, Material Flow, Logistics

The main goal of the A03 project is to design a new extrusion method especially for graded concrete. In contrast to conventional concrete extrusion, the developed pumpless Additive Manufacturing process (PAM) with the state of the art near-nozzle mixing system (NNMS) homogenizes concrete components (both dry and liquid) in a mixing head and is able to directly deposit the freshly mixed material. (Fig. 1) This system not only has great potential in terms of resource- and time efficiency, but also compensates disadvantages of conventional printing systems.

Most established processes convey premixed material to the nozzle via eccentric screw pumps. This poses a high risk for innovative materials such as lightweight concrete with pressure-sensitive constituents. Introduced energy during pumping as well as mixing must be kept to a minimum to prevent material destruction. PAM is developed to compensate the conflict between pumpability before and stiffness after material deposition on the one hand and material protection on the other hand.

This system is currently being tested together with research group of Prof. Dr.-Ing. Gehlen at the AMC Lab in Freising.

Particle-bed 3D printing by selective cement activation: Particle surface functionalization, particle bed compaction and reinforcement

06.08.2021 

Meier, Niklas; Researcher;
Zetzener, Harald; Leading researcher;
Kwade, Arno; Project leader;
TU Braunschweig, Institute for particle technology

The main goal of our research at A01 is to improve the mechanical strength and shape accuracy of the printed concrete parts as well as the printing speed. While the project partner iBMB focuses on the material-process interaction, the work packages performed at the iPAT are targeted at improving the powder properties. To reach higher mechanical strengths, one approach is to increase the bulk density of the powder and therefore the density of the final part. Another approach is to control the liquid intrusion behaviour to achieve a good interlayer bonding, while also improving the shape accuracy. Therefore the particle surfaces are modified, for example with nanoparticles (Fig. 1), to increase the flowability of the powder and with it the bulk density. Furthermore, the surface modifications are used to change the wetting behaviour of the powder. Another part of the ongoing research is to tailor the particle size distribution to improve both, the pore size distribution to control the liquid intrusion behaviour and the bulk density.

Integrated Additive Manufacturing Processes for Reinforced Shotcrete 3D Printing (SC3DP) Elements with Precise Surface Quality

23.07.2021 

Freund, Niklas; Researcher;
Dreßler, Inka; Leading researcher;
Lowke, Dirk; Project leader;
TU Braunschweig, Institute of Building Materials and Concrete Construction and Fire Safety (iBMB)

The manufacturing of reinforced Shotcrete-3D-printed (SC3DP) components is one of the main research topics of project A04. The new possibilities of additive manufacturing in combination with suitable strategies for reinforcement integration will allow a resource- efficient manufacturing of geometrically complex and structurally efficient components. In addition to the process related challenges (e.g. automation) research on the material side is prerequisite in order to guarantee a high quality of the manufactured components. In terms of reinforcement integration, this primarily involves the resulting bonding zone between reinforcement and concrete matrix, which is evaluated mechanically and visually by pull-out tests and μCT analyses (see Fig 1), respectively. By means of a systematic evaluation routine, different reinforcement materials and integration methods can be compared in an overall reinforcement-bond- matrix. Thus, requirements and restrictions for the integration into the SC3DP process can be defined.

Figure 1 shows an example of a μCT image of a bond zone between a rebar and a concrete matrix. The rebar was deposited in an interlayer in parallel to the printing process. In the shown section, you can see a homogeneous bond to the concrete matrix. In general, bond imperfections and voids can be detected and quantified non-destructively with this method.

Integration of Passive and Active Functions in Additively Manufactured Construction Elements

16.07.2021 

Auer, Thomas; Project leader; 
Briels, David; Researcher;
Nouman, Ahmad; Researcher; 
Technical University of Munich, Chair of Building Technology and Climate Responsive Design

One key aspect of Additive Manufacturing is geometric freedom. C03 intends to benefit from this freedom by integrating multiple active and passive functionalities within additively manufactured building elements.

Among other concepts, C03 is setting up a simulation model for a multi-functional, multi-layered murocaust façade. A thorough observation of the temperature patterns in the air layers helped to develop advanced coupling strategies to improve indoor thermal comfort in all seasons. The initial results revealed espacially cooling effects in summer.

Recent studies indicate that air trapped inside closed- cellular structures can improve the thermal performance of building elements (Dielemans et.al., 2021). A parametric study including in-situ measurements, analytical calculations, and simulations was carried out, to acquire an optimized version of these cellular structures. The resultant element shows further improvement in the thermal characteristics compared to its predecessors. The cell diameter, cell count, and surface finish were the most dominant factors for the thermal behavior of a closed- cellular wall element.

Vom 28. Juni bis zum 2. Juli 2021 fand die TRR 277-National-Summer-School im Haus der bayerischen Landwirtschaft am Ammersee statt. Dank der günstigen Pandemielage konnte das Treffen, vor einigen Monaten noch undenkbar, als hybrid kombinierte On- und Offline Veranstaltung stattfinden. Unter Einhaltung aller Schutz- und Hygienekonzepte und täglichen Tests, haben dabei wechselnd zwischen 40-60 Personen in Präsenz teilgenommen und ca. 20-40 Personen verfolgten die Vorträge online und nahmen digital an der Diskussion teil.

Den Auftakt der Summer-School am Montag machten die Sprecher des TRR 277 Harald Kloft und Christoph Gehlen mit inspirierenden Impulsvorträgen, denen noch insgesamt sechs spannende Impulsvorträge von Projektleitenden (PLs) am Dienstag und Donnerstag folgten.

Kerne der Summer-School waren die Vorträge der 20 Teilprojekte, in welchen die Doktorand*innen den Stand ihrer Forschungsarbeit vorstellten und zusammen mit den Projektleitenden wichtige Fragestellungen und die Zukunft ihrer Arbeit diskutierten.

Um neben seinem wissenschaftlichen auch seinen gesellschaftlichen Zielsetzungen gerecht zu werden, wurde am Mittwoche der Fokus bewusst auf das Thema „Gender & Diversity“ gelegt. Beginnend mit ihrem Vortrag über „Gender & Diversity - Kognitive Biases im Hochschulkontext“, stieß Frau Dr. Lisa Horvath (http://www.drlisahorvath.at) eine angeregte Diskussion an, welche im anschließenden von TRR 277 Vorstand geleitet Workshop auf die Gleichstellungsmaßnahmen im TRR277 bezogen werden konnte. Neben der Vermittlung und Verbesserung der bereits im TRR 277 implementierten Strukturen und Maßnahmen zur Gleichberechtigung, Familienfreundlichkeit und Karriereförderung, entstanden hier neue Ideen wie u.a. die Planung einer voll gendergerechten TRR277-Student-Spring-School im Jahr 2022. 

Neben dem fachlichen Austausch stand natürlich nach fast 1,5 Jahren Pandemiebeschränkungen das persönliche Kennenlernen und die direkten „Face to Face“ Gespräche im Vordergrund. Begünstigt wurden diese durch viele kleine Sitzecken im Garten und das bunte Freizeitprogramm wie Baden im Ammersee, Spaziergänge zum Bayrischen Biergarten, ein wenig Disko und Liveübertragung der Fussball-EM auf der große Leinwand im Vortragssaal. 

Auch wenn die Durchführung als hybride Veranstaltung eine neue technisch-organisatorische Herausforderung war, blicken wir (erschöpft vom gefüllten Wissensdurst und den Tücken der Technik) sehr zufrieden auf diese intensive und bereichernde Woche zurück. Es war ein großartiges Zusammentreffen und hat nicht nur die interdisziplinär vernetzte Forschung, sondern insbesondere den Teamgeist des TRR 277 beflügelt.

Vielen Dank an alle, die On- und Offline teilgenommen haben oder hybrid zwischen der digitalen und realen Welt hin und her gesprungen sind. 

Structural Timber by Individual Layer Fabrication (ILF)

25.06.2021 

Henke, Klaudius; Project leader; 
Talke, Daniel; Doctoral researcher;
Buschmann, Birger; Doctoral researcher; 
Technical University of Munich, Chair of Timber Structures and Building Construction 

The main goal of the project ‘Structural Timber by Individual Layer Fabrication (ILF)’ is to find a way to additively manufacture large scale elements from wood composites with a minimum content of adhesive and strength values suited for applications in construction.

Similar to other particle bed binding technologies, in ILF, a thin layer of wood particles is bound by selectively applying adhesive according to the target geometry of the object. However, here each layer is manufactured individually with the added step of applying mechanical pressure. In doing so, the amount of required adhesive is drastically reduced while at the same time the mechanical properties of the panel as well as the finished product is increased. Preliminary tests have produced promising results with material strengths well above those of common particle boards. Current research is focused on automating the individual steps of the manufacturing process and exploring the process parameters and their influences. 

Wire and Arc Additive Manufacturing (WAAM) of complex individualized steel components

11.06.2021

Müller, Johanna; doctoral researcher, TU Braunschweig, Institute of Joining and Welding

The Wire Arc Additive Manufacturing (WAAM) of complex individualized steel parts presents different challenges. One of them is the thermal cycle during the fabrication of WAAM-parts and its effects on the material properties.

WAAM uses conventional gas metal arc welding for the layer-wise deposition of single weld beads. During this process, the deposited structure is frequently reheated. Especially for ferritic steel this may affect the mechanical properties since the material is exposed to high temperatures for a long period of time and undergoes several phase transformations. 

Within the scope of TP A07 the mechanical properties as well as the microstructure of WAAM wall structures manufactured with different energy inputs and interpass temperatures were analyzed and an active cooling device was used to shorten the manufacturing time and to reduce the effects of those thermal cycles. 

The results showed a reduction of the tensile strength with increasing energy inputs whereas high interpass temperatures led to an increase of the tensile strength. 

Regarding the yield strength, welding with high energy inputs and interpass temperatures leads to a decreased yield strength.

Especially at high energy input the active cooling had a positive effect as it led to a strong increase of the mechanical properties such as tensile strength and yield strength compared to cooling by free convection. When welding with higher interpass temperatures the active cooling showed no significant effect on the mechanical properties. 

Integrated Additive Manufacturing Processes for Reinforced Shotcrete 3D Printing (SC3DP) Elements with Precise Surface Quality

07.05.2021

Dörrie, Robin; doctoral researcher, Technische Universität Braunschweig, Institute of Structural Design

Based on the digital simulations and numerical analysis, coming from a FEM plugin (Karamba 3D), of different reinforcement layouts in beam elements, the research was continued with the production of these specimens as well as the testing. 

The calculated forces and principal stress lines of the element were translated into a rebar reinforcement by using handmade templates to shape the rebar according to the visualized stress lines. The specimens were separated into two categories with different reinforcement layouts in each group. The first category contains the casted specimens with a non-reinforced beam, a standard reinforced beam and three optimised versions. All specimens from the second category were produced by SC3DP. In this category non-reinforced beams along with two optimised versions were produced. 

The results of the 4-point bending tests showed the great potential of optimising reinforcement layouts. On the one hand a higher efficiency can be reached by keeping the amount of steel equal in both designs. On the other hand, a high amount of steel could be saved to reach the same flexural strength as a standard reinforced beam. 

ZEIT 28. Juni 2021

Weitere Informationen auf AdvanceAEC

You can find the video on TRR277s YouTube Channel (https://www.youtube.com/watch?v=8NGRprlKQsU&t=8s)

Gewinner des "German Innovation Award 2021"

Deutschlands erstes Haus aus dem 3D-Drucker gewinnt den "German Innovation Award" unter der Beteiligung der TU München und dem "Ingenieurbüro Schießl Gehlen Sodeikat".

more

Reinforced Concrete Components from the 3D Printer

Dr. Inka Dreßler on her research in the SFB "Additive Manufacturing in Construction"

How can reinforced concrete components be produced as geometrically precise and high-strength as possible using 3D printing? To this question, Dr. Inka Dreßler has now received support from experts from France during a TRR277-funded research stay in Brittany.

read more

Modelling and Simulation of Shotcrete 3D Printing (SC3DP) Based on a Massively Parallel Multi-Phase, Multi-Component Coupled LBM-DEM Approach

28.04.2021

K. Kutscher (PostDoc); TU Braunschweig, IRMB
M. Geier (PI); TU Braunschweig, IRMB
M. Krafczyk (PI); TU Braunschweig, IRMB

A new numerical model for Bingham fluids has been developed in this project [1]. In this approach we made use of the fact that we found an analytical solution to the implicit problem of finding a relaxation rate for a given shear stress. Previous models relied on iterative solutions [5]or smoothing functions [6]. Differences between the new and the iterative method [5] are seen at higher resolution. It is observed that neither methods convincingly displays second-order convergence down to a resolution of 256 lattice nodes in the span. While both methods give nearly identical results for the lowest resolution, the approximate method levels off at higher resolutions. The next test is a planar Taylor-Couette flow. We investigate the flow between a rotating outer and a resting inner cylinder. Perpendicular to the plane periodic boundary conditions are used such that the setup is quasi two dimensional. Interpolated bounce back with and without velocity is used for the outer and the inner cylinder, respectively. In this test case, flow attached to the outer cylinder will be below the yield threshold and hence move as a solid with the same angular velocity as the outer cylinder. This plug flow domain attached to the outer cylinder is reduced in size with higher angular momentum.

Extrusion of Near-Nozzle Mixed Concrete – Individually Graded in Density and in Rate of 3D Fibre Reinforcement

23.04.2021

Hechtl, Christian Maximilian; TP editor, TUM, Chair of Materials Science and Testing (cbm)
Matthäus, Carla; TP editor, TUM, Chair of Materials Science and Testing
Dr.-Ing. Kränkel, Thomas; PL, TUM, cbm
Prof. Dr.-Ing. Gehlen, Christoph; PL, TUM, Chair of Materials Science and Testing

The main goal of the A03 project is to design a new extrusion method for graded concrete. In contrast to conventional concrete extrusion, the Near-Nozzle Mixing System (NNMS), homogenizes the concrete components (both dry and liquid) in the mixing head and directly deposits the fresh material. This system has many advantages over the conventional approach. Figure 1 shows a rendering of the NNMS.

One of the essential advantages is the opportunity to immediately adjust the material properties during the printing process (gradation). This way, it is for example possible to switch between lightweight concrete structures with high thermal insulation properties and high-strength concrete, allowinghigh load transfer. Since the raw materials for this system can be selected relative freely after rheological adjustment, this system also offers to incorporate reinforcement into the printing process in the form of steel fibers or, as shown in Fig. 1, with the help of a second robot that inserts the steel reinforcement into the already printed layers.

Also, the conflict between pumpability and stiffness of the material is eliminated so that the focus can be on high processability and fast printing. More precisely, the green stability of the fresh material can be significantly increased, since the soft properties of the material are no longer needed for pumping. 

Bridging Scales – From Geometric Part Details to Construction Elements

16.04.2021

Kollmannsberger, Stefan; PL, TUM, CMS
Oztoprak, Oguz; WiMi, TUM, CMS
Rank, Ernst; PL, TUM, CMS

Additive Manufacturing (AM) offers unprecedented flexibility in design and production of geometrically complex components. This flexibility puts a strain on the conventional numerical analysis tools aiming to understand the physical behaviour of the components. As the geometry and material properties get more and more complex, the computing power needed by the numerical tools rapidly increase. The challenge is then to utilize the computing capabilities of the modern hardware to perform large-scale “virtual experiments” on AM components.  Moreover, one needs not only an efficient implementation that can take advantage of the state-of-the-art compute nodes, but also a robust numerical approach that can handle such complex geometries with ease. The Finite Cell Method is one simulation approach that is well-suited to handle such geometric complexities, as it can avoid the time-intense task of mesh generation. To overcome the above challenges, we have extended our numerical analysis tool, an implementation of Finite Cell Method (FCM), to allow for solution of large-scale simulations of AM parts on massively parallel machines. The extension enables solution of problems with billions of unknowns where such problems have been close to impossible to tackle before.

Particle-Bed 3D Printing by Selective Cement Paste Intrusion (SPI) - Particle Surface Functionalisation, Particle Synthesis and Integration of WAAM Reinforcement

09.04.2021

Straßer, Alexander, TP editor, TUM, Chair of Materials Science and Testing
Matthäus, Carla, TP editor, TUM, Chair of Materials Science and Testing
Kränkel, Thomas, TP editor, TUM, Chair of Materials Science and Testing
Gehlen, Christoph, PL, TUM, Chair of Materials Science and Testing

The goal of A02 is the implementation of reinforcement with Wire and Arc Additive Manufacturing (WAAM) in concrete elements produced by Selective Paste Intrusion (SPI). Due to the application of cement paste in the SPI process onto the aggregates and the fact that the cement paste has to percolate into the aggregates by gravity alone, consistent and adjusted rheological properties are essential for a high layer bonding and a good print quality. The welding process with WAAM generates high temperatures – more than 1500°C at the welding point. Therefore, the first step is to verify which temperature loads affect on the cement paste through the WAAM process, what the temperature gradients are in the particle bed, and which temperatures the cement paste can withstand. According to preliminary results, the temperature load of WAAM exceeds the limiting temperature at which cement paste retains its rheological characteristics and can be processed accordingly. To prevent the cement paste used by SPI from dehydrating, the heat transfer and propagation into the particle-bed must be minimized, various parameters in the processes must be optimized, and different cooling strategies developed. Various cooling strategies can be considered to minimize the temperature in the particle bed. This includes varying the time needed to print a layer with the WAAM process. Furthermore, the distance between the welding point and the particle bed surface (in the z- direction) should be increased, and active cooling strategies implemented. Besides, the cement paste is to be optimized concerning temperature loads to retain consistent rheological properties even at higher temperatures. Another aspect is the optimization of the aggregates. As part of the research work, various coatings are to be tested so that the particle bed is more robust in case of a higher temperature load.

Particle-bed 3D printing by selective cement activation: Particle surface functionalization, particle bed compaction and reinforcement

26.03.2021

Herding, Friedrich; Researcher, TU Braunschweig, Institute of Building Materials and Concrete Construction and Fire Safety (iBMB)
Dreßler, Inka; Leading researcher, TU Braunschweig, Institute of Building Materials and Concrete Construction and Fire Safety (iBMB)
Lowke, Dirk; Project leader, TU Braunschweig, Institute of Building Materials and Concrete Construction and Fire Safety (iBMB)

The main objective of our research is to understand the material-process interaction in particle bed 3D printing in order to produce concrete elements with high mechanical performance and geometric precision. The research focuses on the effect of fluid application on the mechanical performance of printed objects from a material (w/c-ratio) and process (fluid discharge rate from the nozzle) point of view. A positive correlation between increasing water to cement ratio and compressive strength is observed. This is in contrast to common concrete technology and is the result of a better bonding between the layers. Additionally, the compressive strength of 3D printed specimens with constant w/c-ratio is increasing with increasing fluid discharge rates from the nozzle. One reason may be the fact that a higher injection depth of the fluid into the particle-bed is achieved. Moreover a rearrangement in particles may take place and a mechanical interlocking of the layers may be prevalent. 

Jointing Principles for Combination of Concrete Elements Produced by Different Additive Manufacturing Processes

17.03.2021

Baghdadi, Abtin; Research Assistent, Institut für Tragwerksentwurf (ITE)

This project aims to investigate the execution process and load-bearing capacity of the concrete-dry joints, considering different printed concrete material to be utilized in the construction of segmental beams. Accordingly, C05 (ITE) is mainly working on the application of the post-processinggrinding technique (milling and cutting) for making pre-selected types of dry joints and on developing innovative connection geometries, which can be produced by the robotic CNC method. These studies will be followed by experimental tests applied to the concrete specimens prepared by different printing technics (AM).   

Through the first working package (2020), ITE prepared appropriate clamping systems, software and milling tools, which can be adaptively applied to a wide range of geometries. Then, for the first CNC applications, multi joint-geometries were selected (10x10x10cm).  Their parametric CAD models(Rhino-Grasshopper) were prepared and exported to the CNC software (EasyStone) to simulate and make the G-codes. Finally, these dry joints in DBFL were produced, and the geometries scanned to once entirely complete and evaluate the process.

Integrating Digital Design and Additive Manufacturing through BIM-Based Decision Support and Digital Twin Methods

05.03.2021

Li, Chao; Doctoral researcher, TU Munich, Chair of Architectural Informatics
Slepicka, Martin; Doctoral researcher, TU Munich, Chair of Computational Modeling and Simulation

In the context of AMC, C04 workgroups attempt to cohesively integrate AM and BIM-based early design, through the design decision support and fabrication- enhanced multi-LOD BIM models.

Knowledge Base Formalization

Domain-specific knowledge base usually serves as a backbone in a Knowledge-Based System (KBS). Furthermore, the knowledge base of proposed DDSS has to be formalized in an extensible, reusable and interoperable manner. In the first stage of work, C04 workgroups have conducted semi-structured interviews between other sub-projects (A01-A05, C01- C06). From the interviews, four groups of knowledge have been initiated while need to be updated iteratively. Accordingly, Semantic Web technology stack has been chosen by WP1 to approach the formal description of AMC-specific knowledge, for its capability, over the individual Knowledge Representation (KR) techniques, to holistically embody rules, ontology, knowledge querying and reasoning[1][2]. To prove the workability of integrating Semantic Web based knowledge into BIM authoring system, a Revit add-in has been developed to query the preliminary AMC-related ontology through the dotNetRDF[3]. Up to now, basic queries from code-behind to the knowledge base turned out a success, which paves the road of upcoming milestones. As inspired from Design for Additive Manufacturing (DFAM) ontologies, adaptations of the initialized knowledge base is under work. Basically, the new ontology aims to loosely couple manufacturability of a building component from its form and function while intermediating those using parameters, manufacturing features and design rules.

Automatic derivation of fabrication information from a BIM model

Both BIM-based design and additive manufacturing processes describe the same object once it has been manufactured, but design focuses more on the final form and function of the component and AM processes focus more on the manufacturing process itself. In the construction industry, the two disciplines are currently handled separately, even though a common database and mutual integration would be beneficial in create a continuous digital chain from design to the finished product [4]. In the field of mechanical engineering, this is realized by linking Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM) processes in uniform software solutions and further improved with the extension of the exchange data format STEP to STEP-NC, to contain a database for the numerical control of machine tools [5]. This makes it possible, for example, to be informed about possible conflicts or obstacles caused by manufacturing processes directly during the design phase [6].

To integrate design decision support and an automated system to derive fabrication information into the BIM-workflow we propose a new methodology, the Fabrication Information Modeling (FIM). As an iterative workflow (shown in Fig. 1), it enables an efficient integration of AM information and workflows into BIM, starting from the early design phase.

Particle-bed 3D printing by Selective Cement Paste Intrusion: Particle Surface Functionalisation, Particle Synthesis and Integration of WAAM Reinforcement

26.02.2021

Hamilton, Leigh Duncan; Researcher, TU Braunschweig, Institute for Particle Technology (iPAT)
Breitung-Faes, Sandra; Leading Researcher, TU Braunschweig, Institute for Particle Technology (iPAT)
Kwade, Arno; PL, TU Braunschweig, Institute for Particle Technology (iPAT)

Selective cement paste intrusion (SPI) is an additive manufacturing method where aggregate particles are spread in small layers, followed by the local intrusion of the cement paste into the aggregate layers. These steps are repeated layer-by-layer and the consequent hardening forms the structure. In comparison to other AM processes, the necessity of support structures for cantilevers is redundant for SPI. In addition, research to date has shown that SPI-made components closely acquire isotropic compressive strength (>70 MPa), reliable shape accuracy as well as high durability.

Whilst the aforementioned advantages are promising for future industrial implementation, the SPI process is in need of a reinforcement mechanism in order to perform a scale-up, and thus, produce structural concrete elements. Hence, the goal of the project A02 is the implementation of Wire and Arc Additive Manufacturing (WAAM) as a means of simultaneously printing the reinforcement during SPI. A successful implementation of WAAM would provide the production of reinforced concrete structures in accordance with the principle of “form follows force”, leading to economically and ecologically viable components. 

The combination of SPI and WAAM is accompanied by obstacles that must be overcome in order to ensure the collaborated functionality. One major challenge occurs from the propagated thermal load of WAAM (approx. 1600 °C), which has negative effects on the paste rheology and resulting concrete strength. Therefore, the overall goal is to minimise heat propagation into the particle bed.

Integration of Individualized Prefabricated Fibre Reinforcement in Additive Manufacturing with Concrete

19.02.2021

Rothe, Tom; Doctoral researcher, TU Braunschweig, Institute of Mechanics and Adaptronics (IMA)
Hühne, Christian; Project leader, TU Braunschweig, Institute of Mechanics and Adaptronics (IMA)

One of the biggest challenges in 3D printing with cementitious materials is the integration of reinforcement. The project aims to develop textile-based reinforcement strategies for additive manufacturing with concrete and to utilize the advantages of textile reinforcement (e.g. corrosion resistance and material flexibility) for the production of material-efficient, individualized structures. These structures should be produced by a robotic winding process, which provides a high degree of freedom in shaping in combination with a minimal amount of tooling and formwork. To be able to do so, a highly autonomous production process is required. Therefore an in situ fiber preparation is integrated. Within this process, fiber rovings are formed to strands. Furthermore, the fiber preparation includes the resin impregnation and the application of a helix surface structuring by wrapping a secondary yarn around the preformed strands to increase the interlocking between the reinforcement structure and the concrete. 

Besides their structural task, the winded reinforcement meshes serve as a base for additively applied concrete. Different methods for applying the concrete can be used.

First experiments to produce reinforcement structures by the winding of glass fiber strands have successfully been conducted. Fig. 1 shows the used robot while winding fiber strands around pins on a rectangular frame. The preparation of the fibers occurred in situ with an end-effector, which has been developed for this purpose within this project. After the winding, concrete was applied on the winded frame by shotcreting. 

Further investigations on the winding process and the use of different additive manufacturing techniques to apply the concrete are planned for the near future.

Laser Powder-Bed Fusion (PBF-LB/M) of Steel Elements for Construction – Basics of Design and Mechanical Resilience

12.02.2021

Diller, Johannes; Doctoral researcher, TU Munich
Dorina Siebert; Doctoral researcher, TU Munich, Chair of Metal Structures
Wenzler, David; Doctoral researcher, TU Munich
Kolb, Cara; Doctoral researcher, TU Munich, Institute for Machine Tools and Industrial Management

The reproducibility of the mechanical properties of PBF-LB/M parts needs to be increased. This requires a more detailed understanding of the correlation between the process parameters and the mechanical and metallurgical properties of the manufactured parts. In project A06 a first step towards this goal has been taken:

With a thermography camera, the cooling rates during the fabrication of fatigue test specimens were measured. Two process parameter sets with different scanning speed and laser power were used for the manufacturing. Afterwards, strain-controlled fatigue testing was performed to investigate the plastic deformation behaviour resulting from the different processing conditions. The first results show significant correlations between the manufacturing conditions, cooling rates, and mechanical properties.

Currently, the thermography set-up is being optimised by a high-speed camera to increase the spatial and temporal resolution. In the next step, the process parameter space will be extended and comprehensive tensile and fatigue testing will be conducted.

1st aaec network member symposia:

“research insides in Additive Manufacturing Construction”

See the full video recording of the online symposia now for free on TRR277s YouTube Chanel (https://youtu.be/EHaXGHG8e_4)

The CRC/Transregio TRR 277 - Additive Manufacturing in Construction based in Braunschweig and München has organised the 1st research insides on 1st of february 2021 within the Research Network for Advancing Architecture, Engineering and Construction" (AdvanceAEC) (https://www.advanceaec.net). The Video of the Symposia shows different Presentations adressing Additive Manufacturing Construction.

Wire and Arc Additive Manufacturing (WAAM) of Complex Individualized Steel Components

29.01.2021
Unglaub, Julian; Associate Researcher,TU Braunschweig, Institute of Steel Structures
Jahns, Hendrik; PhD Researcher, TU Braunschweig, Institute of Steel Structures
Thiele, Klaus; Project Leader; TU Braunschweig, Institute of Steel Structures

Project A07 investigates structural design, WAAM methods and component testing of complex, large-scale, individualized steel components. The objective is to connect conventionally manufactured steel components and semi-finished products with additively manufactured, complex steel components The Institute of Steel Structures develops a novel test method based on fill field strain data. 

This test method considers potentially anisotropic component behaviour, surface topographies, geometric irregularities and residual stresses in addition to the relevant material properties.

Structural Timber by Individual Layer Fabrication (ILF)

22.01.2021
Bunzel, Frauke; Project leader; Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut WKI
Asshoff, Carsten; Doctoral researcher; Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut WKI

In order to produce future-oriented timber structures in the building industry that meet the requirements of ecological and economic sustainability, an additive manufacturing process with wood chips is being developed using the new approach of individual layer fabrication (ILF). In first steps,established wood chip fractions and adhesive systems from the wood-based materials industry are used e. g. for particleboards or oriented strand boards.

For an acceptable adhesive-wood-chips ratio the amount of adhesive must be as low as possible, which is one of the challenges in developing ILF, see Fig. 1. In addition to the distribution of the adhesive over the wood chips surface, the intrusion behavior into the bulk is decisive. On the adhesive side, approaches such as reducing the viscosity by emulsifying with water or reducing the surface tension can lead to better processing results. In first steps, the wood chips should remain untreated. However, it is necessary to determine whether one wood chip fraction can be processed better than others. It is known that higher stiffness and strength can be produced by coarser wood chips fractions, which is also considered. The structural performance of the final component is not only determined by the strength and stiffness of the material but also significantly by the geometry of the part.

For the repeatable and automatable application of the adhesive from above onto the wood chips, a pre-selection of potential valves was made. First, the pressure-time, spray- and jet-valves are investigated. Each of the mentioned valves has advantages and disadvantages in the general application technique of liquids. Experiments will be conducted to determine which of the valves offers the best potential for the ILF process by varying materials and application parameters.

Process Control and Adaptive Path Planning for Additive Manufacturing Processes Based on Industrial Robots with an Extended Degree of Freedom

14.01.2021
Ekanayaka, Virama; Doctoral researcher, TU Braunschweig, Institute of Machine Tools and Production Technology (IWF)

The integration of robot-guided additive manufacturing in the construction industry increases the degree of automation and can thus lead to an increased productivity and increased component quality. In shotcrete 3D printing (SC3DP), reproducible manufacturing results and ensuring component qualities are a major challenge, as the properties of shotcrete depend on many different parameters (e.g. temperature, pressure, water-cement ratio, hardening accelerator).

The goal of this research project is to develop a reproducible, robot-guided shotcrete process based on multi-model adaptive path planning for the production of high-quality large and complex components. The core of this multi-model based path planning is the combination of geometric data and a physical material model into an application process model.

Within the scope of this research, a MATLAB framework is created which enables the coupling of the path planning to a Finite Element model. The STL data of the CAD Model to be printed represents the input used in the MATLAB framework.

Based on the printing path, a novel finite element approach was implemented which builds the mesh independently from the printed component’s ideal CAD geometry.  This has the clear advantage that the actual printed structure is simulated instead of the ideal target geometry. In this way, it is possible to directly simulate the material behavior during application and thus, to determine deviations from the CAD model.

By achieving better results from detailed FEA, the information on the obtained loads and deformations as seen in Figure 1, can be used within an additional feedback loop to adapt the printing path and printing parameters. Using those optimized paths will finally lead to better component quality, reduced test effort, and fewer buildability failures.

Integration of Additive Manufacturing in the Construction Process

08.01.2021
Mawas, Karam; Doctoral researcher, TU Braunschweig, Institute of Geodesy and Photogrammetry (IGP)
Gerke, Markus; Project leader, TU Braunschweig, Institute ofGeodesy and Photogrammetry (IGP)
Maboudi, Mehdi; Associated scientist, TU Braunschweig, Institute of Geodesy and Photogrammetry (IGP)
Riedel, Björn; Associated scientist, TU Braunschweig, Institute of Geodesy and Photogrammetry (IGP)

Additive Manufacturing (AM) allows us to print objects in unprecedented and novel ways, pushing the boundaries of what was previously possible in construction. By seamlessly embedding the process of the design directly into the printing process, ever more complex and free form objects can now be realized.  Nonetheless, AM remains a challenging and involved process that is influenced by a variety of factors. To ensure that a robust process is followed and that the printed object adheres to the model of the original, continuous monitoring and inspection of the process is required. 

Fig. 1 shows a freeform doubly-curved reinforced wall. A laser scanner was used to scan the object as it was constructed, after which it was compared directly to the 3D design model. The resultant model was then colorized based on Cloud to Cloud distance.

As we have stated, while 3D construction printing affords unprecedented freedom, it also poses new challenges for quality control. These challenges include collecting adequate data while ensuring the optimal time for data capturing, the size of the object, and its material properties, all while utilizing the proper type of sensor needed to control the structure's progress as it is being built. It is worth noting that many of these challenges are interrelated and interdependent. For instance, data capture must return reasonably rapid data within a predetermined time window so that the data acquisition of the object is in the range of the predefined time window. However, the type of sensor needed for a project is also dependent upon the size and material properties of the object in question.

One of the defined objectives of the Institute of Geodesy and Photogrammetry of TU is to continuously and effectively monitor the quality of 3d printed construction objects with the use of several different methods of data capturing. This includes the use of quality control during the printing process, as well as data capturing to inspect the object after printing is completed. For this process to be effective, several types of sensors are needed to be investigated, allowing for enhanced data capture, enhanced accuracy, and ongoing comparison with the designed model. Also, the challenges related to each step-in quality inspection process has to be considered.

Wire and Arc Additive Manufacturing (WAAM) of complex individualized steel components

01.01.2021
Christoph Müller, doctoral researcher, TU Braunschweig, Institute for Structural Design (ITE)

This sub-project of the SFB 277 deals with the design process of components for additive manufacturing by Wire and Arc Additive Manufacturing (WAAM). In contrast to large industrial sectors such as mechanical engineering, aeronautical engineering or medical technology, components in the construction industry have to be designed under different general conditions.

If no building system is used to create a structure, the components are usually individual. These components are usually used in the building as a single part or in small quantities. With the implementation of additive manufacturing processes, these components are usually free-form geometries that result from the fulfilment of a wide range of boundary conditions.

This includes improvements in material utilization through topology or shape optimization, geometries suitable for production and architectural design requirements.

Due to the frequently small number of identical components, the effort required to create the geometry must also be kept low, as otherwise the economic advantages of additive manufacturing are outweighed by the effort required in the design process.

The approach in this research project is to automate as many work steps as possible. As a further guideline, the respective effort per work step should be kept as low as possible. Topology optimization serves as an example here. Up to now, this has often been a decisive part of the design process. However, since geometry suitable for production is also required, time and resources can be saved by reducing the precision of topology optimization in favor of design speed.

For this purpose, a basic geometry is created that represents the design space. This geometry is transferred into a spatial framework and calculated by FEM for the corresponding load. Subsequently, the connection points are moved depending on the beam forces of the spatial beam system. In this process step, the points are considered as cellular automata and are all subject to the same set of rules.

AAEC Network Member Symposia

The TRR 277 is pleased to inform, that on Monday, 1st of February 2021, the first AAEC network member symposia will take place:

• Organisation: sfb/trr 277
• Agenda:
  1. Guest Keynotes by Ena Lloret-Fritschi and Fabian Meyer-Brötz
  2. TRR 277 selected project insides
  3. Discussion
• Time: 6:00-8:00 pm
• Further information under : https://www.advanceaec.net/aaec-network-member-symposia/

This event is open to all registered AdvanceAEC members.

If you haven’t registered yet, you are welcome to do so under:  

https://www.advanceaec.net/register/

We are looking forward to your participation!

Architektur und Bau: Mehr Dialog zwischen Forschungsverbünden

Fünf Forschungsverbünde, unter anderem der TRR 277,  haben das „Research Network for Advancing Architecture, Engineering and Construction“ ins Leben gerufen. Das Netzwerk bringt internationale Wissenschaftlerinnen und Wissenschaftler zusammen, die danach streben, Architektur, Ingenieur- und Bauwesen durch digitale Technologien und einen interdisziplinären Ansatz voranzubringen. Es zielt darauf ab, die vielfältigen ökologischen, wirtschaftlichen und soziokulturellen Herausforderungen anzugehen, mit denen die Bauwelt konfrontiert ist.

Der vollständige Text ist unter folgendem Link zu finden: 

https://www.tu-braunschweig.de/abu/aktuelles-und-termine/news-detailansicht/ite-architektur-und-bau-mehr-dialog-zwischen-forschungsverbuenden

Mehr als ein Betondrucker

Interview mit einem Großgerät: das DBFL

16 Meter lang, neun Meter breit und ein Arbeitsraum von 370 Kubikmetern: Das Digital Building Fabrication Laboratory (DBFL) des Instituts für Tragwerksentwurf (ITE) der Technischen Universität Braunschweig ist ein echtes Großgerät. Es schlicht 3D-Betondrucker zu nennen, greift zu kurz. Für Dr. Jeldrik Mainka vom ITE ist es das „größte Schweizer Taschenmesser“, das er kennt. Warum das so ist, hat das DBFL unserer Redakteurin Bianca Loschinsky selbst erzählt.

Das vollständige Interview ist unter vollgendem Link zu finden:

https://magazin.tu-braunschweig.de/m-post/mehr-als-ein-betondrucker/

Best Presentation Award - Digital Concrete 2020

Der Beitrag "Studying the Bond Properties of Vertical Integrated Short Reinforcement in the Shotcrete 3D Printing Process" von Niklas Freund, Inka Dreßler und Dirk Lowke wurde auf der Digital Concrete 2020 mit dem Best Presentation Award ausgezeichnet. Die Digital Concrete ist eine internationale Konferenz, dessen Fokus auf der digitalen Fertigung zementgebundener Baustoffe liegt. Aufgrund der aktuellen Covid-19-Situation musste die diesjährige Konferenz auf ein vollständiges Onlineformat umgestellt werden.

Niklas Freund präsentierte die Ergebnisse experimenteller Untersuchungen, in denen das Verbundverhalten von Bewehrungsstäben untersucht wurde, die in den Shotcrete-3D-Printing-Prozess integriert wurden. Die Ergebnisse sind im Beitrag „Freund, N.; Dreßler, I.; Lowke, D.: Studying the Bond Properties of Vertical Integrated Short Reinforcement in the Shotcrete 3D Printing Process.“ veröffentlicht (https://www.researchgate.net/publication).

Die Integration von Bewehrungselementen in die bestehenden Beton-3D-Druckprozesse stellt ein sehr aktuelles und wichtiges Forschungsthema dar, welches durch Niklas Freund im Teilprojekt A04 des TRR 277 - „Additive Manufacturing in Construction (AMC)“ untersucht wird. Mehr Informationen erhalten Sie unter www.tu-braunschweig.de/trr277/projects/amc-structure/a-projects/a04

Das Institut für Tragwerksentwurf (ITE) der Technischen Universität Braunschweig ist beim diesjährigen Wettbewerb der Deutschen Gesellschaft für Nachhaltiges Bauen (DGNB) unter den drei Finalisten in der Kategorie „Forschung“. Der Beitrag des ITE befasst sich mit robotischer Fabrikation von Bauteilen aus Stampflehm.

Bis zum 13. September 2020 kann für das Projekt abgestimmt werden.

Abstimmen können Sie unter folgenden Link: https://blog.dgnb.de/sustainability-challenge-2020/kategorie-forschung/voting/

Digital Concrete 2020

Professor Dr.-Ing. Dirk Lowke, head of the institute of building materials, concrete construction and fire protection and head of the projects A01 and A04 within the TRR 277 was Keynote Speaker at this year's Digital Concrete 2020 conference. 

The whole presentation can be heard in full at the following links

https://digitalconcrete2020.com/

https://www.youtube.com/watch?time_continue=2359&v=lOS7cKndnA4&feature=emb_logo  

TRR 277 Youtube Channel