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

 

[05.06.2026]

Authors

Müggenburg, Marc; Doctoral Researcher, marc.mueggenburg@tu-braunschweig.de

Hinz, Felix; Doctoral Researcher, felix.hinz@tu-braunschweig.de

Unglaub, Julian; Project Leader, j.unglaub@tu-braunschweig.de

Institute of Steel Structures, Technische Universität Braunschweig

 

A07 focuses on developing load-specific, individual high-strength low-alloy steel DED-Arc components, understanding strengthening solutions for existing structures and designing various manufacturing strategies. The specific challenges of adaptive design and adaptive manufacturing of different scale components are addressed and a digital twin including data from the design and manufacturing process, surface geometry and component performance is elaborated. Physical and virtual component tests are carried out to gain  comprehensive knowledge on load-carrying capacity, buckling behavior, the effect of imperfections and fatigue life performance. The project aims to advance DED-Arc application in construction by understanding, predicting and enhancing structural performance of DED-Arc steel.

Summary 

Working group (WG) Unglaub is currently performing virtual tests of DED-Arc high-strength low-alloy steel components. In particular, the effect of the irregular as-built surface, inherent to the DED-Arc printing process, on the fatigue life is investigated with the goal to predict component performance.

In the first step, as-built specimens with differing surface topography were 3D-scanned in collaboration with C06 / WG Gerke. Subsequently, in collaboration with C01 / WG Kollmannsberger, scan-based Finite Cell Simulations were set up and performed to derive stress distribution and, after further processing, obtain Stress Concentration Factors (SCF). Specimen geometry and resulting local stress distribution are shown in Fig. 1 for specimens with different as-built surface topography (e.g. from two different sets of DED-Arc manufacturing parameters).

The results highlight that the complex as-built surface geometry governs local stress distribution and leads to distinct stress concentrations at the layer boundaries. Specimens with more regular surface topography also exhibit more regular stress distribution while irregular surface topography leads to high local stress peaks. Additionally, physical fatigue testing of all specimens was performed to obtain the experimental fatigue life.

Current state of research 

Based on the results from the virtual testing, two models for fatigue life prediction have been set up. As shown in Fig. 2, the fatigue life predictions from the regression-based model show good agreement to the results from experimental testing, thus highlighting that fatigue life can be predicted with similar accuracy across different DED-Arc specimens. These results highlight that DED-Arc load-carrying behavior and performance is intrinsically linked to the as-built surface and thus the manufacturing parameters and the overall approach in component design.

 

 

Earth Additive Manufacturing (EAM) – Material and Process Combinations for AM with Earth-based Materials

 

[13.05.2026]

Machner, Alisa; Project Leader, alisa.machner@tum.de

Tsiotou, Sofia; Doctoral Researcher, sofia.tsiotou@tum.de

Technical University of Munich, TUM School of Engineering and Design, Professorship for Mineral Construction Materials

 

Project A10 aims to design and investigate two novel processes for Earth Additive Manufacturing (EAM), namely, Sprayed Earth Additive Manufacturing (SEAM) as a deposition-based EAM process, and Intrusion Earth Additive Manufacturing (IEAM) as a particle-bed-
based EAM process. Alongside the investigations on the two processes, earthen binder mixtures will be evaluated from a material’s perspective regarding the material-process interaction and their variability and suitability for large scale EAM applications. The assessment of both methods and materials will revolve around tackling issues commonly associated with Earthen Construction such as shrinkage, long drying times and strength development and additionally issues introduced with Additive Manufacturing such as maintaining pumpability while ensuring sufficient buildability during the construction of 3D-printed elements.

Summary

The sub-project summarized in this report highlights the significance of the origin of earthen raw materials used in earthen binders for EAM, as reflected in the quality and quantity of clay minerals as well as the presence of non-clay mineral phases. As earthen construction is re-emerging and gaining popularity in the industry, significant research and development efforts are underway to standardize
earthen raw materials for specific applications. The composition and origin of materials from different geographical locations in Germany and worldwide need to be further investigated in order to generate data that can eventually be used to predict the suitability of different soils for EAM.

The present study investigates the microstructure of a range of different earthen materials and focuses on identifying properties that can help assess the suitability of these materials for 3D printing. We distinguish between two main deposits of clay minerals, primary and secondary, with primary being a product of chemical weathering of silicate feldspathic host rocks in high energy environments [1] and secondary being formed from the physical weathering of minerals as they undergo transportation, erosion and sedimentation further away from the host rock setting [2].

In earthen construction raw materials are mostly sourced from secondary clay deposits, which causes clay minerals to exhibit a higher disorder degree (Figure 1) and to also include phases created through diagenesis (alteration of sediments during burial) such as illite (2:1) (K₀.₇₅Al₂(Si₄O₁₀)(OH)₂·nH₂O).

Weathered earthen materials also tend to have higher amounts of non-clay minerals such as feldspars and carbonates as well as iron oxides and hydroxides. The overall effect of weathering results in a higher Specific Surface Area (SSA) and a shift in the grain size distribution both of which are expected to affect the rheological behavior and strength gain during drying of earthen materials.

Current state of research
During the first part of the study in 2024 – 2025 we managed to establish a promising fundamental characterization protocol for a set of different clay products with variable clay mineral contents and qualities, which allows tracking the effects of mineralogical (clay minerals and bulk chemistry) and physicochemical properties (grain size and surface charges) directly to the rheological and mechanical properties of earthen binders.

The relationship between material mineralogy (microstructure), workability (fresh-state) and mechanical (hard-state) properties is currently being evaluated through analysis of X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR) and rheology and strength investigations, with the aim of determining the origin of the available SSA in each clay material and how it reflects on the particle-water interaction and therefore on the performance of the material as an earthen binder. Solid state NMR is currently being implemented in an attempt to more closely characterize the microstructure of clay minerals and H1 NMR (relaxometry) is tested for observing the saturation and drying mechanism, meaning the rate with which the water is entering and leaving the mineral structure, more closely.

Material rheology is currently tested by means of penetration measurements and flow table slump tests. The goal is to observe the material behavior for the first few hours after mixing and to correlate the results to mineral microstructural data. To further investigate the microstructure in the hardened state CT scanning is currently implemented for visual observations.

 

Integration of Additive Manufacturing in the Construction Process

 

[07.05.2026]

Savadkouhi, Mohammad; Doctoral researcher, m.savadkouhi@tu-braunschweig.de

Mawas, Karam; Doctoral researcher, k.mawas@tu-braunschweig.de

Maboudi, Mehdi; Associated scientist, m.maboudi@tu-braunschweig.de

Gerke, Markus; Project leader, m.gerke@tu-braunschweig.de

all: TU Braunschweig, Institute of Geodesy and Photogrammetry (IGP)

 

The main goal of C06/IGP

Following a comprehensive study of geometric quality control approaches and stages for integrating additive manufacturing (AM) into construction, the second phase of C06/IGP focuses on integrating AM into a cyber-physical construction system (CPCS). This system enables bidirectional interaction between virtual and physical environments, supporting continuous digital workflows and automated feedback loops. Therefore, the first goal of C06/IGP is to evaluate reality capture sensors in terms of measurement accuracy and level of automation to identify optimal solutions for quality control. The second goal is to develop a near-real-time localization workflow for localizing dynamic on-site members, such as robots, sensors, and humans.

Summary

A CPCS may consist of multiple interacting physical members, including printing robots, quality inspection sensors, and human workers, some of whom may be equipped with augmented reality (AR) devices. On the one hand, selecting the optimal quality inspection sensor is crucial, as its output directly influences how accurately the physical process is captured and how it can be integrated into the digital system for real-time monitoring and control. On the other hand, a fundamental requirement in a CPCS is the precise and up-to-date spatial localization of all interacting members. In addition to information such as fabrication design, construction progress, and the status of system components, reliable localization is critical for ensuring consistent coordination between the physical and digital environments. Together, these challenges highlight key research needs in sensor selection and real-time localization for the effective integration of AM into a CPCS.

Therefore, several reality capture sensors, namely a terrestrial laser scanner (TLS), a professional photogrammetry system, an industrial structured light scanner (SLS), as well as a handheld SLS, are employed to capture multiple medium-sized 3D concrete-printed objects with varying surface geometries. This experiment provides comprehensive information regarding the accuracy and resolution of 3D modeling for each sensor, as well as the applied co-registration strategies, required manual effort, and flexibility of each reality capture technique, among others.

In addition, to localize the aforementioned members of the CPCS in real time, a motion capture (MoCap) system is employed at the Digital Construction Site (DCS) which serves as the main research infrastructure of C06 in the second phase. As an initial experiment, the MoCap system is used to track the end effector of a large-scale gantry-type shotcrete 3D printing robot (SC3DP) at the DCS (see Fig. 1). Furthermore, research is being conducted on the localization of reality capture sensors for direct registration, as well as on the real-time navigation of mobile robotic systems.

Current state of research

The experiment on optimal sensor selection has been completed by capturing 3D models of five specimens using three reality capture techniques: laser scanning, structured light scanning, and photogrammetry. The objects of interest comprise one 3D-printed concrete box with multiple geometric features, two paddle-shaped specimens, and a pair of positive-negative T-shaped joint specimens. The outputs of the sensors are compared with respect to resolution, noise, geometric deviation, etc.

Moreover, with a focus on the accuracy of end-effector positioning, the end-effector of the large-scale gantry-type SC3DP robot at the DCS is tracked under both static and dynamic scenarios using motion-tracking-based localization. In the former, the deviation is computed at predefined fixed locations, whereas in the latter, it is evaluated along pre-planned paths. The final output is a 3D deviation map of the entire printing area, providing a foundation for future compensation strategies for real-time correction of end-effector position.

 

 

 

[10.04.2026]

 

The fundamental goal of project A01 is to understand material process interactions in particle-bed 3D printing by Selective Cement Activation (SCA). In SCA, a particle-bed consisting of fine aggregates and cement is applied layerwise. In between the layerwise application, a liquid is applied selectively on the upper layer of the particle-bed. Thereby, the cement hydration reaction is induced locally, and the particle-bed hardens at the selected areas, finally building up to a component. In the second funding period of this project, we focus on sustainability, process enhancement and material models.

Summary 

Particle-bed binding processes, such as 3D concrete printing by Selective Cement Activation (SCA), are different compared to extrusion processes. In extrusion processes, all deposited material ends up in the printed part. On the contrary, in particle-bed binding processes for each layer, material is applied over the complete area of the building chamber (Figure 1, top). In a second step, the material is selectively bound for each layer (Figure 1, bottom). Thus, after binding the last layer, the printed component is surrounded by an unbound particle bed. Advantageously, the particle bed acts as support, so overhangs can be printed without additional effort, compared to extrusion processes. However, depending on the component geometry, the required material volume can be much higher compared to the component volume itself. The difference ends up as unbound particle-bed. To operate particle-bed binding processes environmentally sustainable, the unbound particle-bed must be reused in the next print(s) (cf. Figure 2). This is especially challenging for SCA as the particle bed is a mixture of fine aggregates, cement and admixture. The large difference in median particle size of aggregate (e.g. 300 µm) and cement (e.g. 9 µm) poses the risk for segregation. Due to the low particle size of the cement, dust can be generated during handling and is lost for the printing process. As cement reacts with water, the quality can degrade due to ambient moisture.

Current state of research 

To investigate potential material degradation in SCA, we conducted an experimental study. In this study, we used the same material for 10 consecutive passes through the SCA printer, printed specimens during the 1st, 5th and 10th passes and further collected samples of the non-activated material. During the prints, some material was bound in the specimens. To account for that, we started with more material than necessary for one print, and passed all of the material through the printer in each pass. This way, we could ensure that all material used in each print passed through the printer the same number of times. On the contrary, in normal use, the bound material would be replaced with fresh material for the next print (cf. Figure 2). Hence, our experimental procedure represents a worst-case scenario. Nonetheless, we could not detect a significant decrease in compressive strength of the specimen after the material mixture went through multiple printer passes. For some materials, the compressive strength even increased with multiple printer passes. We conclude that it is generally possible to reuse the unbound material in SCA, which is a necessity to use the process environmentally sustainable.

 

 

The application of Additive Manufacturing (AM) technology requires careful consideration of AM methods’ boundary conditions. Determining suitable AM methods is critical during the early design stages since changes in design are costly when design becomes more mature. To this end, WP1 of sub-project C04 aims to develop a design decision support system (DDSS) that assists architects and engineers in choosing feasible AM methods for BIM-based design. To achieve this, a knowledge base is formalized, which consists of information on different AM methods and design rules. On top of that, the DDSS analyzes building components’ geometric features and functional properties to provide recommendations for suitable AM methods, as well as visualization for design adaptations.

Summary

How can we effectively evaluate the printability of a given geometry? Project C04-WP1 addresses this challenge through the lens of robotic kinematics. By integrating Fabrication Information Models (FIM) with task-oriented manipulability maps, geometric feasibility can be assessed with ease. Furthermore, for printable geometries, the system generates feedback regarding optimal orientation and positioning. This automation eliminates the need for manual repositioning, significantly enhancing the efficiency of the form-finding process during early design stages.

Robot’s capability plays a decisive role to the printability of building elements. To numerically evaluate if a certain robot is capable to accomplish the printing task, one needs to transform the waypoints into robot’s intrinsic manipulation space, verify the reachability while avoiding collisions, then opt for certain metrics to plan for the (optimal) motion and control. Such a pipeline is non-trivial but inevitably needs to be included into the early stages when forms can rapidly change. To address this, we provide a framework to assess geometry with considerations of robot kinematics and printing process constraints.

Precisely, constraints of nozzle orientation and robot’s workspace are unified in a manipulability map. It provides visualization of robot’s reach capability, as well as the input of base position optimization. Instead of manual reposition and reorientation of the building elements/robots, it is now possible to automate the process with efficiency, as the algorithm can provide feedback in few seconds. If the computation fails to converge, i.e., the geometry is beyond the robot’s kinematic capability, then design adaptations should be made accordingly.

Current state of research

In the current phase, we have strengthened the BIM-based robotic simulation tool (RoboBIM) to facilitate fabrication-aware design. Based on previous efforts that build up the skeleton enabling BIM-based robotic simulation, now we have included task-oriented manipulability analysis and base optimization.

The robot’s workspace is divided into a 3D grid with high resolution. Within each grid cell, we sample various possible robotic poses required for the printing tasks incorporating the process constraints of the end effector. Using this data, manipulability maps are pre-computed. Finally, a search algorithm is applied to automatically optimize the position and orientation of the building element—or, conversely, the initial setup of the robot itself.

The pipeline tackles the challenge of validating geometry printability and will be used to collaborate with selected projects as proof-of-concept.

Forschende der TU Braunschweig entwickeln in Kooperation mit dem TRR277 AMC ein 3D-gedrucktes Spundwand Quartier: Bundesumweltminister stellt Prototyp in Hamburg vor

Februar 2026 – innovatives Umweltprojekt aus der Forschung der Technischen Universität Braunschweig wurde letzte Woche in Hamburg offiziell vorgestellt: Das sogenannte SpundwandQuartier wurde von Bundesumweltminister Carsten Schneider sowie Hamburgs Zweiter Bürgermeisterin Katharina Fegebank präsentiert und bepflanzt. Unterstützt wurde die Entwicklung von der Stiftung Lebensraum Elbe im Rahmen des Projekts „Hamburg – Deine Flussnatur“.

Das SpundwandQuartier ist eine innovative, 3D-gedruckte Habitatstruktur, die bestehende Spundwände ökologisch aufwertet, ohne die tragende Infrastruktur maßgeblich zu verändern. Entwickelt wurde der erste Prototyp im Forschungsprojekt „Future Urban Coastlines“ in zusammenarbeit mit dem Teilprojekt Integrated Additive Manufacturing Processes for Reinforced Shotcrete 3D Printing (SC3DP) Elements with Precise Surface Quality des Sonderforschunsgbereischs TRR 277 Additive Manufacturing in Construction an der TU Braunschweig.

Neue Perspektive auf urbane Ufer

Viele urbane Gewässer sind durch glatte, technisch optimierte Spundwände geprägt. Sie stabilisieren Böschungen, bieten aber kaum Lebensraum für Pflanzen und Tiere. Hier setzen die Forschenden rund um den Nachwuchsforschergruppe "Future Urban Coastlines" Dr.-Ing. C. Gabriel David, die Institutsleiter Prof. Harald Kloft und Prof. Nils Goseberg an: Mit Hilfe von 3D-Druck im Betonbau (Shotcrete 3D Printing) entwickeln sie modulare Bausteine, die in bestehende Spundwände eingehängt werden können. So entstehen neue Strukturen im und am Wasser, ohne aufwendige Umbauten oder Eingriffe in die Statik. Die Idee dahinter ist einfach und wirkungsvoll: Bestehende Infrastruktur nicht ersetzen, sondern intelligent ergänzen.

Forschung mit direktem Nutzen für Umwelt und Städte

Unterhalb der Wasseroberfläche schaffen die 3D-gedruckten Module differenzierte Oberflächen, Nischen und Strömungsräume, in denen sich Biofilme, Algen und wirbellose Tiere ansiedeln können. Oberhalb der Wasserlinie bieten bepflanzbare Elemente Raum für überflutungstolerante Pflanzen. Damit verbindet das Projekt Bauingenieurwesen, digitale Fertigung des Sonderforschungsbereichs AMC TRR 277 und Ökosystemforschung, um urbane Gewässer ökologisch aufzuwerten.

Beitrag zu europäischen Umweltzielen

Das SpundwandQuartier unterstützt die Ziele der EU-Wasserrahmenrichtlinie und der EU- Biodiversitätsstrategie. Gleichzeitig zeigt das Projekt, wie innovative Bau- und Fertigungstechnologien konkret zum Umwelt- und Klimaschutz beitragen können.
Was als Forschungsprototyp begann, soll perspektivisch als übertragbares Modell zur ökologischen Nachrüstung urbaner Gewässer dienen.

Projektteam der TU Braunschweig
Christine Schottmüller (Institut für Geoökologie)
Robin Dörrie (Institut für Tragwerksentwurf/TRR277 AMC)
Jeldrik Mainka (Institut für Tragwerksentwurf /TRR277 AMC)
Natasche Holl (Institut für Geoökologie)                                                                                                                                                                         Yamen Abou Abdallah (Institut für Tragwerksentwurf)
Gabriel David (Leichtweiß-Institut für Wasserbau)
Jennifer Rudolph (Institut für Baustoffe, Massivbau und Brandschutz/ TRR277 AMC)
Nils Goseberg (Leichtweiß-Institut für Wasserbau)
Harald Kloft (Institut für Tragwerksentwurf/TRR277 AMC)
Boris Schröder-Esselbach (Institut für Geoökologie)

 

Researchers at TU Braunschweig develop 3D-printed Spundwand Quartier: Federal Environment Minister presents prototype in Hamburg

February 2026 – An innovative environmental project from Technische Universität Braunschweig was officially presented in Hamburg last week. The so-called SpundwandQuartier was introduced and planted by Federal Environment Minister Carsten Schneider and Hamburg’s Second Mayor Katharina Fegebank. The development was supported by the Stiftung Lebensraum Elbe within the framework of the project “Hamburg – Deine Flussnatur.”

The SpundwandQuartier is an innovative, 3D-printed habitat structure designed to ecologically enhance existing sheet pile walls without significantly altering their load-bearing infrastructure. The first prototype was developed within the research project Future Urban Coastlines at TU Braunschweig.

A new perspective on urban waterfronts

Many urban waterways are characterized by smooth, technically optimized sheet pile walls. While they stabilize embankments, they provide little habitat for plants and animals. Researchers led by institute directors Prof. Harald Kloft and Prof. Nils Goseberg address this challenge using Shotcrete 3D Printing (SC3DP). They have developed modular elements that can be integrated into existing sheet pile walls, creating new structures both below and above the waterline, without extensive reconstruction or structural intervention.
The idea is both simple and effective: not to replace existing infrastructure, but to intelligently upgrade it.

Research with direct benefits for cities and the environment

Below the water surface, the 3D-printed modules create differentiated surfaces, niches, and flow conditions that encourage the settlement of biofilms, algae, and invertebrates. Above the waterline, plantable elements provide space for flood-tolerant vegetation.
The project combines structural engineering, digital fabrication within the Collaborative Research Centre AMC TRR 277, and ecosystem research to enhance urban waterways ecologically.

Contributing to European environmental goals

The SpundwandQuartier supports the objectives of the EU Water Framework Directive and the EU Biodiversity Strategy. At the same time, the project demonstrates how innovative construction and manufacturing technologies can make tangible contributions to environmental protection and climate resilience. What began as a research prototype is intended to evolve into a transferable model for the ecological retrofitting of urban waterways.

TU Braunschweig Project Team
Christine Schottmüller (Institute of Geoecology)
Robin Dörrie (Institute of Structural Design)
Jeldrik Mainka (Institute of Structural Design)
Natasche Holl (Institute of Geoecology)
Yamen Abou Abdallah (Institute of Structural Design)
Gabriel David (Leichtweiß Institute for Hydraulic Engineering)
Jennifer Rudolph (Institute for Building Materials, Concrete Construction and Fire Safety)
Nils Goseberg (Leichtweiß Institute for Hydraulic Engineering)
Harald Kloft (Institute of Structural Design)
Boris Schröder-Esselbach (Institute of Geoecology)

 

 

 

 

Project A04 investigates cooperative Additive Manufacturing (AM) processes based on Shotcrete 3D Printing (SC3DP). The aim of this project is to fundamentally understand the SC3DP technology to manufacture sustainable, multi-objective optimised, reinforced concrete components with geometrically precise surface quality and improved building physics by functional integration.

Current state of research

Current SC3DP systems typically rely on single-nozzle configurations, which limit the process to the application of a single material. To enable more sophisticated material control, we are investigating two novel nozzle concepts: a near-nozzle active mixing setup and an adjustable dual-nozzle configuration.

This experimental series has been carried out in collaboration with WG Dröder and WG Kloft. The end effectors used for both nozzle concepts were conceived and fabricated by WG Dröder. We examined the mixing quality of two differently pigmented material streams, which were pumped through separate lines and deposited using both nozzle concepts under varying parameters. The printing strands were cut into slices and analyzed via greyscale imaging and density measurements. These analyses provide insight into the homogeneity and density distribution of the printed strands.

The results show that the active mixing nozzle produces a highly uniform blend of the two streams, largely independent of mixing intensity, making it well suited for two-component (2K) printing.

The dual-nozzle setup behaves differently: the homogeneity of the deposited material depends on the nozzles angel (α) and the distance of the jet intersection to the printing base (A). Figure 1 shows the dual-nozzle spraying process with two differently pigmented material streams, clearly visible as white and black jets intersecting during deposition. The configuration shown corresponds to a nozzle angle of α = 25° and a distance of 100 mm between the jet intersection point and the base.

Depending on the printing direction of the dual nozzle, it is also possible to influence lateral density variation and enable simultaneous side-by-side deposition, thereby opening new possibilities for multi-material structures (see Figure 2).

To enable selective paste intrusion (SPI) for practical applications, the inclusion of reinforcement is mandatory. The focus of the first funding period was set on implementing reinforcements in SPI parts by using wire arc additive manufacturing (WAAM). During the first funding period, two main challenges were identified: the need for increased ecological sustainability for the combined process of SPI+WAAM and the need for accelerated process velocities to improve the economic efficiency. Therefore, the main goals of the project A02 for the second funding period are the ecological material optimisation of SPI and the reduction of the required number of (time-consuming) welding operations within the WAAM process.

Summary:

Within A02, the working group (WG) Zaeh is researching the use of semi-finished products to replace reinforcement sections with low geometrical complexity (e.g., straight rebar sections). The complex geometrical sections (e.g., the nodes) are manufactured with WAAM. Stud welding, which is characterised by coaxial welding, is used to join the semi-finished products to the WAAM sections. The use of semi-finished products and the resulting reduction of welding operations increases the building rate and sustainability and leads to less heat generation, reducing the risk of detrimental effects on the concrete. Suitable process parameters and strategies are identified, supported by a numerical thermal model and feature-based computer-aided manufacturing.

 

Current state of research

The setup for the stud welding process, which consists of a six-axis collaborative robot and a stud welding gun as the tool of the robot, was further developed. It was determined that the rigidity of the system is insufficient to produce a repeatable quality of the stud welds. Therefore, a gripper system has been developed, manufactured, and implemented to stiffen the robot by connecting it to the structure onto which the stud is welded. Furthermore, a pneumatic cylinder was integrated to apply the preload for the stud welding process. This also increased the rigidity of the setup. Beforehand, the robot had to apply the preload, which caused positioning inaccuracies. The new stud welding setup is depicted in Figure 1.

A new shielding gas nozzle, which was optimized with regard to the shielding gas coverage of the melt pool, was developed. For this purpose, computational fluid dynamics simulations were carried out to simulate the influence of different geometries on the shielding gas flow. The optimized nozzle design was then manufactured in collaboration with the project A06 utilizing powder bed fusion of metals using a laser beam. It was then integrated into the gripper system of the stud welding setup. With the new nozzle, the shielding gas coverage of the melt pool could be improved.

With the new setup, a parameter study will be conducted to assess the influence of the stud welding parameters on the mechanical properties of the welds. The combination of the WAAM and the SPI process will be carried out on a dedicated machine, which consists of a SPI printer and a welding robot mounted on a three-axis portal. With this setup, large-scale reinforced SPI parts can be produced. The commissioning of the setup is in the final stage, and the first test welds and SPI prints have already been performed. A digital model of the machine is depicted in Figure 3.

A digital and automated workflow for the generation of parts is now implemented. The focus lies on the automated generation of robot code for a collisionfree
manufacturing of the WAAM reinforcement. The software Rhinoceros 3D and the plug-in Grasshopper are used for the parametrized generation of parts and the translation of the weld trajectories to robot code.

Summary

Project B05 investigates additive manufacturing in construction using mobile robotic systems on building sites. By combining the mobility of a robotic base with the dexterity of a manipulator, the project extends fabrication beyond the geometric reach and situational constraints of stationary system. It aims to develop transferable methods with relevance for the in-situ fabrication of large-scale components as well as for future renovation and repair applications. The project focuses on fundamental methods that allow architectural-scale components to be fabricated directly on site, including in confined or existing environments where large gantry systems are not applicable.

A central motivation of B05 is that construction environments are inherently spatially constrained, obstacle-rich, and shaped by existing structures. While mobility increases the reachable workspace, it also substantially increases the complexity of generating feasible and precise robot trajectories for in-situ 3D printing of building components in their final location. The core research contribution of B05 therefore lies in advancing motion planning for mobile manipulators operating in confined spaces. The project develops fabrication-aware planning strategies that coordinate the coupled degrees of freedom of the mobile platform and robotic arm, enabling continuous, collision-free toolpaths that satisfy process constraints, geometric tolerances, and material behaviour. This includes methods for redundancy resolution, adaptive base positioning, and the structuring of fabrication sequences into executable motion units, evolving from segmented print–drive–print approaches toward integrated printing-while driving strategies that enable uninterrupted material deposition under spatial constraints.

In recent work, we have demonstrated and validated this integrated planning framework through the in-situ fabrication of a self-supported vaulted ceiling using extrusion-based 3D concrete printing. The vaulted geometry provides a structurally demanding and fabrication-relevant test case, while the existing support beams create a spatially constrained, obstacle-rich environment characteristic of real construction sites.

The limited clearance, overhead obstructions, and restricted repositioning space require coordinated planning of base placement and manipulator trajectories to ensure collision-free execution and geometric precision during material deposition. Within this setting, fabrication was implemented using a segmented print–drive–print strategy, in which printing phases are executed from discrete base positions and connected through planned relocation manoeuvres. This scenario serves as a rigorous validation environment for our collision-aware and redundancy-resolving motion planning framework under realistic spatial constraints (Figure 1). At the same time, it establishes the methodological foundation for advancing toward more tightly integrated printing-while-driving strategies in future work.

 

 

Summary

In order to enable a successful print in Concrete in Suspension, the used materials need to be well known and retain their desired properties over the period of production and subsequent hardening of the injected concrete. Therefore, currently the mixture design and rheological characterisation of i) the injected material as well as ii) the non-hardening carrier liquid are focused. Additionally, iii) the usage of reinforcement is being explored as this is critical for using I3DCP to fabricate a wider range of structures.

While a high thixotropic build-up of the  injected material allows the injected strands to better maintain their shape, it prevents sufficient mechanical bonding of nodes when paths are crossing. These affects must be balanced together with the other rheological properties of the injected material to achieve the desired geometric and mechanical results.

The non-hardening carrier liquid is required to sediment not at all or very slowly and be stable enough to keep the injected material in suspension. The yield stress τ0 and the plastic viscosity µ of the carrier liquid are the primary parameters relevant for achieving these properties. Moreover, the yield stress and plastic viscosity are not supposed to be too high in order to prevent deformations due to the further movement of the nozzle. These deformations are shown in Fig 1 where the initially printed strands differ significantly from the print path.

Rheological properties are the key in order to understand material-process interactions, which are in turn the basis for enabling and controlling a successful print.

The usage of pre placed reinforcement bars faces unique challenges in I3DCP as the carrier liquid which initially surrounds the reinforcement must be fully displaced from the surface of the reinforcement by the injected material to ensure a covering of the reinforcement. Here again the rheology plays a critical role together with process parameters like the nozzle speed and geometry.

Current state of research

The current research phase focuses on refining the rheological control of the carrier liquid and its interaction with the injected concrete. Building on earlier studies of sedimentation stability in limestone suspensions, the usage of methyl cellulose reduces sedimentation during the fabrication process significantly. The goal of reusability (enabling at least five prints within one batch of carrier liquid) has largely been achieved without substantial loss of performance. Recent work further investigates how variations in solid volume fraction influence yield stress, geometric stability, and deformation behaviour during printing. The carrier liquid must ensure suspension stability throughout the hardening period of the injected material while maintaining a yield stress and plastic viscosity within an optimal operational window. Increased solid volume fractions improve stability, but excessive yield stress and plastic viscosity can increase strand deformations.

Additionally, a first study on reinforcement integration has been conducted [1]. Pre-placed reinforcement bars were encased using I3DCP while systematically varying process parameters (Fig 2). Current analysis evaluates the encasement quality and strand shape. Using alternate nozzle geometries, and by adjusting relevant process and material parameters the encasement quality can be significantly improved. The yield stress of the carrier liquid must be balanced to support the injected material but not hinder flow around the reinforcement (Fig 3).