Customized material properties through porous structures
The Institute of Assembly Technology and Robotics (match) at Leibniz University Hannover is investigating additive manufacturing processes for hybrid porous metal components. The aim is to manufacture components with locally adjustable density and thus specifically adapted mechanical properties. Such structures have the potential to significantly advance lightweight construction. For example, they enable improved energy absorption, adapted stiffness, or the integration of additional functions such as sensors for monitoring the condition of the material.
The Collaborative Research Center Transregio 375 “HyPo” is thus creating multifunctional high-performance components from various metals, combined with controlled porosity. In order for these complex structures to be manufactured reliably, the manufacturing process must be plannable and controllable from the beginning. To this end, match is developing model-based methods for path planning in additive manufacturing in subproject B05.
Challenge: Creating systematic porosity instead of avoiding it randomly
In wire and arc additive manufacturing (WAAM), material is produced along a specified tool path. Traditional planning methods focus exclusively on the desired component geometry. Porosity is traditionally considered a defect and is avoided.
However, the opposite task arises for hybrid porous components: Porosity should be created in a spatially defined manner while achieving the most accurate component geometry possible. This makes the process more complex because process parameters such as wire feed rate, current, or travel speed strongly influence the weld bead geometry and pore formation. In addition, the thermal state changes continuously during layer build-up, resulting in interactions between successive paths.
The match addresses this challenge with a model-based planning approach that combines process models, inverse parameter calculation, and thermal simulation. Based on a digital component design, the system generates weld seams and suitable process parameters and adjusts them iteratively until the target values for geometry and porosity are achieved.
Digital evaluation of path quality and material application simulation
In addition to model-based planning, match is developing a pixel-based deposition simulation for evaluating generated tool paths (see Figure 1). The material deposition is simplified, discretely mapped, and simulated layer by layer. This allows path strategies to be analyzed in terms of coverage, material distribution, or potential defects before real-world trials are conducted.
This simulation allows for a quick qualitative assessment of path quality and supports the selection of suitable planning strategies. It supplements physical process models with an efficient method for geometric analysis and reduces the experimental effort in the development process. In order to experimentally verify the validity of the simulation, the resulting path strategies are then examined on a test bench.
Validation by experiments
The match operates a robot-assisted test bench for additive manufacturing using arc and wire (see Figure 2). With this setup, the team systematically generates process data to experimentally investigate model-based planning approaches.
The focus is on parameter studies that capture the relationship between adjustable process variables and the resulting weld bead geometry and porosity. These investigations serve to validate the developed pixel-based deposition simulation and evaluate its significance in terms of material distribution and path quality. At the same time, the test stand provides measurement data for identifying process models that describe the interactions between path planning, thermal conditions, and material application.
For example, the behavior during cornering and overlapping paths is analyzed in order to specifically parameterize the deposition simulation. Various filling algorithms such as zigzag, contour, or hybrid patterns are specifically adapted to the WAAM process and tested.
Modular software architecture as a research platform
In parallel with its experimental work, the match is developing a modular software architecture for path planning and process evaluation (see Figure 3). This architecture allows individual functional modules to be specifically replaced or expanded without having to rebuild the entire system. This enables the team to flexibly integrate and compare different planning strategies, process models, or simulation methods. The platform supports both the development of new scientific approaches and their adaptation to different manufacturing processes.
Among other things, the platform is to be integrated into the test stand of the Institute of Materials Science (IW), which is also working on WAAM as part of “HyPo” to produce graded hybrid and porous structures. The Institute for Measurement Sensor Technology at the RPTU University Kaiserslautern-Landau is also investigating control approaches for powder-based direct energy deposition in subproject B05. Integration of this software architecture is also planned there.
The match thus creates a technical basis for efficiently addressing future research questions and facilitating cooperation with related disciplines.
