Todays generations of researchers focus on a more efficient and sustainable use of available resources. Key issues of the department Functional and Composite Structures are the manufacturing and the scientific basis of forming functional materials. Furthermore, joining by forming is objective of this department. The PtU dedicates its work to all of these complex objectives on all degrees of abstraction. The research activities cover the broad field between fundamental research on the joint formation and the characteristics of forming functional materials to the manufacturing of complex components with integrated sensors and actuators.

Materials and components for medical technology and mobility

In the context of e-mobility, the topic of lightweight construction continues to gain importance. In order to meet this trend, both the materials and components used and the manufacturing processes employed must be further developed and new approaches to solutions have to be created. One innovative technology for mastering these challenges is the stringer sheet forming developed at PtU. In a novel process chain, a flat sheet is provided with stiffening stringers using laser welding and then formed into the desired geometry, which offers enormous potential for increasing stiffness in car body construction. Current research projects are working on the utilisation of the stringer sheet construction method for the adaptation of product properties analogous to tailored blanks. The flexibility in the design of process and product is to be used to tailor product parameters such as crash or vibration behaviour.

In order to exploit lightweight construction potentials resulting from the use of materials with optimised mechanical, thermal and chemical properties, suitable joining technologies are indispensable that allow materials with different properties to be joined without the performance of the overall structure being affected by the joint. Collision welding processes can be used for this purpose, with which high-strength material-fit joints of different metal alloys can be created. Current research is focused on the robust design of processes and joints in order to pave the way for a broader industrial application, e.g. in automotive support structures.

Powerful permanent magnets are an important factor in efforts for the containment of climate change. These are needed to increase the energy efficiency of electric drives and at the same time minimise the use of rare earths despite the advancement of electrification. At PtU, research is currently being carried out on processes that make it possible to produce materials with outstanding permanent magnetic properties using forming technology. Strong plastic deformations with high shear rates can be used to produce an ultra-fine-grained structure in suitable alloy compositions, which is suitable for producing permanent magnets with reduced use of rare earths.

A comparable approach to the generation of nanostructured microstructures is also being pursued in the production of ultrafine-grained titanium alloys. These not only have outstanding properties in terms of their mechanical behaviour, but also allow use in medical technology due to their simultaneously improved biological properties. Specifically, it is possible to provide materials for implants and osteosynthesis products through the use of novel process routes that, compared to previously used materials, result in improved bone cell growth or a reduction in bacterial colonisation, for example.

Production of actuators and e-motor components

In addition to the basic mechanisms that lead to material-fit or mechanical bonding, the department functional and composite structures is also dedicated to the creation of structures with integrated sensory or actuator functions. One example of this are paraffin-based phase change actuators (PCA), which make it possible to provide high forces at small strokes in an energy-efficient manner. This means that additional functionality can be introduced into applications with limited installation space without increased handling and assembly costs. Up to now, paraffin-based PCAs have been used particularly in micro actuators due to their high power density. At PtU, the transfer of this technology to the macroscopic range is being investigated. One application example is screw connections in which setting processes that lead to loosening of the connection are compensated by the use of PCA.

In order to increase the efficiency of electric drives, intensive research is being carried out to optimise the materials used and the motor topologies to be employed. However, the properties of electrical energy converters are also significantly influenced by the manufacturing processes used. This is particularly true for the rotor and stator cores, which are constructed from thin, electrically insulated individual sheets to reduce iron losses. One joining process used for this purpose, which is gaining in importance especially with increasing production volumes, is interlocking. It enables purely mechanical joining of the individual laminations with short cycle times in progressive dies. In order to take into account the influences of the manufacturing process on the subsequent mechanical and electromagnetic product properties, an investigation of the relevant design, tool and process parameters is carried out at PtU, which can then be used in the form of semi-analytical models for the targeted design and monitoring of interlocking processes.

Qualification of sustainable materials for the packaging industry

Another main research topic is the forming of natural fibre-based materials. In contrast to metallic materials, the forming behaviour of fibrous materials such as paper is not fully understood. For this reason, the PtU has developed its own research methods and test rigs to assess the forming behaviour of fibre materials. Thus, a broad industrial implementation is being prepared through various research projects concerning paper forming. The processes of deep drawing with punch, deep drawing with active medium and incremental forming in interaction with different materials are being investigated.

Current research projects deal with the characterization and modelling of paper as a material in forming processes, taking into account its special properties such as inhomogeneity and pronounced anisotropy. In addition, a uniform methodology for evaluating material behaviour in forming processes is developed. In order to qualify natural fibre materials such as paper and vulcanised fibre as sustainable materials for e.g. the packaging industry and to substitute ecologically problematic plastic-based materials, known processes from sheet metal forming are adapted and optimised for the material paper. Among other things, single- and multi-stage deep-drawing processes are being researched. Since the forming properties of paper are extremely challenging compared to metallic materials in terms of process control, one method is to influence the material properties via variation temperature and humidity in the process.

Vulcanised fibre is a compostable cellulose-based material that has been used in the past to make hard cases or as a substrate material. With the help of incremental manufacturing processes such as Single Point Incremental Forming (SPIF), cost-effective prototypes and small series can be produced from this material. For this purpose, on the one hand the influence of the moisture content during forming is investigated, and on the other hand a model-based control is set up to adjust the component quality.