Research focus Mechanical joining

We respond to current technological and economic changes in mechanical engineering and the automotive industry with new and further developments in joining technology. Proven joining processes are adapted to current requirements and new technologies are researched against the background of resource-efficient production.

Mechanical joining technology offers innovative and cost-effective processes for joining similar and dissimilar materials. With regard to current lightweight construction concepts and the associated mixed construction methods, thermal joining processes are increasingly reaching their limits. Mechanical joining processes are often a more cost-effective and energy-efficient alternative to resistance spot welding and other thermal joining processes.

Our research into mechanical joining covers the entire process chain of a component and its effects on the quality properties of the end product. This includes, for example, testing dimensional accuracy or component behavior under load. We use equipment that is both based on current industry standards and exploits the possibilities of modern scientific methods. Several robot cells with joining systems from various system providers and modern press technology enable us to reproduce an industrial environment from the forming process to joining.

There is also potential for lightweight construction in the targeted use of manufacturing processes. Adhesive bonding technology is a good example of this. Adhesive bonds are becoming increasingly important in view of the more favorable operating load distribution and corrosion protection in mixed joints. Combinations of joining processes are used to combine specific advantages of individual processes and to compensate for deficits in elementary processes. Our research focuses on the combination of clinching or self-pierce riveting with adhesive bonding and seam bonding, as these combinations have particularly high potential.

Due to interactions between mechanical joining and adhesive bonding, tool and process parameters of the elementary joining processes cannot always be transferred to hybrid joining technology. Research tasks therefore include evaluating the influence of relevant process parameters (e.g. adhesive viscosity, joining speed) and deriving appropriate measures to improve hybrid joints.

A key aspect of our research into hybrid joining is global process analysis and improvement. In addition to determining the joining point quality, suitable process parameters are determined, with the focus on the dimensional accuracy of the entire assembly. To this end, we are increasingly carrying out structural and flow simulations as well as experimental parameter studies on the entire process chain.

Mechanical joining processes are often characterized by complex stress distributions and high local plastic deformations. With adapted process models and taking into account all real tool movements and geometries, we can investigate a wide range of joining processes using numerical simulation and understand the key process influencing variables. In this way, the stress distributions at the joint can be analyzed and suitable process parameter windows identified.

Various test methods such as tensile, shear and compression tests as well as optical measurement methods are used to characterize the material properties in the calculation. The numerical results are always validated using macrosections, hardness tests and the evaluation of experimental process data.

The real joining point behavior under load is determined using specially developed sample shapes and a variety of measurement methods and transferred to the equivalent model. The result is a component model that allows the joining point behavior to be mapped while maintaining practicable calculation times. This allows more precise statements to be made about the load limits of the joined structure and potential for improvement to be derived.

An important aspect of the holistic approach is the detachability of joints after the product life cycle. Research work at Fraunhofer IWU is therefore aimed at the further development of joining technology with a focus on the sustainability and recyclability of mechanically joined products. In the field of detachable joints, the focus is on both the high requirements of large series quantities (e.g. short cycle times) and smaller batch sizes (e.g. flexibility):

• Consideration of the life cycle of detachable connections under the aspects:
  • Resource efficiency
  • Costs/benefits
• Dismantling
  • Reuse, recycling, disposal
  • New dismantling technologies
  • Observance/consideration of legal or automotive guidelines/requirements
• Surface modifications, joining preparation
• Design guidelines

With modern system technology, we can realize the following standard processes of forming joining, among others:

• Self-pierce riveting, clinching, blind riveting
• Hybrid joining processes
• Seaming, seam bonding
• Hydro-pierce riveting, clinching
• Joining with lockbolts
• Setting of functional elements

The range is supplemented by other joining processes developed by us.

We advise you on the selection of processes for specific joining tasks and on the design of components to suit the joining process, taking into account the requirements profile, material and accessibility. We offer testing from the individual sample to the component in accordance with applicable standards and guidelines:

• Monitoring of component geometry in furnace processes
• Quasi-static, cyclic and crash testing
• Climate change, salt spray test