Punching tools for shear cutting of fiber composites

Components made of fiber-reinforced plastic (FRP) and organo sheets, which are used in the automotive industry or in high-quality consumer products, require precise contours. To ensure that the material is damaged as little as possible in series production and that short cycle times can still be maintained, the industry relies primarily on waterjet cutting, laser processes and machining processes such as milling. However, due to their long processing times, these processes cause significantly higher costs than shear cutting.

The Fraunhofer IPT is working on the further development of shear cutting for FRP: Up to now, shear cutting processes have been very common in sheet metal processing. The punches are therefore optimized for sheet metal materials. When shearing FRP, cutting punches suffer from high tool wear, deliver only poor cut qualities and often lead to component damage such as fiber pullouts.

For this reason, the Fraunhofer IPT has fundamentally investigated the interactions during the shear cutting of FRP and developed punches as well as wear protection coatings. These have already been extensively tested on a basic test rig.

The aim of the research and development work is to extend the process limits in the manufacturing of larger quantities of FRP components, to reduce tool wear and to improve the cutting quality. For companies that use shear cutting in their production, the extended tool life enables a considerable increase in productivity with higher product quality at the same time.

Process development procedure for FRP shear cutting

The process modeling of the shear cutting of organo sheets and their individual layers already allowed initial process parameters to be determined. This knowledge was further supplemented and validated in tape cutting trials. Cutting knives with an additional coating proved to be particularly suitable for this purpose. Further test series with organo sheets made of glass and carbon fiber reinforced plastic (GFRP and CFRP) showed that small cutting clearances provide the best results. More detailed considerations of the shear cutting process, the cut surfaces and the cut quality on fiber and matrix indicate the need for specially adapted cutting punches. Based on the punching grids and parts, twelve different geometries could be developed and compared with regard to different evaluation criteria. This resulted in a user guideline on how to proceed in future FRP shear cutting processes and which punch geometries are best suited to achieve high-quality cutting results.

High-volume production with progressive dies

Shear cutting of FRP with optimized punch geometries could already be transferred to a three-stage progressive die and tested on the servo press line at the Fraunhofer IPT. The high-frequency production of the components from tape material was carried out from the coil at up to 124 strokes/min, delivering good cut quality as predicted. The in-house developed tool is ready for further validation and wear tests at the Fraunhofer IPT.

Our services at a glance

• Experiments to evaluate the wear resistance during shear cutting of FRP
• Investigations into the applicability of coatings
• Development of optimized punches and adaptation to customer-specific applications
• Shear cutting tests on various FRP materials
• Development of tooling concepts for high volume FRP production
• Provision of a user guideline
• Knowledge documentation and employee training