Improved Process Efficiency with Microtextured Blanking Punches Using MHP

To reduce emissions in the mobility sector, demand for high-strength and higher-strength steels in the automotive sector is constantly increasing, and with it the demands on the tools of the sheet metal processing industry. One important phenomenon is rapid wear which reduces the service life of blanking tools. Compensating with an increased use of lubricants is not advisable from an ecological point of view. It could be shown in literature that through texturing the lateral surfaces of blanking tools their wear behavior can be improved. In this work, machine hammer peening (MHP) was used to texture the surfaces. Compared to other deterministic texturing methods such as laser texturing, MHP has several beneficial effects. No additional surface finish is required after texturing and the surface structure is not weakened by the thermal influence. MHP machining simultaneously induces residual compressive stresses close to the surface, work-hardens the edge zone and smoothes roughness peaks. Combined with deterministic texturing in the same process step, the tribological behavior of the tool surface can be significantly improved. Based on the tribological investigations of the authors in the strip drawing test on different structuring strategies, the findings from the model test are to be transferred to the real test in this work. For this purpose, rotationally symmetrical blanking punches were textured using a specially developed texturing center. The machine hammer peening center allows surface texturing with positioning accuracies of less than 2% by controlling a rotary and feed axis in combination with frequency control of the machine hammer peening set up. A hammer head with micro-milled micro-tip was used as the texturing tool for the MHP. Different degrees of coverage with the same aspect ratio were applied to the surface. These punches were then tested on various materials on an industrial high-speed stamping press. To evaluate the effectiveness, the force curves for different blanking frequencies were analyzed and the evolution of the textured topography was continuously evaluated. The experiments reveal that the withdraw force could be reduced by 38% due to the micro texturing with a coverage of 18%. Other coverages led to an increase. By texturing the lateral surfaces of blanking punches using MHP the service life could also be significantly improved.