Herstellung von Mikrofräsern aus Hartmetall mittels ultrakurzgepulster Laserstrahlung

Abstract

Micro-cutting is one of the most important micromachining processes in manufacturing technology. It excells by its flexibility, productivity and precision compared to other processes. Micro milling and drilling tools are used for machining with geometrically defined cutting edge. Most of the micro cutting tools are made of cemented carbide. The production of these micro tools is carried out by means of grinding. Tool grinding is accompanied by process forces and heat, which can lead to a pre-damage of the tool and a reduction in manufacturing precision. Ultra-short pulse (USP) laser processing is a force- and wear-free alternative to conventional grinding technology. The use of pulsed laser radiation with a pulse duration in the pico- and subpicosecond range allows material removal, regardless of workpiece hardness and with minimal heat exposure. These advantages are particularly evident in the machining of ultra-hard cutting materials such as cemented carbide. Within the framework of this dissertation the suitability of USP-laser processing for the industrial production of carbide micro milling tools is examined. Conventional micro milling tools are ground with the use of CAM software. Some of the tools are coated to increase their life time during the cutting process. A similar process chain should be established for the laser production of cutting tools. In order to create a basis for the development of a CAM software, firstly experiments are carried out to investigate the dependence of the removal rate on the process parameters. In particular, the influence of the angle of incidence and of the pulse duration on the ablation volume per pulse is analyzed. Analytical models are developed and compared to the experimental findings. The results show that the removal rates can be calculated analytically by using such models and experimentally determined material parameters. In further experiments, the heat influence in carbide processing is investigated and evaluated theoretically and experimentally. The findings on the laser ablation of cemented carbide are used to develop a strategy for laser production of micro milling tools and to propose the development of a possible CAM software. To demonstrate the potential of the developed laser processing strategy, two-sided carbide micro milling tools with a diameter of 0.2 mm and 1.0 mm are manufactured based on CAD models and subsequently measured. In order to be able to assess the coating adhesion of laser processed carbide surfaces, carbide blocks are laser-ablated with different process parameters, cleaned, coated and then subjected to hardness impression tests. The results show that laser-machined carbide surfaces can be coated robustly and well by PVD. The benefit of the alternative process chain for laser production of micro milling tools is assessed by the performance of the produced tools during milling tests. For this purpose, laser-manufactured milling tools are coated and successfully tested together with ground reference milling tools in the machining of hot work steel.