Ryan Lake¹, Eli Roberts¹, Christoph Schiffers^2
1CemeCon Inc., Horseheads, NY
²CemeCon AG, Würselen, Germany
Almost all objects around us in daily life require metal machining for their production. This includes cars, trains, and aircrafts. Almost any product used in engineering, medical implants such as hip joints and even the housings of our cell phones are milled to shape. Despite all additive manufacturing activities, classical machining centres using cutting tools made of cemented carbide stand for >95% of the market. As a rule of thumb, a milling centre utilizes 30% of its maximum power consumption just when switching the unit on. This considerably high energy share is required for running the drives systems and their cooling, for the pumps and filtration units of the coolant.
Clear message is to increase the number of parts machined per time to reduce the energy footprint per part. This is where coating technology comes into the picture: HSC (high-speed cutting with highest cutting speed) and HPC (high performance cutting with maximum feed and chip thickness) both depend on the next generation coating technology for carbide cutting tools.
The trend to dry machining without oil in the coolant liquid makes the already extreme temperature in HSC processes due to the extraordinarily high cutting speed even more problematic. Doping an AlTiN chemical composition with Si is known to improve the resistance against wear and oxidation. HiPIMS overcomes the brittleness of traditional TiSiN coating by a fine-grained morphology for a fully new level of toughness of super hard TiAlSiN coatings. With HiPIMS, the energy per pulse can be finely tuned to influence the physical properties of the film independently from its chemical composition. Increasing the cutting speed directly increases the metal removal rate and thus the number of parts machined per time. The avoidance of oil makes high-speed cutting even more sustainable compared to conventional cutting. A case study of machining medical implants from CrCo will be presented. SteelCon® – a HiPIMS TiAlSiN – allows milling of this highly abrasive material with so far unachieved cutting speeds. Anther HiPIMS plus: medical implants always require a perfect surface. HiPIMS is based on sputtering and the 100% droplet-free nature of the technology gives smooth coatings.
The other strategy for sustainable machining is high performance cutting. Such heavy-duty machining for railway tracks and pipeline tubes is characterised by extremely high cutting forces and mechanical loads on the cutting edge. To cope with this, the coating should be as thick as possible. Traditional CVD technology can make thick coatings, however with high tensile stresses, which makes it unsuitable for high performance milling. Important in today’s discussion about sustainability: HiPIMS is a clean process using solid target materials and inert gases only. Very different from CVD systems which rely on toxic precursors.
The HiPIMS innovation is stress management by synchronising the HiPIMS pulses on the cathodes with the substrate bias. A case study of FerroCon®Quadro as a 12 µm PVD coating illustrates how HiPIMS moves the frontiers of the possible in tool coatings. Applications such as the milling of crank shafts, railway tracks and heavy duty turning show the enormous performance benefit of very thick PVD coatings for cutting tools. 12 µm PVD work, in HiPIMS. HiPIMS coatings are a contribution to sustainable machining by improving the energy efficiency of the metal cutting process and by the clean sputtering technology itself.