Self-Lubricating Physical Vapor Deposition Coatings for Dry Cold Massive Forming

Abstract

Cold massive forming, particularly forward extrusion of steel, is characterized by high material utilization, product quality, and resource efficiency. Currently, enormous quantities of mostly ecologically harmful lubricants are required, leading to the demand for lubricant-free cold forming. Furthermore, cost savings are achievable due to shorter lead times. However, the requirements for the tools cannot be met without the application of wear-resistant and friction-reducing hard coatings. The self-lubricating hard coatings (Cr,Al)N + Mo:S and (Cr,Al)N + W:S with attuned material design deposited by physical vapor deposition (PVD) offer high potential for the realization of dry cold forming of steel. The process chain for the comprehensive characterization of the developed coating systems comprises analyses of coating and compound properties as well as two different model tests to determine the tribological behavior. One of the used tribometers represents an open tribological system, which is particularly suitable for simulating the loads occurring during cold massive forming of steel. The analyses reveal that with Mo and S modified coatings exhibit higher potential for ecologically sustainable cold forming due to their better mechanical properties and compound properties between the coatings and the cold work steel substrate compared with W and S modified coatings.