Thermal Consideration of the Design of Multilayer Coated Tools for High Speed Machining

Abstract

Quantitative assessment of the thermal role of multi-layer coating in cutting tools was approached through the analysis of mechanical contact problem at the tool–chip interface and the constriction resistance phenomenon. The micro-contact configuration on the surface asperity level (size and density of contact points, and surface approach) and the macro-contact configuration (contact pressure distribution and the size of the adhesion and sliding zones) were defined. The effect of multi-layer coating on stiffness of the contact interface was experimentally investigated and used to estimate effective flow stress of contacting solids. Thermal constriction model, based on the concept of heat flow channel, was developed. Using FE simulation, the correlation between the contact pressure and the thermal contact resistance of uncoated and multi-layer coated tools were established and validated. The thermal interaction and heat redistribution in the workpiece–chip-tool system was then examined for multi-layer coated tools in conventional and high speed machining. Analysis of the results showed that the tool coating causes the reduction of the heat flowing into the tool and the reduction of the maximum temperature rise. The thermal constriction model developed in this work provides a methodology for the design of coated tools based on thermal considerations.