Advanced calculation of the stress distribution in milling tools during cutting under consideration of residual stresses and tool wear

摘要

Milling is an irreplaceable technology for finishing turbomachinery components made of nickel-based alloys. Cutting tools in milling are exposed to high thermomechanical loads causing tool wear or ultimately tool failure. The initial condition of the tool’s surface layer determines the propagation of tool wear. “Surface layer” denotes the zone near the tool surface, which is affected mechanically, thermally, and chemically during the manufacturing process of the tool (e.g. due to grinding, polishing). So far, only limited knowledge is available on the specific effects of wear-induced changes in tool geometry as well as of residual stresses on the distribution of stresses in the cutting wedge of milling tools. This publication presents a method to consider residual stresses of cutting tools and tool wear in a 2D FEM chip formation model for detailed analysis of certain tool failure phenomena in the milling process. In order to represent a depth distribution of residual stresses in the surface layer of the uncoated tool in the simulation, residual stress measurements at grinded milling tools were performed. Tool wear was taken into account by adapting the geometry of the cutting tool. The geometry changes were based on measurements of the width of the flank wear land and of the cutting edge radius. Principal stresses and von Mises equivalent stress distribution were analyzed. The described method may improve the understanding of surface layer effects on tool life of milling tools. With decreasing chip thickness, a second, more localized zone of tensile stresses was formed at the rake face subsurface, which can be critical in terms of fracture. With compressive residual stresses and with increased flank wear, these critical tensile stresses were reduced or even eliminated.