Surface integrity of hot work tool steel after high speed milling-experimental data and empirical models

High speed milling (HSM) using small diameter solid or indexable insert tungsten carbide end mills, with coatings such as TiAlN is now an established technology for manufacturing moulds and dies in a range of hardened tool steels. The paper presents experimental results and corresponding empirical models for workpiece surface integrity (SI) of hardened AISI H13 hot work tool steel, when HSM using solid carbide ball nose end mills coated with TiAlN. The influence of cutting speed, feed rate and workpiece angle on SI (workpiece surface roughness, microstructure, microhardness and residual stress) was studied using a full factorial experimental design with two levels of each factor. Where appropriate, empirical models were proposed in order to predict SI based on cutting parameter inputs. No significant changes in microstructure and microhardness below the machined surface were found. Within the range of cutting parameters tested, the operating parameters that gave the lowest workpiece surface roughness did not result in the most compressive residual stress distribution below the machined surface. A compromise in parameter selection is therefore necessary to achieve desired roughness and integrity.