Machinability evaluation of pre-hardened plastic mould steels

Abstract

There are multiple demands placed upon plastic mould steels, depending on the application they will have. Among these requirements, machinability has generally a great economic importance in mould steels and in pre-hardened mould steels in particular. The machining cost can exceed more than half of the cost of a mould. Nevertheless, to avoid subsequent heat treatment, distortion and dimensional inaccuracy, there has been the tendency to use even higher hardness in the pre-hardened mould steels, a hardness range of 38-40 HRC instead of 30-32 HRC. In this work, machinability of some of the most popular grades of pre-hardened plastic mould steel at 38-40 HRC is compared in two milling and two drilling operations. The materials have shown very different properties in different machining operations. This, beside the high requirements upon the plastic mould steels, such as polishability, hardness, impact toughness etc. makes it very complicated to improve these types of steels to be superior in all mould applications.