Machinability evaluation of prehardened plastic moulding steels

Paper in proceeding, 2008

There are multiple demands placed upon plastic mould steels, depending on the application they will have. Among these requirements, machinability is of great economic importance. Mould steel influences the cost of plastic parts more through its machinability, since machining cost exceeds more than half of the cost of a mould. Milling and drilling are the machining operations that are mostly used in production of a mould and the highest volume of material removal performs through these two categories of operations and specially milling. Recently, there has been a high tendency to use prehardened mould steels with the hardness range of 38-40 HRC, for the higher demands on mechanical properties and wear resistance. Additionally, to avoid distortion and dimensional inaccuracy, the mould steels are supplied in prehardened condition which impairs their machinability. In this work, machinability of some of the most popular grades of prehardened plastic mould steels 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 and hardness, impact toughness and etc. makes it very complicated to improve these types of steels to be superior in all mould applications in addition to that material selection becomes crucial with respect to mould making cost.