Effects of online workpiece preheating on the machinability of hardened steel AISI H13 during end milling and development of prediction models using RSM

Abstract

Hardened materials like AISI H13 tool steel are generally regarded as a difficult to cut materials because of their high hardness due to intense carbon content, which however allows them to be used extensively in the hot working tools, dies and moulds. The challenges in machining steels at their hardened state led the way to many research works in amelioration its machinability. This Masters dissertation introduces online heating as one of the new variable parameters to improve the machinability of H13 hardened steel. In the current work the influence of heating parameter i.e. heating temperature; cutting variable, such as cutting speed, feed and axial depth of cut and cutting tool materials, TiAlN coated carbide and PCBN inserts; on different aspects of machinability of H13, were investigated during end milling operation on a CNC Vertical Machining Center (VMC). The study includes identification of relationship between tool life and surface roughness on one hand and the variable parameters, mentioned above on the other. The machining experiments were conducted in two phases, namely, room temperature and preheated machining condition. Response Surface Methodology (RSM) was used to develop empirical models of surface roughness and tool life both for room temperature and preheated machining condition using the data generated from the machining experiments. The comparison between room temperature and preheated machining were made in terms of surface roughness, tool life and machine tool vibration. It was found that preheating had reduced the tool wear, surface roughness and vibration acceleration amplitudes to a desired level. The effects of preheating temperature were also investigated on the chip morphology during the end milling of AISI H13 tool steel, which resulted in reduction of primary chip serration frequency.