Cost models for comparing room temperature and preheated end-miling of AISI D2 tool steel

Abstract

Preheated machining was found to yield improvements in the machinability of the AISI D2 tool steel, such as longer tool life and lower surface roughness. For preheated machining to be more preferred than room temperature machining, it has to be economically more attractive –besides being better in the context of machinability–. In this research, a thorough investigation was conducted to determine the conditions under which; preheated machining would yield lower machining cost. The conditions under which; room temperature machining would yield lower machining cost were determined as well. User-friendly and accurate mathematical models to estimate the cost of machining in terms of the machining parameters were developed. Initially, the components of machining cost were identified, followed by establishment of equations to evaluate their contributions to the cost of machining. All the required data were made available and the bottom-up approach was adopted for evaluating the cost of end-milling the AISI D2 tool steel. The cost of machining corresponding to each of fifteen experimental runs in each of the two machining methods was evaluated; this was done for two types of cutting tool insert: TiAlN coated carbide inserts and polycrystalline cubic boron nitride inserts, and four levels of utilization: 15%, 25%, 80%, and 90%. Machining costs in room temperature machining were compared with the corresponding ones in preheated machining to determine the conditions under which; preheated machining would yield lower machining cost, and those under which; room temperature machining would yield lower machining cost. The results indicated that when 15% utilization and TiAlN coated carbide inserts are considered, preheated machining would yield lower machining cost in two out of nine experimental runs. The number of experimental runs in which preheated machining would yield lower machining cost increases as the level of utilization is increased. At 90% utilization, preheated machining would yield lower machining cost in eight experimental runs. When PCBN inserts were used, preheated machining yielded lower machining cost in all the nine experimental runs irrespective of the utilization level. Increasing the utilization was found to significantly reduce the cost of machining. The Response Surface Methodology was used to develop the models for both the machining methods considering the two types of inserts, and the four levels of utilization, based on this, sixteen models were developed. The statistical adequacy at 95% confidence interval of the developed models was checked using ANOVA tables. All the developed models were found to be very adequate.