Minimum quantity of lubricant drilling of stainless steel using refined palm olein: Effect of coating tool on surface roughness and tool wear

Abstract

Abstract This study investigates the effect of cutting tool coating during minimum quantity of lubricant (MQL) drilling of austenitic stainless steel using refined palm olein (RPO) as lubricant/cutting fluid. Two types of tool coating, TiAlN and TiSiN, on tungsten carbide drill with diameter 4 ± 0.01 mm, point angle of 130° and helix angle of 30° were used in this study to machine AISI 316L stainless steel workpiece with hardness of 179.5 HV. Drilling tests were conducted with cutting speed of 12 m/min and feed rate of 0.025 mm/rev. Tool overhang was set at 30 mm. The MQL system in this trial was with 5.5 bar of air, the spray output was 27 ml/h, adjusted 20° and located 35 mm away from the cutting tool. Tool wear was measured during experiment using tool microscope connected to image analyser. Surface roughness (Ra) was measured with cut–off and sampling lengths of 0.8 mm and 4 mm, respectively. For each hole, the surface roughness was measured parallel to the drilled axis at four radial positions at 0°, 90°, 180° and 270°, repeated three times repeated for each position. Tool life of the drill and surface roughness of the drilled hole were the machining responses investigated. It was found that the MQL-RPO drilling using TiSiN coated carbide tool produced better result in terms of tool life (reaching 7.54 minutes) compared to using TiAlN coated tool (of only 4.19 minutes). Related to surface roughness, the best result was obtained by TiAlN coated tool. Through two-factor analysis of variance (ANOVA) with replication on first hole, it was found that the wear of the tool affects the surface roughness significantly while different types of coating has no significant effect on tool wear and surface roughness. In addition, there is no interaction between types of coating and wear of the tool that influence the surface roughness.