Optimizing surface roughness in end milling of additively and conventionally manufactured components of 18Ni300 maraging steel with minimum quantity lubrication

Abstract This work examines the impact of Minimum Quantity Lubrication (MQL) on the surface roughness optimization during end milling of 18Ni300 maraging steel components produced through conventional manufacturing (CM) and additive manufacturing (AM). It investigates the effects of cutting speed, feed per tooth, and cut depth on surface roughness of the components under as-printed (ASP) and direct aging heat-treated (DAT) conditions for various AM build orientations (0, 45, and 90 degree) and CM. AM components’ comparisons are drawn with the CM components in the as-cast (ASC) and DAT conditions. The results show that the lowest surface roughness of 0.125 μm occurs with 0 degree AM-DAT at a cutting speed of 50 m min −1 , a feed rate of 0.01 mm per tooth, and a depth of cut of 0.1 mm. Surface roughness outcomes correlate with microstructural features and surface morphologies, evaluated using microscopic techniques. The feed marks are more closely spaced for a superior surface finish of 0.125 μm compared to other roughness values. Metallurgical studies were conducted on both the untreated group and the group that underwent heat treatment. After aging, maraging steel exhibits refined microstructure and a reduced number of defects were found in DAT-processed milled specimens. Consequently, the surface finish values are better for all the cases of AM-DAT and CM-DAT in comparison to all the cases of as-printed AM and as-cast CM. It was observed that the application of MQL, although able to achieve better surface quality, was not very effective in suppressing the growth trend of surface roughness with increasing feed conditions across all build orientations and sample conditions.