Effect of Machining Directions on Surface Integrity of AISI 1018 Steel in a Face Milling Process

Abstract

This study analyses the effect of machining directions on surface integrity of AISI 1018 steel by performing a face milling operation using the zag toolpath strategy; undertaking a detailed surface roughness check of the machined surface in the cutting and feed directions; studying the microstructure of the as-received workpiece and subsurface of the machined part in the cutting and feed directions in 2% Nital etching; and comparing the grain size before and after the cutting process. Results show that surface roughness values were minimal when measurements were conducted at the middle of the machined surface. Also, surface roughness values were higher in the feed direction than in the cutting direction by 13% due to the presence of feed marks which were clearly visible on the machined surface. The grains at the top machined surface were deformed, elongated, and oriented in the cutting direction as a result of plastic deformations experienced in the machining process, while the grains were also elongated and disoriented in the feed direction. Surface damages caused by the cutting tool’s engagement of the workpiece were clearly seen at the side of the machined surface’s edge. The average grain size value before machining was higher than the average grain size value after machining by 27%, attributed to the plastic deformation of the grain structure as a result of machining. This study has provided an in depth knowledge and understanding of the influence of plastic deformation due to machining on surface roughness and microstructure of the machined part.