Investigation of surface roughness, tool wear and chip morphology in turning AISI 304 stainless steel

In this experimental thesis study, turning experiments were carried out according to the Taguchi experimental design sequence depending on the cutting parameters (cutting speed, feed and depth of cut) and cutting tool heat treatment type (cryogenic heat treatment) conditions of AISI 304 stainless steel. Cutting parameters were selected as 80 - 100 and 120 m/min cutting speed, 0.15-0.20 and 0.25 mm/rev feed and 1- 1.5 and 2 mm depth of cut. The cutting tool used in the machining experiments was subjected to heat treatment at -196 °C degrees. Accordingly, the cutting tool was used as heat treatment type with and without cryogenic heat treatment. Turning experiments were carried out according to Taguchi mixed L36 (2^1 3^3) design, which is one of the experimental design methods. Here (2^1) represents the cutting tool heat treatment and (3^3) represents the cutting parameters. In the experiments carried out according to Taguchi experimental design sequence, measurements were taken from the surface of the workpiece. These measurements were calculated by measuring from three different points of the workpiece surface and taking their averages. The chips formed as a result of turning experiments were collected and chip morphologies were compared. Cutting tool life was compared according to constant chip volume. Cutting tool life experiments were carried out at constant depth of cut, cutting speed and feed. Considering the wear conditions and machine capacity of both cryogenically treated and untreated cutting tools, cutting speed was selected as 100 m/min, feed as 0.25 mm/rev and cutting depth as 2 mm. When the experimental results obtained in terms of surface roughness were evaluated with Taguchi analysis, the surface roughness values of the workpieces processed with cryogenic heat-treated cutting tools were lower than those of the workpiece processed with untreated tools. The machining parameters obtained for optimum surface roughness were obtained with the cryogenic heat treated cutting tool, 100 m/min cutting speed, 0.15 mm/rev feed and 1 mm depth of cut. According to Taguchi signal/noise ratios, it was seen that the most effective parameter on surface roughness was feed. This was followed by depth of cut, heat treatment condition and cutting speed. In addition, SEM images of cutting tools with and without cryogenic treatment and the morphology of the chips obtained from the workpiece were analyzed. According to the SEM analyzes obtained, it was seen that the wear of the cryogenic heat treated cutting tool was less than that of the cutting tool without any heat treatment.