Investigation of Machinability in Heat Treated SAE 1040 Steel by Experimental Design Method

The purpose of design in engineering experiments is not only to investigate effects of the variables on production, but also to investigate effects of interactions between them. Especially statistical-based experiment design techniques are quite useful for improving the manufacturing process performance in the engineering world. It can be decided to subset of process variables that are the most effective ones by using experimental design. Using experimental design offers advantages such as easier production, better performance, more reliable and shorter design, development and production. In problems that two or more problems are considered, factorial experiment design is a powerful technique. Double-phase steels are widely used in the automotive industry, especially due to their high strength / weight characteristics. These steels provide high strength with the hard martensite phase that is dispersed in the ferrite phase. When the heat treatment parameters are applied correctly between the critical temperatures, a double phase structure is obtained. In this study, the bars prepared from SAE 1040 steel were cooled in water after annealing process between critical temperature, and specimens having double phase microstructures were obtained with two different martensite volume ratios. In the machinability study, the experiments were carried out with full factorial experiment design technique as three factorials (k = 23 and 8 experiments). Type of cutter (CBN and Ceramic cutter), feed rate (0.02 and 0.06 mm / rev) and martensite volume ratio (55% and 78) was used as independent variable (factor) in the experiments, average surface roughness value (Ra) that is dependent variable was determined by measurement from 6 different points with three experiments. Experiments were performed in dry cutting conditions in CNC Turning Table that has 1.5 kW power and rotates with maximum 2000 rpm.As a result, these three factors are effective in turning these steels on their own. The most effective parameters on the surface quality were the cutter tool, the martensite volume ratio, dual interaction of the cutter tool-martensite volume ratio (material hardness), respectively. The results obtained were interpreted together with evaluations that were previously included in the literature.