Experimental study on surface integrity in cryogenic milling of 35CrMnSiA high-strength steel

In this present research, a cryogenic machining system with adjustable jet temperature (-196 similar to 20 degrees C) has been developed, and then a series of cutting experiments have been conducted to investigate the surface integrity of 35CrMnSiA high-strength steel under dry machining and cryogenic machining. The influences of cutting speed, jet temperature, and cooling condition on cutting force, surface roughness, microhardness, microstructure, and residual stress have been investigated. Experimental results are evaluated by means of a surface roughness tester, digital microhardness tester, digital microscope, and X-ray diffractometer. The experimental results reveal that the jet temperature, cooling condition, and cutting speed have a remarkable influence on the cutting force and surface integrity of 35CrMnSiA high-strength steel. At the same cutting speed, a reduction in jet temperature results in an increase in cutting force and decrease in microhardness. The lower jet temperature, the smaller the surface roughness. Compared with dry machining, the tensile residual stress can be effectively reduced under the condition of cryogenic machining. At the same jet temperature, as the cutting speed increases, the cutting force increases firstly and then decreases. In contrast, the surface roughness decreases firstly and then increases. With the increase of cutting speed, under the same cooling condition, the microhardness and residual stress shows a decreasing and increasing trend, respectively. This research contributes to providing a guide to optimize the machining process and improve machined surface integrity.