Experimental Research On HSC Hardened Die Steels

Due to its high production efficiency, accuracy, surface quality and lower cost, high speed machining technology has been widely used in aerospace, automotive, mold, and other manufacturing fields. But ferrous metals and difficult-to-cut materials cannot be fully machined with high speed machining techniques compared to non-metallic materials and non-ferrous metals and their alloys. Therefore, how to make high speed machining technology apply to ferrous metals and difficult-to-cut material becomes the technical problem to be solved. Polycrystalline Cubic Boron Nitride (PCBN) tool, plays a significant role in HSC ferrous metals and hard-to-cut materials, because of its extremely high hardness, wear resistance and red rigid. This paper studied the mechanism of chip formation of hardened die steel Cr12MoV in HSC with PCBN tools and optimized the tools geometry parameters, in order to provide the theoretical basis for high speed cutting ferrous metal and other hard-to-cut materials.The experiment results indicated that, the degree of chip aliasing first increases then decreases and finally becomes zero as cutting speed increases during high speed turning. It's the first time to find the phenomenon that chip shape from saw-tooth to banding when high speed turning hardened steel, and its changing speed is between 267～339m/min. It was considered that the mechanism of chip deformation is the results of interaction of adiabatic shear, metal thermal softening and material thermal conductivity changes in the high speed cutting. Metal thermal softening and thermal conductivity offset each other at a certain extent, thus adiabatic shear occurs at low cutting speeds; At high cutting speed, metal thermal softening dominates. Dramatic transformation of adiabatic shear zone can be seen in low cutting speed, and its metallurgical structure is the same as the bottom of the chip. With cutting speed increasing, adiabatic shear zone becomes wider and wider, finally the entire chip changes its metallurgical structure because of thermal softening. Cutting speed has a great impact on chip morphology, followed by the feed rate, cutting depth has a little impact when it increases to a certain value.The results of cutting parameters and tool geometric parameters indicated that higher cutting speed, small feed rate and a small cutting depth make higher surface roughness. The reasonable cutting parameters are,cutting speed is between 118～150m/min, the feed is less than or equal to 0.1mm/r and cutting depth less than 0.15mm. Through X-R analysis, the main impact factors on surface roughness are the cutting speed and chamfering degree, followed by the feed and chamfering width, finally the cutting depth and flank angle; the main impact factors on cutting length are followed by cutting speed, feed rate, cutting depth, chamfering angle, flank angle and chamfering width are the last. The tool's reasonable geometric parameters are closely associated with cutting parameters, the reasonable tools geometry parameter, Rake angleγ0 is 0°, flank angle(?)o is between 6°and 8°,chamfering width bγ1 is from 0.15mm to 0.2mm,chamfering angleγ01 is between -10°and -15°and the tool nose radius is 0.4mm.