| Manufacturing continues to be a significant sector of modern economies and an important growth sector in the world. Manufactures continually search for new and lower cost methods to manufacture products as well as more efficient application of existing process technologies. There are a variety of precision mechanical components such as bearings, gears and mould & die, which are made of hardened steels, have to be machined to a high degree of precision. The availability of PCBN(Polycrystalline Cubic Boron Nitride) cutting tools has opened up the possibility of achieving these requirements by a finish machining process, while requiring little or no grinding.With the development of super-hard cutting tool materials such as ceramics and PCBN etc., the technology of hard turning has created considerable interest to several leading manufacturers. In this paper, the hardened bearing steel GCr15 is selected to be the material, a series of cutting forces experiments were done with AMBORITE DBC50 PCBN tool which was supplied by DeBeers Industrial Diamonds Corporation with CA6140 lathe. The results indicated that in general, the radial force was the highest, followed by the tangential and axial forces. When roughing, cutting forces were approximately 3 times higher than when finishing. Cutting forces increased almost linearly with feed rate and depth of cut , but decreased slightly as the cutting speed was increased when the cutting speed lower than 200m/min, with higher cutting speed, the cutting forces increase linearly with cutting speed. The results show that there is a critical cutting speed to decided the cutting forces information. One of the significant observations during hard turning which is different from machining of ductile materials is that consistently cyclic saw-tooth chips are produced. Experiments are conducted with AMBORITE DBC50 PCBN tools to investigate the influence of workpiece hardness, cutting speed, feed rate and cutting depth on the saw-tooth chips formation. The experimental results shows the workpiece hardness and cutting speed are the major factors which decided the chip shape. The Wavelet results of cutting forces signals show that there are inherence relations between chip shape and the cutting forces.A new cutting force model coupled with edge forces and ploughing forces for hard turning is developed to predict the cutting forces. An new analytical chip flow angle model based on the cutting process was developed to calculate the chip flow angle during cutting , the new chip flow angle model divided all possible cutting geometry to the single cutting edge tool and pure tool nose radius, and it is very easy to understood and implied. The cutting forces prediction program is write in MATLAB and the results show good agree with the experimental results.The materials soften phenomena is decided by the cutting temperature during hard turning,this special cutting performance is investigated by the temperature distribution through a series experiments vary cutting conditions such as cutting speed, feed rate, cutting depth, the original material temperature and the materials hardness etc. It could be draw a conclusion from the experimental results of five hardness HRC30,HRC40,HRC50,HRC60,HRC62 that the hardness HRC50 is a line to divide the common cutting and the hard turning. While the material machined hardness is lower than HRC50, the changing rule of cutting force and cutting temperature was accordant with the common cutting theory. While the material machined hardness is above HRC50, the above parameters aren't accordant with the common cutting theory. While the material machined hardness is closed to HRC50, the cutting temperature hits the highest point, the machined surface quality is the worst.Topography of surfaces produced in finish hard turning using PCBN tools is affected by a large number of factors including different edge geometry , cutting parameters and the mechanics of the chip formation process. The paper compares several aspects of finish turning of hardened be...
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