Study On The Prediction Of Grind-hardened Layer And Its Friction And Wear Performance

Grind-hardening is a new compound machining technology, which utilizes the grinding heat to harden the surface of the workpiece in the coarse grinding, the temperature of the surface layer is rose to the austenitic temperature in a short time, the martensitic transformation occurred in surface layer by cooling rapidly, the hardness and wear resistance of surface are enhanced. The grind-hardening technology utilizes the finish grinding to achieve the required accuracy. The grinding burning and the difficulty of integrating the surface hardening technology into the machining processes can be solved. In this way, the surface hardening technology can be integrated into the machining processes. Grind-hardening technology utilizes grinding heat to harden the surface layer of the workpiece in grinding process, which exploits a very potential field, and has a theoretical significance for development and improvement of the grinding technology. With the application of the grind-hardening technology in the manufacturing field, the grind-hardening technology will have good social and economic benefits. The content of research and innovative achievements in this paper are as follows.The heat source generating positions are analyzed. Basing on the heat sources generating in the interface of grain-workpiece and shear plane, the grinding heat partition model is developed. The calculated results by the established model indicated the grinding heat partition is lower than the value of the W.B.Rowe's model because of the considering the heat partition in the shear plane. The depth of cut and the table speed had less effect on the heat partition, while the wheel speed has an important effect on it. The incline moving heat source model is used to analyze the relationship between the grinding parameters and the incline moving heat source model. Comparing with Jeager's model, with increasing of the depth of cut and table speed, the difference of the max temperature in grinding zone between the two models is increased. Various sources of heat distribution shapes by using of the incline moving heat model are analyzed. The result indicated the effects of various sources of heat distribution shapes on the two heat models are the same. Considering the variation of the grain's force, the triangular shape sources of heat distribution is chose to calculate and predict the grinding temperature in this paper.Basing on the normal distribution assumption of the grains, the grains in the grinding zone are divided into two kinds, one is the sliding grain, the other is the cutting grain. The force of the single cutting grain and sliding grain are analyzed, then, the grinding force model of single cutting grain and sliding grain are built. The process of the grinding is analyzed by the statistical probability theory, the numbers of the cutting and sliding grains are obtained, therefore the grinding force model is established. The grinding parameters are analyzed by using of the grinding force model. The result indicates, with the depth of cut increasing, the grains in grinding zone and the probability of the cutting and sliding grains are increased, therefore, the grinding force is increased; With the table speed increasing, the probability of the cutting and sliding grains and the number of the grains in grinding zone are increased, so the grinding force also is increased; With the grinding wheel speed increasing, the probability and the number of the grains in grinding zone are decreased, the grinding force is decreased.Based on the grinding and heat transfer theoretical analysis, the mathematical model and finite element model of the grinding temperature field are established, the grinding force and the grinding heat intensity are calculated by using the forward grinding force model. The temperature field of the surface layer and the history of the temperature within the various grinding parameters are analyzed by using of the finite element model. The grind-hardening occurred whether or not, the hardness of the surface and the depth of hardened layer are predicted by the heat treatment theory and the simulation results. The depth of hardening layer is analyzed by the infinite element model within various grinding parameters. The result indicates, the depth of hardening layer increased with the depth of cut; the trend of the depth of hardening layer with increasing of the table speed is increased firstly, and then decreased with the higher table speed, the trend is non-linear. Therefore, the highest depth of cut and the appropriated table speed should be chose for getting the higher depth of hardening layer in the grind-hardening. The grind-hardening technology is studied by some experimental researches, the grinding force and grinding temperature are measured during the experiments. The results of the grinding force indicate the established grinding force model can predict the grinding force accurately, which can be provided the datum for the simulation researches in the grind-hardening technology. The results of the grinding temperature show that the temperature prediction by using of the finite element method is feasible. The error between the predicted results and the experimental results is in less than 11 percent, the max error is the 10.3 percent. The surface micro-hardness by prediction is consistent with the experimental results. The error of depth of grind-hardening between the prediction and experiments with different parameters is in 15 percent. The max error is 14.1 percent. This indicates the depth of grind-hardening forecast was feasible. Basing on the analysis of the grind-hardening technology and heat treatment, the new coolant supply method in grind-hardening is introduced. The experimental results indicated the hardness of the surface layer improved by the new coolant supply method, which can guarantee the depth of grind-hardening layer and broaden the application range of grind-hardening. Comparing with the dry grind-hardening technology, the new coolant supply method can improve the surface topography of the workpiece and avoid the occurrence of the oxidation.The friction and wear tests of the grind-hardening layer are carried out in the MG-2000 high-temperature-wear test machine. The results of the tests indicate, the friction and wear properties of the grind-hardening steel is the best one. The size of martensite produced by grind-hardening technology is smaller, this kind of martensite has higher dislocation density. The performance of the wear and tear in the plastic deformation resistance, tensile strength, crack initiation of stress and the wear-resistant materials performance are improved. In the dry friction and wear tests condition, the main wear mechanism of the grind-hardening layer is abrasive wear within the low-load, low-speed and a short distance conditions. With the increasing of the test load, sliding speed and sliding distance, the wear mechanism of the grind-hardening layer is transformed into oxidation and abrasive wear. With the high-load, high-speed and long-sliding distance, the wear mechanism of the grind-hardening layer was transformed into adhesive wear. There are three kinds of abrasive dusts, massive dust, flake dust and mss dust, in various friction and wear test conditions.