Research On Mechanism Of Thermo-mechanical Coupling On Grinding Interface And Surface Performance Generating Of Spiral Bevel Gears

Spiral bevel gears are the key parts in the national defense, energy, carry, equipment manufacturing and traffic areas, and so on. Its NC grinding method is widely used in its precision machining. As the space shape and processing of spiral bevel gears are complicated, the key grinding technologies have been monopolized by companies such as Gleason in the long term. The researcher in China has also developed the grinding machines of spiral bevel gears in the past decade, but it has been difficult to improve the grinding quality in manufacturing spiral bevel gears. The grinding quality of grinding tooth machines produced by Gleason Corporation is up to two precision, but at present, the ones in China is 4-6 precision, and the grinding surface roughness is not stable, it is easy to produce grinding burn, cracks, and other grinding surface quality defects. The grinding tooth quality of spiral bevel gears is closely related to the grinding tooth machine and process. Therefore, it is a fundamental way to solve our problems of grinding quality of spiral bevel gears that the body precision of grinding tooth machine is improved, the grinding tooth mechanism is understood, and the optimum pre-control of grinding parameters is achieved. However, now there is the serious lack of research on grinding mechanism and process parameters control in China. Taking increase grinding surface quality as the goal, according to the machining principle and process characteristic of spiral bevel gears, the thesis carries out the research on mechanism of thermo-mechanical coupling on grinding interface and surface performance generating of spiral bevel gears. The main contents are as follows.Study on the mechanism of thermo-mechanical coupling on grinding interface of spiral bevel gears. According to the six axis five linkage NC machining principle of spiral bevel gears, its adjusting calculation and grinding mechanism analysis were made, and the physical meaning formulas of grinding forces were built. The heat distribution ratio was gotten by applying the thermal model of a single grinding grit, the heat flux was computed by using a rectangle distributing heat source, and the 3D single tooth model of spiral bevel gear was established by applying the finite element method. On the basis of researches of thermo-mechanical coupling, the grinding temperature field of spiral bevel gears was simulated and analyzed by using theories of heat conduction and the thermo-elastic-plastic, and it was verified by test. The constitutive relationships of stress and deformation fields on grinding interface have been set up by applying PRANDTL-REUSS method, and the distribution of stress and deformation fields at different location of grinding tooth were simulated and analyzed.Study on the grinding residual stresses of spiral bevel gears and its influencing factors. Combined with meshing principle of spiral bevel gears, tooth surface equations were built by applying vector analysis method, and the solid model of analyzing grinding tooth residual stresses was established by applying the bottom-up solid modeling method. Based on the Von Mises yield criterion, the Mises flow rule and the MISO model, the material relationship model of the gears was built. According to the Gleason contact principle, the mathematical models of basic grinding parameters were gotten. Based on the thermo-mechanical coupling, the grinding residual stresses of spiral bevel gear were simulated and verified by experiment, and its change laws with the variation of process parameters were obtained.Study on the grinding surface roughness of spiral bevel gears. According to the principle of space coordinates transformation, the mathematical models of grinding tooth of spiral bevel gear were set up by constructing the tooth surface coordinate system, cutting tool surface and grinding mesh equation of spiral bevel gears. Based on the cutter enveloping principle and analysis of influencing factors of surface roughness, the grinding trajectory was computed by using the constraint solving method of tooth surface grid nodes. Then, the 3D theoretical residual area heights were translated from 2D's ones of cross section along tooth depth, and the theoretical surface roughness model of grinding tooth of spiral bevel gear was built by taking into account a plastic side upheaval phenomenon, and the model was examined by test. The changing regularity of surface roughness affected by the grinding process parameters was reached.Experiment study on the grinding surface layer behavior of spiral bevel gears. The change regularity of micro-hardness and structure of grinding surface layer of spiral bevel gears were tested and analyzed by applying the mechanism of the thermo-mechanical coupling and dislocation theory. Through the test and analysis of temperature, micro-hardness and structure of grinding surface layer of spiral bevel gears, the critical condition of grinding burn was obtained, and the generating rules and its influencing factors of grinding burn and cracks were gotten.Based on the above study of mechanism of thermo-mechanical coupling on grinding interface and surface performance generating, the parameters optimization and the test optimal analysis of grinding surface performance of spiral bevel gears were carried out. According to the results of grinding orthogonal test, the optimizing configuration of grinding process parameters of spiral bevel gears was obtained by using range and variance analysis method. Then, the test regression models of grinding evaluating indicators were conducted by using multivariate nonlinear least squares method. Through the test optimal analysis of grinding surface performance, the value of grinding surface roughness Rαwas more less 0.1μm than ones of the average grinding process, and other comprehensive performance of grinding surface were better. These provided a basis for improvement of grinding surface quality of spiral bevel gears.