Conjugate curves are cut by the different parts of a pre-grinding hob with protuberance, appearing in subsection nonlinearly, which makes the combined fillet curves difficult to describe with explicit equations and makes the tooth profile complex. Due to the complex tooth profile, the general CAD/CAE methods of geometrical modeling and structure analysis are rarely applied in the strength calculation and transmission performance study. Based on the generating principle, conjugate curve equations of the gear, cut by the pre-grinding hob, are derived. These conjugate curves cut by the different parts of the hob are solved, compressed, linked and synthesized numerically, and then the shape of complex tooth profile are calculated exactly. Combined by strong numeric calculating performance of MATLAB and the facility of ANSYS'S APDL, compositely modeling program with MATLAB full-text data files and APDL is developed based, then FEM (Finite Element Method) geometrical model of tooth profile machined by pre-grinding hob accurately established. According to the built gear model, the relations of bending strength to grinding allowance are researched. The studies show that the grinding allowance of the optimum bending strength is not in allowance value recommended by the pre-grinding JB/T Standard 7968.1-95. The surface quality of gear ignored, less pre-grinding allowance usually leads to more optimal bending strength.
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