Research On Contour Error Mechanism And Accuracy Improvement Of Cam Grinding

The non-circular parts such as camshaft, rotor engine cylinder are the core of enginewhich contour grinding accuracy affects the performance of the engine directly. Thecalculations coordinate of maching this kind of parts are complex. The contour accuracyis affected by some factors such as tracking error change, speed and acceleration shock,grinding force fluctuation, and work piece deformation etc. The mechanism of contourerror and improvement of accuracy are the difficult problems to be solved in camgrinding. The cam shaft of motor car engine and cavity of Wankel rotary piston enginecylinder are the objects of study in this paper.The fluctuation law of cam contour grinding is studied focusing on profilegeometric characteristics such as radius of curvature and contour convexity. At theaspect of cam contour motion model, X-C linkage grinding model of stiffness movementbetween grinding wheel and work piece is established based on relative motion betweenwork piece and grinding wheel during grinding. It is provided that the position model ofunified inner and outer cam profile grinding by vector calculation. On this basis, themodels of linkage velocity of each axis and the moving velocity of grinding point arededuced, which can envelop the target contours of inner and outer cams, analyze thegrinding point condition, control the grinding process precisely, and realize the precisegrinding of non-circular workpieces such as inner and outer cams.It reveals the law that the contour geometry characteristics of radius of curvatureand concave&convex contour affect the fluctuation of cam grinding force. It deducesthe calculation method of cam contour grinding arc length applied to Variable curvatureand concave&convex change. The opinion is proposed that the nature of layer grindingis local plate grinding affected by contour characteristics. It builds the cam contourgrinding calculation model on the basis of plate grinding force model by which itanalyzes quantitatively the relation between grinding force and radius of curvature andconcave&convex contour under normal grinding allowance.It proposes the contour planning method of layering grinding process. According tothe volatility of contour error at the inflection point, the smooth grinding atrategy is putforward based on contour characteristics and adjusting normal grinding allowance. It cansmooth the fluctuations of grinding force and reduce the error at the inflection point bythis method.The research of profile error calculation method during cam profile grinding andcontour compensation is carried out. The definition and calculation methods of contourerror and tracking error are analyzed at the polar coordinate. Online calculation model ofcontour error is established based on lead lag relationship of axis on the grinding process.Online profile compensation controller is designed along the contour error and trackingerror of X-C axis direction. Error compensation decoupling matrix of X-C linkage axis isgiven. Simulation machining of the Wankel rotary piston engine cylinder profile contouris carried out.In addition, in view of difficulties to feeding back factors online in machiningprocess of grinding force fluctuation, installation error, machine tool precision, anoffline compensation model is built based on the tangent point method to approximatethe forming principle. In the similar crank-slider triangle, the profile error is decoupledto two axis compensation, so as to achieve the offline pre-compensation to reduce theprofile error.The grinding experiments of Wankel rotary piston engine cylinder are carried out onthe vertical grinder. It compilshes the experiments of gathering server axis speed and lag during grinding. The comparison experiments of grinding optimization and off-linecompensation are carried out on two numerical control cam grinder. The results showthat the models are correct and can reduce the contour error effectively.