Studies On Theory And Key Techniques Of Tangential Point Tracing Grinding

Conventionally, crankshafts have to be ground using several positioning and clamping operations because of the differences in axes orientations of the journal and the crankpin. In this operation, there are many problems such as relatively excessive errors of positioning and clamping, low productivity, large investment of equipment and workshops, long period in the adjustment of the machine tool and fixtures and poor surface finish of the ground part etc. To help with conquering these mentioned shortcomings, a new grinding principle named grinding of tracing tangent point is studied, which allows both crankpin and journal of the crankshaft to be ground in only one positioning and clamping operation. Theory of grinding of tracing tangent point and some key techniques in the realization and application of this new method are focused on. At first, a mathematical model of motion in the grinding of tracing tangent point is established according to the principle of constant removal rate of grinding based on the analyses of the grinding motion. Taking the characteristics of the motion model into carefully considered, the variation law of the machining error caused by tangential point tracing and its NC compensation methods are presented. Secondly, the NC interpolation algorithms of the special curve, which is formed by the rotational motion of crankshaft and to-and-fro motion of grinding wheel in the grinding of crankpin, and a corresponding controlling strategy of interpolation are studied. Then, the stiffness-error caused by the elasticity displacement of crankshaft because of its poor rigidity and the grinding forces etc and the error compensation method are preliminary analyzed, at the same time, factors which may cause the machining error hi the processiiof grinding, such as the variation of diameters of grinding wheel, the deviation of the height between the center of grinding wheel and the rotational center of crankshaft, grinding forces, the difference between the real radius of crankpin and the one used to calculate the motion data for CNC, are took into account for the error analyses. Based on these analyses, experimental study is carried out. The correctness of the motion model is verified by the realization of this new principle for grinding of tracing tangent point on the grinding machine tool. The stiffness of crankshaft is measured and its characteristics are analyzed. Finally, based on theoretical and experimental studies mentioned above, preliminary researches on the computer simulation concerning the motion state and machining process of grinding tangential point tracing are carried out.