Research On The Key Technique On Noncircular Crankshaft Grinding

The crank shaft is a key part of the internal-combustion engine so that machining it with high efficiency and precision is the goal pursued by the manufacturers. The crank pin is conventionally grinded by means of the eccentric fixture, the efficiency of which is low and the grinding machine of which is far from flexible. Although the non-circular grinders for the crank shaft are available from the foreign countries, their critical technologies are kept secret, especial the practical control techniques of the non-circular grinding, about which there is hardly any substantial open thesis and information. In China, only some theoretical researches have been made on the non-circular grinding by Huazhong University of Science and Technology and Hunan University without launching commercial grinders.The quality requirement of crank shaft can not be satisfied by non-circular grinding just according to the theoretical movement trajectory because of complex grinding mechanism, the randomicity and uncertainty of grinding process, and the influence of NC system as well as the characteristics of crank shaft such as complex structure, low rigidity and large deformation. Therefore, how to build the exact error compensation model on the basis of analyzing the various influences on non-circular grinding is the crux of non-circular grinding control.According to the grinding mechanism and based on the general consideration of the process precision and the surface quality, this dissertation analyses the various influences on crankshaft non-circular grinding, builds the error compensation model as well as the motion model, and makes creative researches on the following aspects:1.To get high grinding precision and fine surface quality, the motion model based on constant linear velocity control with the error compensations is built up to approximate constant removal rate control for the crank shaft non-circular grinding. In the non-circular grinding, the constant linear velocity is used to guarantee the surface quality of crank pin and the constant removal rate guarantees the precision, which realize both the control of the surface quality and the machining precision.2.Due to the complex structure of crank shaft, its stiffness varies in different angles, which results in the varying forced deformation error. Not only the calculation method of the forced deformation based on Four Points'Stiffness but also the calculation formulae of the grinding force are proposed, which lay a foundation for the compensation of the forced deformation error in crank shaft non-circular grinding.3.The investigation in the influence of NC interpolation and servo lag on grinding quality is conducted in this thesis, which comes to the conclusion that the response lag of servo brings about sharp increase in roundness error of crank pin. Consequently, the machining precision of crank pin is difficult to guarantee by NC system without the compensation for response lag of servo. In the light of the servo response, the calculation formula of this error is proposed to achieve the compensation control.