Parametric Optimization Of High-accuracy Low-rigidity Part In Multi-step Machining

The design of component structure are increasingly intend to be thin-wall or slender axle, and was called Low-rigidity part. This kind of structure shows a bad performance in resisting to cutting force and cutting heat during processing. It also have little tolerance of deviance. A specific process often process oversized cutting depth which cannot be finished in a single cut. This thesis aim at the excessive deviation problem due to deformation of traditional low-rigidity part in turning process. The rules for parameter design were discussed. Based on the traditional research of single cut optimization, the optimization issue of multi-step cutting were studied. Mathematical model of the cutting parameters-cutting force relation as well as the cutting parameter-heat generation relation were built. With the model, the optimization of parameters was achieved. Details are as follows:Firstly this the relationship between cutting deformation and cutting force was analyzed, the factors affecting the deformation of turning was discussed and conclusion were reached. Analyzing the cutting force formula and theory of heat generation,it was found that adjustment of the cutting parameters is a useful way to control the cutting force and heat generation. Aiming at selection of cutting parameters, the principles and methods involved in allocation of cutting depth was discussed. Aiming at optimization of parameter,the regularity of optimization function and constraints for multi-objective optimization methods in cylindrical turning was discussed. An algorithm for optimization of a two-step cutting was designed and genetic algorithms was briefly introduced.The basic theory and reason of chatter phenomenon in turning was discussed and the mathematical expression of critical cutting width with respect to each rotation speed was obtained. An experiment of the gear cutting system was conducted and the chatter stability lobes and model parameter was obtained.Then, using the finite element software Abaqus, a two-dimensional finite element(FE)model was established for first turning step. An orthogonal experiment was designed and finished with the FE model and data were extracted. With the data, mathematical models of the relationship between cutting parameters and deformation as well as the relationshipbetween cutting parameters and heat generation were established. Using Matlab genetic algorithm toolbox, dual objective optimization for the first turning step was finished based on the mathematical model and optimized parameters of the first turning was obtained.Via Abaqus software, a 3-D FE model for the first turning step was established and using the optimized parameter above simulation was conducted from which the heat generation and deformation data was obtained. Combined with the data as pre-defined character, a FE model for the second cutting step was established. An orthogonal experiment model was established and simulation was conducted with the FE model from which deformation and heat temperature data were extracted. Using the data,a cutting parameter-deformation relationship was built. Using this model along with material remove rate formula, a dual objection optimization model was established and conducted in Matlab software. A set of developed cutting parameter was obtained.Finally, a gear ring turning experiment involving first and second cutting step was conducted. In this experiment the temperature data of the first step and the deformation data on the second step were contrast with the simulation. The validation of simulation was verified and difference was briefly analyzed.