Surface Roughness Prediction and Multi-Objective Optimization of Honing Cylinder Liner

The surface machining quality of cylinder liner is usually evaluated by surface roughness R_k set, it is of great significance to establish a prediction model between roughness R_k set and machining parameters, and analyze the influence of machining parameters on honing quality of cylinder liner. Based on the rough honing experiments on cylinder liner under different honing pressure (P), different honing head rotation speed (V_R) and different reciprocating speed (V_Re), the values of the surface roughness R_k set were obtained. In order to predict the R_k, R_pk and R_vk of the surface roughness R_k set of the inner bore of cylinder liner during the rough honing process, and to optimize the honing parameters, the P, V_R and V_Re were taken as decision variables, and R_k roughness set was taken as the object response, multi-objective optimization was implemented to obtain the optimal machining parameters of P, V_R and V_Re. The roughness prediction models based on generalized regression neural network (GRNN) and response surface methodology (RSM) were established respectively. For the GRNN method, it was necessary to use the K-fold cross validation method to optimize the smoothing factor (i.e., spread), the value of the smoothing factor can greatly affect the prediction performance of the network. The minimum MSE can be obtained in the process of five-fold cross validation, the smoothing factor was 0.01 when the MSE had the minimum value. Twenty-one groups of experiment data were trained to achieve the prediction model by GRNN, and other 6 groups were regarded as test samples to verify the accuracy of the proposed model. The Box-Behnken Design (BBD) method of response surface method was used to design the experiment, and 17 groups of experiments were conducted to establish the response relationship between the honing parameters and the surface roughness R_k set. The surface roughness R_k set can be predicted by the optimized regression models based on RSM. And comparing with a full factorial honing test with three factors and three levels, the result showed that the prediction results obtained by the proposed models were in good agreement with the experimental results. The mean value of R² of the coefficient of determination of GRNN prediction model was 0.959, the mean value of R² of the coefficient of determination of the multiple regression prediction model established by RSM was 0.963. Comparing with the multiple regression prediction model established by RSM, the GRNN prediction model had higher prediction accuracy and smaller prediction error for prediction of R_k and R_pk, and R² of R_k and R_pk increased by 0.025 and 0.020 respectively. The multiple regression model established by RSM was better than the GRNN prediction model when predicting R_vk, and R² increased by 0.057. The influence significance of three decision variables on the roughness was analyzed by the RSM, and the ranking result for R_k was V_Re > P > V_R, for R_pk was P > V_Re > V_R, for R_vk was P > V_Re > V_R.In order to select the appropriate values of P, V_R and V_Re to make the R_k roughness set relatively small, based on the regression model established by the RSM, a multi-objective optimization was implemented to obtain the Pareto front of the Pareto optimal solutions by combining the multiple regression models with NSGA-II (non-dominated Sorting Genetic Algorithm II) optimization algorithm. More machining parameters combinations for rough honing of cylinder liner were provided to get high honing quality. Eight groups of optimum roughness values and the corresponding rough honing parameters of cylinder liner were given.