Study On Thermal Deformation Modeling And Reduction For Ball Screws

Performance of high-level CNC machines is directly affected by precision and stability of ball screws which has been widely applied in transmission systems owing to its high speed,precision,high stiffness and sensitivity.In high speed and precision machining process,temperature rise leads to axial thermal deformation and thermal error of ball screws,which decreases the position accuracy of the feed system in machine tools.Currently,thermal deformation compensation and reduction are the two main effective technologies to decrease the thermal error.This paper provides the support to ensure the position and machining accuracy of machine tools from the perspective of thermal deformation modeling and reduction.The main contents are:(1)Aiming at the problems of robustness and generalization ability of thermal error compensation model,a data-driven thermal deformation prediction model of ball screws based on particle swarm optimization algorithm optimized long short-term memory network(PSO-LSTM)is proposed.Firstly,in order to provide the preliminary reliable data for PSO-LSTM model,a finite element simulation model of ball screws is established.The temperature and thermal deformation data of the simulation under the step speed condition are used to drive PSO-LSTM model for predicting the thermal deformation of ball screws.The result shows that the predictive value agrees with the simulated value.Simultaneously,the absolute error is controlled within 3?m.The prediction accuracy of the PSO-LSTM model is good.The predictive performance of PSO-LSTM model is evaluated by four criteria,and the feasibility and accuracy of the proposed model are verified.(2)The key points of temperature sensors of the ball screws are determined based on the thermal modal analysis.In order to verify the feasibility and effectiveness of the proposed model,two thermal characteristic experiments based on step and random speed are conducted on a self-designed test bench.The performance of the proposed model is compared with that of RBF model and BP model,the result shows that the PSO-LSTM model has higher accuracy compared to that of the RBF model and BP model with high robustness.(3)In order to reduce the temperature rise and thermal deformation of ball screws for improving the position and machining accuracy of machine tools,a graphene coated ball screws with heat dissipation is designed based on the thermal characteristics of advanced material.The finite element model of graphene coated ball screws is established based on shell-solid bonded MPC contact.The feasibility and effectiveness of graphene-coated ball screws are verified based on the numerical result.The thermal characteristics experiment is conducted on a self-design heating test bench,and the effectiveness of the proposed method is validated further.(4)The influence of the material formula and spraying process of graphene coating on the heat dissipation of graphene coated ball screws is considered,and the graphene coating with different material formula is prepared.The influence of graphene nano sheet,silver nanopowder and nozzle flow on the effect of thermal deformation reduction of graphene coated ball screws is explored based on orthogonal experimental design.Thermal characteristics experiments are carried out,and the optimal combination of key design parameters of material formula and spraying process is obtained further.The research above provides a specific guidance for the practical application of the thermal deformation reduction method based on graphene coated ball screws.