Research On Geometric Error Model And Precision Control Strategy Of Spring Forming Machine

Spring parts are widely used in aerospace,rail transportation,military and other high-end manufacturing industries.The quality of spring parts directly affects the development of China’s manufacturing industry.With the promotion of the replacement of the core scientific and technological parts in China,the precision of the domestic spring needs to be improved urgently.Spring forming machine is a special manufacturing equipment for spring parts forming,its precision directly affects the quality of spring forming.Therefore,the research on the precision of the spring forming machine is the necessary means and the only way to improve the precision of the spring.When studying the precision of spring forming machine,it is faced with the problem that the tool combination of spring forming machine is various and modeling is difficult.In order to solve this problem,based on the structural characteristics of the spring,the spring was divided into arc,corner,spiral and straight line.According to the shape characteristics,the three tool axes of the forming machine were selected for research,and the geometric error of the forming machine was modeled.When studying the precision of the forming machine,according to the function,the spring forming machine was divided into two parts: forming tool group and steel wire feeding assembly.For the forming tool group,this paper proposed a tool positioning error compensation method based on PMAC system,and then carried out the compensation test for the specified position error of curve and pitch tool positioning error;When studying the precision of wire feed assembly,orthogonal test method and finite element analysis method were used to optimize the structure of wire feed assembly and wire feed process parameters.Finally,the evaluation indexes were established to verify the accuracy of the spring forming machine.The test results showed that the error compensation method proposed in this paper can effectively improve the accuracy of the spring forming machine and improve the first pass rate of the spring.The main research contents of this paper cover four aspects which are as follows:(1)Based on the theory of multi-body system and homogeneous coordinate transformation method,the topological structure description of tool chain and wire chain of the forming machine was established,and 20 geometric errors of the spring forming machine were identified.According to the principle that the forming points coincide in the tool coordinate system and the wire coordinate system,a complete model of geometric errors of spring forming machine with 20 geometric errors was established.(2)In order to solve the problem that the complete model of geometric error of forming machine has many parameters and is difficult to monitor and compensate,a sensitivity analysis model based on variance decomposition form was established by using SOBOL sensitivity analysis method.The Monte Carlo random simulation sampling method was used to generate 20000 groups of geometric error values,and the quantitative analysis of the influence of 20 geometric errors on the spring size was completed.The key geometric error terms were determined,which provided theoretical basis and research object for subsequent tool chain error compensation.(3)Aiming at the optimization of wire feeding precision,the wire feeding total is selected as the research object,and the precision of wire feeding chain is studied.Four factors and three levels of orthogonal test were designed to identify the significant factors affecting the accuracy of wire feeding,and the finite element analysis model of wire feeding process was established.The structure of wire feeding roller was optimized based on the stress distribution of wire and the stress distribution of wire surface,and the process parameters of wire feeding roller were optimized.(4)A tool positioning error compensation method based on PMAC system was proposed.The curve gauge was selected as the research object,and the motor pulse value was compensated based on the PMAC system of the forming machine to complete the tool positioning error compensation.The tool positioning error decreases by 44.6% after compensation,and the qualified rate of spring size increases from 67% to 93%.