| Since its invention in the last century,CNC machine tools have been playing a pivotal role in the manufacturing industry.For the numerical control machine tool design and manufacturing technology has also been the focus of research in various countries.Accuracy is an important indicator to measure the performance and processing level of CNC machine tools,and reasonable accuracy design is an effective means to improve the precision of the machine tool in the design stage.Support is the basic part of the machine tool,which greatly influences the final machining accuracy of the machine tool.Therefore,the reasonable design of tolerances has great significance for the improvement of machine tool accuracy.The existing tolerance optimization design methods are mostly based on deterministic parameter design,that is,the optimized performance response or constraint response is regarded as a deterministic value solving optimization problem,without considering the influence of various uncertainties in practice.The tolerance obtained by deterministic optimization method has limited improvement in machine tool accuracy.Therefore,this paper proposes an optimization model for the accuracy tolerance of machine tools considering the influence of uncertainties in the actual work of the machine tool.The main work is as follows:(1)Introduction and literature review of current domestic and international precision design and uncertainty analysis and robust design methods and research status are presented,and the advantages and disadvantages of existing precision design methods are analyzed.(2)The commonly used machining cost model is introduced,and listed machining cost function of several typical geometric feature.The general evaluation index of machine tool accuracy is analyzed,and the concept of qualified rate of product processing is put forward to evaluate the accuracy and robustness of machine tool.The uncertainty factors which affect the precision of machine tool are analyzed,and the factors such as manufacturing error and force error of the machine tool support are taken into consideration.In view of the geometric tolerance of the supporting part,the optimization model of the robustness tolerance of the support parts is established on the basis of the machining cost and the robustness of the precision.(3)Considering the uncertainty of bearing tolerance and load,the uncertainty distribution of support system is solved.The Monte Carlo simulation method is used to solve the manufacturing error of the single support parts of the machine tool.The elastic deformation of the support parts is calculated by the finite element software,and then the distribution of the machining error of the machine tool is obtained.(4)In order to improve the efficiency of optimization,this paper constructs the Response Surface Model(RSM).Firstly,10000 sets of test points are extracted by the Latin hypercube test design method,and the error distribution parameters corresponding to the test points are calculated,and the least square method is used to fit the response surface polynomials.Finally,the accuracy of the response surface model is verified.(5)With the static precision index of machine tool as the constraint,the shape and position tolerance of the support parts is preliminarily optimized.Then the robustness optimization method is used to further design the shape and position tolerance of the characteristic surface of the moving parts which are connected to the moving parts of the guide rail,and to optimize the robustness of the machining precision of the machine tools.By comparing the results of the deterministic tolerance optimization,it is found that the average product qualification rate of the product processing qualification rate is 8.4%,but the difference between the processing cost is small.It can be seen that the uncertainty optimization method proposed in this paper can effectively improve the accuracy and stability of the support parts while ensuring the low cost. |
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