Multi-objective Optimization For Saddle Of High-speed Precision NC Lathe

Saddle is a key component which links the feed system and tool. Dynamic drivingforces produced by the joint surface of screw nut, and random dynamic load generatedby the tool hold and friction from the guide way. These are born by the saddle totally.Static and dynamic performance of the saddle impacts on the machining accuracy andprocessing efficiency of the NC machine tool seriously. Static and dynamicperformance of the saddle is influenced by its structural parameters of the saddledirectly.Combining with national major projects of “high-end CNC machine tools andbasic manufacturing equipment”(2012ZX04005-021), aiming at the saddle of theADGM high-speed precision CNC machine tool, the Modal, the static deformation andsensitivity of saddle are analyzed by finite element method. The rules of the Modaland the deformation of static mechanics impacted by the geometric parameters and theparameters of constraint location are explored. Referencing the analysis results, fiveparameters which have a great influence on the modal frequency and staticdeformation of saddle are selected as variables to optimize the multi-objective of thesaddle’s structure. The five parameters are span of guide rail, distance of sliding block,length of tailstock, thickness of upper plate and thickness of boards, and named N, H,T, D, S respectively, and the optimization objectives are the mass, the first order modalfrequency, the second order modal frequency, and the max deformation of the saddle,named m, f1, f2, δ respectively. Contrasting the characteristics and scope of applicationof ant colony optimization, particle swarm optimization and genetic algorithm, theparticle swarm optimization is selected to optimize the mode of saddle. Base on thefuzzy comprehensive evaluation method, the best project is selected from four kinds ofoptimization scheme. The result show that the first modal frequency is improved by34.2%, the second modal frequency is improved by6%, static deformation is reduced by19.8%and mass of saddle is reduced by1.4%. To validate the correctness ofsimulation and optimization results, an experimental apparatus is designed which canprovide a series of corresponding parameters. The result shows that the simulationresult is consistent with the experimental results and then verifies the correctness ofthe simulation. The errors of sensitivity analysis of first order modal frequency to N, H,S between the test and simulation are7.0%,8.1%and7.1%respectively; The errors ofsensitivity analysis of second order modal frequency to N, H, S between the test andsimulation are4.2%,3.6%and7.8%respectively.The saddle with the optimized parameters has been used in the assemble ofprototype actually.