Finite Element Analysis And Optimization Of Fixture Structure Used For Mold Electrode

Mold is the fundamental technological equipment of industrial production. It is called asthe mother of all sectors. Most of parts in the products of electronics, automobile, motor,electrical appliance, instrument, household appliances and communication are formed bymold. The development of mold flexible manufacturing depends on the degree of automationof various process technology and machine tool fixture. Mold electrode must be repeatedlytransformed among CNC electrode fixture, wire cutting fixture and EDM electrode fixture inthe process of machining. It is of great significance to design universal fixture used for moldelectrode （short for universal fixture） which is clamped only once for realizing flexiblemanufacturing of mold.In this paper, universal fixture was designed from positioning device, clamping deviceand clamp part combining fixture design theory. Then positioning error and clamping force ofuniversal fixture were checked. Finite element model of layer-type fixture and universalfixture were established in ANSYS software. The statics analysis of layer-type fixture anduniversal fixture were respectively carried out under the following three conditions-thesymmetrical of end milling condition, the asymmetry of the up milling and the asymmetry ofthe down milling. The copper electrodes which was respectively clamped by layer-typefixture and universal fixture were milled by the same CNC machining center. The accuracy ofthe copper electrodes which had been processed was measured by trilinear coordinatesmeasuring instrument. Then the measurements and the statics analysis results were compared.Modal analysis of universal fixture and universal fixture-copper electrode system were carriedout basing on the statics analysis. Finally, the main dimensions of universal fixture’s structurewere optimally designed by the advanced structure analysis function of ANSYS. Finiteelement model of the optimized universal fixture was established and the statics analysis of itwas carried out.In this paper, the designed universal fixture satisfied the processing requirements ofcopper electrode in terms of positioning error and the clamping stability. The statics analysisresults under symmetrical of end milling condition, asymmetry of the up milling, asymmetryof the down milling condition between the layer-type fixture and the universal fixture werecompared. Under the asymmetry of the up milling condition, the maximum deformations oflayer-type fixture was6.0×10^-4mm. Under the asymmetry of the down milling condition, themaximum deformations of universal fixture was1.1×10^-3mm. Within the limits of0.02mmfor the machining error of the copper electrode, in CNC processing, the maximum stress of the fixture was2.3MPa and the fixture could be better optimized. The accuracy of the copperelectrode which had been processed was measured by trilinear coordinates measuringinstrument. The measurements and the statics analysis results were compared and analyzed.The correctness of the finite element model of fixtrue used for mold electrode which wasestablished and the rationality of the boundary conditions which was imposed were indirectlyverified. The first natural frequencies of universal fixture and universal fixture-copperelectrodes system wasf1=3641.6Hzandf1′=1314.1Hzrespectively. They were greaterthan the frequency of exciting force （633.3Hz） and the resonance phenomenon would notoccur. The total volume of the universal fixture decreased by32.8%after optimized. Theoptimized universal fixture could satisfy the processing accuracy requirements of the copperelectrode.