Cathode And Device Design For Moving Electrochemical Machining Of U71Mn Stretched Parts

Stretched parts have been widely applied in rail transit and other fields,these parts are often machined by conventional methods such as milling and grinding.However,due to these parts have high hardness,the main working surface is composed of complex curved surfaces and the length is long,there are defects such as serious wear of the tool,low machining efficiency and easily appear fatigue failure after milling or grinding.These phenomena directly increase the machining cost and reduce the service life of the parts.Electrochemical machining(ECM)has unique advantages such as good surface quality,high machining efficiency,machine metal materials of any hardness and no tool wear.When ECM is employed to machine stretch surface,which can improve the machining efficiency and surface quality.Combining the theoretical foundation with engineering practice,this thesis has carried out four researches on cathode design and optimization,traveling equipment development and flow field analysis,moving electrochemical machining(MECM)simulation analysis,and machining experiment verification.The main contents are as follows:(1)A "slope" cathode is designed that in consideration of the structural characteristics of the outer profile of the stretched part.Firstly,the design scheme of "slope" cathode is proposed.Then the solution model of the cathode line is established based on the simplified electric field theory and the cathode working face and cathode structure are designed respectively to obtain the initial cathode.Finally,the initial cathode was corrected by the simulation analysis of the machining gap flow field and the electrochemical field.The corrected initial machining gap is 0.2 mm at the inlet and 0.15 mm at the outlet.(2)Aiming at ensure that the electrolyte fills the machining gap uniformly and steadily,a moving electrochemical machining equipment is designed and the flow field is simulated.The designed equipment includes a diversion device(consisting of a diversion section and a rectification section),a back-pressure regulating device(consisting of a steady flow section and a back-pressure section)and a movable sealing device.The simulation results show that the average value of the machining gap flow velocity fluctuation is reduced to 0.45 m/s and the negative pressure is eliminated by using the equipment.(3)Transient-process simulation of the MECM of stretched parts to provide guidance for actual machining carried out by use the electrochemical field.The 3D model is simplified into a2 D model firstly.The parameters are set according to the actual machining situation and the problem of non-convergence of simulation is solved,which caused by the deformation of the mesh in the perpendicular direction of the part surface and the part stretching direction.When the voltages are 15 V,20 V and 25 V the corresponding cathode moving speeds are 16.8 mm/min,22.8 mm/min and 28.8 mm/min respectively.(4)A single factor experiments on the pulse voltage,pulse frequency,duty cycle and cathode moving speed is performed and the influence of each factor on roughness and material removal rate(MRR)is analyzed.Obtaining the ideal machine parameters are 15 V pulse voltage,600 Hz pulse frequency,90% duty cycle and 16.5 mm/min cathode moving speed by orthogonal experiments,gray correlation analysis method and machine parameter optimization analysis.It is shown that the surface roughness of the stretched part can reach Ra 0.443 ?m,the MRR is 44.6g/min,compared with the standard parts the dimensional deviation is 0.093 mm after machining,which meets the mechanical requirements by the experimental verification that machining distance is 100 mm.The researches show that it is feasible to machine the stretched parts by the MECM technology,which can save the machining cost,improve the surface quality and there is no white layer on the surface of the workpiece after machining,and avoids the defects caused by mechanical machining.Theoretical analysis and experimental show that MECM technology is feasible to machine the stretched parts,which can improve the surface quality,machining efficiency,save the machining cost and there is no white layer on the surface of the parts after machining,and avoids the defects(such as low efficiency,high cost and so on)caused by mechanical machining.