| Electrical discharge machining(EDM)is widely used in difficult-to-machine materials.Because those materials are not limited by strength and hardness.However,the study on the mechanism of EDM has not been deepened with the wide application of EDM in difficult-to-machine materials.This is because the EDM process is complex.In particular,it involves electromagnetic,thermal,fluid and other multi-physical fields and the interaction between the fields,which makes it difficult to further understand the mechanism of EDM.Therefore,this paper conducted a simulation study on the electrical discharge micro process under the multi-physics coupling action.Based on the obtained results,the workpiece material erosion process was studied,combined with the EDM experiment to verify the simulation results.It is instructive to further reveal the mechanism of EDM and improve material erosion efficiency.(1)Establishment of multi-physics model of discharge process.The actual discharge process of EDM was analyzed.Based on the theory of magneto hydrodynamics and heat transfer,the multi-physics coupling relationship of the EDM process was clarified from the actual machining process and theoretical formula derivation,and it was used as the simulation basis of the multi-physics coupling analysis.The mutual coupling effect of electromagnetic,thermal and fluid was analyzed.After reasonable simplification,a two-dimensional simulation model of the discharge process under multi-physics coupling was established.(2)Study on discharge breakdown process of EDM.By specifying the terminal current and setting the physical field interfaces to couple electromagnetic,thermal and fluid,combined with the aforementioned multi-physics model,a sub-model of the discharge breakdown process simulation was established.The plasma channel was formed within 0.1μs.The distribution between tools of current density,electric field intensity,Lorentz force,temperature and velocity during the discharge process were obtained and analyzed.The influence of different discharge current and gap on the results of the above discharge process was studied as well.(3)Study on discharge deionization process of EDM.By setting the form of an improved step function,the terminal current was rapidly reduced in a short time to simulate the deionization process of EDM.Combined with the multi-physics coupling model,a sub-model of the discharge deionization process simulation was established.The current density between tools decreased rapidly with the increase of time,and finally only distributed at the two tools.The decreasing trend of electric field intensity between tools was slow at first and then fast,and finally zero.Compared with the breakdown process,the Lorentz force between tools was faster first and then slower.The central temperature between tools decreased with time due to the influence of the temperature diffusion between the tools compared with the breakdown process.The velocity between tools was affected by the inertia of dielectric.The decrease of velocity was slower than that of breakdown and tended to zero with time.(4)Study on the erosion process of workpiece material.Based on the results of temperature field in the process of discharge breakdown,a thermal-hydraulic coupling model of workpiece material erosion was established.The results of temperature field were used as the heat source of material erosion process.The level set method was used to track the workpiece erosion interface and the mass conservation equation and the level set equation were revised.The workpiece material erosion was simulated.The effects of different peak current and discharge duration on material erosion were studied.The EDM experiment was carried out and compared with the simulation results.Results showed that the radius of simulated crater was basically the same as that of the experimental crater,while the simulated crater depth was slightly greater than the experimental crater depth.The simulation model was accurate within the allowable error range. |
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