Analysis Of Heat Flow Field And Material Erosion Mechanism Study In Short Electric Arc Milling Process

Short electrical arc machining technology（SEAM）belongs to the technical field of electrical processing in the field of special processing,and the material is etched away by continuously generating continuous arc discharge between the non-contact two electrodes.This technology inherits the advantages of electrical processing and is not limited by the mechanical properties such as strength,hardness and toughness of difficult-to-machine materials.For the processing of large super-strong,super-hard and super-tough alloy parts,such as cement grinding rolls,coal grinding rolls,large-scale machine boring,etc.,SEAM has shown good processing performance and has become an important technical means for efficient processing of difficult-to-machine conductive materials.However,SEAM is a new type of high-efficiency electric discharge machining technology.Most of the current researches are concentrated in the technology and experimental stage.There are still many scientific and key technical issues that need to be further explored and studied.The arc discharge is essentially a gas self-sustaining discharge,which reveals the arc characteristics from four aspects: the basic characteristics,the shape,the anode power density,and the static characteristics.After the discharge channel is established,the cathode region,the anode region and the arc column region are formed three regions.The spatial scale of the cathode and the anode is very small,the electric field strength changes drastically,and the arc column region is essentially the region where the plasma is thermally ionized.The arc shape and the arc discharge process are obtained by a high speed camera.At the beginning of the arc release,a large amount of arc light is generated between the poles,and the maximum intensity is an arc column,and most of the substances that are ejected are spherical molten metal droplets and spherical liquid droplets.The arc anode power density distribution conforms to the Gaussian distribution,and the power density is the largest at the center of the arc.As the distance from the point to the arc center increases,the power density decreases.At the beginning of the arc discharge,the arc static characteristic curve shows a downward trend,and the voltage decreases as the current increases.When the current reaches a certain threshold,the static curve of the arc remains basically flat,and the voltage does not change with the change of current.The short electrical arc discharge energy is mainly transmitted to the electrode in the form of thermal energy,and the energy obtained by setting the surface of the anode and the anode is 30% and 20% of the total energy,respectively.Short electrical arc discharge etching material process is a complex heat transfer process.This microscopic process is to achieve the erosion of materials under the combined effects of electric force,electromagnetic force,thermal force,fluid dynamics and the like.Based on the arc discharge erosion mechanism,the finite element simulation of the heat conduction process of nickel-base superalloy GH4169 in SEAM is carried out.The heat source model,heat source radius,definite solution conditions and phase transformation are selected.The mathematical model and the finite element model are used to obtain the temperature field distribution,stress field distribution,molten pool formation law and thermal strain law in SEAM,and predict material removal rate（MRR）,heat affected zone and surface roughness of the workpiece after SEAM.It can provide a theoretical reference for the basic problems of high-speed processing of nickel-base alloy in SEAM,removal of recast layer and improvement of surface quality,and improve the engineering application value of nickel-based alloy.During the short electric arc milling process,the etched particles are carried away from the gap under the action of the high-pressure and high-speed working fluid,and the discharge of the etched particles depends on the flow rate and flow rate of the working fluid.Therefore,the flow field distribution of the inter-electrode working fluid directly affects the processing quality,processing efficiency and electrode loss.However,the inter-electrode working fluid flow field is difficult to observe,detect and analyze.From the perspective of simulation analysis of machining gap flow field,the finite element simulation of the gap flow field of nickel-based alloy GH4169 in SEAM was carried out by FLUENT,and established appropriate flow field physical model,mathematical model and finite element model,and analyzed the distribution law of flow field pressure,velocity and erosion particle under different factors such as flushing mode,flushing pressure and electrode speed,in order to provide a theoretical basis for further improvement of process conditions.In order to reveal the process rule of short electrical arc milling electric discharge machining technology,the machining effect could be effectively controlled as much as possible,and achieved a high efficiency and a low loss in SEAM.Therefore,based on the experimental research of the system,the graphite,copper or composite material（tungsten-copper alloy）was selected as the tool electrode to carry out the influence of different electrode materials on the injection of working medium,the extraction of the etched material and the utilization of electric energy.The effects of various process parameters on the MRR,electrode loss（TWR）,surface morphology and recast layer were evaluated,and the causes of the effects were further explained to give full play to the advantages of high efficiency processing cemented carbide by SEAM.