Simulation Of Electrical Discharge Coating Cermet In Iquid And Particle-in-cell

Electrical discharge coating (EDC) cermet in liquid is a surface strengthening technology which is base on the mechanism of electrical discharge machining. Its coating has high hardness as well as many properties such as good abrasive resistance, inoxidizability and superior heat stability. It is too difficult to use conventional measuring method to study electrode temperature, discharge channel radius, extended mode and other discharge parameters because of EDC technology’s own limitations. This thesis utilizes finite element analysis (FEA) method combine with EDC’s mechanism to take thermal analysis of workpiece electrode at the time of deposition coating. Establishing reasonable heat source model is in order to utilize FEA to find the influence between discharge crater area and metabolic parameters such as peak current and pulse width. It has been gotten general influence rules with those parameters. This thesis uses the EDC technology to get several cermet coatings in liquid and measure them to test and verify the feasibility of the simulation. We are also utilizing particle-in-cell (PIC) method to track electron and positive ion’s motion in discharge channel plasma. Research results and main conclusions were summarized as follow:(1) Discharge channel formation and expansion process have been considered in the simulation, for different time, the workpiece surface appear different temperature gradient. The highest temperature has appeared near the center of discharge channel, but the cooling curve is over time to crisscross type fitting. Junction temperature is near the melting temperature of material, that may be influenced by complex phase transition.(2) Each position on workpiece materials is affected by the heat How likes "wave" from the center of discharge, which results in that locations in heat area can reach their own peak temperature in short time, then they will falling Slowly. This mechanism can contribute to study discharge crater measurement, parameter design. Simulation verification, etc.(3) Peak current and pulse width are two important parameters for preparation of ceramic coating in liquid using EDC. Simulation shows that discharge crater’s size is expansion with the increase of peak current no matter in axial or radial but is smaller changes with the increase of pulse width because of the mechanism of EDC. The more current the more energy workpiece surface can get, which directly leads to regional reaction temperature changes drastically, and enlarges heat influence area. However, as pulse width ton itself value is small, it can cause the increase of the load and weaken the corresponding heat flow density at the same time. So it impact on the discharge area is smaller than peak current.(4) Electronic movement is active in discharge channel plasma, it is advantageous to the tool electrode consumption and accelerate formation of the coating in edm with reversed polarity. Positive ions of the movement is relatively slow, which may be related to ion size and impact factors.