Wansheng Zhao

Influence of flushing holes on the machining performance of blasting erosion arc machining

Blasting erosion arc machining is a novel electrical erosion process depending on the hydrodynamic arc-breaking mechanism to achieve a reliable high-efficiency machining. In blasting erosion arc machining, the high-velocity fluid field in the discharging gap is the precondition of the mechanism to control arc plasma to efficiently remove workpiece material. Therefore, this study mainly investigates the influence of flushing holes on the fluid field distribution directly and on the machining performance indirectly. Three multi-hole solid electrodes with different types of flushing holes are designed out according to the distributing principle. The influence of their flushing holes on the fluid field is conducted by a comparison fluid simulation which demonstrates that the electrode with flushing-hole diameters decreasing gradually from the inner to the outer in the radial direction attains the best flushing velocity distribution on the workpiece surface. Furthermore, the influence of their flushing holes on the blasting erosion arc machining performance is investigated by a comparison machining experiment in order to verify the comparison results of fluid field simulation. The experimental results illustrate that these electrodes have very different machining performance when machining nickel-based high-temperature alloy GH4169 (similar to Inconel 718) under the conditions of same discharge peak current and flushing inlet pressure. The electrode with the best flushing velocity distribution rather than with the highest velocity at a particular point achieves the best machining performance of the highest material removal rate, the least relative tool wear ratio and the least surface roughness (Ra), indicating an optimized design of flushing holes in the multi-hole solid electrode.

High efficiency blasting erosion arc machining of 50 vol.% SiC/Al matrix composites:

Blasting erosion arc machining (BEAM) is adopted to improve the machining efficiency of high fraction (50 vol.%) SiC/Al matrix composites. Results of the fractional factorial experiments and full factorial experiments indicate that the electrical parameters (peak current, pulse duration and pulse interval) are the main impact factors of the machining efficiency, and when the peak current is 500 A, the pulse duration is 8 ms and the pulse interval is 2 ms, the material removal rate reaches to 6000 mm 3 /min. Furthermore, the material removal rate was optimized and could be as high as 7500 mm 3 /min with the tool wear ratio about 10%. Simulation of the single discharge heat transfer illustrates that the SiC particles have negative influence on the machining performance due to their temperature dependent characteristics. The polarity effect was also studied and it is disclosed that different machining polarities have different influences on the machining performance, surface integrity and even the formation of SiC particles. Finally, a 50 vol.% SiC/Al workpiece was machined with blasting erosion arc machining.

Dependence of pre-breakdown time on ionization processes in a pseudospark discharge

The formation and development of pseudospark discharge, especially the onset of the breakdown, are of great technological interests in multiple applications due to their influences on the limits of current rising and fast switching performances of the devices. In this work, the development of pseudospark discharge in the pre-discharge and hollow cathode phases in a single-gap device are investigated by a time-dependent model to calculate the temporal development of total ionization cross section in varying times and regions. The simulations in our work are performed using the two-dimensional kinetic plasma simulation code XOOPIC. The time-dependent evolutions of the ionization cross section in pre-discharge and hollow cathode phases are presented under varying electric fields and hollow cathode configurations. Thus the electron multiplications and plasma generation processes by ionizing collisions in varying phases are examined and their dependences on a variety of external parameters are determined in di...

Research on the Machining Performance of SiC/Al Composites Utilizing the BEAM Process

The Blasting Erosion Arc Machining (BEAM) process was applied to improve the machining efficiency of SiC/Al composites. A set of experiments were conducted on 20 vol% SiC/Al composites to find out the relationship between the parameters and machining performance. Results revealed that when the peak current was 500 A, the material removal rate (MRR) could be greater than 8,200 mm3/min and the tool wear ratio (TWR) was about 2%. Besides, the influence of polarity on the surface properties was also studied by using scanning electron microscope (SEM) and metalloscope. It disclosed that machining with a large peak current and a negative BEAM is suitable for bulk mass material removal, while the surface quality could be improved by applying the positive BEAM. Finally, a machined sample demonstrated the fesibility of BEAM for the machining of SiC/Al materials.Copyright

Study of the Gaussian Distribution of Heat Flux for Micro-EDM

Gaussian heat flux boundary conditions are widely used to simulate the plasma in the electrothermal models for electrical discharge machining (EDM). However, the plasma thermophysical properties are different under different processing conditions. So it is important to find out the optimal Gaussian distributions of the heat flux for different electrothermal models. This paper suggests a Gaussian distributed heat flux to estimate the plasma heat source based on the law of energy conservation. A parameterized electrothermal model has been developed with the finite element method. By solving the developed model, the temperature field in the workpiece material is calculated. Then the crater radius and depth are estimated based on the calculated molten cavity. Afterwards, the simulated results are compared with the results obtained from single discharge experiments and the optimal Gaussian distribution is determined according to the least mean square error principle. The result shows that the optimal parameter value for micro-EDM is 1.25.Copyright