Interelectrode gas–liquid-solid three-phase flow analysis and simulation for drilling holes with high aspect ratio by micro-EDM
Interelectrode gas–liquid-solid three-phase flow analysis and simulation for drilling holes with high aspect ratio by micro-EDM
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DOI：
10.1007/s00170-023-12220-4
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发表时间：
2023-09
期刊：
影响因子：
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通讯作者：
Peiyao Cao;H. Tong;Yong Li;Jialong Chen
中科院分区：
文献类型：
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作者：
Peiyao Cao;H. Tong;Yong Li;Jialong Chen
在利用非空心圆截面工具电极与侧冲技术进行微细电火花加工（micro-EDM）时，当期望进一步提高加工的微孔长径比时，放电碎屑排出速度和工液更新效率被削弱，阻碍了加工效率和精度随加工深度的增加而提高。为了揭示工作流体在微细电火花加工间隙内的流动特性，从而实现高展宽比微孔的高精度、高效率加工，在连续放电产生高压气泡的理想假设下，在Fluent中建立了流体、气泡和碎屑的三相流动仿真模型。仿真结果表明，当侧隙入口冲刷压力边界条件设为0时，高温下工作流体在电极间瞬间气化形成的高压气泡膨胀时发出的压力波是驱动微米尺度工作流体流动的气动力源。受间隙流道结构和内壁粘性阻力的影响，拖动排出碎屑向上排出的流体的流速方向会发生变化，形成一个动态的进出侧面加工间隙入口的交替过程。随着加工深度的增加，由于压力波从底部间隙传播到侧间隙入口处的能量衰减，排屑在侧间隙入口处的排屑速度呈指数级下降，导致加工效率和精度降低。然而，当模拟气泡产生频率增加到兆赫时，碎片的排出效率呈阶梯状提高。连续高频产生的高压气泡能在底部间隙内保持较高的压力梯度，排出的碎屑能不断向上运动而不落回堆积在底部间隙内，有利于加工过程平稳、光滑，实现高纵横比微孔的高精度、高效率加工。
In micro-electrical discharge machining (micro-EDM) using the non-hollow circular cross-section tool electrode with the side flushing technique, when the aspect ratio of machined micro-hole is expected to be further increased, the discharge debris expelling speed and the working fluid renewal efficiency are weakened, which hinders the improvement of machining efficiency and accuracy with increased machining depth. In order to reveal the flow behavior of the working fluid in the micro-EDM gap, so as to realize the high-precision and high-efficiency machining of micro-hole with high aspect ratio, a three-phase flow simulation model of fluid, bubble, and debris is established in Fluent under the ideal assumption that the spark discharges occur continuously to generate high-pressure bubbles. The simulation results show that when the boundary condition of the flushing pressure at the side gap entrance is set to 0, the pressure wave emitted when the high-pressure bubble expands, which is formed by the instantaneous gasification of the working fluid between electrodes under high temperature, is the source of pneumatic force that drives the working fluid flow at the micron scale. Affected by the gap flow channel structure and the viscous resistance from inner wall, the flow velocity direction of the fluid dragging the discharge debris to rise up and expel will change, forming a dynamic alternation process of flowing into and out of the side machining gap entry. As the machining depth increases, due to the energy attenuation of the pressure wave propagating from the bottom gap to the side gap entrance, the expelling speed of the discharge debris decreases exponentially at the side gap entrance, resulting in the reduced machining efficiency and accuracy. However, when the simulated bubble generation frequency is increased to the megahertz level, the expelling efficiency of debris has a step-like improvement. The continuous and high-frequency generation of high-pressure bubbles can maintain a high pressure gradient in the bottom gap, and the discharge debris is able to continuously move upward without falling back to accumulate in the bottom gap, which is beneficial to the stable and smooth machining process, realizing the high-precision and high-efficiency machining of micro-hole with high aspect ratio.