Research on sub-micron EDM with high production

首先，通过实验研究了放电弧坑尺寸、热影响区深度，特别是残余应力和材料显微组织对热影响区极限的影响。对于残余应力的负面影响，在加工之前已经存在的残余应力和加工本身产生的残余应力进行了研究，使用钨和硬质合金作为微棒工件材料。为了确定材料微观结构的影响，研究了碳化钨晶粒尺寸对硬质合金棒材最小可加工直径极限的影响。比较了多晶钨和单晶钨的极限，发现单晶钨的各向异性对微加工特性有显著影响。在此基础上，提出了一种基于静电感应进给的微细电火花加工方法。该方法可以消除电路中杂散电容的影响，从而降低每脉冲的最小放电能量。此外，由于非接触式电进给是可能的，该方法使得能够使用高速旋转主轴进行EDM。结果表明，用该方法计算的差距电压与实验结果吻合较好。使用普通电火花加工机获得的表面粗糙度为Rz0.27 μm。

Firstly, possible factors which influence the limits are discharge crater size, depth of heat affected zone, especially residual stress and material micro-structure were experimentally examined. For the negative effects of residual stress, both residual stress already present prior to machining and residual stress generated by machining itself were investigated using tungsten and cemented tungsten carbide as micro-rod workpiece materials. To determine the effects of material micro-structure, the influence of tungsten carbide grain size on the limits of minimum machinable diameter of cemented tungsten carbide rods was investigated. Comparing the limits between poly-crystal tungsten and mono-crystal tungsten, it was found that micro-machining characteristics were affected significantly by the anisotropy of the mono-crystal tungsten. Then, a new micro electrical discharge machining method using electrostatic induction feeding was developed. This method can reduce the minimum discharge energy per pulse because the influence of the stray capacitance in the circuit can be eliminated. Furthermore, since non-contact electric feeding is possible, this method enables EDM using a high speed rotating spindle. It was found that the gap voltage calculated from the equivalent circuit of this method agreed with the experimental results. Surface roughness of Rz 0.27μm was obtained using a normal electrical discharge machine.