Research On Fundamental Techniques Of Micro ECM For Array Hole Fabrication

The stray current corrosion and the difficulty of electrolyte renewal in the micro machining gap impair the performance of micro ECM. Influening factors should be considered and comprehensive techniques should be adopted to improve machining accuracy.The main influencing factors on machining performance are discussed, especially the effect of electrolytic products. The accumulation of electrolytic products (mainly the hydrogen bubbles) in the machining gap is the key factor controlling the anodic dissolution rate. In the feeding procedure of electrode, as the gap decreased to a certain extent, the electrolytic products can not be removed immediately from the gap, leading to the decrease of anodic dissolution rate and the breakdown of balance state of machining, therefore, the practical machining rate of micro ECM usually decreases with the decrease of the gap. Thus, the servo control strategy of intermittent retraction of electrode during feeding procedure is employed to remove electrolytic products and promote the machining efficiency.The effect of side-insulated electrode on machining accuracy is numerically simulated. The results indicate that the side insulation layer can effectively confine the electric field to the area near the conducting end face of the electrode, thus restraining the growth of diameter and taper angle of the hole. Results also indicate that the section shape of hole tend to be rounded even if the electrodes with triangle or square sections are applied in micro ECM because of the geometry effect of the corner on the distribution of electric field.A micro ECM setup is developed, which includes mechanical body, servo control and gap status detection system, pulse power supply and electrolyte circulation system. The spindle, driven by a linear moving coil actuator, can provide accurate smoothly positioning and rapid servo response, the feed resolution of which is 0.1μm, the peak time is less than 10ms in step response, and the repetitive positioning accuracy is about 0.55μm. The control system, based on a programmable multi axes controller embedded in an industrial computer, can concurrently and real-timely implement human-computer interaction, process control and position servo control with high reliability.A process to fabricate micro pin with uniform diameter is proposed. The mechanism that affecting the shape and the diameter of micro pin is discussed by analyzing the distribution of electric field. Micro array electrodes are fabricated by LIGA process. To confine electric field and restrain stray current corrosion, a side insulating process based on spin-coating is developed. Uniform and compact epoxy films are coated on the surface of electrode by centrifugal force. The spin-coating process provides a feasible technical approach to improve the machining accuracy of micro ECM.A serial of experiments are carried out in which side insulating of electrode, micro machining gap servo control, high frequency vibration of electrode, low concentration passivating electrolyte and other techniques are synthetically adopted to improve the performance of micro ECM. By optimizing machining parameters, various micro array holes, with 130~140μm edge length or diameter and less than 3°taper angle, are simultaneously machined by using side-insulated array electrodes and have obvious and uniform shape feature.