Mechanism Design For Micro Edm Drilling Of Negative Tapered Holes And Its Experiments

With the auto industry development and environmental protection requirements increase, the diesel engine with straight nozzles has been difficult to adapt to new emissions requirements under the international standards. Related study showed that inverted cone nozzle could improve the atomization and increase the flow coefficient. To promote the micro-EDM applications in the micro negative tapered nozzles processing, this paper developed a special mechanical module. Main factors that affected taper holes precision were studied, and series of machining experiments were carried out to research the influence of machining parameters such as pulse power supply voltage, capacitance, module deflection rate, and so on.On the base of original micro straight holes EDM equipment, this paper designed a new mechanical guide module for negative tapered holes. After installing the end guide module, EDM equipment could process negative tapered nozzles while the electrode wire clamping and servo feeding function was still provided by the primary system. With a precise ceramic cylinder to restrict the end of the wire by passing through it, a spherical positioning block was set to make the cylinder deflect by certain angle. Then a DC motor drove the whole block to rotate. As a result, the electrode wire end was constrained therefore formed the envelopesurface of a negative tapered shape, completing the processing of the negative tapered hole.To research the effectiveness and characteristics, the mechanism was fixed on the original micro-EDM machine for experimental processing. The quality of a negative tapered hole was mainly determined by its inlet diameter and outlet diameter. Using wire with the same diameter to process the holes of a same inverted angle, a smaller entrance diameter was preferred. In the feasibility experiment, results showed effectiveness of the mechanism. Upon processing experimental basis, the processing error sources of this module was analysed from a theoretical view. After quantitative analysis, we presented an adjusting way to reduce errors and proved it by experiments. Further experiments were carried out to research processing properties by changing the pulse voltage, capacitance, module deflection rate and other processing parameters.Experimental results show that the validity of negative tapered holes processing module was obvious. Selecting the wire with diameter 120μm, length of 300 mm as a tool electrode, negative tapered holes were machined out on the 1mm metal plate. The outlet diameters were 192μm and the inlet diameters were 220μm with a inverted cone vertex angle of 1.60°.