Research On The Electrical Discharge Machining(EDM) Process Of Large Aspect Ratio Hole In Tungsten

The process of large aspect ratio hole has always been a big challenge in the field of mechanical machining. The features of electrical discharge machining technology(EDM), such as non-contact ing machining method, no obvious macroscopic applied force, give it a greater advantage when it comes to deep hole process, especially large aspect ratio hole in workpiece with difficult-to-machine material. Therefore, the EDM technology of large aspect ratio hole parts has become important for machining technology and applicat ion nowadays. Yet there also existed obvious limit at ions in EDM of large aspect ratio hole such as large electrode wear and low processing efficiency and so on.This paper aims to analyze EDM technology for micro hole machining whose aspect ratio is more than 80:1. The basic EDM technology of tungsten material will be studied. That will provide est imates to choose electrical parameters for the process of small hole. Then special met hod is proposed to complete the process of large aspect ratio hole. Meanwhile the shape of crater formed by single pulse discharge and the distribut ion rule of mut i-pulse discharges will be analyzed and simulat io n model of the evolut ion of surface topography will be constructed. The main study and conclusio n are listed below:(1) Through the basic EDM processing experiment, the influence of peak current, gap voltage, pulse durat ion, pulse interval on material remo val rate, electrode wear rate and surface roughness has been quant itatively analyzed, and the mechanism of material remo val and electrode wear are studied.(2) The shape of a single crater is ident ified with considering the influence of main electrical parameters, including pulse current and pulse duratio n. Then, the material remo val mathemat ical model is built under a single pulse discharge. The surface topography evolut ion process based on two distribut ion models is simulated by MATLAB, and the machined surface roughness and material remo val rate is predicted. Finally, the simulat io n results about surface roughness and material removal rate are verified by the experiments of aluminum allo y machined by EDM with copper electrode, t he relat ionships between electrical parameters and surface topography, surface roughness, material remo val rate are established.(3) According to the characterist ics and applicat ion requirements of large aspect ratio hole in tungsten, several process methods are put forward. The special method, which combines EDM wit h metallic bonding, is selected through tentative experiment. The microgrooves are machined on the surface of two pieces of tungsten plates with same dimensio n. Then the machined surfaces are covered with nickel. Finally, the two pieces of the tungsten plate s are formed to one piece by using bonding method under high temperature, high pressure and vacuum condit io n.