| Electrical discharge machining(EDM), which has the advantage of high processing precision and not limited to the mechanical property of material, is appropriate for difficult-to-machine material. However, there are many problems with EDM such as processing energy limited to the pulse power supply, low processing efficiency. Therefore, this paper has proposed electrical discharge machining ablation machining(EDM ablation), with the processing efficiency which is several times of that of EDM or even higher. EDM ablation provides a new approach for high-speed processing of metal material. Different machining properties of EDM ablation has been explored, too. First of all, a new technology utilizing spark inducement has been developed, in which the spark heats metal in sparking area of workpiece surface to its burning point, forming activation region to get high inducing efficiency. The inducement can make the ablation points distributing equably due to the distribution of discharge points. Secondly, based on the activation of the surface, result in oxygen to react with the activated metal, releasing large amount of heat to remove metal and heat the metal underlayer. As a result, the energy between discharging gap was enlarged and the removing rate of material was improved. Finally, finish the machining surface machined by ablation through electrical discharge to weed out melted metal on the surface of workpiece. To study its mechanism and process rules, the EDM ablation method needs a new processing system since that it has exceeded the intrinsic EDM.The work this paper has done is as follows:(1) The basic macroscopic theory of EDM ablation was studied, including spark inducement, oxidation removal and discharge finishing. Single discharge process of EDM ablation companied by oxidation of material at the same time, oxide film formed has properties of resistance. Equivalent discharge model for EDM ablation was established, providing theoretical support for its micro process. Functions of spark and oxygen flow to EDM ablation.(2) Single pulse experiment system was established, which included a three-dimensional worktable, a tank, a power supply system, a detect-feedback system and a servo control system. The pulse power supple consisted of self-made RC power supply and chopper. The mechanism of EDM ablation was studied through single pulse experiment, which divided the micro process of EDM ablation into five stages using the characteristic waveforms in single pulse discharge, Discharge activation, Rapid oxidation, Oxidation blocked, Oxidation extension, Gradually stop of oxidation. The discharge inducement energy was calculated, finding out that the releasing energy of single discharge used in removing material was enough to heat all removal material to its burning point. The changing rule of discharge pits with the energy of power supply was the same with that of normal EDM, indicating that the EDM ablation was limited to the discharge energy. According to the shape of discharge pits by single pulse discharge, the expanding of oxidized pits could be divided into two kinds, channel-type expending and spread-type expending. Discharging model, burning model and explode model of EDM ablation were proposed in this study.(3) The controllable machining characteristics of EDM ablation were studied. There were two methods: controlling the gas flow to let in oxygen intermittently in EDM ablation and controlling the amount of discharge pulse in single-pulse efficient perforation of titanium alloy. The theory of EDM ablation with letting in oxygen intermittently and the mechanism of single-pulse efficient perforation were analyzed. Special settings for ablation milling machining were made, advantage of material removal rate, relative electrode loss and machining surface quality of ablation milling machining was proved, and the reasons of polarity effect were started in this study. The distribution of gas pressure brought on the spread-type expansion, proving that single pulse of big current could realize the fast perforation of titanium and its alloy. Titanium alloy with thickness of 10 mm is perforated by monopulse discharge, and assistant current was used to restrain the stray corrosion of titanium alloy ablation and discharge pits.(4) Continuous removal characteristics of EDM ablation were started in this study. Atomization ablation process using atomized dielectric can control the progress of oxidation and finishing the machined surface. The mechanism of atomization ablation and its process rules were studied, and small hole of high aspect ratio machining with atomization EDM ablation were carried out. Observe the breakdown voltage of discharge gap to verify the properties of dielectric. The reason why discharge gap became larger in atomization ablation was analyzed in theory. The micro process of atomization ablation was analyzed and was divided into three stages: inducement stage, fast oxidation stage and oxygen-free maintaining stage. The machining system for atomization ablation was established and the material removal rate, surface quality and relative electrode wearing rate of the atomization ablation were studied. Experiments of machining high aspect ratio hole were carried out, realizing the high-precision machining of holes of which the aspect ratio was 20 on model steel Cr12.(5) Composite machining method of EDM ablation and mechanical finishing was proposed and its mechanism and technical characteristics were analyzed. Special experiment settings were made for the machining. Double servo system for EDM ablation based on the effective discharge probability and cutting force of mechanical tool was established, which could improve the machining efficiency effectively. The servo feed control strategy for mechanical tool of cutting force based on intenerating layer theory could control the removal of intenerating layer stably, without cutting the non-oxidized layer. Comparing experiment of the finishing EDM ablation, the EDM ablation and the normal EDM were carried out, and the corresponding technological tests were analyzed. The influence of discharge parameters and gas parameters on the finishing EDM ablation was studied. |
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