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Research On Deep Small Hole Machining Based On Analysis Of Flow Field

Posted on:2010-04-15Degree:MasterType:Thesis
Country:ChinaCandidate:J G LiFull Text:PDF
GTID:2121360278962783Subject:Mechanical Manufacturing and Automation
Abstract/Summary:PDF Full Text Request
Hole processing has been a difficult process for a long time. EDM is one of the important technology in the field of deep-small hole machining due to its advantages of none macroeconomic forces and none restrictions of the mechanical strength and stiffness of workpiece. However, with the depth increasing, the speed of processing declined sharply, which would lead to the low machining efficiency. At present, hollow rotating electrode with high pressure water is often used to achieve the purpose of high-speed processing. Many scholars in the field of EDM focus on the principles of electrical discharge machining, very little do some research on the flow field of gap dielectric. This paper will analyze how the flow field of gap dielectric influnce the speed of EDM deep-small holes through both fluid theory and experiments. It mainly includes the following:Relationship between machining time and the hole depth machined has been studied from EDM experiments with different rotary speed of electrode. Mathematical model of gap flow field produced by the rotary electrode has been set up and numerical solutions are calculated when gap flow is stable. Results of experiments have demonstrated that only specific rational speed can lead to maximum machining efficiency,which would go down whenever the speed increases or decreases. Based on solutions of theoretical model, force analysis is done on debris in both side gap and bottom gap. Theoretical analysis demonstrates that rotation of electrode can make debris at the bottom suspend and move to the side gap, but result in collision between debris in the side gap and electrode and decline of machining efficiency if the rotary speed is too high. Experimental results are explained qualitatively by theoretical analysis. Principle of influence on machining efficiency by the rotary speed of spiral electrode has been also studied. Mathematical model of gap flow produced by the rotary spiral electrode has been set up and numerical solutions are calculated when gap flow field is stable. Results of experiments have demonstrated that compared with cylindrical electrode, machining efficiency of spiral electrode increased substantially. However, spiral electrode's principle of influence on machining efficiency with different rotary speed is the same with the one of cylindrical electrode, only specific rational speed can lead to maximum machining efficiency,which would go down whenever the speed increases or decreases. From many points of view such as pressure, streamline, flow rate and velocity etc, calculation solutions of theoretical model has been analysed and force analysis is done on debris in the gap flow. Fresh working fluid can flow into the gap due to geometrical asymmetry of spiral electrode, and it makes working fluid containing debris get rid of the gap in a spiral climb way. Increment of spiral electrode's rotary speed can lead to increment of buoyancy on debris and flow rate of working fluid with debris, hense the increment of machining efficiency. However, machining efficiency goes down for collisions between debris in the side gap and electrode happen due to increasing velocity gradient force if the rotary speed becomes too high. Experimental results are explained qualitatively by theoretical analysis.At last, influence on machining efficiency by geometrical parameters of spiral electrode has been analysed from theoretical point of view. Optimizations on the geometry of spiral electrode is done according to analysis results. The following conclusions is safely got that thread pitch of spiral electrode should be smaller and width of groove produced on spiral electrode should be wider, which is in favor of increment of buoyancy on debris and flow rate of working fluid with debris.
Keywords/Search Tags:EDM, deep-small hole, debris, flow field, CFD
PDF Full Text Request
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