| SiCp/Al consists of an aluminium alloy matrix composite reinforced with SiC particles and it has many excellent features,such as high thermal conductivity,light weight,low expansion rate,wear resistance and low cost.Therefore,SiCp/Al has been widely utilized in many industry fields.However,SiCp/Al is difficult to machining.EDM is considered to be a suitable non-traditional machining method for metal matrix composites SiCp/Al machining Compared with traditional machining methods,EDM can machine precisely any electrically conductive materials into complicated shapes without any cutting force regardless of material hardness.Compared with laser processing,machined surface produced by EDM has a smaller heat affected zone.However,the splashing of discharge debris made up of molten Al alloy wrapping the falling SiC particles is easy to cause short circuit and arc discharge,which leads to poor the surface quality,serious electrode loss and low material removal rate when EDM is used.In order to solve the above problems,carbon nanotube mixed EDM method of SiCp/Al was proposed based on the study of the removal mechanism of SiCp/Al to improve the discharge state between electrodes,and its machining characteristics were studied.Firstly,in order to reveal the removal process and mechanism of SiCp/Al in EDM,the gap phenomena such as arc plasma,molten pool on the workpiece surface and discharge debris were observed by a high-speed video camera during a single discharge and compared with those of Al alloy.Moreover,the processing efficiency and the machined surface characteristics of SiCp/Al were investigated through continuous discharge.It was found that the low single removal rate and discharge rate of SiCp/Al are the main reasons for its low machining speed.Otherwise,the splashing of discharge debris and the movements of molten pool are easy to cause short circuit and arc discharge,which makes the surface quality worse.Therefore,it is proposed to increase discharge gap by mixing powder to improve the surface quality.The effectiveness of powder mixed EDM method in improving the machining characteristics of SiCp/Al EDM is verified by comparing those of EDM.Secondly,the temperature field simulation of SiCp/Al in powder mixed EDM during single pulse is studied.The modeling is based on the two most important parameters which affect material removal,those are the diameter of arc plasma and the energy distribution between electrodes.The powder characteristic constant K is proposed to express the influence of powder on energy distribution.The size of arc plasma is observed by high-speed camera.And then,the influence of concentration of powder,discharge time and discharge current on temperature field are analyzed based on the modeling.Finally,the machining characteristics of SiCp/Al in powder mixed EDM were studied.The effects of powder type and concentration,voltage amplitude,pulse width and servo reference voltage on material removal rate,electrode wear,surface morphology,surface roughness,discharge rate and short circuit and arc discharge rate of SiCp/Al were studied.The machining characteristics of SiCp/Al in EDM were improved by using optimized parameters. |
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