Research On The Conductive Carbon Film Properties And Experimental Characters In The Machining Of Insulating Ceramics By Wedm

Insulating ceramics are considered one of the key materials in the 21st century and expected to have widely engineering applications because of its high-hardness, wear resistant properties, high-temperature resistance and many other superior functions. However, there exist constraint in the manufacturing process from cutting raw material to forming shapes, especially complex shapes because of its high hardness and brittleness.Electrical discharge machining (EDM) is particularly suitable method for the conductive materials that is difficult for the traditional machining method because it is not influenced by the mechanical properties of material, such as hardness, brittleness and so on. For many years, people always thought that EDM method could only machining conductive materials and had little possibility to machining the insulating materials. In this thesis, we have successfully machined the insulating ceramic Si3N4 material by the assisting electrode method.Firstly, this thesis introduces the assisting electrode method which is used to machining the insulating ceramics and machining process after EDM principle is explained briefly. This thesis also analyzes the forces of the particle around the electrode wire using theoretical analysis method. The surface which is formed by the motion of lots of negative particles is draw using the MATLAB software, so the formation of the black conductive carbon film is explained by this method clearly. The formation process of black carbon film which adhered to the ceramic surface was analyzed too.Secondly, this thesis analyzed the transient thermal field of the insulating ceramics which is under single pulse condition using non-linear FEM software MSC.MARC after a heat conduction equation is established by choosing a suitable heat source model, thermal boundary conditions and the discharge channel radius. At the same time it is concluded that the radius and depth of discharge crater are varying with the different peak current, pulse duration and interval time by analyzing the simulation result. The relationship plot of the peak current, pulse duration and interval time with the crater depth and length has been draw. The effect of the peak current and duration on the WEDM of the insulating ceramics has been researched.Finally, This thesis also studies the machining of insulating ceramic Si3N4 material using the WEDM devices .The effect of peak current, pulse duration and pulse interval on the resistance of the black conductive carbon film, discharge gap, cutting speed is analyzed. We also analyze the material of the ceramic surface which is machined using WEDM method and the material that locate in the wire electrode crater using the SEM and EDS method.It is concluded that insulating ceramics can be machined successfully with the assisting electrode method by WEDM, the conductive carbon film play a important role in the machining process. The longer the pulse duration is, the better the conductive carbon film is. Compared with the conductive material, the machining speed of insulating ceramics is very low. C,Si,Mo is the main elements of the Si3N4 surface after machining.