Surface Characteristic Analysis Of Workpiece Machined By Powder Mixed EDM

Electrical discharge machining (EDM) as a nontraditional machining method can machining any kind of electrical conductive material by pulsed discharge process which erodes electrode materials. Because of its processing quality independence of part shape and material mechanical properties such as hardness, strength and toughness, EDM becomes one kind of basilic machining means and is playing an important role in the field of modern manufacturing, especially in mould manufacturing industry. However, there exist some obvious disadvantages for conventional EDM, such as poor workpiece surface quality, low efficiency of finishing machining, and poor machining stability during large area machining, and this leads to the directly unavailable mould function surface whose quality has to be improved by polishing process for future use.Powder mixed EDM (PMEDM) as a process variant adding the suspended powder like silicon or aluminium into the dielectric fluid, successfully overcomes the above shortcomings. It can reduce surface roughness and improve machined surface quality of workpiece, increase speed and stability of machining process, and decrease electrode wear, so that the finish machining surface of large area can be achieved. However, to make sure the PMEDMed surface as final surface, it's necessary to effectively control every performance index in practical PMEDM. This paper makes an experimental comparative study of the surface characteristics for conventional EDM and PMEDM in different machining conditions, particularly the study on surface micro topography and surface degenerating layer characteristics in EDM.Firstly, the surface micro topography of EDM is investigated. Based on the formation process of discharge caves, aiming at various materials, the differences of surface micro topography between conventional EDM and PMEDM in different machining conditions have been discussed, the change of surface micro topography are analyzed, and the influence factors of surface quality are also explored. Consequently, the scientific basis for finish machining surface of large area is put forward.Secondly, the microscopic features (especially micro hardness and micro crack) of surface degenerating layer of EDM are deeply investigated. By orthogonal experiment, the research of some remarkable influence factors on surface micro hardness in conventional EDM and PMEDM has been done, the influence mechanisms and laws are analyzed, and the optimum processing parameters of micro hardness for PMEDM are presented; according to the comparative study of the differences in micro crack distribution maps of conventional EDM and PMEDM, some remarkable influence factors and their influence mechanisms are conducted in order to set parameters reasonably, avoid appearance of micro cracks and improve quality of machined surface effectively.