The Technical Study Of Electrical Discharge Machining To Micro-hole On B₄C Ceramic

B₄C was one of the engineering ceramics as a kind of ideal material for its excellent performance in physics and chemistry such as high heat-resistant,acid-proof and alkali-proof, high hardness, high strength, high chemical durability,high elasticity coefficient,light specific density. but it was difficult to process with the traditional machining method for its high hardness, bad plastic deformation and brittle failure which restricted its application. It became the key point to resolve the problem of machining B₄C.EDM-hole was one of the special methods that had been used extensively to machine metal, it was a non-contact machining technique with little cutting force between work piece and electrode, so the product wouldn't be fracture during the processing to the stress(shear stress mainly), or the residual stress greatly to reduce product properties after machining, so it was a kind of ideal means to machining advanced ceramics.This paper made the study under the theory of the EMD mechanism and mainly focused on the technics machining small hole on B₄C with EDM. Copper was used as the tool material. The experiments were carried out to investigate how the single parameter affected the machining process and results, such as material removal rate(MRR),expanding hole and diameter variation between entrances and exits (DVEE). In the end, the principle and rule of choosing the process parameters (pulse time (ti),pulse off-time (toff),peak current (ie),the depth of hole etc.)were got . The results is followed.(1) The rule of the process parameters for MRRThe MRR increased with the increase of ti at the start , when ti increased to given level it descend and the MRR increased obviously with the augment of ie. The MRR descend with the augment of toff . When the tool material rotated the MRR increased and the MRR was bigger with brass than red copper.(2) The rule of the process parameters for expanding holeThe expanding hole increased with of the augment of ti ,ie, the depth of hole. The opposite situation was the influence of toff ,and the expanding hole became smaller with brass than red copper.Although the rotation of tool material made the expanding hole larger , it was good for the exclusion of particles and reduced the probability of second discharge . at the same time it made the hole circinal better .so it was necessary to make the tool material rotate.The experiments proved that in the influence factors for expanding hole the second discharge between the removing particles was the main factor. So it was important to resolve the problem.(3) The rule of the process parameters for the DVEEThe DVEE decreased with the augment of the ti and toff in a small range. The peak current made the reduction obviously, but the effect of the depth of hole was opposite. It made no difference between brass and red copper.The further experiments devised by orthogonal experiment method showed the affecting sequence of these parameters to different technical goal.The results was: the light order for the MRR was peak current , pulse time ,the depth of hole,duty ratio; the light order for the expanding hole was the depth of hole,pulse time,peak current,duty ratio;the light order for for the DVEE was the depth of hole,pulse time,peak current,duty ratio. The results of these experiments indicated how to achieve the stable and efficient machining performance by the adjustment of these erosion parameters to the requirement of different technical goal.The removal mechanism was also studied by contrasting with the Micro shape looks made by SEM.