Tham khảo tài liệu 'developments in heat transfer part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 430 Developments in Heat Transfer increases MRR. Higher flushing pressure hinders the formation of ionized bridges across the gap and results in higher ignition delay and decrease discharge energy and reduces MRR. It was found by many researchers that the influential machining factors on MRR are the current intensity and voltage. Usually EDM is carried out by electrical sparks between the electrode and the workpiece using a single discharge for each electrical pulse. Some researchers have carried out experiments using a multi-electrode discharging system delivering additional discharge simultaneously from a corresponding electrode connected serially. The design of electrode was based on the concept of dividing an electrode into multiple electrodes which are electrically insulated. The energy efficiency were claimed to be better than the conventional EDM without any significant difference in work suface finish. Material removal rate is expressed as the ratio of the difference in volume of the workpiece before and after machining to the machining time . volume of mnterinl removed from the workpiece MRR ----------J-------- f------------------i--- machmmg time WPVB-WPWA MRR --------- ATT where WPVB and IV IVA are the volumes of the workpiece before and after machining and ATT is the machining time. Material removal rate vs current Fig. 13. Relationship between current and MRR Relationship of MRR with current during machining of aluminum and steel using brass and copper electrodes are illustrated in Fig. 13. It is to be noted that at a low current MRR is very low but with increase in current MRR increases sharply. At a low current a small quantity of heat is generated and a substantial portion of it is absorbed by the surroundings and the Role of Heat Transfer on Process Characteristics during Electrical Discharge Machining 431 machine components and the left of it is utilized in melting and vaporizing the work material. But as the current is increased a stronger .
