Research On Slotted Electrode EDM And Self-adaptive Flushing Technology

Electrical Discharge Machining(EDM)is a widely used non-traditional machining technology,which has unique advantages in the machining of conductive and difficult-to-cut materials.However,the difficulty in discharging the electrical corrosion products in the discharge gap restricts the development of EDM towards high efficiency and refinement.Internal flushing is the effective ways to avoid the accumulation of the electrical corrosion products.However,it is difficult to apply internal flushing to die-sinking EDM,mainly because it is easy to produce residual material column at the bottom of the workpiece cavity affect the machining quality.Therefore,slotted electrode EDM technology was proposed.The slotted electrode is a new type of internal flushing electrode which uses the narrow slit to deliver fresh working liquid to the discharge gap.For the molding hole of the rectangular block electrode,the straight slot electrode and the inclined slot electrode are designed.Combined with the production conditions of the electrode,the red copper was selected as the material of slotted electrode,and the thermal expansion analysis of slotted electrode was carried out by using the finite element software ABAQUS 2016.It was found that the thermal deformation of slotted electrode was greater than that of the solid electrode,and the thermal deformation of the inclined slot electrode was greater than the straight slot electrode.In order to improve the utilization of working fluid,the side slit of slotted electrode was sealed by high temperature resistant conductive adhesive,and the processing experiments were carried out on high speed steel(W9Mo3Cr4V)and SiCp/Al composite(20%volume fraction).It is found that there is no large residual material column left on the bottom of the workpiece cavity processed by slotted electrode,and the high temperature resistant conductive adhesive used is safe and reliable,and there is no premature falling off phenomenon.It is proved that the slotted electrode is feasible for EDM.Computational fluid dynamics(CFD)software Fluent 2019 R2 was used to simulate the flow field between the straight slot electrode and the inclined slot electrode.Combined with the discrete phase model(DPM),the motion and discharge of the electrical corrosion products between the straight slot electrode and the inclined slot electrode were simulated.The simulation results show that the slot electrode has the function of increasing the flow rate of working fluid;By adjusting the direction of the slit,the velocity of the flow field in some areas can be increased,which is conducive to promoting the rapid discharge of the electrical corrosion products in this area;The average flow velocity of the discharge gap at the bottom of the inclined slot electrode is higher than that of the straight slot electrode,but the uniformity of the flow velocity of the inclined slot electrode is poor,and there are large areas of low flow velocity.The results of the simulation of DPM show that the discharge capacity of the electrical corrosion products of the straight slot electrode is higher than that of the inclined slot electrode.The processing performance of solid electrode,straight slot electrode and inclined slot electrode was analyzed by contrast experiment.The experimental results show that:compared with solid electrode,slotted electrode can obtain higher material removal rate(MRR),smaller surface roughness and fillet radius,but the relative tool wear rate(RTWR)of slotted electrode is greater than that of solid electrode.And in slotted electrode,the processing performance of straight slot electrode is better than that of inclined slot electrode.Single factor experiments were carried out to study the effects of pulse width,pulse interval and flushing pressure on material removal rate,electrode wear rate and relative electrode wear rate for the straight slot electrode with good machining performance.The results show that:with the increase of pulse width,the MRR first increases and then decreases,while the tool wear rate(TWR)and the RTWR increase;With the increase of pulse interval,MRR decreases,while the TWR and the RTWR increase;With the increase of flushing pressure,the MRR first increases and then decreases,while the TWR and RTWR rate increase.The application of internal flushing fluid increases the TWR of slotted electrode and affects the forming accuracy of work piece.To solve this problem,the self-adaptive flushing technology based on gap state detection was proposed.The gap state detection circuit is used to detect the processing state in real time.When the frequent short circuit or long-time short circuit between two poles is detected,the control unit controls the two position three-way electromagnetic directional valve to switch the flow direction of working fluid for internal flushing processing.After the predetermined flushing time,the electromagnetic valve is powered off and returns to the initial state for non-flushing processing,and waits for the next short circuit signal.Processing experiments show that under the condition of self-adaptive flushing,the slotted electrode can obtain the MRR equivalent to that of continuous flushing and the TWR equivalent to that of non-flushing,so as to achieve the dual purpose of ensuring the processing efficiency and reducing the electrode wear.