Study On High Efficiency Electrical Discharge Grinding For Non-conductive Engineering Ceramics

A novel technique named double electrodes synchronous servo electrical discharge grinding (DESSEDG) for non-conductive engineering ceramics, which can integrate the advantages of electrical discharge machining (EDM) and grinding, is presented to achieve high efficiency precision machining. This method employs a conductive grinding wheel which rotates fast on the surface of workpiece, and a sheet electrode which is automatically fed to the place where the wheel and workpiece meet. Discharges happen between wheel and sheet electrode under pulse power supply. The sheet electrode is very thin, so it can be considered that discharges are just on the surface of workpiece. The high temperature and pressure of plasma channel can be directly exerted to the workpiece surface to remove material. Then the sparks eroded layer is machined a second time by grinding of the conductive wheel. The advantages of DESSEDG are high efficiency, low processing costs, environmental pollution-free, and so on.The DESSEDG machine is designed. The sheet electrode servomechanism and other key mechanical components are designed. And the whole prototype machine is developed. The sheet electrode servomechanism can keep a right discharge gap between the sheet electrode and the wheel, and store unused sheet electrode within it.A new pulse power supply with novel topology and control strategy is put forward, taking into account specific requirement of the EDG machine and the low energy utilization rate of traditional pulse powers which use limiting resistors. The new power supply can provide large-scale adjustable peak voltage, pulse width and pulse interval. Current limiting resistors, which consume high energy, has been eliminated and the energy utilization rate is almost doubled.A servo-control system for the DC motor of the sheet electrode servomechanism is designed based on PWM with feedback. It can guarantee the stable low-speed turning of the motor. Using AC-DC-AC frequency control and computer control technology, the control circuit of the motor for grinding wheel spindle is designed.Through a series of experiments, the effects of electrical and non-electrical parameters such as pulse width, pulse interval, peak voltage, peak current, feeding speed, working fluid etc. on material removal rate and surface roughness of the non-conductive engineering ceramic workpieces are discussed in detail.Experiments for single-pulse discharges on non-conductive engineering ceramics are studied. Effects of the parameters on the discharge craters size are discussed. The mechanism of discharge and material removal is analyzed.