Research on the impulse force in electrical discharge machining using a new measuring method

A microscopic applied force exists during the electrical discharge (EDM) machining process. Researches on the impulse force in EDM are meaningful for revealing mechanisms and optimizing processes of EDM. Two methods are commonly adopted to measure the impulse force, including the direct method and Hopkinson bar method. The direct method which measures the impulse force directly by sensors is simple but inaccurate, while Hopkinson bar method which measures two displacements in a bar to calculate the impulse force is more accurate than the direct method but complex in measuring setup and calculating. To measure the impulse force simply and accurately, a new method containing an impulse model and an impulse force model based on the mass-spring-damper system of vibration theory is proposed. Experiments were designed to verify the validity of the new method and study the impulse force. The impulse and the impulse force were calculated by the experimental results and verified each other. It was found that the impulse force had two durations as the corresponding discharge process, namely the bubble expanding duration and the plasma pressure duration. The bubble expanding duration appeared as the dielectric was broken down and lasted for about 25 μs, during which the bubble expanding played a major role. The impulse force of the bubble expanding duration grew to its positive maximum value and dropped to negative dramatically. Then the plasma pressure duration appeared until about 80 μs when the plasma pressure was dominant. The impulse force of the plasma pressure duration became stable, positive, and attenuating.