Multilevel variable control for impulse-discharge thermochemical truing of diamond cutting edges in precision grinding

Abstract

Precision grinding depends on the diamond cutting edges with good protrusion uniformity that are acquired by impulse-discharge thermochemical truing. However, the impulse-discharge thermal is unstable due to the uncertain discharge gap derived from irregularly changed grain top heights, leading to random diamond thermochemical removal. Under the uncertainty, a multilevel fuzzy-based control of kinematic and electrical variables is proposed to stabilize the impulse-discharge power during truing. The objective is to realize the cooperation of impulse-discharge, thermochemical and mechanical processes for diamond truing effect trace. First, the impulse-discharge signal was collected to acquire the transfer functions of impulse-discharge power. Then, an on-site experiment with small sample was processed to determine the discharge voltage sensitivities of kinematic and electrical variations. In order to improve the control performance, the control process with fuzzy logic was modeled to tune the output ratios of kinematic and electrical variations by particle swarm algorithm. Finally, the designed controller was experimentally applied to the impulse-discharge thermochemical truing, followed with dry plunge grinding of hardened steel. It is shown that the kinematic and electrical variables for the uncertainty compensation are linearly related to the spark-discharge voltage. Accordingly, the fuzzy-based control may be applied to the multilevel variable adjustment. The controller with tuned output ratios reaches small steady-state error, few trigger times and no overshoot to regulate the impulse-discharge power within 5 % error in actual truing. By integrating physical behavior and experiential knowledge rather than big data driving, the controllable impulse-discharge power for required diamond cutting edges advances the stable smooth surface grinding.