Modeling and Form Error Control for the Surface Grinding Process

Grinding is one of few choices being able to machine very hard materials to deliver ultra high precision at high material removal rate. Surface grinding has been widely used to achieve high accuracy for high quality mechanical, electrical, and optical parts, such as silicon wafers and optical lenses.;With the rapid advances in semiconductor and optics industries, more challenges have been posed than ever before to machining quality in terms of form error in surface grinding process. To improve machining form quality with higher efficiency in a surface grinding process, form error control is necessary.;In the existing studies, it was found that the motor driven wheel infeed control is the most widely used method for form error control. However, the output precision and bandwidth of this control method are limited. The piezoelectric actuator driven tool motion or workpiece infeed table has high resolution and wide dynamic response frequency.;In order to combine the advantages of both the wheel infeed system and the piezoelectric actuated workpiece infeed system to achieve fast active control and large driving force, a new variable infeed control method has been proposed and investigated.;To realize variable infeed for form error control, a basic discrete system model for the surface grinding process was firstly established. The model was useful for obtaining surface form profile, workpiece size reduction, grinding force and the surface form error.;To avoid significant remounting errors caused by offline measurement in the modeling process, a high precision in-process surface form measurement system was developed. To deal with the two key problems, opaque barrier and vibration, an air beam technique to remove coolant, a damping technique and a moving average technique to reduce vibration were proposed.;With the developed in-process surface form sensing system, an improved discrete system model was proposed to address the partial removal and precision control problems. Models for partial removal, full removal, and sparking out conditions were established. Significant improvements were obtained by the improved model compared with the basic system model.;To utilize the developed piezoelectric actuator based precision positioning table for form error control, dynamic hysteresis of the PZT table was studied under loading conditions. A concept of upper frequency limits for dynamic hysteresis stability was proposed and the values were determined when a 10% performance reduction was considered.;For the new variable infeed control system constructed for the study, an iterative control algorithm was proposed to obtain compensation infeed of workpiece table. Computational studies were carried out. Experimental studies were also successfully conducted for validation and assessment. Through the studies, it was found that the surface form error decreased exponentially as more grinding passes were involved. In addition, using the new variable infeed approach, surface form error can be reduced by up to 20% when compared with the existing approach. The best result can achieve 88.9% based on computational study. The proposed models and control method should be very useful for many precision machining industries.