Theoretical and experimental investigation of a tool path control strategy for uniform surface generation in ultra-precision grinding

摘要

The increasing demand of a high-quality surface in optics has imposed stringent requirement to improve the accuracy and uniformity of a machined surface. At present, ultra-precision grinding is a primary machining process in fabricating optical elements. However, in the grinding process, the unbalanced vibration of the wheel frequently appeared, which will seriously affect the precision and surface quality of the parts. A tool path as a critical factor directly determines the form error and surface quality in ultra-precision grinding. In conventional tool path planning, the constant angle method is widely used, which leads to the inhomogeneous ground surface that resulted from the different relative speeds between the grinding wheel and the workpiece with respect to different radical positions, degrading the functional performance of optical elements. From the edge area of the workpiece to the rotation center of the workpiece, the surface profile height is gradually decreased with decreasing linear speed. In this paper, a novel method of control strategy for the grinding wheel is presented so as to make the distribution of surface profile height and waviness on the machined surface uniform. The surface generation model along the circumference direction is first developed to relate the vibration amplitude of the machine tool and the spatial amplitude of the ground surface profile. Hence, the distribution of the cutting points on the workpiece surface is determined by considering the variation of linear speed, and a constant scallop height model is established. The results show that the uniform surface generation can be achieved by controlling the cutting point distribution of the grinding wheel. In addition, the sinusoidal surface texture by adopting this control strategy agrees well with that for the machined surface. The surface profile height can be held constant. Moreover, it is found that the amplitude of the waviness of the ground surface can be reduced by controlling the cutting point distribution.