A new centerless grinding technique using a surface grinder

This paper proposes a new centerless grinding technique using a surface grinder. By this technique centerless grinding operations can be performed at low cost by installing a compact centerless grinding unit on the worktable of a multipurpose surface grinder and without the employment of a costly centerless grinder. The unit consists mainly of an ultrasonic elliptic-vibration shoe, a blade, and their respective holders. The shoe is produced by bonding a piezoelectric ceramic device (PZT) on a metal elastic body (stainless steel, SUS304), and an elliptic motion occurs on its end-face when two phases of AC voltage are applied to the PZT. The function of the shoe is to hold the cylindrical workpiece in conjunction with the blade, and to control the workpiece rotational speed with the elliptic motion on its end-face during grinding. The detailed structure of the unit was designed by Finite Element Method (FEM) analysis, and an actually constructed unit was installed on the worktable of a CNC surface grinder to perform tangential centerless grinding operations after its fundamental performance such as elliptic motion generation and capacity to control workpiece rotational speed had been investigated. As a result, it was clarified that the workpiece rotational speed changes linearly with variation in the applied voltage. This indicates that the workpiece rotational motion can be precisely controlled by the elliptic motion of the shoe. In addition, the workpiece roundness was clearly improved from an initial value of 23 μm to a final value of 2.6 μm after grinding, indicating that the constructed unit performed well in actual grinding operations.