High-rate centreless grinding of ferrous components
A prototype centreless grinding machine was modified extensively to operate satisfactorily at high grinding wheel speeds and in the high rate centreless grinding regime. The principal modifications included the provision of a 75 k. W. d. c., variable speed, main drive motor which enables grinding wheel speeds up to 120 m/s to be employed and a coolant supply manifold was designed and manufactured-which was capable of delivering a high velocity coolant stream to the grinding zone. In addition, a measurement system was developed-which-allowed the grinding forces to be monitored and recorded in process. Two solutions for the accepted kinematic model of plunge feed cylindrical grinding are proposed. The general and more accurate solution takes account of the variable grit height and separation of the grinding wheel, whilst the particular and approximate analytical solution makes provision for variable grit separation only. The particular solution enabled parametric studies to be undertaken and allowed comparisons with the solutions proposed by other workers. The trends of theoretical grinding forces were predicted from analysis of the undeformed chip dimensions. The trends indicated two methods of achieving high stock removal rates, firstly, for a constant force value, higher stock removal rates are possible by increasing the grinding wheel speed and infeed-rate. Secondly, at a constant grinding wheel speed, and force level, reducing the workpiece speed and increasing the infeed-rate will yield higher stock removal rates. Experimental results were in agreement with these predictions. An extensive experimental programme investigating plunge feed centreless grinding of ferrous components was undertaken. Results from approximately 300 grinding experiments were used to establish a data bank of grinding parameters for a range of grinding conditions. High-rate centreless grinding has been shown to be a feasible first machining process. It has also been shown that the choice of kinematic conditions is important in achieving high stock removal rate grinding. Incorrect choice of kinematic conditions can cause problems of, workpiece burn, grinding vibrations and excessive power demands. Limit charts have been constructed which outline the boundaries to the process in terms of burn, grinding vibration and power limit. Operation between the boundaries is best achieved if the ratio of grinding wheel to workpiece speeds is in the range 90 - 200. The results enable a data based control strategy to be formulated and it is proposed that in process variable kinematics will allow a single cycle roughing and finishing operation on a suitably adapted centreless grinding machine.