The main route to increasing removal involves increasing the number of abrasive grains that remove material within the grinding period. The number of active grits can be increased by:
• Increased grinding wheel diameter
• Increased grinding wheel width
• Increased grinding wheel speed
A larger number of active grits means more material can be removed in a given time. This is because active grits can only remove so much material per engagement. Productivity is, therefore, directly related to the number of grits in engagement per unit time.
19.9.2.1 Increasing Removal Rate per Grit
Another route to increasing production rate is to optimize the removal of material per grit engagement. In practice, the material removed per grit cannot be easily determined. This means that overall efficiency of the process and removal rate must be investigated by grinding trials. The effect of grinding cycle parameters on process efficiency is considered further in Section 19.10 on process economics.
Power consumed increases with the number of grits removing material per unit time. Highest removal rate is achieved when removal rate per grit is optimized. If, then, grinding wheelspeed is increased, removal rate per grit is reduced from the optimum value. This reduces efficiency. To optimize removal rate per grit, feedrate must be increased in the same proportion as wheel speed. This restores removal rate per grit to the optimum value and increases overall removal rate. The technique of changing wheel speed and feedrate in a constant proportion maintains kinematic similarity to maintain an optimized process. Ideally, workspeed should also be increased in the same proportion.
It is important to achieve long wheel redress life. Material removal per grit should be maximum consistent with required quality and consistent with long wheel life between redressing. The large diameter and wide grinding wheels employed in centerless grinding mean that long redress life can usually be achieved more easily than in other grinding processes. Redress life is further explored under process economics. Redress life is strongly dependent on the combined nature of the abrasive, the workpiece material, and the severity of the grinding conditions.