Specific grinding energy can be considered as a measure of grinding efficiency. A low specific energy implies low energy consumed to remove a given volume of material. Low specific energy allows greater removal rate before meeting the power limit. Since specific energy is proportional to the grinding forces, it usually means that removal rate can be greater before meeting the burn limit and before meeting the chatter limit.
Specific energy reduces with increasing infeed rate due to the size effect as discussed previously. An example is shown in Figure 19.24. Table 19.1 shows that the constant speed ratios in Figure 19.24 allow constant depth of cut and constant chip thickness with varying wheel speed.
If grinding wheel speed were increased on its own, the size effect would reduce efficiency. However, the purpose of increasing grinding wheel speed is to allow increased feedrates. By increasing wheel speed and feedrate in direct proportion to each other, the size effect is eliminated. By this means, speed may be increased maintaining depth of cut and chip thickness constant.
It is found that specific energy reduces to a minimum as wheel speed is increased at constant chip thickness and then starts to increase again. This is clearly illustrated in Figure 19.24. Specific energy starts to increase again at higher wheel speeds possibly due to an increased rubbing contribution at higher wheel speed. As feedrate is increased, chip thickness is also increased. This increases the value of optimum wheel speed and suggests that even higher wheel speeds would be an advantage.
Figure 19.24 is typical of grinding processes and suggests an optimum wheel speed applies for particular depth of cut and feedrate conditions. For this example, it appears that the optimum wheel speed is close to 45 m/s at the lower depth of cut and is close to 60 m/s at the higher depth of cut.