Tool wear is an important factor of grinding tool performance. Already in 1914, Alden proved that a larger depth of cut causes greater tool wear [MALK68, ALDE14]. Tool wear can be split into macro effects (tool profile loss) and micro effects (sharpness loss). Marinescu et al. [MARI07] add roundness deviation as performance characteristic to profile and sharpness loss.
6.3.1 Macro Effect—Tool Profile Loss
Dimensional wear at the grinding tool leads to a loss in workpiece dimension and profile. Cylindrical abrasive layers wear at the radius and at the edges, so that both wear volumes define the dressing allowance to retrieve the original tool profile (Fig. 6.9). Corner wear [MALK08] is also known as edge wear [KLOC09]; radius wear [WERN73] is called radial wear [KLOC09] or uniform wear [MALK08].
Werner explains that both wear effects are induced by similar process characteristics, which are average single grit cutting force, friction speed, contact time, and contact frequency [WERN73, p. 69]. At tool corners, grit support within the abrasive layer is weaker, so wear rate is faster [WERN73, p. 69]. During each wheel
rotation, the grinding forces are more likely to overload the weaker bond bridges at the wheel edges until an equilibrium between grit retention forces and grinding forces is achieved [BIER76, p. 77 ff]. In external cylindrical plunge grinding, the edge wear appears with an elliptical contour [WEIN76, BIER76, p. 77 ff]. Circular edge profiles occur only for small material removal rates or short process times [BIER76].
Konig and Henn [KONI84] explained the wear behavior of grinding wheels in centerless throughfeed grinding or other traverse grinding operations (Fig. 6.10). The grinding wheel can be divided in parts being as wide as the workpiece feed per wheel revolution. Every part has to remove a certain amount of workpiece volume. Due to inevitable wear, each part cannot remove as much material as originally intended, causing higher work load for the following part. This results in even more wear at the next parts until the spark-out zone of the grinding wheel is reached, where originally no material removal took place. The spark-out zone works as buffer and takes over some part of grinding of the workpiece allowance. Decreasing spark-out zone width leads to decreasing overlap ratio and increasing workpiece roughness. If the whole spark-out zone is worn, the workpiece dimension will deviate [KONI84].
Load direction, e. g. defined by feed direction, affects the wear profile (Fig. 6.11). Furthermore, similar profile wear behavior exists at other tool types. Bfittner
Original grinding wheel profile Worn grinding wheel profile
•e
[BUTT68, p. 64 f.] for example examined the formation of main wear area and side wear area at cup grinding wheels.