9.1.1 Introduction
As a result of process forces during grinding, a grinding wheel is subject to modification by a process of wheel wear. Wear leads to changed process conditions and quality deviations in the component. Figure 9.1 shows three different types of grinding wheel wear: profile deviation, roundness deviation, and changes in grinding wheel sharpness.
In plunge grinding, where the wheel profile is reproduced in the ground component, profile deviations lead to workpiece shape defects. In the case of longitudinal grinding, profile deviations lead to screw thread undercuts. Roundness deviations make the machine system vibrate by dynamic alternating forces, which cause chatter marks to be machined on the component.
Loss of grinding wheel sharpness leads to higher grinding forces, which may entail dynamic and thermal deflections between the grinding wheel and workpiece, as well as uncontrolled grinding processes leading to chatter marks on the component. Finally, there will be shape and position errors, as well as dimensional deviations on the component. These modifications of the grinding wheel in the course of the grinding process are due to wear and result from microscopic changes in the abrasive grains and alterations in the chip space.
Wheel wear results from material loss at the wheel surface, which can be traced back to mechanical contact between the wheel moving relative to the workpiece or any other body such as the dressing tool. Wear effects can be ascribed to the following main mechanisms: abrasion, adhesion, tribo — chemical reactions, surface disruption, and diffusion [DIN 50320 1979, DIN 50323 1988].
9.2.1 Abrasive Wheel Wear
As a prerequisite of abrasive wear, the surface of one of the two interacting partners of the abrasive process must be penetrated and a tangential movement must take place between them. The result is plastic and elastic deformations with groove and chip formation in the microrange. Grooving wear dominates, when hard workpiece material particles or loose particles of grain in the contact zone lead to surface changes in the wheel [Engelhorn 2002].