Sharp grinding wheel grains are essential for removing material from a workpiece. Understanding the microscopic and macroscopic interactions in the grinding zone is essential for fully optimizing the grinding process and eliminating quality issues. This article will discuss these interactions, as well as methods for maintaining grinding wheel sharpness and optimal performance.
Each individual abrasive grain on a grinding wheel acts as a cutting tool. As the grinding wheel applies forces to remove material, the workpiece applies resistance forces to the wheel.
When using vitrified or metal-bonded grinding wheels, these resistance forces lead to fracturing of the abrasive grain from the bond. In the case of organic- and resin-bonded wheels, the heat produced from the grinding interaction releases dull abrasive grains over time, exposing the new sharper grain beneath it.
As the abrasive grains encounter the workpiece, other microscopic interactions take place beyond the chip-making process. For example, when dull grains are not released efficiently or the grain does not fracture properly, these dull grains begin plowing and sliding rather than removing material.
During the grinding process the workpiece material undergoes localized deformation, with this deformed material being displaced later. The localized deformation between the workpiece and the abrasive is called plowing. The plowed material slides — more on that later — on the grinding wheel surface prior to leaving the grind zone. The microchips produced by this deformation can clog the pores of the grinding wheel. The chances of this problem are increased by factors such as insufficient grain exposure, extremely hard wheel bonds and gummy workpiece material.
While uncontrolled plowing can cause issues, planned plowing can improve surface finish. Plowing increases the Specific Grinding Energy (SGE), which is the energy required to remove a unit (cubic inch or millimeter) of workpiece material. SGE serves as a measure of efficiency of the grinding process and is calculated from the grinding power by the following equation: