The grinding wheel's hardness refers to the adhesive strength of the bond to the abrasive (how easily the abrasive detaches from the grinding wheel). The bonding strength of the binder, not the hardness of the abrasive, determines the hardness of the grinding wheel. If the abrasive particles fall off the grinding wheel easily under the same conditions and external forces, the hardness of the wheel will be relatively low (or soft). The grinding wheel, on the other hand, has a relatively high hardness.
The grinding force acting on the abrasive particles increases after the abrasive particles on the grinding wheel are passivated, causing the surface abrasive particles of the grinding wheel to fall off automatically. The sharp cutting edge of the new abrasive particles in the inner layer is used, and the grinding wheel regains its original cutting performance. The grinding wheel's ability to sharpen itself is known as "self-sharpening."
The hardness of the grinding wheel has a significant impact on the grinding quality and productivity. In general, the softer the grinding wheel, the harder the component material. This is due to the high hardness of the parts and the rapid abrasive wear. Using a softer grinding wheel promotes the "self-sharpening" of the wheel. However, if the hardness is too low, the grinding wheel will wear quickly and the correct sand profile will be difficult to achieve. If the grinding wheel's hardness is too high, it is difficult to achieve self-sharpening, which not only results in low productivity but also makes it easy to produce high-temperature burns on the surface of parts.
If the grinding wheel is soft, it is easy to dress, but shape and contour retention are usually not ideal. If the hardness of the grinding wheel is too high to improve the surface roughness of the workpiece, heat, and shaking will occur, resulting in poor surface roughness.
The best way to keep the force on the forming wheel is to increase the hardness of the wheel. However, the problem of cutting force is common. If the cutting force of the grinding wheel is good, the grinding resistance is low, the feeding speed can be increased, the heat is reduced, the grinding wheel cooling and heat change degrees are reduced, and the grinding wheel consumption is reduced. If only hardness is required, the grinding temperature may rise even higher, and the consumption of grinding wheels may increase.
The selection of abrasive particle size is mostly determined by surface roughness and productivity. The bond is the key to the grinding wheel's self-sharpening and the primary determinant of its hardness.
In terms of forming grinding, in addition to balancing cutting force and shape-keeping force, if heat dissipation and grinding ratio can be enhanced further, grinding efficiency will be substantially improved.
In addition to significantly improving the grinding ratio, the reduced binder means that more space is available in the pores, more space for heat dissipation, and less chance of blockage.