Relationship between Abrasive Grain, Hardness and Grinding Status

1. Wheel dull type

When the abrasive grains have serious abrasion and wear, the cutting edges of the abrasive grains are dull, the surface of grinding wheel will be smooth and flat. At this time, with the total dull area of the cutting edges increasing, the friction increases and it is difficult for the cutting edges to cut into the surface of the workpiece. However, due to the high hardness of the grinding wheel, the abrasive grains can not break off in time. If this wheel is continued to use, the grinding force and heat will increase with obvious vibration and noise, which cannot cut the metal effectively. Therefore, the grinding wheel must be dressed at this time.

This kind of abrasion and wear generally occurs in the situations when the   abrasive grain has low hardness but workpiece has high hardness, grinding wheel has high hardness, abrasive grains are fine and workpiece has high tensile strength (such as steel).

2. Wheel clogging type

In grinding process, when a large number of chips are covered on the surface of grinding wheel, we call it as grinding wheel is clogging.
Grinding wheel blockage is generally divided into two categories, one is called immersion blockage, that is, chips drill into the gaps or pores of the surface of grinding wheel, which easily happens in grinding steel.
The other type is called adhesive blockage, under which, chips are melted and integrated with abrasive grains and bond, covering the cutting edges of abrasive grains.
This kind of adhesive blockage often occurs in grinding non-ferrous metals such as titanium alloy, copper alloy, magnesium alloy and other metal materials with good ductility and low melting point.
When the grinding wheel is clogging to a certain extent, its cutting performance decreases obviously, and it is prone to obvious vibration and noise, even burns.

The type and degree of blockage of grinding wheel are mainly related to the mechanical properties of workpiece, the characteristics of grinding wheel, stock removal, types of coolant, and ways of coolant pumping, etc.

3. Wheel breaking-off type

In grinding process, when the grinding force on abrasive grains is higher than the ability of the bond to resist breaking off the abrasive grain, bond posts break, so abrasive grains break off. Therefore, the softer the wheel, the easier it is for the abrasive gain to break off. When the wheel is too softer or grinding load is higher, the self-sharpening effect   is so intense that wheel loses its shape and can’t work normally. At this time, although grinding wheel still have cutting ability, the geometric accuracy and surface finish have been lost. Therefore, the surface of grinding wheel must be returned to normal.