What is grinding?

Grinding wheels, made by bonding hard abrasive particles with organic or inorganic binders, rotate at high speed on the grinding machine and are brought slowly into contact with the workpiece. This point is taken as zero, and material is removed at small depths (ideally no more than 0.1 mm in surface grinding, the most common method), taking into account the properties of the wheel and the workpiece, to finish the surface to a precise dimension.

Why grind after heat treatment?

Hardened surfaces are hard to turn or mill, and heat treatment can cause small dimensional changes and distortion. That is why zones that need precise dimensions, such as bearing and seal seats, gear shafts and die surfaces, are ground after hardening to bring them to final size and the required surface finish. Grinding is done in small passes with a suitable wheel and coolant so that the hardened surface does not soften or crack from overheating.

Types of grinding

Surface grinding

As the name suggests, this method grinds flat surfaces. The part is held on a magnetic table, or occasionally a vacuum table, while the wheel rotates. The wheel first touches the highest point of the part and grinding continues until the whole surface is ground. The part is then measured and grinding continues in passes until the required dimension is reached. Depending on the wheel and the material, a mirror-like finish can be achieved.

Cylindrical (external) grinding

Used to improve the outer surface of cylindrical parts. Unlike surface grinding, it can be done with both wheel and part rotating, with only the part rotating, or, as in centreless grinding, with the free workpiece between two rotating wheels. As with surface grinding, the main grinding should start after a reference measurement.

Internal grinding

The opposite of cylindrical grinding: internal surfaces are ground. Wheels can be supplied in cylindrical, conical and other shapes to suit the bore. The workpiece stays still while the wheel rotates. For precise dimensions, material is again removed after a reference measurement.

For a quote

Attach your drawing and state the surfaces to be ground, the dimensional tolerances, the required surface roughness (e.g. Ra) and the heat treatment applied to the part in the quote form.

Grinding