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How It Works

Most diamond and cBN abrasive is used in so called 'bonded tools'. However much lapping, polishing and fine finishing, particularly with Micron+ products, is carried out using the abrasive as a loose powder or in a slurry when mixed with an oil or other carrier medium. Diamond and cBN abrasives are normally used in particle sizes of approximately 1mm down to less than 0.1 micron, and their sizing is subject to international standards.

In a bonded tool, the abrasive particles are held in a bond or matrix material, usually distributed randomly but in a controlled concentration. The main functions of the bond are:-

  • to hold the abrasive particles
  • to form a moulded profile of the required shape which is usually attached to a hub or carrier;
  • to release worn abrasive particles as they reach the end of their useful lives, thus exposing new ones.

It is therefore a general requirement of a bonded tool that the abrasive and the bond material wear at similar rates.

The most common types of bond used are:

  • Resin, normally thermosetting phenolic or polyimide resins.
  • Vitrified; based on glass frits.
  • Metal; normally sintered alloys.
  • Electroplated; a single layer or a few layers of abrasive attached to a hub by an electro-deposited metal layer, normally nickel.

In the case of the first three bond types, it is very important to match the size, impact strength and fracture mode characteristics of the abrasive to the properties of the bond if optimum performance is to be obtained. Workpiece material plays a major role in this selection process, but the type of machining operation, the machining conditions used and the primary requirement of the operation are also important considerations. Maximum tool life, high rates of material removal or high quality of surface finish are common requirements but normally a compromise has to be made between one or more. In the case of the fourth bond type - electroplated or E.P. - abrasive particles are embedded in a metal layer to something less than 50% of their total dimension.

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