Innovation Quantification Customization

Grinding/Coating Overview

The most detrimental failure-mode for super-abrasive tools is a weak-bond between the crystal and matrix material. An effective bond should be strong enough to retain the crystals while they wear and resharpen themselves through fracture or attrition. Ideally, only after the super-abrasive crystals have become too small to be effective should they be released and replaced by new crystals emerging from the bond.

Coated super-abrasives have become essential for optimizing bond systems in many grinding applications. These metallic coatings or surface treatments are applied to diamond and CBN crystals before the crystals are combined with a bond material and formed into wheels and tools for grinding, honing, cutoff, drilling, and other applications where consistent tool geometry, free cutting capabilities, long tool life, and dissipation of heat from the tool/workpiece interface are important.

The strength between the wheel-matrix and super-abrasive crystals affects the efficiency of the bond system. One major purpose of a coating is added texture on the diamond/cBN surface, which improves mechanical adhesion in the bond during use. Texture also increases the retention strength of the crystals in the bond, which helps to prevent the entire crystal and its coating from pulling out of the bond, whereby extending wheel life.

A coating also provides a more rigid hold on the crystal than the matrix alone, and prevents bare crystals from pulling out of the coated-shell. Additionally, the coating has a “wrapping” or “girdling” effect on the crystal. This reduces catastrophic fracture, where a crystal, which typically fractures just enough to expose a new cutting edge, shatters and is no longer usable.

Although super-abrasive coatings are most commonly used in resin- and metal-bond grinding wheels, special coatings or surface treatments enhance the performance of diamond and CBN in vitrified-bond and single-layer wheels as well.

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