In a recent article in Modern Machine Shop, author Alfredo Barragan explains how different grains and coatings in grinding wheels bring different strengths. Understanding which grains and coatings are best suited to specific applications can, over time, save manufacturers money. “Matching applications to their optimal superabrasive grinding wheels can reap dividends through improved part quality and throughput, making deep knowledge of grain, bond and coating properties vital for grinding machine users.”
What Makes a Good Superabrasive Wheel?
“Superabrasive wheels,” Mr. Barragan states, “must exhibit a variety of properties, including hardness at elevated temperatures, high thermal conductivity to transfer heat away from the cutting edge, composition stability, heat resistance, lubricity and ability to prevent plastic deformation.” It is, therefore, important to focus on the shape of the abrasive grains and the type of coating the wheel uses.
Grain Shape Determines Strength
The shape of the diamond or CBN grains is a key determinant of how tough or friable the abrasive particle will act during the grinding application. Toughness refers to how well the abrasive particle resists cracking, chipping and breaking. Friability refers to the ability of the grain to break down and self-sharpen.
Abrasive particles come in two categories of shape: blocky and angular. The blockier or rounder the abrasive particle, the less efficient it is for stock removal, but the better it is for form holding. Blocky particles endure higher grinding forces before breaking.
Angular shapes are more aggressive and better able to penetrate and remove material. However, angular grains crack under lower forces.
Ideally, it is best to have a grain that balances both these shapes, staying tough but also achieving a natural breakdown to expose new, sharp cutting edges.
Coating Fortifies Wheel Integrity
Coating is the process of completely and uniformly covering the superabrasive grains with a layer of additional material. This process increases the size and weight of the grain and is usually performed to boost qualities such as strength and durability during grinding applications. Nickel, copper and silver are the most common superabrasive coatings.
One key benefit of coatings is they texturize the diamond or CBN particle for better adherence to the bond of the wheel, whether that wheel is resin, vitrified, metal, a hybrid material or something else. The improvement in mechanical and chemical retention to the bond system fortifies wheel integrity.
Superabrasive grain shape and coating composition play a large role in the suitability of grinding wheels for different applications. Matching applications to their optimal superabrasive grinding wheels can reap dividends through improved part quality, throughput and can give your machine shop a competitive edge.