Grinding is a machining process found at almost all shops. Some grinding operations, such as snagging castings, grinding welds or bench grinding, are relatively simple. Other grinding activities can be complex like those used to hold very close tolerances or machine difficult materials. Grinding has a broad range of applications in manufacturing. As with many procedures, selecting the best tool is critical.
Although the cutting edges are much smaller and arranged in a random order, grinding wheels are cutting tools and perform the same job as endmills, drills and turning tools. Whether snagging castings or grinding gears, wheels are similar.
Grinding wheels are made from several types of abrasive materials, from aluminum oxide — the softest and most common — to diamond, which is the hardest and most expensive. Most wheels are manufactured by mixing the abrasive material with a bonding agent and then placing the mix in a mold to achieve the desired shape.
A vitrified wheel is formed under pressure and then baked at a very high temperature, which turns the bonding materials — for example, clay — to glass, giving strength and rigidity to the wheel. Resinoid-bonded wheels use the same sort of abrasives with a softer resin bond that often is reinforced with other materials like fiberglass to add strength. Resinoid wheels can operate at higher cutting speeds than vitrified wheels and are less likely to fail, with uneven loading making resinoid wheels ideal for use on hand tools or machines, such as chop saws. Vitrified wheels hold their shape better and are stiffer than resin-bonded wheels, making them best suited for close-tolerance work performed on rigid machine tools. Both kinds of wheels can break and fragment during use, but vitrified wheels are more susceptible to catastrophic failure, which is another reason they typically are not used for hand work.
Super-abrasives like diamond and cubic boron nitride are expensive. To reduce the amount of abrasive needed to make a usable wheel, an abrasive is bonded to the periphery of a metallic disc. Diamond and CBN bonds can be vitrified, resinoid or metallic. Metallic-bonded wheels use metal powder, such as cobalt and copper, mixed with an abrasive. Using a process known as sintering, the mixture is formed around the periphery of a wheel. The abrasive and metal powder are baked at a high temperature, causing them to bind together.
Super-abrasive wheels have better performance characteristics but a narrower range of applications as the wheels do not perform well on softer materials. CBN wheels are used most often on hardened ferrous materials and can be found in machines like tool and cutter grinders, camshaft grinders and gear grinders. Compared with Al2O3 wheels, CBN wheels run cooler, last longer and can function at higher speeds. Diamond is used to grind carbides, glass and other extremely hard nonferrous materials. Super-abrasives are more productive but expensive. They frequently cost 10 times more than other types of wheels, and their applications are typically very specific.
Read more: Choose the proper grinding wheel