Grinding is a process that involves removing small thicknesses of materials using an abrasive material. Grinding is used when more precise dimensions and surfaces are required than can be achieved by other machining processes. For grinding to be effective, the work piece must be a hard material like metal, ceramic, or mineral. Precision grinding services are contracted from a "job shop" or "machine shop" when in-house capabilities are not available or are inadequate. The service provider receives the rough parts along with the required finish and dimensions. The precision grinder completes the work and returns the finished parts to the customer.
Precision grinding services perform operations such as centreless grinding, creep feed grinding, double-disc grinding, internal grinding, external grinding, jig grinding, surface grinding, and thread grinding. Precision grinding services that perform other types of grinding operations are also available.
Centreless grinding is used for parts without centres or places to hold the part. It is an OD machining operation in which an abrasive wheel grinds metal from a bar's surface while a regulating wheel forces the bar against the grinding wheel. The part will rotate between the regulating wheel and the grinder. The regulating wheel is tacky in order to grip the part and spins in the same direction as the grinder. This is a very fast process as the parts are being continuously fed into one end and out the other end.
Creep feed grinding is a type of plunge grinding that uses specialized grinding equipment. It is used to produce slots or intricate forms in difficult-to-grind materials such as pre-hardened tool steels and high-temperature nickel-based aerospace alloys. The grinding wheel is fed into the work at very slow rates. Creep feed grinding has two advantages over machining including being able to work on materials that are difficult and expensive to shape and allowing easy modification of the form on the grinding wheel to enable quick design changes and changeovers.
Disc grinding and double-disc grinding use a large wheel to produce flat, parallel parts for high-volume production. Double-disc grinders are machines with two independent grinding wheels. With double-disc grinding, the work passes between the faces of the two grinding wheels. Single-disc grinders exist, but are less common than double-disc devices. In a single-disc machine, the grinding wheel is usually mounted to a vertical spindle.
Internal grinding or ID grinding is used to grind the inner diameter (ID) of holes. It uses a small high-speed grinding wheel on tubular parts. The high speed is used to maintain the proper surface speed. The parts are held in place with a collet or chuck.
External grinding or OD grinding is used to grind the outer diameter (OD) of cylindrical parts. The grinding is preformed between centres in the workpiece. The work piece and the grinding wheel rotate in the same direction so the surface of the work piece and the grinding wheel are moving in opposite directions at the point of contact.
Jig grinding uses very precise machines for locating and generating very accurate holes, contours, and surfaces to tolerances of .0001" or less. They can also be used for a variety of difficult grinding tasks such as blind holes, pockets, and to add reliefs.
Super abrasive grinding uses grinding machines made from extra hard materials such as diamond, cubic boron nitride (CBN), and borazon. Often a super abrasive grinding machine can replace two-or-more standard process because they allow for closer tolerance machining and less tool wear. This results in overall cost savings and higher quality machining.
Surface grinding mounts the workpiece to a table for back and forth feeding under the grinding wheel. They produce flat and parallel surfaces. The grinding wheel is mounted to a horizontal spindle and the work is ground with the outside diameter of the wheel
Thread grinding is used to produce lead screws, ball screws, and worms. Thread grinding is a metal removing process preformed with a single-point contact or formed wheels.