In-Feed Grinding
In-feed centerless grinding is used to grind work-pieces with relatively complex shapes, such as an hourglass shape. Before the process begins, the work-piece is loaded manually into the grinding machine and the regulating wheel is moved into place. The complexity of the part shapes and grinding wheel shapes required to grind them accurately prevent the work-piece from being fed axially through the machine.
Process
In centerless grinding, the work-piece is held between two wheels, rotating in the same direction at different speeds, and a work-holding platform. One wheel, known as the grinding wheel (stationary wheel in the diagram), is on a fixed axis and rotates such that the force applied to the work-piece is directed downward, against the work-holding platform. This wheel usually performs the grinding action by having a higher tangential speed than the work-piece at the point of contact. The other wheel, known as the regulating wheel (moving wheel in the diagram), is movable. This wheel is positioned to apply lateral pressure to the work-piece, and usually has either a very rough or rubber-bonded abrasive to trap the work-piece.
The speed of the two wheels relative to each other provides the grinding action and determines the rate at which material is removed from the work-piece. During operation the work-piece turns with the regulating wheel, with the same linear velocity at the point of contact and (ideally) no slipping. The grinding wheel turns faster, slipping past the surface of the work-piece at the point of contact and removing chips of material as it passes.
Centerless Grinding
is a machining process that uses abrasive cutting to remove material from a work-piece. Centerless grinding differs from centered grinding operations in that no spindle or fixture is used to locate and secure the work-piece; the work-piece is secured between two rotary grinding wheels, and the speed of their rotation relative to each other determines the rate at which material is removed from the work-piece.
Centerless grinding is typically used in preference to other grinding processes for operations where many parts must be processed in a short time.