Design rules of centred grinding

Grinding is a finishing process used to improve surface finish, abrade hard materials, and tighten the tolerance on flat and cylindrical surfaces by removing a small amount of material. In grinding, an abrasive material rubs against the metal part and removes tiny pieces of material. The abrasive material is typically on the surface of a wheel or belt and abrades material in a way similar to sanding. On a microscopic scale, the chip formation in grinding is the same as that found in other machining processes. The abrasive action of grinding generates excessive heat so that flooding of the cutting area with fluid is necessary. Reasons for grinding are: the material is too hard to be machined economically, the material may have been hardened in order to produce a low-wear finish, such as that in a bearing raceway. Grinding for surfaces of rotation (axially symmetric surfaces) can be either centred or centreless. This article will focus on centred grinding and the dos' and don'ts to avoid wheel breakages. Centred grinding In centred grinding, the grinding is performed at the centre. There are two types of centred grinding: outside diameter (OD) grinding and inside diameter (ID) grinding. In OD grinding, the workpiece has centre drilled ends, accommodating centre points and surface is removed by rotating the grinder's face plate. With OD grinding the workpiece and the grinding wheel moves or rotates in clockwise directions. ID grinding is performed on tubular parts that are generally held in a chuck or collet. The grinding wheel turns at very high-speed to maintain the proper surface speed but it moves anticlockwise. Centred grinding is accurate and stable, but set-up takes time and thru-put feeding is slower. Centred grinding external part design When grinding external part design, avoid undercuts; for inside corners, the best practice is to machine a relief at the corner prior to grinding so that a sharp ninety-degree male object can be placed in the corner; plunge grinding is a centred form of grinding in which the wheel "plunges" radially into the part. Centred grinding internal part design Undercuts should be avoided. Radii should be the same in order to simplify wheel dressing and minimise tool changes. Hole depth to diameter aspect ratio should be minimised. This is for the same reasons that bored holes are not too deep. Avoiding length to diameter ratios of more than six is a good practice. If possible, blind holes should be avoided. Blind holes restrict the flow of coolant. Circumferential interruptions should be avoided. Even axial interruptions should be avoided. An option to consider is a hardened and ground liner. This option must be weighed against the tolerance build-up and extra logistics involved. Adequate access for coolant flow should be provided. This can be difficult since the coolant shed by the rotating grinding wheel provides an effective curtain, which prevents coolant exchange.(finished) Safety tips Improper mounting of depressed centred grinding wheels can lead to wheel breakages. Store grinding wheels properly. Check all wheels for cracks or other damage before using. Use grinding wheels on machines that are designed and guarded for the grinding wheel. Check machine speed before mounting a grinding wheel-never overspeed a grinding wheel. Adjust grinding wheel guard properly. The guard must be between the operator and the wheel. Mount grinding wheel properly. During new wheel start-ups or after storage, do always test wheel and machine by running it in a protected area at least one minute before grinding; wear required PPE (personal protective equipment) such as eye and face protection and other protection as required by the work being done; employ dust controls and/or protective measures appropriate to the materials being ground; grind using the proper grinPuma Rihanna Creeper