Grinding Machine

It is one of the various processes various processes in which a raw material is cut into a pre-defined shape and size by employing a controlled process that involves removal of material. The controlled process used for this purpose is either abrasive cutting or grinding.

It differs from centred grinding in that there is no spindle used to hold in place the material on which the work is being carried out.

centerless grinding, as the name implies, is a process that grinds the surface of a turned part or round bar of material, without the need to support the work piece on centers.For grinding round bar stock, a "through grinding" process is used. A bar of material, typically twelve feet long, feeds into the grinding machine between a grinding wheel and a regulating wheel. A carbide-tipped strip of steel, the work blade, supports the bar and holds it at the correct height, above the centerline of the grinding and regulating wheels. This is critical to the roundness and diameter tolerances of the bar. Both wheels rotate. The regulating wheel is slanted up a little from the horizontal. As it turns, it pulls the bar past the grinding wheel, so no external feeding mechanism is required.

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Each abrasive grain on the surface of the grinding wheel takes a little bite of material every time it passes the bar being ground. This produces a lot of heat, of course, so the grinding area is flooded with a generous flow of coolant. The regulating wheel does not remove any material. It just presses the work piece against the grinding wheel and controls how fast the bar rotates and how fast it moves past the grinding wheel.

A grinding wheel is made from grains of abrasive material bonded together into a cylindrical shape. Different grinding wheels have different sized grains of different abrasives, different bonding agents and different "porosity," which is the density or spacing of the abrasive grains and bonding material.

The hardness or tensile strength of the material being ground determines which type of grinding wheel to use, explains Steven Tamasi, CEO of Boston Centerless. The company uses primarily silicon carbide and aluminum oxide abrasives. The grinding wheels used on many of the company's centerless grinding machines are 24 inches in diameter when new, and eight inches wide. The regulating wheels are the same width and 16 inches in diameter. Other machines use different-sized wheels.

The operator first selects the right abrasive grinding wheel for the job, then installs the correct work blade. The work blade must hold the bar at the right height above the centerline of the wheels. The operator adjusts the inclination of the regulating wheel and shapes it to provide a full line of contact with the part. As the grinding wheel is used, it wears down and loses some abrasive grains from its surface. The operator must keep it dressed, or trued, in the correct shape and surface condition for optimum grinding.