Abrasive Machining

1. Abrasives

       Abrasives can be natural or manmade.

Abrasive Requirements

•High hardness at room & elevated temperure

•Controlled toughness or rather ease of fracture, allows fracture to occur under imposed mechanical and thermal stresses

•Low adhesion to the workpiece of material

•Chemical stability

•The grains must have a shape that presents several sharp cutting edges

Hardness dan Tempratur

2. Abrasive Grain Size

        Grains are separated by mechanical sieving machines.  The number of openings per linear inch in the sieve(or screen) through which the particles can pass determines the grain size.

*Typical classifications:

–Course, medium, and fine

–Silicon Carbides range from 2-240 in size

–Aluminum Oxides range from 4-240 in size

   •600 range are generally used in honing or lapping operations

3. Forms

Abrasive particles can be:

    •A Free slurry

    •Adhered to resin on a belt   

    •Close packed into wheels or stones held together by a bonding agent.

4. Cylindrical Grinding

     •Cylindrical grinding is used to produce external cylindrical surfaces

    •In cylindrical grinding the workpiece is mounted and rotated on a longitudinal axis, the grinding wheel rotate in the same axis, but in opposite directions.

     •With long workpieces, the workpiece typically is moved relative to the wheel.

     •With smaller high production parts, a chuck-type external grinder is used, and the wheel moves relative to the workpiece.

5. Centerless Grinding

     •In centerless grinding the workpiece can be ground internally or externally without requiring the material to be mounted in a center or chuck.

     •The workpiece rests between two wheels, one providing the grinding and the other providing regulation of the grinding speed.