Superfinishing Procedures

Superfinishing Procedures

Superfinishing Procedures - Fig. illustrates various superfinishing procedures.

Superfinishing Procedures of Crankpin

Superfinishing Procedures of Camshaft

The superfinishing of the crankpin on a crankshaft. Abrasive head 1. with two abrasive sticks 2 oscillates along the crank pin with frequency of 450 strokes per minute and a stroke length of 2 or 3 mm. This imparts the required class of finish to the surface,

Fig. shows an arrangement for superfinishing the cams of a camshaft. The abrasive tool is a Wheel which in continuously in contact with the cam surface during the operation. The camshaft has simultaneous rotary; and oscillating motions, as well as an axial motion, to obtain a fine surface finish.

Fig shows the superfinishing of external surface of a piston. The piston only rotates. Abrasive head 1 in this case has a somewhat longer stroke than in the previous cases.

Abrasive/block stick

For superfinishing, loosely bonded abrasive sticks are used with an action which comprises a short scrubbing motion, light pressure and slow abrasive cutting speed.

The abrasives used for r making sticks are aluminium oxide for materials of high tensile strength such as carbon and alloy and high speed steels and materials of considerable hardness. Silicon carbide abrasives are preferred for low tensile materials such as cast iron, aluminium, brass etc.

Bonded diamond dust is used for finishing cemented carbide tools. The grit size of abrasive used varies from 400 to 1000: mesh. The selection of the grit size depends on the surface roughness on the job before superfinishing. Normally, a bakelite or vitrified bond is used. Stones are virtually self dressing.

The number of abrasive sticks fitted to the holder or abrasive head depends upon the surface to be machined.For finishing cylindrical work, an abrasive stick or stone is used. An abrasive cup is employed for flat or spherical work. The action of the abrasive stick or stone is similar to a scrubbing movement.