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Work holding and releasing is the most essential act to carry out machining. These are commonly used in the machine shop.
1. To hold the job in proper position
2. To release the job quickly
3. To hold the job rigidly
4. To prevent vibration of the job while the machining is carried out.
There are many types of work holding devices like machine vices swivel vices, universal vice, pipe vice, T-Bolt’s ‘U’ clamps, Goose neck clamp, angle plate, Jigs and fixtures etc. These are all mechanical type work holding devices. In this project we are dealing about the pneumatic plain vice used in drilling machine. Here the loading and unloading is quick. The job can be held more rigidly.

INTRODUCTION
There are three major types of work holding devices which are:
1. Mechanical type
2. Hydraulic type
3. Pneumatic type
In mechanical type, the screw rod is actuating the movable jaw. One end is connected to the movable jaw and it passes through a fixed type nut. When we rotate one end of the screw rod it will rotate in the nut and in turn moves the movable jaw. Here the rotary motion is converted into reciprocating motion.
In Hydraulic type’s one end of the piston rod is connected to the movable jaw and the piston slides in the cylinder. Here the hydraulic fluid actuates the movement of the piston; this in turn actuates the movable jaw. Here the principle movement is only a reciprocating movement. Pneumatic type is same as the hydraulic type. Here instead of hydraulic fluid, air is used.


ADVANTAGES:

1. Idle time of the machine is reduced.
2. When compared with the mechanical vices, it consumes less time for clamping and unclamping the job.
3. It reduces the manual labour
4. Hence, production rate is higher
5. In this mechanism there is no backlash.
DISADVANTAGES:

1. Initial higher cost.
2. May be a choice of air leakage
3. Cylinder stroke length is constant