JIG & FIXTURE

CHAPTER-I

INTRODUCTION

A fixture is a special tool used for locating and firmly holding a work piece in the proper position during a manufacturing operation.

As a general rule it is provided for supporting and clamping the work piece. In addition, it may also contain devices for guiding the tool prior to or during its actual operation. Thus, a jig is a type of fixture with means of positively guiding and supporting tools for drilling, boring and related operations. Hence the drilling jig, which is usually fitted with hardened bushings to locate, guide, and support and rotating cutting tools.

DEFINATION

Jig:- A jig is a device which holds and positions the work, locates or guides the cutting tool relative to the work piece and usually is not fixed to the machine table. It is usually lighter in construction.

Fixture:- A fixture is a work holding device which holds and positions the work piece, but does not in itself guide, locate or position the cutting tool.

PURPOSE

The main purpose of the fixture is to locate the work quickly and accurately, supported properly, and hold it securely, thereby ensuring that all parts produces in the same fixture will come out alike within specified limits. In this way accuracy and interchangeability of the parts are achieved.

To fulfill their basic function, both jigs and fixtures should possess the following elements or components:

A sufficiently rigid body (plate, box or frame structure) into which work piece is loaded.
Locating elements.
Clamping elements.
Tool guiding elements (for jigs) or tool setting elements (for fixtures).
Elements for positioning or fastening the jig or fixture on the machine on which it is used.

ADVANTAGES

Reduce the cost of production, as it eliminates the laying out of work and setting up of tools.
Increases the productivity.
It assures high accuracy and interchangeability of the parts.
It reduces quality control expenses.
It enables heavy and complex shaped parts to be machined.
Increases the versatility of machine tool.
Less skilled labour required.
It partially automates the machine tool.
Provides safety for man and machine.

Reduce the cost of production, as it eliminates the laying out of work and setting up of tools.
Increases the productivity.
It assures high accuracy and interchangeability of the parts.
It reduces quality control expenses.
It enables heavy and complex shaped parts to be machined.
Increases the versatility of machine tool.
Less skilled labour required.
It partially automates the machine tool.
Provides safety for man and machine.

APPLICATION

It is obvious to use jigs and fixtures in mass production, where large quantity output offers ample opportunity for recovery of the necessary investment. However, the advantages in the jigs and fixtures are so great and so varied, that these devices have also naturally found there way into the production of parts in limited quantity as well as into manufacturing process outside of the machine shop, and even outside of the metalworking industry. The many problems of geometry and dimensions encountered within the aircraft and missile industry have greatly accelerated the expanded use of jigs and fixture.

Classification :

Jigs and fixtures may be classified into:

Machining fixtures: -Fixtures that are used within the machine shop are known as machining fixtures. They further may be classified according to the type of machining operation to be performed on the work piece.

Planning fixtures
Shaping fixtures
Slotting fixtures
Turning fixtures
Milling fixtures
Grinding fixtures
Broaching fixtures
Sawing fixtures
Drill jigs
Tapping jigs
Reaming jigs
Honing and lapping jigs
Boring jigs

2. Manual work fixtures: -Fixtures that are used outside the machine shop and are operated manually. They further may be classified according to the type of the operation to be done.

Preparatory operation (e.g. layout fixtures)
Metallurgical operation (e.g. heat treatment fixtures)
Joining operation (e.g. welding, soldering, brazing, riveting, wire-stitching, crimping, assembly fixtures etc.)
Quality control (e.g. inspection, measuring, pressure testing fixtures etc.).