Jigs & Fixtures-1

7/30/2019 Jigs & Fixtures-1

1/25


2/25

Jigs

Jigs are provided with tool guiding elements

such as drill bushes.

These direct the tool to the correct position

on the workpiece.

Jigs are rarely clamped on the machine table

because it is necessary to move the jig on the

table to align the various bushes in the jig with

the machine spindle.


3/25

Fixtures

Fixture hold the workpiece securely in thecorrect position with respect to the machine /cutter during operation.

There is sometimes a provision in the fixturefor setting the tool with respect to theworkpiece / fixture.

But, the tool is not guided as in the jig. Fixtures are often clamped to the machine

table.


4/25

Elements of Jigs and Fixtures

Locating elements: position the workpiece

accurately with respect to the tool guiding or

setting elements in the fixture.

Clamping elements: These hold the workpiece

securely in the located position during operation.

Tool Guiding and Setting elements: These aid

Guiding (drill bushes) or Setting (setting pieces)the tools in correct position with respect to the

workpiece.


5/25

Advantages of Jigs and Fixtures

Productivity

Interchangeability

Skill Reduction

Cost Reduction


6/25

Presentation of workpiece


7/25

Materials used in Jigs and Fixtures

High speed steels:

18% W for toughness and strength.

4.3% Cr for better hardenability and wear

resistance

1% V for retention of hardness at high

temperatures

Air or oil hardened to RC 64-65.

contd.


8/25


Die Steels:

Also called High Carbon (1.5 to 2.3 %) High Cr

(12%), Cold working steels and are used for press

tools and thread forming rolls. Hot die steels with lesser carbon (0.35%) and Cr

(5%), but alloyed with molybdenum (1%) and

vanadium (0.3 1%) for retention of hardness at

high temperature are used for high temperature

applications like forging, casting and extrusion.

contd.


9/25


Carbon steels:

0.85 to 1.18% C and can be oil hardened to

RC 62-63.

Used for tools for cutting softer materials like

wood work, agriculture, etc. and also for hand

tools such as files, chisels and razors.

Bushes and locators are also made up of carbonsteels

contd.


10/25


Collet steels (Spring steels):

1 % C and 0.5 % Mn.

Usually tempered to RC 47.

Mild steels: Cheapest and most widely used material in Jigs

and Fixtures.

Contains 0.3 % C. Used for parts which are not subjected to much

wear and are not highly stressed.contd.


11/25


Cast iron:

It contains 2 to 2.5 % C

Used in milling fixtures as it absorbs vibrations

well.

Self lubricating properties make CI suitable for

machine slides and guide-ways.

High machinablity.

contd.


12/25


Nylon and Fibre:

Used as soft lining.

Phosphor bronze:

Widely used for replaceable nuts in screw

operated feeding and clamping systems

Case hardening steels

High Tensile steels

Steel castings


13/25

Principles of Location

Six degrees of freedom


14/25


Twelve degrees of freedom


15/25


Three pins arrest Five degrees of freedom


16/25


17/25


Six pins arrest Nine degrees of freedom


18/25


Workpiece Requirements


19/25


Accuracy


20/25


Motion Economy


21/25


Redundant Locators


22/25


Workpiece distortion due to redundant location


23/25


Adjustable support


24/25


Fool proofing


25/25


Distance between locators

Documents

Jigs & Fixtures-1