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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.
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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.
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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.
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Advantages of Jigs and Fixtures
Productivity
Interchangeability
Skill Reduction
Cost Reduction
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Presentation of workpiece
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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.
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Materials used in Jigs and Fixtures
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.
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Materials used in Jigs and Fixtures
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.
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Materials used in Jigs and Fixtures
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.
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Materials used in Jigs and Fixtures
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.
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Materials used in Jigs and Fixtures
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
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Principles of Location
Six degrees of freedom
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Principles of Location
Twelve degrees of freedom
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Principles of Location
Three pins arrest Five degrees of freedom
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Principles of Location
Six pins arrest Nine degrees of freedom
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Principles of Location
Workpiece Requirements
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Principles of Location
Accuracy
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Principles of Location
Motion Economy
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Principles of Location
Redundant Locators
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Principles of Location
Workpiece distortion due to redundant location
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Principles of Location
Adjustable support
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Principles of Location
Fool proofing
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Principles of Location
Distance between locators