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MET 33800 Manufacturing Processes
Chapter 27
Workholding Devices for Machine Tools
Chapter 27 - 1
Workholding DevicesIntroduction
Workholding device locates work in machine tool with respect to the cutting tool.
Critical for repeatability.
Trend toward flexibility: family of parts and manufacturing cells.
Primary functions:
Locating
ClampingChapter 27 - 2
INTRODUCTION
Fixture – Specialized workholding device that holds workpiece during machining or assembly operations and establishes size dimensions.
Jig – A special type of fixture that, through built-in features, determines both location and size dimensions that are produced by machining or fastening operations.
Chapter 27 - 3
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Fixture size Jig location and size
INTRODUCTION
Chapter 27 - 4
FIXTURE DESIGN
Chapter 27 - 5
FIXTURE DESIGN
Chapter 27 - 6
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1. Locating – function is to orient and position workpiece in the machine tool:
Provides positive location for the 12 degrees of location freedom:
o Linear: X, Y, Z
o Rotational: A, B, C
Location by 3–2–1 principle
FIXTURE DESIGN
Chapter 27 - 7
3-2-1 FIXTURE DESIGN
Chapter 27 - 8
3 Points
1 Points
2 Points
1.Locating (continued):
Repeatability: fool proofing.
Low profile: clear cutting path.
FIXTURE DESIGN
Chapter 27 - 9
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1.Locating (continued):
Cutting forces: press part into locators.
Accommodation: allowing workpiece variance.
FIXTURE DESIGN
Chapter 27 - 10
FIXTURE DESIGN
Chapter 27 - 11
2. Clamping – Function to hold and/or maintain location:
Adequate: balance strength & deflection.
Reliability: repeatable clamping forces.
Clamping forces: toward locators.
Loading/Unloading time: dependent on clamp type.
FIXTURE DESIGN
Chapter 27 - 12
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3.Other Design Factors:
Chip disposal and removal: heat and interference concerns.
Ruggedness
Construction ease
Ergonomics and safety
Flexibility
FIXTURE DESIGN
Chapter 27 - 13
4.Additional Jig Functions:
Location - position geometric shapes with respect to each other.
Size - size of geometric shapes.
Dimension control.
Examples:
Drill jig
Welding jig.
JIG DESIGN
Chapter 27 - 14
JIG DESIGN
Chapter 27 - 15
Drill Bushings:• Press Fit• Slip Fit
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Plate jig - plate w/drill bushings and locating pins, clamped to part.
Channel jig - part in open side, locate on outside of part.
Ring jig - for end/surface of round parts.
Diameter jig - for cylindrical surfaces.
Leaf jig - hinged leaf or cover.
Box jig - boxlike construction, tumble.
Assembly jig - welding or riveting, open frame typically.
TYPES of JIGS
Chapter 27 - 16
TYPES of JIGS
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TYPES of JIGS
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Fixtures categories include:
Vises
Lathe chucks and collets
Faceplate fixtures
Milling and grinding fixtures
Modular fixtures
TYPES of FIXTURES
Chapter 27 - 19
TYPES of FIXTURES
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TYPES of FIXTURES
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TYPES of FIXTURES
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Example of a Lathe Faceplate Fixture
TYPES of FIXTURES
Chapter 27 - 23
Example of Multiple Parts on
Single Fixture
TYPES of FIXTURES
Chapter 27 - 24
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Modular fixtures provide versatility and adaptable to
different workpieces.
MODULAR FIXTURES
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MODULAR FIXTURES
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MODULAR FIXTURES
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MODULAR FIXTURES
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MODULAR FIXTURES
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ASSEMBLY FIXTURES
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Used for part families:Group Technology (GT) concept.
MASTER (GROUP) FIXTURES
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MASTER (GROUP) FIXTURES
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CLAMPING
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CLAMPING
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Fixture types which used other clamping methods:
Magnetic chucks - ferromagnetic materials only.
Electrostatic chucks - conductive materials only.
Vacuum chucks.
CLAMPING
Chapter 27 - 35
CLAMPING
Chapter 27 - 36
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Permanent-Magnetic Chucks
CLAMPING
Chapter 27 - 37
Electro-Magnetic Chucks
CLAMPING
Chapter 27 - 38
CLAMPING
Chapter 27 - 39
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ECONOMICS of FIXTURES
Chapter 27 - 40
ECONOMICS of FIXTURES
Chapter 27 - 41
FIXTURING EXAMPLE
Chapter 27 - 42
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FIXTURING EXAMPLE
Chapter 27 - 43
The End – See Oncourse for Videos
Chapter 27 - 44
