work holding
TRANSCRIPT
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Workholding
General Manufacturing Processes Engr.-20.2710 Instructor - Sam Chiappone
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Workholding Devices
– Holding or clamping the workpiece is an important factor in the manufacturing process. Parts are clamped, relative to their datum planes, for machining, assembly, welding, and inspection. Workholding devices range from simple vises to microprocessor controlled fixturing systems.
– A correct fixture will assist in achieving desired part tolerances time after time.
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Basic Functions
Two basic functions of a workholding device: – Locate - Refers to positioning a part with respect to its
datum(s) for manufacturing purposes – Clamp - Refers to holding the part for manufacturing
purposes
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
321 Fixturing Method
One of the basic fixturing methods is the 3-2-1 system. This method cancels the twelve degrees of freedom of a part and positions it in three perpendicular planes.
» X axis = +, -, CW, CCW » Y axis = +, -, CW, CCW » Z axis = +, -, CW, CCW
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
3-2-1 Set Up
(3) Three points establish base plane (2)Two points establish vertical plane for
reference (1) One point in third plane positively locates part
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
3-2-1 Set Up
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
3-2-1 Set Up
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Types
Four basic types of workholding devices include: » Standard » Jig » Fixture » Modular fixturing systems
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Standard
Vises Clamps 3,4,or 6 Jaw Chucks Collets Magnetic & Vacuum Chucks
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Standard
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Standard
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Standard
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Standard
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Standard
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Standard
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Jig
Is a special device that through built in features automatically determines location dimensions for machining or assembly. A jig can assist in guiding tools and will clamp the workpiece. – Examples include:
» Plate, Diameter, Channel, Leaf, Ring, and Box
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Jig
1 2
6 4 5
3
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Jig
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Fixture
A device which clamps work during machining. Usually designed for a specific part or family of parts. The primary purpose of a fixture is to clamp the workpiece.
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Fixture
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Modular Fixturing Systems
General purpose components ( clamps, build-up blocks, locating pins, angle plates, etc.) which are assembled into specific fixturing arrangements for a specific job. All components are reusable.
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Modular Fixturing Systems
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Design Criteria
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GMP-20.271 Chiappone Rensselaer Polytechnic Institute
Economical Considerations for Special Fixtures
– Cost of tooling – Savings in machine set-up time – Number of units which will be produced using the
fixture – Overall savings
» Reduced cycle times » Improved quality » Reduced operator interaction