Workholding

General Manufacturing Processes Engr.-20.2710 Instructor - Sam Chiappone

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.

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

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

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

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

3-2-1 Set Up

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

3-2-1 Set Up

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Types

Four basic types of workholding devices include: » Standard » Jig » Fixture » Modular fixturing systems

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Standard

Vises Clamps 3,4,or 6 Jaw Chucks Collets Magnetic & Vacuum Chucks

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Standard

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Standard

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Standard

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Standard

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Standard

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Standard

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

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Jig

1 2

6 4 5

3

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Jig

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.

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Fixture

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.

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Modular Fixturing Systems

GMP-20.271 Chiappone Rensselaer Polytechnic Institute

Design Criteria

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