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Workholding Devices for Machine Tools
Introduction
Workholding devices = JIGS and FIXTURES
HOLD and LOCATE
Introduction
Workholding devices have become more flexible
they are able to hold more than 1 part of the material they can be changed rapidly
Conventional Design
Two Primary Functions Considered in
Designing Workholding Devices
LOCATING
- refers to orienting
and positioning
CLAMPING
- refers to holding
Conventional Design
Dimensions
SIZE Dimension
- denotes size of geometrical shapes
LOCATION Dimension
- determine the position or location
JIG
- determines the location dimensions
- guides tools and holds the work
Conventional Design
Conventional Design
FIXTURE
- establishes size dimensions
- holds the work
Conventional Design
Design Steps
Analyze workpiece and visualize operations.
Determine the orientation of workpiece.
Estimate magnitude and direction of forces.
Study standard devices available.
Form a mental picture and make a 3-D sketch of the workpiece with the workholder.
Make a sketch of the workholder and workpiece in the machine tool.
Design Steps
3-2-1 LOCATION PRINCIPLE
Design Steps
Clamping Consideration
Why should it be considered?
closely related to support of the work
induces some stresses
can cause some distortion
Clamping Consideration
Chip Disposal
Why is this essential?
Heat will not be carried away and tool life can be decreased.
So that they do not interfere with the proper seating of the work in the fixture.
JIGS
JIGS serves as guides
There are several basic forms for jigs, some of the basic types are:
Plate Jig
Channel Jig
Ring Jig
Leaf Jig
Box Jig
Universal Jigs
Plate Jigs- simplest
Channel Jigs- for simple shaped parts only!
JIGS
Ring Jigs
- For drilling
round parts
Leaf Jigs
JIGS
Box Jigs- most common and accurate
JIGS
Universal Jigs - reduces cost
- easier to use
FIXTURES
Conventional Fixtures
A Vise are general purpose fixtures mounted on subplates and can have their jaws interchanged base on part geometry.
Lathe Chucks are general purpose fixtures for rotational parts
Vise most common
- Modified to conform to the 321 location principle
Conventional Fixtures
Chucks - general purpose fixtures for rotational parts
- 3 jaw jacob, self centering
- collet
- quick change
JIGS vs FIXTURE
JIG
In contact with the tool
For guide and control
For location and movement
Acts as a pattern
FIXTURES
Never comes in direct contact with tool
Holds the tool firmly in place
Aligns workpiece
Modular Fixturing
Versatile
Increases capabilities by fixturing more than one part
Reduces cost of designing and building workholders
Reduces overhead cost (storage and maintenance)
Used for prototype tooling and small-batch production runs
Modular Fixtures
Set-up and Changeover
Rapid exchange of workholding devices
Reduction in setup times permits shorter production runs
Set-up and Changeover
Master Jig
Customizable jigs that uses the group technology concept
Set-up and Changeover
Intermediate Jig
Intermediate fixture acting as an adapter
Clamps
Used to secure the workpiece in place
Manual clamps or Power-actuated clamps
Clamps
Manual Clamps
Clamps
Power Actuated Clamps
More consistent than Manual Clamps
Automatic adjustment
Other Workholding Devices
Assembly Jigs Uses some type of fastening equipment
like welding or riveting Assembly of multiple components
Magnetic Workholders
Used for ferromagnetic materials
Clamping force is distributed evenly
Commonly used for thin sheets that are hard to clamp
Demagnetizing of the work is necessary
Other Workholding Devices
Electrostatic Workholders
Similar to magnetic workholders, except this can be used with any electrically conductive material
No residual magnetism in the work
Other Workholding Devices
Vacuum Chucks
Uses vacuum to keep the workpiece secure
Other Workholding Devices
QUIZ