Workholding
Principles
Workholding Fixture Example
Welding Fixture Examples
Introduction
Jigs Vs. Fixtures
Drill Jigs
Jigs and Fixtures
Jigs and Fixtures are critical to repeated manufacturing to with high degrees of accuracy and precision.
Jigs and Fixtures hold one or multiple parts in one or multiple machine centers to provide stability and repeatable alignment of the part.
Locating vs. Holding/clamping
Locating principle - Arrest the degrees of freedom.
Clamping resists the machining forces to keep the workpiece in place.
3-2-1 Principle
Simplest way to fix the degrees of freedom:
Jig & Fixture Components
Avoid A Rookie Mistake
Threaded Connection:
Chips & Burrs
Grinding Relief
Think about how the parts you design will be made
Locating Devices
Image Courtesy of Carr-Lane
Adjustable Locators
Sometimes locators should be adjustable.
This can be done with threaded bases, locknuts, shims and other means.
Spring-Loaded Devices
Remember that parts going into your fixture will not be perfect.
The best you can hope for is that they are in tolerance.
Extending this concept...
Keep in Mind
The part needs to go in and out
The tool needs to fit
Accommodate the chips & burrs
The fixture may need to come apart and go back together
Be aware...
Your workpiece is changing as operations are performed on it. You may be removing material that is keeping your work in place.
Design Steps
Sketch Your Initial Ideas
Start with Knowns
The final workpiece is the starting point.
Fix the assembly in space.
Add components, clamps, locating pins, etc.
Keep in mind materials and manufacturing steps for components.
Chip & Burr Considerations
Unloading and Loading Time
Rigidity is Critical
See other beam diagrams, also.
Clamping Considerations
Clamping forces produce stresses in the part, excess clamping forces can cause distortion
Clamping force should be in the direction of cutting forces
Consider what is reacting to the force vector.
Clamping Considerations
Clamping should be designed such that the cutting forces work against the fixed portion of the clamp, not the movable portion.
Clamping forces should be as near in alignment with the cutting forces to minimize torsional moment.
Distortion During Clamping may not be observed until the part is removed from the fixture.
Vices & Parallels
T-Nuts & T-Slots
Strap Clamp Best Practices
Chucks
For lathes and mills
Soft Jaws
For chucks & vises
Soft Jaws
Collet Fixtures
Tombstones
Generally used in HMCs
Adjustable Parallels & Planar Gages
Sine Bars & Sine Plates
V-Blocks
1-2-3 Blocks, Bench Blocks
Angle Plates
Rotary Tables & Indexing/Dividing Heads
Toggle Clamps
Holding Multiple Parts in a Vise
Adaptix™ Jaws
Kunze Vise (Fractal Vise)
Holding with a Carrier
Often the blank is oversized or has additional features to provide a clamping location.
Modular Fixtures
Modular Fixtures are similar to conventional fixture, except they are more versatile.
Modular systems use dowel pins and T-slots to provide a rigid, adjustable fixture.
Standard elements are positioned to fit the part needs, such as
Riser blocks Vee blocks
Angle plates Cubes
Box parallels Supports
Locator pins Clamps
Modular Fixtures
Clamps
Power Clamps
Manual Clamps
c-clamps
vice-grip pliers/clamps� “Kant twist”
(cantilever clamps)
bar/pipe clamps
Swing Clamps
Strap Clamps
Magnetic Chucks
Permanent & Electro-Permanent
Vacuum Chucks
Keep in mind that the clamping force from a vacuum comes from atmospheric pressure ONLY.
More area, better clamping.
Vacuum Chucks
Vacuum Chucks
Example
Notice tabs
Matt Hale
Adhesive Workholding
Sometimes it works.
See Loctite 380 & Superglue (Cyanoacrylate)
Pallet Systems
Pallet Systems
Jig and Fixture Examples
Hydraulic Workholding
Welding Fixture (modular)
Welding Fixture Example
What is good about this fixture?
What could be improved?
Welding Positioners