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