Tool and Die Design
(MEng 5261)
Pre-requisites: MEng 3504, Production
Engineering
Debre Tabor University
Lectur-1
WEEK-1
12/6/2019
Prepared by: Berhe Syum
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Course Outline
1. INTRODUCTION TO TOOL AND DIE DESIGN
2.WORK PIECE HOLDING PRINCIPLES
3. CLAMPING PROCESS
4. JIG AND FIXTURE DESIGN
5. TOOL MATERIAL SELECTION
6. SINGLE POINT CUTTING TOOL DESIGN
7. DESIGN OF FORM TOOLS
8. DESIGN OF FORMING DIE (. function, and type of forming die ,
Design of punching dies, bending die, Progressive drawing dies
design, Design forging dies and Design of blow and injection
molding dies
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Chapter-One
Introduction
TOOL DESIGN
❖Tool design is the process of designing and developing the tools,
methods, and techniques necessary to improve manufacturing efficiency
and productivity.
❖It does this at a level of quality and economy that will ensure that the
cost of the product is competitive.
❖ No single tool or process can serve all forms of manufacturing, tool
design is an ever-changing, growing process of creative problem solving.
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TOOL AND DIE DESIGN AND MANUFACTURING
Tool and die design and manufacturing -is a
specialized area of manufacturing engineering
which comprises the analysis, planning,
design, construction and application of tools,
methods and procedures necessary to
increase manufacturing productivity.
❖Work holding tools – Jigs and Fixtures
❖Cutting tools
❖Forming Die ( Sheet metal ,Forging , Rolling,
Extrusion dies)
❖ Welding and inspection fixtures
❖ Injection molds
❖Tooling for Casting
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TOOL AND DIE DESIGN OBJECTIVES
The main objective of tool design is to lower manufacturing
costs while maintaining quality and increased production. To
accomplish this, the tool designer must satisfy the following
objectives:
✓Provide simple, easy-to-operate tools for maximum
efficiency.
✓Reduce manufacturing expenses by producing parts at the
lowest possible cost.
✓Design tools that consistently produce parts of high quality.
✓Increase the rate of production with existing machine tools.
✓Design the tool to make it foolproof and to prevent improper
use.
✓Select materials that will give adequate tool life.
✓Provide protection in the design of the tools for maximum
safety of the operator.
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During designing of tool and die the designer must consider
✓Overall size and shape of the part
✓Type and condition of the material used for the part
✓Type of machining operation to be performed
✓Degree of accuracy
✓Number of pieces to be made
✓Locating and clamping surface
✓Sequence of operation
✓ Safety and Ergonomics
✓Tool Materials
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The Tool Design Process
• Statement and analysis of the problem
• Analysis of the requirements
• Development of initial ideas
• Development of design alternatives
• Finalization of design ideas
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Statement of the problem
• Problem without tooling
• What the tool is supposed to do?
• drill four holes
• Bottleneck in assembly
• Low productivity with out tooling
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Analysis of the requirements
Must perform certain functions
Must meet certain minimum precision requirements
Must keep the cost to a minimum
Must be available when the production schedule requires it
Must be operated safely
Must meet other requirements such as Adaptability to the
machine tool.
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JIGS AND FIXTURES
TYPE AND FUNCTIONS OF JIGS AND FIXTURES
• Jigs and fixtures are special purpose tools which are used
to facilitate production (machining, assembling and
inspection operations) when work pieces are to be
produced on a mass scale.
• Jigs and fixtures provide a means of manufacturing
interchangeable parts since they establish a relation, with
predetermined tolerances, between the work and the
cutting tool.
• They eliminate the necessity of a special set up for each
individual part.
• Once a jig or fixture is properly set up, any number of
duplicate parts may be readily produced without additional
set up.
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jigs and fixtures are used:
1. To reduce the cost of production, as their use eliminates
the laying out of work and setting up of tools.
2. To increase the production.
3. To assure high accuracy of the parts.
4. To provide for interchangeability.
5. To enable heavy and complex-shaped parts to be machined
by being held rigidly to a machine
6. Reduced quality control expenses.
7. Increased versatility of machine tool.
8. Less skilled labor.
9. Saving labor.
10. Their use partially automates the machine tool.
11. Their use improves the safety at work, thereby lowering
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JIGS
❖It is a work holding device that holds, supports and locates the
work piece and guides the cutting tool for a specific operation.
❖A jig's primary purpose is to provide repeatability, accuracy, and
interchangeability in the manufacturing of products.
❖A device that does both functions (holding the work and guiding
a tool) is called a jig.
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FIXTURES
• It is a work holding device that holds supports and
locates the work piece for a specific operation but
does not guide the cutting tool.
Examples: Vises, chucks
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How do jigs and fixtures differ?
JIGS
JigS
Fixture
1. It is a work holding device that
holds, supports and locates the work
piece and guides the cutting tool for
a specific operation
1 It is a work holding device
that holds, supports and locates
the work piece for a specific
operation but does not guide the
cutting tool
2. Jigs are not clamped to the drill press
table unless large diameters to be drilled
and there is a necessity to move the jig to
bring one each bush directly under the
drill.
3. The jigs are special tools particularly in
drilling, reaming, tapping and boring
operation.
4.Lighter in construction
2. Fixtures should be securely clamped
to the table of the machine upon which
the work is done.
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3. Fixtures are specific tools used
particularly in milling machine,
shapers and slotting machine.
4. Heavier in construction.
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Fig. 1.2. A Simple Jig and a Fixture
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Advantages of Jigs and Fixtures
Productivity:
• Jigs and fixtures increase the productivity by eliminating the
individual marking, positioning and frequent checking. The
operation time is also reduced due to increase in speed, feed
and depth of cut because of high clamping rigidity.
• Interchangeability and quality:
• Jigs and fixtures facilitate the production of articles in large
quantities with high degree of accuracy, uniform quality and
interchangeability at a competitive cost.
• Skill reduction:
• There is no need for skillful setting of work on tool. Jigs and
fixtures makes possible to employ unskilled or semi skilled
machine operator to make savings in labor cost.
• Cost reduction:
• Higher production, reduction in scrap, easy assembly and savings
in labour cost results in ultimate reduction in unit cost.
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Classification of jigs
Jigs may be divided into two general classes
• boring jigs and
• drill jigs.
Boring jigs are used to bore holes that either are too large
to drill or must be made an odd size (Figure 22)
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• Drill jigs are used to drill, ream, tap, chamfer, counter
bore, countersink, reverse Spot face, or reverse
countersink (Figure 2–3). The basic jig is almost the
same for either machining operation. The only
difference is in the size of the bushings used.
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TYPES OF Drilling JIGS
Drill jigs may be divided into two general types,
• open and closed Jigs .
• Open jigs are for simple operations where work
is done on only one side of the part.
• Closed, or box, jigs are used for parts that must
be machined on more than one side.
• The names used to identify these jigs refer to
how the tool is built
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Type of open jigs
• Template, plate, table, sandwich, and angle plate jigs are
all open jigs
Template jigs are normally used for accuracy rather than
speed.
❑This type of jig fits over, on, or into the work and is not
usually clamped (Figure 2–4).
❑Templates are the least expensive and simplest type of
jig to use.
❑They may or may not have bushings. When bushings are
not used, the whole jig plate is normally hardened.
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Figure 2–4 Template jigs
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• Plate jigs are similar to templates (Figure 2–5). The
only difference is that plate jigs have built-in clamps
to hold the work.
• These jigs can also be made with or without bushings,
depending on the number of parts to be made.
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Figure 2–5 Plate jig
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Box or Closed jig
Box jigs, or tumble jigs, usually totally surround the
part (Figure 2–10). This style of jig allows the part to
be completely machined on every surface without the
need to reposition the work in the jig.
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Figure 2–10 Box or tumble jig.
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Box or Closed jig
Channel jigs are the simplest form of box jig (Figure 2–
11).
• The work is held between two sides and machined from
the third side. In some cases, where jig feet are used,
the work can be machined on three sides.
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Figure 2–11 Channel jig.
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Box or Closed jig
Leaf jigs are small box jigs with a hinged leaf to allow
for easier loading and unloading (Figure 2–12).
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Figure 2–12 Leaf jig.
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Classification of fixtures
Fixtures are normally classified by the type of machine on
which they are used.
• For example, if a fixture is designed to be used on a
milling machine, it is called a milling fixture.
• if it is used in lathe it is called lathe fixture
TYPES OF FIXTURES
• The names used to describe the various types of
fixtures are determined mainly by how the tool is built.
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By construction fixtures are found in the following form
1.Plate fixtures are the simplest form of fixture (Figure 2–17).
The basic fixture is made from a flat plate that has a variety
of clamps and locators to hold and locate the part. The
simplicity of this fixture makes it useful for most machining
operations. Its adaptability makes it popular.
Figure 2–17 Plate fixture
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✓The angle-plate fixture is a variation of the plate fixture
(Figure 2–18).
✓With this tool, the part is normally machined at a right
angle to its locator.
✓While most angle-plate fixtures are made at 90 degrees,
there are times when other angles are needed.
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Figure 2–18 Angle-plate fixtures.
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• Vise-jaw fixtures are used for machining small parts
(Figure 2–20).
• Vise-jaw fixtures are the least expensive type of fixture
to make parts.
• Their use is limited only by the sizes of the vises
available.
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Figure 2–20 Vise-jaw fixture
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• Indexing fixtures are very similar to indexing jigs (Figure 2–
21).
• These fixtures are used for machining parts that must
have machined details evenly spaced components.
• The parts shown in Figure 2–22 are examples of the uses
of an indexing fixture.
Figure 2–21 Indexing
fixtures.
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Figure 2–22 Parts machined with an
indexing fixture
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❖Profiling fixtures are used to guide tools for machining
contours that the machine cannot normally follow.
❖These contours can be either internal or external. Since the
fixture continuously contacts the tool, an incorrectly cut
shape is almost impossible.
❖The operation in Figure 2–24 shows how the cam is
accurately cut by maintaining contact between the fixture
and the bearing on the milling cutter.
Figure 2–24 Profiling fixture.
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SUMMARY
The following important concepts were presented in this unit:
• Jigs and fixtures are production work holding devices designed to
hold, support, and locate a Work piece.
• A jig guides the cutting tool with a drill bushing.
• A fixture references the cutting tool with a set block and feeler, or
thickness gauges.
• Jigs are divided into two general classes: drill jigs and boring jigs.
• The type of jig is determined by how it is built.
• The two types of jigs are open and closed.
• Template, plate, table, sandwich, and angle plate jigs are all open
jigs.
• Box, channel, and leaf jigs are all closed jigs.
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SUMMARY Count…
Other variations, such as indexing, rotary, turnon, pump, and multi station jigs, are made as
either open or closed jigs.
❖Fixture types are determined by the way they are built.
❖The most common types are plate, angle plate, vise-jaw,
indexing, and multi station fixtures.
❖Fixture classes are determined by the machine tools on
which they are used and sometimes by the operations
performed.
❖A fixture used for a straddle-milling
❖operation is classed as a mill fixture, but it may also be
classed as a straddle-milling fixture.
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CHAPTER TWO
CLAMPING AND WORK HOLDING
PRINCIPLES
Debre Tabor University
Lectur-2
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CHAPTER TWO
WORK HOLDING and PRINCIPLES
General Considerations for Work holding
• Physical characteristics of the work piece
•
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Degree of precision
Strength and stiffness of work piece
Production requirements
Safety requirements
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WORK HOLDING PRINCIPLES
Standard work holders
• Placing the work in a specific position in work holding
devices or on a machine table is called a setup which
includes two processes locating and clamping.
• Within a setup, one or more manufacturing operations
may be carried out to process work piece surfaces with
dimensional, form, positional and oriental
specifications.
• A work piece consists of surface; there exist
dimensional and orientation relationships among these
surfaces based on the design specifications.
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WORK HOLDING PRINCIPLES
The datum is the points, lines and surfaces which can be used to determine the
positions and orientation of other point’s lines, surfaces on work piece.
There are two categories of datum (i.e., design datum and manufacturing datum).
❑Design datum is used in specifying the work geometry (dimension, positions,
and orientations, especially with tolerances) in terms of design and functional
requirements.
❑Manufacturing datum is used in specifying the work geometric
relationships in manufacturing processes of the work piece
including operational datum, locating datum and measuring datum.
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Purpose & Function of Work Holder
The main purpose and function of work holder is the
following
❖Locating
❖ Clamping
❖ Support
❖Cutting forces
❖ Safety
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PRINCIPLE OF LOCATING
REFERENCING
✓To ensure precision in any machining operation, the
work must be properly positioned with respect to the
cutter or other tool.
✓ This is called referencing.
✓ To ensure the desired accuracy, the tool designer
must make sure the part is precisely located and rigidly
supported.
✓Locators, in addition to properly positioning the part,
make sure that the tool is easily loaded and unloaded.
✓They must also make the tool foolproof.
✓The tool designer must also provide rigid support for the
part.
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The choice of a location system
Primary datum: This establishes the orientation of the part
(stablies the part ) to the datum reference frame.
❖The part contacts the datum plane with at least three points
of contact. The primary datum restricts Five degree of
freedom ( four rotary and one linear)
Secondary datum: This locates the part (restricts part
movement) within the datum reference frame.
❖Requires a minimum of two points of contact with the
secondary datum. The Secondary datum restricts THREE
additional degree of freedom (Two rotary and One linear ).
Tertiary datum: This locates the part (restricts part movement)
within the datum reference frame.
❖Requires a minimum of one points of contact with the
secondary datum. The tertiary datum restricts the one
degree of freedom ( Linear )
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BASIC RULES FOR LOCATING
❑To restrict the movement of a part and have the part
positioned properly requires skill and planning.
❑A tool designer must keep the following points in mind
while designing the tool:
✓Positioning the locators
✓Part tolerance
✓Fool proofing
✓Duplicate location
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BASIC RULES FOR LOCATING
Positioning the Locators
• Locators should contact the work on a machined surface.
This permits accurate placement of the part in the tool and
ensures the repeatability of the jig or fixture.
• Repeatability is the feature of the tool that allows
different parts to be machined consistently within their
required tolerances.
• Accurate location is an important element in the
repeatability of any tool.
• Locators should be spaced as far apart as possible. This
permits the use of fewer locators and ensures complete
contact over the locating surface.
• the locators should be relieved (Figure 3–1).
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BASIC RULES FOR LOCATING
Figure 3–1 Methods of relieving locators.
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BASIC RULES FOR LOCATING
Tolerance
• When designing a tool, the designer must keep the part
tolerance in mind. As a general rule, the tool tolerance
should be between 20 and 50 percent of the part
tolerance.
Figure 3–2 Tolerance relationship.
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Figure 3–3 Part and tool size relationship.
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BASIC RULES FOR LOCATING
Fool proofing
• Fool proofing is a means by which the tool designer
ensures that the part will fit into the tool only in its
correct position.
• The part in Figure 3–4A must be machined on the
tapered end, so the tool designer includes a pin to
prevent the part from being loaded incorrectly. This pin
fool proofs the tool.
• The part in Figure 3–4B shows a hole that must be drilled
with reference to the holes in the flange.
• A simple pin placed in one of these holes makes it
impossible to load the tool incorrectly.
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BASIC RULES FOR LOCATING
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Figure 3–4 Fool proofing
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BASIC RULES FOR LOCATING
Duplicate Locators
• The use of duplicate locators should always be avoided.
• Figure 3–5 shows examples of duplicate locators.
• Locator duplication not only costs more but also could
cause inaccuracies.
• For example, the flange in Figure 3–5A is located on
both the underside of the flange and the bottom of the
hub. Since these are parallel surfaces, only one is
needed and the other should be eliminated.
• If the reference surface is the flange, as in Figure 3–5B,
the hub locator is not necessary. If the hub is the
reference surface, as in Figure 3–5C, the flange locator is
unnecessary.
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BASIC RULES FOR LOCATING
• To correct this, the tool designer must first determine
which surface is to be referenced. Only then should the
locators for that surface be specified.
Figure 3–5 Duplicate locators.
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BASIC RULES FOR LOCATING
• To avoid this problem(dupolicate locators), the tool
designer must specify whether the part is to be
located from its holes or its edges, never both.
Figure 3–6 Position and locational differences
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PLANES OF MOVEMENT
• An unrestricted object is free to move in any of twelve
possible directions.
• Figure 3–7 shows an object with three axes, or planes,
along which movement may occur.
• An object is free to revolve around or move parallel to
any axis in either direction.
• To illustrate this, the planes have been marked X-X, Y-Y,
and Z-Z.
• The directions of movement are numbered from one to
twelve.
Figure 3–7 Planes of movement.
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Restricting Movement
• To accurately locate a part in a jig or fixture, movements
must be restricted.
• This is done with locators and clamps.
• Restriction the movement of tool should increase
accuracy and productivity of the part.
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LOCATING THE WORK
• Work piece surfaces
• Flat surfaces
• Cylindrical surfaces
• Irregular surfaces
Types of location
• Plane
• Concentric
• Radial
• Combined
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LOCATING THE WORK
Locating from a Flat Surface
• There are three primary methods of locating work from
a flat surface:(solid supports, adjustable supports, and
equalizing supports.
• These locators set the vertical position of the part,
support the part, and prevent distortion during the
machining operation.
• Solid supports are the easiest to use. They can be either
machined into the tool base or installed (Figure 3–13).
This type of support is normally used when a machined
surface acts as a locating point.
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Figure 3–13 Solid supports
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LOCATING THE WORK
Adjustable supports are used when the surface is rough or uneven, such as in cast
parts.
✓ Adjustable locators are normally used with one or more solid locators to allow any
adjustment needed to level the work.
✓ A few of the more common are the threaded (Figure 3–14A),
✓ The threaded style is the easiest and most economical, and it has a larger
adjustment range than the others
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LOCATING THE WORK
spring (Figure 3–14B), and push types (Figure 3–14C ).
Figure 3–14B Adjustable supports, spring type
Figure 3–14C Adjustable support, push type.
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LOCATING THE WORK
Equalizing supports are also a form of adjustable support
(Figure 3–15).
❖They provide equal support through two connected
contact points.
❖As one point is depressed, the other raises and
maintains contact with the part.
❖ This feature is especially necessary on uneven cast
surfaces.
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Figure 3–15 Equalizing supports
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Locating from an Internal Diameter
✓Locating a part from a hole or pattern is the most
effective way to accurately position work.
✓Nine of the twelve directions of movement are
restricted by using a single pin, and
✓Eleven directions of movement are restricted with two
pins.
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Figure 3–16 Internal locators
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Locating from an Internal Diameter
Pin-type locators are used for smaller holes and for
aligning members of the tool (Figure 3–17
Figure 3–17 Pin locators and bushing
❑Pins used for part location are made with either tapered ends or
rounded ends, allowing the parts to be installed and removed easily
(Figure 3–18).
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Figure 3–18 Round and tapered locators.
Locating from an Internal Diameter
❖In the round pin locates the part and the diamond
pin prevents the movement around the pin (Figure 3–
19).
Figure 3–19 Locating with one relieved locator.
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Locating from an Internal Diameter
❖Relieved locators reduce the area of contact between
the work piece and the locator.
✓Decreasing the contact area has little or no effect on
the overall locational accuracy;
✓However, reducing the contact area helps make the jig
or fixture easier to load and unload and lessens the
problems caused by dirt, chips, and burrs.
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Figure 3–21 Relieved locators
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Locating from an External Profile
❖Profile locators position the work in relation to an
outside edge or the outside of a detail, such as a hub or
a boss.
❖common ways a part can be located from its profile are
❖Nesting locators position a part by enclosing it in a
depression, or recess, of the same shape as the part.
❖ Nesting is the most accurate locating device for profile
location.
❖Nests are very expensive to design for complicated
shapes.
❖The most common type is the ring nest, which is
normally used for cylindrical profiles (Figure 3–26).
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Locating from an External Profile
Figure 3–26 Ring nest
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Locating from an External Profile
❑The full nest completely encloses shapes other than cylindrical
(Figure 3–27).
Figure 3–27 Full nests.
❑The partial nest is a variation of the full nest and encloses only
a part of the work piece (Figure 3–28).
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Figure 3–28 Partial nest
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Locating from an External Profile
Vee locators are used mainly for round work.
❖They can locate flat work with rounded or angular ends
and flat discs (Figure 3–29).
Figure 3–30 Vee-block locators.
❖ One advantage vee locators have over other locators is
their centralizing feature.
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Locating from an External Profile
Fixed-stop locators are used for parts that cannot be
placed in either a nest or a vee locator. They are either
machined into the tool body (Figure 3–32), or installed
(Figure 3–33).
Figure 3–32 Machined fixed-stop locators.
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Figure 3–33 Installed fixed-stop locators
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Ejectors
✓Ejectors are used to remove work from close-fitting
locators, such as full nests or ring nests.
✓These devices speed up the unloading of the part from
the tool, which reduces the in-tool time and increases the
production rate.
✓Figure 3–40 shows two styles of ejectors common to
both jigs and fixtures.
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Figure 3–40 Ejectors
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SUMMARY OF LOCATORS
❖To achieve proper location, the locators must properly
reference the part and ensure the repeatability of
location throughout the production cycle.
❖Referencing is the process of properly positioning the
part with respect to the cutter or other tool.
❖Repeatability is the feature of location that permits the
parts to be made within their stated tolerances, part
after part, throughout the production run.
❖The major concerns in locating a part that the designer
must keep in mind are the position of the locators,
locational tolerances, fool proofing the location, and
avoiding duplicate location.
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SUMMARY OF LOCATORS
❑There are twelve planes of movement in any Work piece.
When locating a part, the designer must select the locational
method that will restrict a maximum number of these planes
of movement.
❑The three-two-one, or six-point, location method will
restrict a total of 9 planes of movement.
❑Locating a part by a single center hole will restrict nine
planes of movement with a single locator. By positioning a
second locator in another hole in the part, a total of eleven
planes of movement can be restricted with two locators.
❑In either case, the remaining unrestricted planes of
movement are restricted with the clamping device.
❑Locators positioned under a part are referred to as supports.
Locators that position a part by its edges are called locators
or stops.
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SUMMARY OF locators
✓The three primary supports are solid, adjustable, and
equalizing.
✓The major types of locator used to locate parts on an internal
diameter are shank-mounted locators and pin locators. Pin
locators may also be used to locate a part from its external edges.
✓Other devices used to locate parts include nesting locators, vee
locators, fixed-stop locators, adjustable-stop locators, and sight
locators.
✓Ejectors are devices that are used to help remove a part from
close-fitting locators.
✓Ejectors are made in many variations.
✓In mechanical-level ejector and spring-type ejector are two
examples of these devices.
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CHAPTER THREE
CLAMPING PROCESS
Debre Tabor University
Lectur-3
WEEK-3
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CLAMPING PROCESS
WORKHOLDERS
❖the term work holder identifies the parts of a jig or
fixture that clamp, chuck, hold, or grip the part.
• The main purpose of a work holder, or clamping device, is to
securely hold the position of the part against the locators
throughout the machining cycle.
The clamp used must meet the following conditions:
❖ strong enough to hold the part and to resist movement.
❖The clamp must not damage or deform the part.
❖Be fast-acting and allow rapid loading and unloading of parts.
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CONT…. Clamping
• The proper and adequate clamping of a work piece is
very important, the following design and operational
factors should be take in to consideration :
1. The clamping pressures applied against the work piece
must counteract the tool forces.
2. The clamping pressures should not be directed
towards the cutting operation. Whenever possible, it
should be directed parallel to it, Fig. 2.20.
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CONT…. Clamping
Fig. 2.20.
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CONT…. Clamping
3. The clamping pressure must only hold the work piece
and should never be great enough so as to damage,
deform or change any dimensions of the work piece.
4. The clamping and cutting forces should be directed
towards the locating pins, otherwise the work piece may
get bent or forced away from the locating pins during
machining.
5. Clamping should be simple, quick and foolproof.
Complicated clamps lose their effectiveness as they wear.
6. The movement of a clamp should be strictly limited and
if possible it should be positively guided.
7. Whenever possible, the lifting of the clamp by hand
should be avoided if it can be done by means of a spring
fitted to it.
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CONT…. Clamping
9. The clamps should always be arranged directly above the
points supporting the work; otherwise the distortion of
the work can occur, as illustrated in Fig. 2.21.
10. Fiber pads should be riveted to the clamp faces,
otherwise soft and fragile work piece can get damaged.
11. A clamp should be designed to deliver the required
clamping force when operated by the smallest force
expected.
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CONT…. Clamping
Fig 2.21. Position of Clamping .
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CONT…. Clamping
12. A clamp should be strong enough to withstand the
reaction imposed upon it when the largest expected
operating force is applied.
13. Clamping pressure should be directed towards the
points of support, otherwise work will tend to rise from
its support, Fig. 2.22.
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Basic rules of clamping
❖The function of clamps to hold apart against the locators
during the machining cycle.
Positioning the Clamps
✓Clamps should always contact the work at its most point.
This prevents the clamping force from bending or
damaging the part.
✓The part must be supported if the work is clamped at a
point where the force could bend the part.
✓ The flange in Figure 4–1 shows this point.
✓. If it is held by the outer edge, the part must be
supported (Figure 4–2).
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Basic rules of clamping
Figure 4–1 Flange ring.
Figure 4–2 supporting the flange ring
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The Effect of Tool(cutting) Forces For clamping
✓To clamp a part correctly, the tool designer must know how tool
forces, or cutting forces act in reference to the tool and the
cutting force hold the work.
✓Figure 4–3 is an example of how the cutting force is used to hold
the work
✓Most of the force is in a downward direction against the base of
the tool. The forces that must be resisted cause the part to revolve
around the drill axis, which in turn causes the part to climb the
drill when the drill breaks through the opposite side of the part.
Figure 4–3 using cutting force to hold a part
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Cont….Clamping Forces
❑Clamping force is the force required to hold a part against the
locators.
❑Clamping prevents the part from shifting or being pulled from the
jig or fixture during the machining operation
❑As a general rule, Clamping pressures hold only be enough to hold
the part against the locators.
❑The locators should resist the bulk of the thrust.
Figure 4–4 Clamping forces.
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TYPES OF CLAMPS
❖The type of clamp the tool designer chooses is
determined by the shape and size of the part, the type
of jig or fixture being used, and the work to be done.
❖The tool designer should choose the clamp that is the
simplest, easiest to use, and most efficient.
✓The following are the common type of clamp we have to
use in production process.
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Strap
Clamps
✓Strap clamps are the simplest clamps used for jigs and
fixtures (Figure 4–5).
✓Strap clamps can be grouped into three classes, each
representing a form of lever (Figure 4–6).
✓Figure 4–6A shows the first clamp, which has the
fulcrum between the work and the effort.
✓This is the principle of a first-class lever.
✓The second clamp, shown in Figure 4–6B, places the
work between the fulcrum and the effort, as with a
second-class lever.
✓The third clamp, shown in Figure 4–6C, uses the
principle of a third-class lever by placing the effort
between the work and the fulcrum.
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Strap Clamps
.
Figure 4–6 Lever classes of strap clamps
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Screw Clamps
• Screw clamps are widely used and unlimited application
potential, lower costs, and, in many cases, less complex
designs.
• The only disadvantage in using screw clamps is their
relatively slow operating speeds.
• The basic screw clamp uses the torque developed by a
screw thread to hold a part in place either by direct
pressure or by its action on another clamp (Figure 4–15).
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Figure 4–15 Indirect clamping with a screw clamp.
85
Swing Clamps
✓Swing clamps combine the screw clamp with a swinging
arm that pivots on its mounting stud.
✓The holding power with this clamp is generated by the
screw.
✓The rapid action needed is achieved by the swinging arm
(Figure 4–16).
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Figure 4–16 Swing clamp
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Hook Clamps
• Hook clamps are similar to swing clamps but they are
much smaller (Figure 4–17).
• They are useful in tight places or where several small
clamps rather than one large clamp must be used.
• A variation of the hook clamp is shown in Figure 4–18.
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B) Hook Bolt Clamp
Figure 4–17 Hook clamp
Figure 4–18 Modified hook clamp
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Cam-Action Clamps
✓Cam-action clamps, when properly selected and used, provide a
fast, efficient, and simple way to hold work (Figure 4–20).
✓Because of their construction and basic operating principles, the
use of cam-action clamps is limited in some types of tools.
✓Cam clamps, which apply pressure directly to the work, are not
used when a strong vibration is present.
✓This might cause the clamp to loosen, creating a dangerous
condition.
✓Direct-pressure cam clamps must be positioned to resist the
natural tendencies of the clamp to shift or move the work when
the clamp is engaged.
Figure 4–20 Direct-pressure cam clamp
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Figure 4–21 Indirect-pressure cam clamp.
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Toggle-Action Clamps
❖Toggle-action clamps, shown in Figure 4–29, are made
with four basic clamping actions: hold down, squeeze,
pull, and straight-line.
❖Toggle clamps are fast-acting.
❖Because of how they are made, they have the natural
ability to move completely free of the work, thus
allowing for faster part changes.
❖Another advantage is their high ratio of holding force to
application force.
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Toggle-Action Clamps
Figure 4–29 Toggle clamps
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Chucks and Vises
❖Commercially available chucks and vises offer the tool designer
devices that, when modified, greatly reduce tooling costs.
❖Quite often, because of tight budgets, one chuck must be used
for several tools.
Non Mechanical Clamping
✓Non mechanical clamping is a term that is typically applied to the
group of work holding devices used to hold parts by means other
than direct mechanical contact.
✓This form of clamping is most often employed for work pieces
that cannot be held with other devices due to the size, shape, or
configuration of the fixture parts.
✓Other situations in which non mechanical clamps are frequently
used are where the clamping forces must be applied evenly across
the entire part to minimize any possible work piece distortion.
✓two principal forms of non mechanical clamping used for
production manufacturing are magnetic clamping and vacuum
clamping.
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SUMMARY
✓The term work holder is used to identify the complate jig or
fixture as well as the devices used to actually hold the part.
✓The main purpose of a clamp is to hold the part
✓Against the locators throughout the production cycle Clamps
must be strong enough to hold the part and resist movement.
✓Clamps must not damage or deform the part.
✓Clamps must be fast acting to permit rapid loading and
unloading of parts.
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SUMMARY
❖The position of the clamps, the tool forces acting on
the part, and controlling and directing the clamping
forces.
❖The primary manual clamping devices are strap clamps,
screw clamps, cam-action clamps, wedge clamps, and
toggle-action clamps.
❖Other forms of clamping used for jigs and fixtures
include power clamping, chucks and vises and magnetic
and vacuum chucks used for non mechanical
clamping.
❖Special arrangements may be used for clamping multiple
parts or for holding odd-shaped parts.
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CHAPTER Four
DESIGN OF JIG AND FIXTURE
Debre Tabor University
Lectur-4
WEEK-4
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CHAPTER Four
DESIGN OF JIG AND FIXTURE
❖The design of a work holding device is governed by the
geometry of the work piece and the dynamics of the
manufacturing process in which it is expected to
participate.
❖The jig and fixture must be able to hold the work piece
in place (i.e., preventing motion and deflections) while it
is subjected to external forces.
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CONT…DESIGN OF JIG AND FIXTURE
Elements of Jig and Fixture
✓Jigs and fixtures are manually or partially power operated devices.
✓To full fill their basic purposes, jigs and fixtures are comprised of
several elements (as indicated in Fig 3.1):
❑base and body or frame with clamping features
❑locating elements for proper positioning and
orientation of the blank
❑supporting surfaces and base
❑clamping elements
❑tool guiding frame and bushes (for jig)
❑indexing plates or systems, if necessary
❑auxiliary elements
❑fastening parts
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Elements of Jig and Fixture
Fig 3.1.Major elements of jig and fixtures.
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jigs and fixtures design Considerations
the following factors are essentially considered during design,
fabrication and assembly of jigs and fixtures:
❖Easy, quick and consistently accurate locating of the blank in
the jig or fixture in reference to the cutting tool
❖Providing Quick, strong and rigid clamping of the blank in the
jig or fixture without interrupting any other operations
❖Tool guidance for slender cutting tools like drills and reamers
❖Easy and quick loading and unloading the job to and from
the jig or fixture
❖Use of minimum number of parts for making the jig or fixture
• Use of standard parts as much as possible
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jigs and fixtures design Considerations Cont..
❖Reasonable amount of flexibility or adjustability, if feasible, to
accommodate slight variation in the job - dimensions.
Prevention of jamming of chips, i.e. Wide chips-space and easy
chip disposal
❖Easy, quick and accurate indexing system if required.
❖Easy and safe handling and moving the jig or fixture on the
machine table, i.e., their shape, size, weight and sharp edges
and corners
❖Easy and quick removal and replacement of small parts
❖Manufacturability i.e. Ease of manufacture
❖Durability and maintainability
❖Service life and overall expenses
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Jig and Fixture Design Procedure
Three design stages is involved
✓Stage One deals with information gathering and analysis.
✓Stage Two involves the consideration of supporting,
clamping and locating schemes.
✓Stage Three is the design of the structure of the jig and
fixture body frame.
A comprehensive Jig and fixture research plan should
involve the analysis at different computational levels,
viz., geometric, kinematic, force and deformation
analyses.
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Jig and Fixture Design Procedure Cont…
Geometric Analysis
✓Geometric analysis is closely associated with Jig and
fixture planning and spatial reasoning.
✓It determines the selection of the type and number
of fixturing elements, clamping, support and locating
elements, the order of datum planes, etc.
✓ The analysis also includes the checking of
interference between work piece and fixturing
elements, as well as cutting tools.
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Jig and Fixture Design Procedure Cont
Kinematic Analysis
❑It is used to determine whether a Jig and fixture configuration is able
to correctly clamp, locate and provide complete constraint to a work
piece.
Force Analysis
✓In a machining fixture, different forces are experienced, viz., inertial,
gravitational, machining and clamping forces.
✓While the first three categories of forces are usually more predictable,
clamping force can be rather subjective in terms of magnitude, point of
application as well as sequence of application.
Deformation Analysis
✓Due to the complexity of force interaction, work piece deformation can
be attributed to a combination of factors.
✓Firstly, a work piece would deform/ displace under high cutting and
clamping forces.
✓Secondly, a work piece could also deform/displace if the support and
locating elements are not rigid enough to resist the above mentioned
forces.
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Fundamental principles of Jigs and Fixtures design
❖Locating points: Good facilities should be provided for locating the
work.
❖Fool proof: The design of jigs and fixtures should be such that it would
not permit the work piece or the tool to insert in any position other than
the correct one.
❖Reduction of idle time: Design of Jigs and Fixtures should be such that
the process, loading, clamping and unloading time of the Work piece
takes minimum as far as possible.
❖Weight of jigs and fixtures: It should be easy to handle, smaller in size
and low cost in regard to amount of material used without sacrificing
rigidity and stiffness.
❖Materials for jigs and fixtures: Usually made of hardened materials to
avoid frequent damage and to resist wear.
❖Clamping device: It should be as simple as possible without sacrificing
effectiveness. The strength of clamp should be such that not only to hold
the work piece firmly in place but also to take the strain of the cutting
tool without springing when designing the jigs and fixtures.
❖Economical and safe
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Example1 Design of Drill Jigs
✓Drilling jigs are used to machine holes in mechanical products.
✓To obtain positional accuracy of the holes, hardened drill bushes o
are used to locate and guide drills, reamers etc., in relation to the w
✓The portion of the jig into which the hardened bushes are fitted is
plate.
✓It is clear that during the drilling operation, burrs will be produced.
✓The burr produced at the start of a hole is smaller than that prod
end of the hole.
✓The first type is called 'minor burr ‘and the second type 'Major b
the drill breaks through the material, Fig. 9.37).
✓When designing a drilling jig, these two types of burrs should be
consideration since they may cause difficulty in unloading the work
the jig after a hole has been drilled.
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Design of Drill Jigs Cont…
Fig. 9.37. Major and Minor Burrs.
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Design Principles for Drill Jigs
1. A drilling jig should be of light construction consistent with
adequate rigidity to facilitate its handling because it has to be
handled frequently during the operation.
2. A drilling jig which is not normally clamped to the machine table
should be provided with four feet so that it will rock if it is not
resting square on the machine table and so warn the operator.
3. The stability of a drilling jig should be as good as possible since it
is not usual to clamp it to the machine table and to ensure this,
the feet or base of the jig should extend outside the holes to be
drilled.
4. Drill bushings should be fitted in fixed portion of the jig and not in
clamps except for a few special cases (for example, leaf type jig).
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DRILL BUSHINGS
• Drill bushings are used to locate and guide drills,
reamers, taps, counter bores, countersinks, spot facing
tools, and any other rotating tools commonly used to
make or modify a hole.
• Drill bushings are usually hardened and ground to
exact sizes to ensure the needed repeatability in the jig.
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Designing sizes for drill bushings
DRILL JIG
WING NUT CLAMP
TOP PLATE
LOCATING PLATE
JIG BUSH
BASE PLATE
V - BLOCK
SIDE CLAMP
COMPONENT 74
Figure 5–4 Designing sizes for drill bushings.
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Types of Bushings
❖The most common drill bushings are renewable
bushings, press-fit bushings, and liner bushings.
• Renewable bushings are commonly divided into two
groups, slip and fixed. They are used where bushings are
changed many times during the jig life.
• Slip-renewable bushings are used when more than
one operation is performed in the same location, such as
drilling and reaming
• Fixed-renewable bushings are used where only one
operation is performed in each hole but where several
bushings must be used during the life of the tool
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WELDING Fixture Design
Basic Design Considerations
❖In addition to locating and holding the part, the designer
must also consider several other factors before a welding
fixture can be designed.
❖Heat dissipation is an important consideration with any
welding tool.
❖Several methods can be used to ensure that proper heat
is maintained in the weld area.
❖The primary factor that determines the amount of heat
required is the metal being joined.
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Basic Design Considerations Cont…
❖When metals such as steel and other poor heat
conductors are joined, the excess heat should be
carried off to prevent overheating the weld. To do this,
backup bars of copper, titanium, or beryllium can be
used.
❖For metals that are good conductors of heat,such as
copper or aluminum, too rapid cooling becomes the
problem. To prevent this, the fixture or jig must be
made to contact the part in as small an area as possible
(Figure 17–5).
❖Clamping supports must be provided to prevent
distorting the work while it is in a heated condition.
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Basic Design Considerations for
welding Fixture Cont…
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Common type of welding Fixture
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Common type of welding Fixture Cont..
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SUMMARY
❖The three most common tool body forms are cast,
welded, and built-up.
❖Using preformed materials can save time and money in
building jigs and fixtures.
❖Several types of drill bushing are used for jigs. The most
common types are renewable, press-fit, and liner
bushings.
❖For the jig to perform as desired, the correct bushing
must be selected.
❖To work properly, the bushing must be installed
correctly.
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