gtu ppt - ala - pt design of fixture jig and fixtures production technology production engineering manufacturing process BE MECH 6th sem

1. Production Technology (2161909)
B.E. MECH – Sem VIth
Prepared by,
NAME ENROLLMENT NO.
• PANDYA RUSHI R. 170953119024
• PARMAR RONAKKUMAR V. 170953119026
• PATEL DRUPAD H. 170953119027
• PATEL JEET R. 170953119029
• PATEL MEET M. 170953119030
• PATEL SHREY B. 170953119031
Guided by,
Asst. Prof. Sagar Bhavsar
(Mechanical Deptt)
Batch :- 6B2 Group No :- B6

2. CONTENTS
• Meaning of fixture
• Elements Of Fixture.
• General Requirements of a Fixture
• Design Consideration in Fixtures
• Design principle of fixture
• Fixture Design Fundamentals
• Various aspects of fixture design
• Advantages of fixtures
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3. FIXTURE
• A fixture is a work-holding or support device used in the manufacturing
industry.
• It is used to accurately manufacture duplicate parts.
• Reduces the requirement of skilled labour
• Fixture is a workpiece-locating and holding device used with machine tools. It
is also used in inspection welding and assembly.
• Fixture does not guide the cutting tool, but is always fixed to machine or
bench. By using fixture, responsibility for accuracy shifts from the operator to
the construction of machine tool.
• When a few parts are to be machined, workpiece clamp to the machine table
without using fixture in many machining operations.
• However, when the numbers of parts are large enough to justify its cost, a
fixture is generally used for holding and locating the work
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4. ELEMENTS OF FIXTURE
• Locating Element
• Clamping Element
• Tool Guiding and Setting Element
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5. LOCATOR
• A locator is usually a fixed component of a fixture. It is used to establish and
maintain the position of a part in the fixture by constraining the movement of
the part. For workpieces of greater variability in shapes and surface conditions,
a locator can also be adjustable.
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6. CLAMP
• A clamp is a force-actuating mechanism of a fixture. The forces exerted by the
clamps hold a part securely in the fixture against all other external forces
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7. SUPPORTS
• A support is a fixed or adjustable element of a fixture. When severe part
displacement/deflection is expected under the action of imposed clamping and
processing forces, supports are added and placed below the workpiece so as
to prevent or constrain deformation. Supports in excess of what is required
for the determination of the location of the part should be compatible with
the locators and clamps.
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8. FIXTURE BODY
• Fixture body, or tool body, is the major structural element of a fixture. It
maintains the spatial relationship between the fixturing elements mentioned
above, viz., locators, clamps, supports, and the machine tool on which the part
is to be processed.
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9. GENERAL REQUIREMENTS OF A FIXTURE
• Deterministic location
– A workpiece is said to be kinematically restrained when it cannot move
without losing contact with at least one locator.The workpiece is
constrained by a set of appropriately placed locators so that it is
presentable for the machining operation. Locating errors due to locators
and locating surfaces of the workpiece should be minimised so as to
accurately and uniquely position the workpiece within the machine
coordinate frame.
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10. • Total constraint
– A workpiece should be fully constrained at all times to prevent any
movement. Clamps should provide locking forces to hold the
workpiece in place -once it is located. A totally restrained part should
be able to remain in static equilibrium to withstand all possible
processing forces or disturbance. A necessary and sufficient condition
to warrant workpiece stability is to satisfy the condition of force
closure
• Contained deflection
– Workpiece deformation is unavoidable due to its elastic/plastic
nature, and the external forces impacted by the clamping actuation
and machining operations. Deformation has to be limited to an
acceptable magnitude in order to achieve the tolerance specifications.
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11. • Geometric constrain
– Geometric constraint guarantees that all fixturing elements have an access
to the datum surface. They also assure that the fixture components do not
interfere with cutting tools during a machining operation.
– In addition to these requirements, a fixture design should have desirable
characteristics such as quick loading and unloading, minimum number of
components, accessibility, design for multiple cutting operations, portability,
low cost, etc.
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12. DESIGN CONSIDERATION IN FIXTURES
• The main frame of fixture must be strong enough so that deflection of the
fixture is as minimum as possible. This deflection of fixture is caused because of
forces of cutting, clamping of the workpiece or clamping to the machine table.
The main frame of the fixture should have the mass to prevent vibration and
chatter
• Frames may be built from simple sections so that frames may be fastened with
screws or welded whenever necessary. Those parts of the frame that remain
permanently with the fixture may be welded. Those parts that need frequent
changing may be held with the screws. In the situation, where the body of
fixture has complex shape, it may be cast from good grade of cast iron.
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13. • Clamps should be arranged so that they are readily available and may be
easily removed. Design of CuttingTools and Holding Devices
• Clamps should be supported with springs so that clamps are held against
the bolt head wherever possible.
• If the clamp is to swing off the work, it should be permitted to swing as
far as it is necessary for removal of the workpiece.
• All locator’s clamps should be easily visible to the operator and easily
accessible for cleaning, positioning or tightening.
• Provision should be made for easy disposal of chip so that storage of
chips doesn’t interfere with the operation and that their removal during
the operation doesn’t interfere with the cutting process.

14. • All clamps and support points that need to be adjusted with a wrench
should be of same size. All clamps and adjustable support points should
be capable of being operated from the fronts of the fixture.
• Workpiece should be stable when it is placed in fixture. If the workpiece
is rough, three fixed support points should be used. If workpiece is
smooth, more than three fixed support points may be used. Support
point should be placed as farthest as possible from each other.
• The three support points should circumscribe the centre of gravity of
the workpiece
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15. • The surface area of contact of support should be as small as possible
without causing damage to the workpiece. This damage is due to the
clamping or work forces.
• Support points and other parts are designed in such a way that they may
be easily replaced if they break.
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16. FIXTURE DESIGN FUNDAMENTALS
• Fixture design consists of a number of distinct activities: fixture planning,
fixture layout design, fixture element design, tool body design, etc.
• Fixture design deals with the establishment of the basic fixture concepts:
– Fixture layout is an embodiment of the concepts in the form of a spatial
configuration of the fixture,
– Fixture element design is concerned with the concrete details of the
locators, clamps and supports,
– Tool body design produces a structure combining the fixture elements in
the desired spatial relationship with the machine tool.
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17. FIXTURE DESIGN
• Fixture planning is to conceptualise a basic fixture configuration through
analysing all the available information regarding the material and geometry of
the workpiece, operations required, processing equipment for the operations,
and the operator.The following outputs are included in the fixture plan
– Fixture type and complexity
– Number of workpieces per fixture
– Orientation of workpiece within fixture
– Locating datum faces
– Clamping surfaces
– Support surfaces, if any
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18. VARIOUS ASPECTS OF FIXTURE DESIGN
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19. ADVANTAGES OF FIXTURES
• It saves time.
• It requires less manpower.
• Increases conformity in manufacturing process.
• Improves the economy of production.
• Increase the production.
• To assure high accuracy of parts
• Provides interchangeability
• Enable heavy and complex parts to machine
• Increased versatility of machine tool.
• Partially automates the machine tools
• Use improve the safety, low accidents.
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20. THANK YOU
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