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TABLE OF CONTENTS
CHAPTER.NO TITLE PAGE NO
I ABSTRACT
II LIST OF FIGURES
III LIST OF TABLES
1. INTRODUCTION
1.1. INTRODUCTION... 7
1.2. INTRODUCTION TO COMPONENT
(PETROL BRACKET) 8
1.2.1. Drive shaft ...... 10
1.3. INTRODUCTION TO WORK HOLDING
DEVICES 11
1.3.1 Jigs and Fixtures- Introduction.. 13
1.4. INTRODUCTION TO LOCATING
AND CLAMPING DEVICES 17
1.4.1 PRINCIPLE OF LOCATION ... 17
1.4.1.1. Principle of Pin Location 20
1.4.1.2. Principle of Mutually
Perpendicular Planes . 20
1.4.1.3 Principle of Extreme ... 21
1.4.2. LOCATING METHODS AND
DEVICES .... 22
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1.4.3. PINS AND BUTTON LOCATORS ... 22
1.4.3.1 Locating Pins . 23
1.4.3.2 Conical Locating Pins .... 23
1.4.3.3 Cylindrical Locating Pins .. 23
1.4.4. CLAMPING INTRODUCTION 24
1.4.4.1. Clamping device .. 27
1.4.4.1.1. Bridge Clamp . 27
1.5. INTRODUCTIONS TO SENSORS . 29
1.5.1. PROXIMITY SENSOR ... 30
1.5.2 PROXIMITY LIMIT SWITCH 31
2. METHODOLOGY . 32
2.1. WORKING 33
2.2. DESIGN OF ASSEMBLY FIXTURE.. 35
2.3. FIXTURE MANUFACTURING PROCESS 55
2.4. COST ESTIMATION .. 58
2.5. COMPARISON OF EXISTING FIXTURE
AND NEW DESIGNED FIXTURE... 59
2.6. ADVANTAGES. 61
3. CONCLUSION ... 63
4. BIBLIOGRAPHY .. 65
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LIST OF FIGURES
FIG NO DESCRIPTION PAGE NO
1.1 PETROL BRACKET.....
...... 8
1.2 A SIMPLE DESIGN OF JIG AND
FIXTURE 16
1.3 WORKPIECE IN SPACE
............... 18
1.4 WORKPIECE LOCATED IN A FIXED
BODY 18
1.5 PRINCIPLE OF MUTUALLY
PERPENDICULAR PLANES .... 21
1.6 LOCATING PINS
.. 23
1.7 METHOD OF CLAMPING
... 25
1.8 POSITION OF CLAMP
26
1.9 BRIDGE CLAMP
28
3.1(A) 3D-BOTTOM BASE PLATE WITH
SENSOR STAND .................... 35
3.1 (B) 2D-BOTTOMS BASE PLATES WITH
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SENSOR STAND ....................... 36
3.2(A) 3D-BOTTOM BASE PLATE WITH
LIMIT SWITCH 37
3.2 (B) 3D-BOTTOM BASE PLATES WITH
LIMIT SWITCH 38
3.3(A) 3D-TOP BASE PLATE .. 39
3.3(B) 2D-TOP BASE PLATE . 40
3.4(A) 3D-SENSOR STAND 41
3.4(B) 2D-SENSOR STAND . 42
3.5(A) 3D-PLUNGER 43
3.5(B) 2D-PLUNGER ... 44
3.6(A) 3D-SPACER 45
3.6(B) 2D-SPACER 46
3.7(A) 3D-SENSOR PIN ... 47
3.7(B) 2D-SENSOR PIN 48
3.8(A) 3D-SLIDING CLAMP 49
3.8(B) 2D-SLIDING CLAMP 50
3.9(A) 3D-ANGULAR BLOCK 51
3.9(B) 2D-ANGULAR BLOCK . 52
3.10(A) 3D-FINAL ASSEMBLY OF A FIXTURE . 53
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3.10(B) 2D-FINAL ASSEMBLY OF A FIXTURE 54
3.11 PICTORIAL REPRESENTATION OF
EXISTING FIXTURE AND NEW
DESIGNED FIXTURE 59
LIST OF TABLES
TABLE NO DESCRIPTION PAGE NO
2.1 COST ESTIMATION.... 58
2.2 COMPARISION OF EXISTING
FIXTURE AND NEW DESIGNED
FIXTURE 60
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CHAPTER-1 INTRODUCTION
1.1. INTRODUCTION:
Fixture is one of the most important mechanical members which
are used to hold the work piece. Fixtures are used to securely locate and support
the work, ensuring that all parts produced using the fixture will maintain
conformity and interchangeability. Fixtures are used in order to improve
economy of the production by allowing smooth operation and quick transition
from part to part.
The petrol brackets are used for mounting the drive shaft. The
assembly of petrol bracket includes assembly of a stud which secures the petrol
bracket to the engine bed. There are many cases by which the stud can be
unscrewed. A large number of components are being rejected due to the
mismatching of the stud in the petrol bracket. In order to overcome the errors in
assembling and also to improve production, fixtures are used.
A conventional fixture is used in assembly, but the errors during
the assembly remains the same, so we came up with the idea of designing a
new fixture in order to reduce the errors in assembling the bracket. Sensors are
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used in the new fixture in order to detect the errors committed during the
assembly. When the stud is not related to the tapped hole, the sensor gives a
warning to the operator regarding the stud position until the operator assembles
the stud in proper position. This sensor equipped fixture helps in achieving zero
error in assembly and also improves productivity by reducing the rejection of
the brackets.
1.2. INTRODUCTION TO COMPONENT (PETROL BRACKET):
Petrol bracket is also known as the coupling bracket for a petrol engine.
The main application of the petrol bracket is to provide the bearing surfacefor the drive shaft which is used to connect the electric motor shaft and the
engine shaft (vertical shaft to horizontal shaft) by using bevel gear.
Installation of the drive shaft with coupling bracket is done as vertical drive
shaft between motor-drive and bevel gear. Technically, horizontal is also
possible. This petrol bracket is used for ford (figo) car. The component (petrol
bracket) is made of cast iron.
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FIG. 1.1 PETROL BRACKET
CAST IRON:
Cast-iron is an alloy of iron and carbon, and is popular because of its low
cost and ability to make complex structures. The carbon content in cast iron is
3% to 4.5% by weight. Silicon and small amounts of Manganese, Sulfur, and
Phosphorus are also present in it. The products of cast iron exhibit reasonable
resistance against corrosion. It is neither malleable nor ductile, and it cannot be
hardened like steel. It melts at about 2100 F, and has either a crystalline or a
granular fracture. The mechanical properties of cast iron are very much
dependent on the morphology of its carbon content. Carbon is present in the
form of plates in gray cast iron, whereas, it is incorporated in compound Fe3C
(cementite) in white cast iron. Nodular cast iron, which show better tensile
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strength and strain than gray cast iron, carry carbon in the form of sphere
shaped graphite particles.
COMPOSITION OF CAST IRON:
1. Cast iron is actually an iron-carbon-silicon alloy containing between 3
and 5.5 % carbon.1 to 3% silicon.
2. Other elements such as sulfur, magnesium and potassium totaling about
0.5 %.steels contain less than 2% carbon.
PROPERTIES OF CAST IRON:
1. Tensile strength
2. High compressive strength
3. Resistance to deformation
4. Resistance to oxidation
1.2.1. DRIVE SHAFT:
The drive shaft is the mechanical connection between motor drive and
on-load tap-changer head or off-circuit tap-changer head. The change from the
vertical to the horizontal direction is performed by the bevel gear.
Accordingly, the vertical drive shaft has to be mounted between motor-
drive and bevel gear and the horizontal drive shaft between bevel gear and on-
load tap-changer or off-circuit tap-changer.
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The drive shaft is designed as a square tube and is coupled at both ends
by two coupling brackets and one coupling bolt at the driving end of the drive
shaft ends of the unit to be connected.
An assembly fixture is made to assemble the stud in a petrol bracket
with an alignment, thus preventing misalignment (error).
The stud is designed in such a way that one side is longer and other side
is shorter. The petrol bracket which is assembled here is used for ford car
engine.
.
1.3. INTRODUCTION TO WORK HOLDING DEVICES:
Holding or clamping the work piece is an important factor in the manufacturing
process.
The main objective of work holding is to position or locate a work piece in
definite relation to the cutting tool, and to clamp it with a proper force in order
to withstand the cutting forces while maintaining that precise position.
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Work holding devices include all devices that hold, grip or chuck a work piece
to perform a manufacturing operation. It includes clamps, vises, chucks, fixtures
etc..,
The holding force may be applied mechanically, electrically, hydraulically or
pneumatically.
Parts are clamped, relative to their datum planes, for machining, assembly,
welding, and inspection
Production devices are generally work holding devices such as work holders
with or without tool guiding or setting arrangement, used to locate and hold the
work piece.
Basic functions of a work holding device:
Locate - Refers to positioning a part with respect to its datum(s) for
manufacturing purposes
Clamp - Refers to holding the part for manufacturing purpose
DESIGN CONSIDERATION OF WORKHOLDERS:
1. RELIABILITY
Must maintain the clamping force during operation
Must be easy to maintain and lubricate
2. RUGGEDNESS
Must be able to withstand impact force during operation
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Must resist abrasion
Easy to maintain and replace worn parts
3. DESIGN AND CONSTRUCTION EASE
Use standard parts whenever possible
If possible use modular fixture
ADVANTAGES:
1) PRODUCTIVITY:
Eliminate individual markings, positioning, etc.
2) INTERCHANGEABILITY
Facilitate uniform quality. No need for selective assembly
3) SKILL REDUCTION
Simply locating and clamping of the Workpiece
4) COST REDUCTION
Scrap, easy assembly, saving labor cost.
1.3.1. JIGS AND FIXTURES-INTRODUCTION :
Jigs and fixtures are special purpose tools which are used to facilitate
production (machining, assembling and inspection operations) when workpieces
are to be produced on a mass scale. The mass production of workpieces is based
on the concept of interchangeability according to which every part will be
produced within an established tolerance. Jigs and fixtures provide a means of
manufacturing interchangeable parts since they establish a relation, with pre-
determined tolerances, between the work and the cutting tool. They eliminatethe necessity of a special setup for each individual part. Once a jig or fixture is
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properly set up, any number of duplicate parts may be readily produced without
additional set up.
HENCE 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
6. Reduced quality control expenses.
7. Increased versatility of machine tool.
8. Less skilled labour.
9. Saving labour.
10. Their use partially automates the machine tool.
11. Their use improves the safety at work, thereby lowering the rate of
accidents.
JIG:
A jig may be defined as a device which holds and positions the work, locates or
guides the cutting tool relative to the workpiece and usually is not fixed to themachine table. It is usually lighter in construction.
FIXTURE:
A fixture is a work holding device which only holds and positions the work, but
does not in itself guide, locate or position the cutting tool. The setting of the tool
is done by machine adjustment and a setting block or by using slips gauges. A
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fixture is bolted or clamped to the machine table. It is usually heavy in
construction.
Jigs are used on drilling, reaming, tapping and counter boring operations, while
fixtures are used in connection with turning, milling, grinding, shaping,
planning and boring operations.
To fulfill their basic functions, both jigs and fixtures should possess the
following
Components or elements:
1. A sufficiently rigid body (plate, box or frame structure) into which the
workpieces are loaded
2. Locating elements.
3. Clamping elements.
4. Tool guiding elements (for jigs) or tool setting elements (for fixtures).
5. Elements for positioning or fastening the jig or fixture on the machine on
which it is used.
Locating pins are stops or pins which are inserted in the body of jig or fixture,
against which the workpieces pushed to establish the desired relationship
between the workpiece and the jig or fixture. To assure interchangeability, thelocating elements are made from hardened steel. The purpose of clamping
elements is to exert a force to press a workpiece against the locating elements
and hold it there in opposition to the action of the cutting forces.
In the case of a jig, a hardened bushing is fastened on one or more sides of the
jig, to guide the tool to its proper location in the work. However, in the case of a
fixture, a target or set block is used to set the location of the tool with respect to
the workpiece within the fixture.
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Most jigs use standard parts such as drill bushings, screws, jig bodies and many
other parts. Fixtures are made from grey cast iron or steel by welding or bolting.
Fixtures are usually massive bodies because they have to withstand large
dynamic forces.
Because the fixtures are in between the machine and the workpiece, their
rigidity and the rigidity of their fastening to the machine table are most
important.
Jigs are positioned or supported on the machine table with the help of feet
which slide or rest on the machine table. If the drill size is quite large, either
stops are provided or the jig is clamped to the machine table to withstand the
high drilling torque. Fixtures are clamped or bolted to the machine table.
FIG.1.2. A Simple Design of Jig and Fixture
According to the degree of mechanization and automation, jigs and fixtures are
classified as: (a) hand operated (b)power(c) semi-automatic (d) automatic.
USES OF JIG AND FIXTURE:
Reduce cost of production.
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Increase the production.
To assure high accuracy of parts
Provide for interchangeability
Enable heavy and complex parts to machine
Reduced quality control expenses.
Less skilled labor.
Partially automates the machine tools
Use improve the safety, accidents low
1.4. INTRODUCTION TO LOCATING AND CLAMPING:
The question of properly locating, supporting, and clamping the work is
important since the overall accuracy is dependent primarily on the accuracy
with which the workpiece is consistently located within the jig or fixture. There
must be no movement of the work during machining. Locating refers to the
establishment of a proper relationship between the workpiece and the jig or
fixture. The function of clamping is to exert a force to press the workpiece
against the locating surfaces and hold it there against the action of cutting
forces.
1.4.1. PRINCIPLE OF LOCATION:
In order to study the complete location of a workpiece within jig or fixture, let
us consider a workpiece in space .The workpiece is assumed to have true and
flat faces. In a state of freedom, it may move in either of the two opposed
directions along three mutually perpendicular axes, XX, YY and ZZ. These SIX
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movements are called "movements of translation. Also, the Workpiece rotate
in either of two opposed directions around each axis, clockwise and
anticlockwise. . These six movements are called "rotational movements". The
sum of these two types of movements gives the twelve degrees of freedom of a
workpiece in space. To confine the workpiece accurately and positively in
another fixed body (Jig or fixture), the movement of the workpiece in any of the
twelve degrees of freedom must be restricted
FIG.1. 3 Workpiece in Space
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FIG.1.4 Workpiece Located in a Fixed Body.
1. The workpiece is resting on three pins A, Band C which are inserted in
the base of the fixed body. The workpiece cannot rotate about the axes
XX and YY and also it cannot move downward.
2. Two more pins D and E are inserted in the fixed body, in a plane
perpendicular to the plane containing the pins A. Band C. Now the
workpiece cannot rotate about the Z- axis and also it cannot move
towards the left. Hence, the addition of pins D andErestrict three more
degrees of freedom, namely 6, 7 and 8.
3. Another pinFin the second vertical face of the fixed body, arrests degree
of freedom 9.
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Thus, six locating pins, three in the base of the fixed body, two in a vertical
plane and one in another vertical plane, the three planes being perpendicular to
one another, restrict nine degrees of freedom. Three degrees of freedom,
namely, 10, 11 and 12 are still free. To restrict these, three more pins, one for
each of these degrees of freedom are needed. But this will completely enclose
the workpiece making its loading and unloading into the jig or fixture
impossible. Due to this, these remaining three degrees of freedom may be
arrested by means of a clamping device. The above method of locating a
workpiece in a jig or a fixture is called the "3-2-1"principle or "six point
location" principle.
Some of the principles to be followed for location of a workpiece are explained
below.
1.4.1.1. PRINCIPLE OF PIN LOCATION:
The principle of minimum locating points. According to this principle,
only the minimum locating points" should be used to secure location of the
workpiece in anyone plane. Considering the "3-2-1 principle, these pins are
used to the base of the fixed body.
This is due to the reason that this is the minimum number of locating
points through which a plane can be drawn on which the workpiece will seat.
The workpiece may rock and get strained if more than three locating points are
provided. Now considering the second plane, It is clear that if one locating point
is provided, the workpiece will swivel about this point, but not if there are two
such location points, these two locating points establish a line parallel to the
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first plane. With the workpiece located against a plane and a line, it has only
one direction of movement in third plane. Therefore, one locating point is
sufficient in the third plane to prevent this movement.
1.4.1.2. PRINCIPLE OF MUTUALLY PERPENDICULAR PLANES:
1. The "3-2-1" principle can also be put as a workpiece may be fully located
by supporting it against three points in one plane, two points in second
plane and one point in a third plane. These three planes are not parallel
and are preferably perpendicular to one another. If the locating surfaces
are not perpendicular to one another, the following two difficulties will
arise:
2. The workpiece will tend to lift due to the wedging action between the two
locating surfaces.
3. A large error in the movement of the workpiece introduced due to the
displacement of a locating point or a particle (chip or dirt) adhering to it.
4. The difference of resulting error and introduced error, which is the
projection factor is zero when the locating surfaces are normal and
increases as the angle between them becomes more acute.
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FIG.1.5 Principles of Mutually Perpendicular Planes
1.4.1.3. PRINCIPLE OF EXTERME:
The locating points should be placed as far away from one another possible, to
achieve the greatest accuracy in location.
1.4.2. LOCATING METHODS AND DEVICES:
Locators are those parts of a jig or fixture which helps a workpiece to seat in
proper position in it. Depending on the type of work, locators are designed.
There is a large variety of locating devices or locators and methods of locating
elements available to a jig and fixture design. The majority of workpiece can be
located with these methods. The various locating devices and methods are as
follows:
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Pins of various designs and made of hardened steel are the most common
locating devices used to locate a workpiece in a jig or fixture. The shank of the
pin is press fitted or driven into the body of the jig or fixture. The locating
diameter of the pin is made larger than the shank to prevent it from being forced
into the jig or fixture body due to the weight of the workpiece or the cutting
forces.
1.4.3. PINS AND BUTTON LOCATORS:
This is one of the common methods of location. A round pin or button is used to
support the job firmly and hold it in position. The main difference between pins
and buttons are length. Buttons are generally shorter in length than pins and are
generally used for vertical locations. Pins are generally used for horizontal
locations. Larger sizes are sometimes referred to as plugs.
Depending upon the mutual relation between the workpiece and pin, the pins
may be classified as:
1. Locating pins
2. Support pins
3. Jack pins
1.4.3.1. LOCATING PINS:When reamed or finely finished holes are available in the workpiece,
these can be used for locating purposes in the manner shown in Fig.
Depending upon their form, the locating pins are classified as:
1.4.3.2. CONICAL LOCATING PINS.
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These pins are used to locate a workpiece which is cylindrical and with
or without a hole as shown in Fig. (a) (b).Any variation in the hole size
will be easily accommodated due to the conical shape of the pin.
1.4.3.3. CYLINDRICAL LOCATING PINS:
In these pins, the locating diameter of the pin is made a push fit with the
hole in the workpiece, with which it has to engage. The top portion of
these pins is given a sufficient lead either by chamfering [Fig. (c) and
(d)] or by means of radius [Fig(e)] to facilitate the loading of the
workpiece.
FIG1.6 LOCATING PINS
1.4.4. CLAMPING INTRODUCTION:
If the workpiece cannot be restrained by the locating elements, it becomes
necessary to clamp the workpiece in jig or fixture body. As already noted, the
purpose of clamping is to exert a pressure to press a workpiece against the
locating surfaces and hold it there in opposition to the cutting forces i.e. to
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secure a re1iable (positive) contact of the elements and prevent the work m the
fixture from displacement and vibration In machining. The most common
example of a clamp is the bench vise, where the movable jaw of the vise exerts
Force on the workpiece thereby holding it in the correct position of location in
the fixed jaw of the vise.
PRINCIPLES FOR CLAMPING PURPOSES:
Since the proper and adequate clamping of a workpiece is very important, the
following design and operational factors should be taken care of:
1. The clamping pressures applied against the workpiece 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
FIG 1.7 METHOD OF CLAMPING
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3. The clamping pressure must only hold the workpiece and should never be
great enough so as to damage, deform or change any dimensions of the
workpiece.
4. The clamping and cutting forces should be directed towards the locating
pins, otherwise the workpiece may get bent or forced away from the locating
pins during machining.
5. Clamping should be simple, quick and fool proof. 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.
8. Clamps should never be relied upon for holding the workpiece against the
cutting force. The cutting force should be arranged against a fixed stop or a
substantial part of the fixture body.
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.
10. Fibre pads should be riveted to the clamp faces, otherwise soft and fragile
workpiece can get damaged.
11. A clamp should be designed to deliver the required clamping force when
operated by the smallest force expected.
12.A clamp should be strong enough to withstand the reaction imposed uponit 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.
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FIG 1.8 POSITION OF CLAMP
1.4.4.1. CLAMPING DEVICE:
1.4.4.1.1. BRIDGE CLAMP.
It is very simple and reliable clamping device. The clamping force is applied by
the spring loaded nut Fig , The relative positions of the nut, the point of contact
of the clamp with the work and with outer support should be carefully
considered, since the compressive force of the nut is shared between the
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workpiece and the clamp support inversely as the ratio of their distances from
the nut.
The distance 'x' is less than or equal to but never greater than the distance 'y'.
The spring is fitted with the clamp for its automatic lifting when the nut is
loosened to remove the workpiece from the jig or fixture. To avoid the complete
removal of the nut every time a workpiece is changed the clamp may be slotted
to draw it back as shown in Fig. A two way clamping can be obtained by the
bridge clamp as shown in Fig.
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FIG.1.9 BRIDGE CLAMP
1.5. INTRODUCTION TO SENSORS:
Sensors are devices which produces a proportional output signal
(mechanical, electrical, magnetic, etc.) when exposed to a physical phenomenon
(pressure, temperature, displacement, force, etc.). Many devices require sensors
for accurate measurement of pressure, position, speed, acceleration or volume.
Transducers are devices which convert an input of one form of energy in to an
output of another form of energy.
The term transducer is often used synonymously with sensors. However,
ideally, the word transducer is used for the sensing element plus any associated
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signal conditioning circuitry. Typically, a transducer may include diaphragm
which moves or vibrates in response to some form of energy, such as sound.
Some common examples of transducers with diaphragms are
microphones, loudspeakers, thermometers, position and pressure sensors.
Sensors are transducers when they sense one form of input energy and produce
output in a different form of energy.
TYPES OF SENSORS:
Passive and Active sensors
Analog and digital sensors
1.5.1. PROXIMITY SENSOR:
A Proximity sensor can detect objects without physical contact. A proximitysensor often emits an electromagnetic field or beam and look for changes in the
field. The object being sensed is often referred to as the proximity sensor's
target. Different proximity sensor targets demand different sensors. For
example, a capacitive or photoelectric sensor might be suitable for a plastic
target; an inductive proximity sensor requires a metal target.
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A proximity sensor that measures current flow between the sensing electrode
and the target provides readouts in appropriate engineering units. Usually, one
side of the voltage source or oscillator connects to the sensing electrode, and the
other side connects through a current-measuring circuit to the target, which
generally is a metal part at earth or ground potential.
Proximity sensor selection depends on the material to be sensed. Proximity
sensor probes for sensing no conducting surfaces or insulators vary slightly
from those for conducting surfaces. No conducting probe signals are also more
difficult to linearize.
TYPES:
Hall Effect sensor
Capacitive sensors
Eddy current proximity sensors
Inductive proximity sensors
Pneumatic proximity sensor
Proximity switches
1.5.1.1. PROXIMITY LIMIT SWITCH:
Proximity switches are used to detect the presence of an object. These can
be achieved by the presences of an object in order to give output which is either
on or off. These can be classified in two types:
Non contact type
Contact type
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The non-contact type switches detect the presence of an object without a
physical contact. Examples: magnetic reed switch, photoelectric sensors,
inductive proximity sensor. The contact type switches detect the presence of an
object with a physical contact.
The function of a limit switch is to produce electrical signal
corresponding to the position of the mechanical member to be detected. Limit
switches have operating heads which incorporate some types of lever arm or
plunger mechanism, the selection of which is application dependent. When a
limit switch has the positive opening of the normally closed contact, it is
typically suitable for use in machine safety application.
PROXIMITY SWITCH APPLICATIONS:
1. Don't use the limit switch as a mechanical stop (use another
component)
2. Use cam surfaces to allow gradual actuation
3. Don't apply side forces to the switch roller or lever (will wear
Bearings quickly)
4. Use appropriate switch actuator for type of force/motion applied
5. Dont switch excessive currents through the switch contacts
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CHAPTER-2 METHODOLOGY
2.1. WORKING:
Work holding is one of the efficient methods. The main purpose of
using fixtures is to reduce the setting time of the workpiece. The fixture is
designed in such a way that the loading and unloading of the workpiece is done
easily and quickly. Work holding devices play a major role in manufacturing as
they ensure smooth and efficient operation of the component. Fixtures are used
for holding the work piece during machining.
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Petrol brackets are used to mount the drive shaft in automobiles. The
petrol bracket is casted from cast iron into the required shape and further
machining processes are carried out to achieve good precision component with
good surface finish. A stud is used in the petrol bracket in order to hold the
drive shaft with the petrol bracket.
The Stud is provided with a neck such that the length of thread is
longer on one side and shorter on the other side. During assembly of the stud
into the petrol bracket, the thread with the shorter side should be inserted first, if
the longer side is inserted the entire component is rejected. The stud is
screwened through torque wrench.
Here the sliding element is used for clamping the work piece
efficiently. The cylindrical locator are used for setting the workpiece in the
fixture easily in which both clamping and locators arrest six degrees of freedom
efficiently.
Human error occurs during screwing the stud as the operator
inserts the longer side of the stud into the petrol bracket. Due to lack of
concentration or continuous work, human error occurs which results in rejection
of the component.
Hence we came up with the idea of introducing fixtures in the
assembly. A sensor (proximity limit switch) equipped fixture is designed in
order to eliminate the chances of error.
An assembly fixture is used to assemble the stud in a petrol bracket
and is manufactured using mild steel. As we know that mild steel has good load
bearing capacity and corrosion resistance, mild steel is chosen. Wear and tear
occurs in the petrol bracket during clamping, so brass is used for clamping in
order to reduce the wear and tear.
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When the stud is misassembled in wrong position (i.e.) instead of
inserting the shorter side, longer side is inserted, the limit switch warn the
operator through alarm sounds when the stud is assembled wrongly.
This assembly fixture can be easily operated, so even a semi-
skilled labor can operate the fixture with ease. This reduces the manpower,
labor cost and also the manufacturing cost.
Due to implementation of the sensor equipped fixture, zero error is
achieved, assembling time is reduced and rejection of components is eliminated.
Hence due to the above mentioned factors the production rate can be increased.
2.2. DESIGN OF ASSEMBLY FIXTURE:
BOTTOM BASE PLATE WITH SENSOR STAND:
3D-DIAGRAM
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FIG.3.1 (A) BOTTOM BASE PLATE WITH SENSOR STAND
The bottom base plate holds all the component of the fixture such as sensor kit,
angle plate, clamping device, locating pins in an efficient way. The pillars are
provided in order to connect the top and bottom base plate by using bolt. The
bottom base plate is made of mild steel.
BOTTOM BASE PLATE WITH SENSOR STAND
2D-DIAGRAM
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FIG.3.1 (B) BOTTOM BASE PLATE WITH SENSOR STAND
BOTTOM BASE PLATE WITH LIMIT SWITCH:
3D-DIAGRAM
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FIG.3.2 (A) BOTTOM BASE PLATE WITH LIMIT SWITCH
BOTTOM BASE PLATE WITH LIMIT SWITCH
2D-DIAGRAM
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FIG.3.2 (B) BOTTOM BASE PLATE WITH LIMIT SWITCH:
TOP BASE PLATE
3D-DIAGRAM
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FIG 3.3 (A) TOP BASE PLATE
The top base plate is fixed above the bottom base plate by using spacer. The
angular block and clamping device is placed above top base plate. The hole is
provided to the sensor pin in order to indicate the error during assembly. It is
made of mild steel.
TOP BASE PLATE
2D-DIAGRAM
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FIG 3.3 (B) TOP BASE PLATE
SENSOR STAND:
3D-DIAGRAM
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FIG.3.4 (A) SENSOR STAND
The design shown above is a sensor stand. The sensor stand is used to hold the
proximity limit switch. Hence the sensor stand is fixed to the bottom base plate
of the fixture. The two bottom holes in the sensor stand are used to fix with the
base plate of the fixture. The holes provided at the top are used to hold the limit
switch using bolt and nut. The sensor stand is made of mild steel.
SENSOR STAND
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2D-DIAGRAM
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FIG.3.4 (B) SENSOR STAND
PLUNGER:
3D-DIAGRAM
FIG.3.5 (A) PLUNGER
The plunger consists of a spring loaded roller which is attached to the limit
switch. It is located below the sensor pin. The sensor pin will push the plunger
when a stud is misassembled and gives indication to the sensor. It is made of
mild steel (EN-8).
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PLUNGER
2D-DIAGRAM
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FIG.3.5 (B) PLUNGER
SPACER:
3D-DIAGRAM
FIG.3.6 (A) SPACER:
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The top base plate is supported by the Spacer. The limit switch is placed in
between the top and bottom base plate in order to operate the sensor easily. The
Spacer is made of mild steel.
SPACER
2D-DIAGRAM
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FIG.3.6 (B) SPACER:
SENSOR PIN:
3D-DIAGRAM
FIG.3.7 (A) SENSOR PIN:
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The sensor pin is placed above the limit switch. When a stud is misassembled it
pushes the sensor pin down and gives indication to the sensor. It is made of mild
steel (EN-36).
SENSOR PIN
2D-DIAGRAM
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FIG.3.7 (B) SENSOR PIN:
SLIDING CLAMP:
3D-DIAGRAM
FIG.3.8 (A) SLIDING CLAMP
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The sliding clamp is used while clamping and removing the workpiece in the
fixture. The clamp pad is provided in the sliding clamp. The clamp pad is madeof brass material, because it eliminates wear and tear to the component.
SLIDING CLAMP
2D-DIAGRAM
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FIG.3.8 (B) SLIDING CLAMP:
ANGULAR BLOCK
3D-DIAGRAM
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FIG 3.9 (A) ANGULAR BLOCK
ANGULAR BLOCK
2D-DIAGRAM
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FIG 3.9 (B) ANGULAR BLOCK
FINAL ASSEMBLY OF A FIXTURE:
3D-DIAGRAM
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FIG.3.10. (A) FINAL ASSEMBLY OF A FIXTURE
FINAL ASSEMBLY OF A FIXTURE
2D-DIAGRAM
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FIG.3.10. (B) FINAL ASSEMBLY OF A FIXTURE
2.3. FIXTURE MANUFACTURING PROCESS:
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1. RAW MATERIAL -MS, EN-8, EN-36, EN-24.
2. SIZING -SHAPER, CONVENTIONAL,
TURNING, MILLING
3. HEAT TREATMENT -HRC (e.g. 60-62)
4. GRINDING -SURFACE OR CYLINDRICAL GRINDING
5. BLACKENING -BLACK OXIDE COATING
6. INSPECTION
7. ASSEMBLING
RAW MATERIAL:
The fixture is manufactured using the above processes. Initially raw material is
collected which consists of properties such as MS, EN-8, EN-36, and EN-24.
EN8 is grade of through-hardening medium carbon steel, which can be readily
machined in any condition. EN8 is suitable for the manufacture of parts such as
general-purpose axles and shafts, gears, bolts and studs.
SIZING:
The raw material is converted in to required shape by using a casting. After that
the machining operation is carried out such as shaping, turning and milling.
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Machining is any of various processes in which a piece of raw material is cut
into a desired final shape and size by a controlled material-removal process.
The traditional machining processes are turning, boring, drilling, milling,broaching, shaping,planing, reaming and tapping.
Turning operations are operations that rotate the workpiece as the primary
method of moving metal against the cutting tool.
Milling operations are operations in which the cutting tool rotates to bring
cutting edges to bear against the workpiece.
Drilling operations are operations in which holes are produced or refined by
bringing a rotating cutter with cutting edges at the lower extremity into contact
with the workpiece. Drilling operations are done primarily in drill press but
sometimes on lathes or mills.
HEAT TREATMENT:
Heat treating is a group ofindustrial and metalworking processes used to alter
thephysical, and sometimes chemical, properties of a material. Heat treatment
involves the use of heating or chilling, normally to extreme temperatures, to
achieve a desired result such as hardening or softening of a material. Heat
treatment techniques include annealing, case hardening,precipitation
strengthening, tempering and quenching.
It can be furthersurface-hardened typically to 60-62 HRC by induction
processes, producing components with enhanced wear resistance.
The Rockwell scale is a hardness scale based on indentation hardness of a
material. The Rockwell test determines the hardness by measuring the depth of
penetration of an indenter under a large load compared to the penetration madeby a preload.
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GRINDING:
Grinding is one of the methods of surface finishing. There are two types of
grinding such as cylindrical and surface grinding. Cylindrical grinding is usedfor finishing the flat surface and surface grinding is used for finishing the
cylindrical surface.
BLACK OXIDE COATING:
Black oxide is a conversion oxide coating formed on the metal surface as a
result of a chemical reaction of the metal atoms with an oxidizing agent (air,aqueous solution, molten salts).
Black oxide coating is used mostly forCarbon steels, Alloy steels, Tool and die
steels and Cast irons. Stainless steels and Copper alloys may also be black oxide
coating.
INSPECTION:
Most high precision parts and components need to be inspected either visually
or mechanically in order to confirm dimensions. This is an efficient method
which improves productivity.
ASSEMBLING:
Finally the components of the fixture are assembled in an efficient way by using
bolt, nut, welding, which is designed in such a way to increase productivity.
1.6. COST ESTIMATION:
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S.NO EQUIPMENT MATERIAL QUANTITY COST
I.
FIXTURE COST
1 Angular block Mild steel 1 4000
2 Clamping device(sliding
block)
Mild steel 1 1500
3 Clamp pad Brass 1 500
4 Top base plate Mild steel 1 1500
5 Bottom base plate Mild steel 1 1500
6 Spacer Mild steel 4 1000
II. ELECTRICAL SPARES COST
1
Electrical spares (limit
switch 2no,control box
1no,Cable and others)
TYPE-OMRON D4C-
3332
---- ------ 7000
III. TOTAL COST 17000
TABLE NO 2.1COST ESTIMATION
2.5. COMPARISION OF EXISTING FIXTURE AND NEW DESIGNED
FIXTURE:
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EXISTING FIXTURE:
NEW DESIGNED FIXTURE:
FIG. NO 3.11 PICTORIAL REPRESENTATION OF FIXTURE
CHARACTERISTICS EXISTING FIXTURE NEW DESIGNED
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FIXTURE
Operation Difficult to operate Easy to operate
Sensor Does not indicate the
error, due to absence of
sensor.
Indicate the error, due to
the presence of sensor.
Setting time Assembling time for the
component is up to 90
seconds.
Assembling time for the
component is reduced to
65 seconds.
Productivity Productivity is less
compared to designed
fixture.
Productivity is more.
Labour availability Skilled labour is
required.
Semi skilled labour can
operate.
Clamp usage Two clamping is used,
so makes more time.
Single clamping is used,
so assembling time is
reduced.
Component rejection There is a chance of
misalignment of stud, so
component is rejected.
There is no chance of
misalignment of stud. So
component rejection is
eliminated.
TABLE 2.2 COMPARISION OF EXISTING FIXTURE AND NEW
DESIGNED FIXTURE
2.6. ADVANTAGES:
1. It reduces or eliminates the efforts of setting the work piece and
maintains the accuracy of performance.
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2. Assembling time is reduced when comparing the conventional fixture
due to single clamping device instead of using two clamping devices
which is also an efficient method.
3. It reduces the production cycle time so increases production capacity.
4. Semi-skilled labour can assemble the workpiece using fixture with ease.
5. Operators working become comfortable as his efforts in setting the work
piece can be eliminated.
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CHAPTER-3 CONCLUSION
CONCLUSION:
The design of fixture is effective and efficient in assembly of the petrol bracketthere by reducing the assembling time and increasing the productivity. Due to
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implementation of the sensor equipped fixture, zero error is achieved, and
rejection of components is eliminated. The assembling time of existing fixture
for a petrol bracket is 90 seconds and the assembling time of new designed
fixture for a petrol bracket is 70 seconds. It reduces the assembling time of each
component by 20 seconds comparing the conventional fixture. This meets the
major advantages which increases the productivity. Even a semi-skilled operator
can handle this fixture in assembly with ease which reduces the manpower,
labor cost resulting in a minimized manufacturing cost.
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CHAPTER-4 BIBLIOGRAPHY
BIBLIOGRAPHY:
1. AMERICAN SOCIETY OF TOOL AND MANUFACTURING
ENGG HAND BOOK
2. PRODUCTION TOOLING EQUIPMENT PARSONS
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3. ENGINEERING PRODUCTIVITY-WALKER
4. JIGS AND FIXTURES INTRODUCTION -HASTLEHURST
5. ADVANCED FIXTURE DESIGN FOR FMS -ANDREW YEH
CHRIS NEE, KENNETH WHY BREW, A.SENTHIL KUMAR 1995.
6. A FUNCTIONAL APPROACH FOR THE FORMALIZATION OF
THE FIXTURE DESIGN- R.HUNTER, J.RIOS, J.M.PEREZ,
A.VIZAN 2006.
7. COLVIN, FRED HERBERT 1867-MACHINE TOOLS.
8. HAAS, LUCIAN LEVANT 1881-MACHINE TOOLS.
9. JIGS AND FIXTURES-INTRODUCTION -PRAKASH HIRALALJOSHI-2010.
10. JIG AND FIXTURE DESIGN MANUAL-ERIK KARL
HENRIKSEN 1973.