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DESIGN AND DEVELOPMENT

OF TEST SETUP FOR

MEASURING BOLTED JOINTCLAMPING FORCE

Department of Mechanical Engineering

.

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ABSTRACT

Bolts are widely used in industry for joining members together. The

behavior and service life of bolted joints depend on several factors

including bolt material, dimensions, surface finish, surface coating

and thread tolerances. However, the uppermost factor affecting the

reliability and durability is the correctness of the clamping force

exerted by the bolt. Thus it is very important to monitor the bolt

clamping force to ensure a proper preload during assemblyprocess. Each of the available monitoring techniques including

torque control, torque-angle control and strain gauged bolt suffers

from one or more limitations which affect the reliability of

measurement.

In this project report, we simultaneously measure the tension in the bolt, load

on the bush and the torque while rotating the bolt at the desired

angle. Experiments conducted on bolted structures with plates of

different bolt diameter have demonstrated the reliability andusefulness of this new approach.

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Index

CONTENT PAGE

1. LIST OF TABLES 6

2. LIST OF FIGURES 7

3. ABBREVIATIONS AND 8

NOMENCLATURE

4. INTRODUCTION 9

5. THE PROBLEM 14

6. DESING AND FABRICATION 20

OF SETUP

7. TEST PROCEDURE AND 39

RESULT

8. FUTURE SCOPE 46

9. CONCLUSION 48

10. REFERENCE 50

11. APPENDIX 51

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LIST OF TABLES

Table No. Description Page no.

1 PROCESS SHEET FOR MAIN BLOCK 24

2 PROCESS SHEET FOR TOP PLATE 25

3 PROCESS SHEET FOR SIDE PLATE 26

4 PROCESS SHEET FOR BUSH 27

5 PROCESS SHEET FOR CUBIC BUSH 28

6 PROCESS SHEET FOR SIDE PLATE 29

7 PROCESS SHEET FOR L-SHAPE BASE

PLATE30

8 EXPERIMENTAL SETUP

319 DEVICES 33

10 BILL OF MATERIALS 36

11 MACHINING COST 37

12 COST OF PURCHASED PARTS 38

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LIST OF FIGURES

FIGURENo.

Description Page no.

Figure 1 TIGHTENING MECHANISM 16

Figure 2 MAIN BLOCK F.V 31

Figure 3 MAIN BLOCK S.V 32

Figure 4 MAIN BLOCK T.V 32

Figure 5/6 DIGITAL TORQUE WRENCH 33/34

Figure 7 LOAD CELL 34

Figure 8 DISPLAY 35

Figure 9/10/11 EXPERIMENTAL PROCEDURE 43/44/45

ABBREVIATIONS AND

NOMENCLATURE

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p = pitch (mm)

D =major dia. (mm)

=coeff. of friction

F=friction force (N)

N=normal force (N)

T1=torque reqd. to raise the nut (N-m)

Dp=pitch dia. (mm) P=clamping force (N)

T2=torque at thrust collar (N-m)

T=total torque req. to tighten the bolt (N-m)

K=torque coeff.

= angle b/w two threads

= Lead angle

Pi = bolt preload

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CHAPTER 1

INTRODUCTION

INTRODUCTION

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LIMIT LOAD

Limit load is the maximum expected external load a joint will experience during

service. Limit load does not include the preload and the positive and negative

thermal loads (as defined in this section).

AXIAL LOAD

An axial load is a load (or component of a load) that is parallel to the bolts

longitudinal axis. An axial load may be either tensile or compressive.

YEILD LOAD

Yield load is limit load multiplied by the yield factor of safety.

ULTIMATE LOAD

Ultimate load is limit load multiplied by the ultimate factor ofsafety.

JOINT SAPERATION LOAD (Psep)

Joint separation load is the limit load multiplied by the joint separation factor of

safety. The joint separation load must always be greater than or equal to limit load.

MAXIMUM PRELOAD (PLDmax)

The maximum preload is a reasonable estimate of the maximum expected preload

in a bolted joint at operating conditions. The maximum preload must be calculated

using one of the procedures

PROOF LOAD

The proof load of a nut is the axially applied load the nut must withstand without

thread stripping or rupture, that of a bolt, screw or stud is the specified load the

product must withstand without permanent set

PRELOAD

The tension created in a fastener when first tightened. Reduces after a period of timedue to embedding and other factors

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PITCH

The nominal distance between two adjacent thread roots or crests

NOMINAL DIAMETER

The diameter equal to the external diameter of the threads

MINOR DIAMETER

This is the diameter of an imaginary cylinder which just touches the roots of an

external thread, or the crests of an internal thread

MAJOR DIAMETER

This is the diameter of an imaginary cylinder parallel with the crests of the thread; in

other words it is the distance from crest to crest for an external thread, or root to rootfor an internal thread

LENGTH OF ENGAGEMENT

The axial distance over which an external thread is in contact with an internal

thread.

K FACTOR

The factor in the torque tightening equation: T=KDF where T is the fastener

tightening torque in Newton metres, D is the fastener diameter in metres, F is the

fasteners preload in Newtons and K is a factor whose value is often taken as 0.2.

The formula gives the approximate tightening torque for standard fasteners used

under normal conditions.

GRIP LENGTH

Total distance between the underside of the nut to the bearing face of the bolt head;

includes washer, gasket thickness etc

CLAMPING FORCE

The compressive force which a fastener exerts on the joint.

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BOLT

A bolt is the term used for a threaded fastener, with a head, designed to be used in

conjunction with a nut

BREAKAWAY TORQUE

The torque necessary to put into reverse rotation a bolt that has not been tightened.

BEARING STRESS

The surface pressure acting on a joint face directly as a result of the force applied by

a fastener.

BREAKLOOSE TORQUE

The torque required to effect reverse rotation when a pre-stressed threaded assembly

is loosened.

PLASTIFICATION

Process of successive yielding of fibers in the cross section

of a member as the bending moment is increased beyond the yield moment.

Its been said that mans invention of nails, rivets, screws, and other basic fasteners

helped pave the road from the Stone Age to the Space Age. If that is true, then

fastener loosening has provided quite a few of the speed bumps and pot holes on that

road.Keeping fasteners tight, particularly threaded fasteners seems like a simple

task, but the moving nature of the machinery they are used on is what makes them

so troublesome. How nails and rivets work is fairly well known. But because the

physics of the threaded fastener is not as well understood, it tends to cause the most

problems.

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CHAPTER 2

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THE PROBLEM

NEED OF PRETENSION/PRELOAD

Threaded fasteners can do a good job of holding things together only when they areproperly tightened. The fastener to ensure the proper performance of the joint must

produce an appropriate tension. To this day a simple, inexpensive, and effective way

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to determine if a fastener is properly tightened has not been found. Through the

years, satisfactory ways have been discovered, but they are neither simple nor

inexpensive. In most situations we rely on less-than-perfect, but adequate traditional

methods.

Were most joints not massively over-designed to accommodate inaccuratetightening, simple tightening procedures could prove catastrophic. Designers willspecify more or larger bolts than needed in order to ensure that the joints are

clamped together with the amount of force required. Fewer or smaller fasteners can

be used when accurate control of bolt tension or preload is assured during assembly.

For most applications the over-design of the joint has been far cheaper than

controlling the assembly process.

Current trends for most applications, however, no longer favor the use of

over-design. Increasing demands on cost, strength-to-weight ratios, product safety,

product performance, and environmental concerns have put pressure on designers,manufacturers and assemblers to do a better job with fewer, lighter parts. This trend

has lead to the discovery of more options in controlling design preload.

Whenever we tighten a bolt, a sequence of events takes place. [2] Bickford

puts it neatly: When we tighten a bolt, (a) we apply torque to the nut, (b) the nut

turns, (c) the bolt stretches, (d) creating preload. In most cases it is this tension or

preload that we need to make a fastening. By controlling torque, turn, or stretch, we

can control the buildup of tension. The closer we approach direct control of tension,

the more accurate and expensive the method will be. Some options for tension

controls during assembly are: Torque control, Angle control, Stretch (Yield) control,and Direct Tension control

Millions of threaded fasteners are used each year to assemble products

ranging from hand-held electronic devices to cars and trucks to heavy-duty

earthmovers. As part of their quality control efforts, manufacturers have searchedfor the best way to effectively measure how well the assembly was put together.

Since some sort of hand or power tool applies torque to the fastener, the easiest and

most popular means of assembly verification is to measure the torque either

dynamically during assembly or statically after the fact. Although these methods

may be useful for many non-critical assemblies, a more complete method is needed

for auditing critical joints where the clamping force holding the joint together mustbe of a sufficient amount to hold the assembly together. This complete method must

somehow be able to determine, or at least estimate, the clamp load to ensure that the

assembly is adequately tightened.

BOLT TIGHTENING MECHANISM

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A screw thread is essentially an inclined plane that has been wrapped around

a cylinder to create a helix. If we unwrapped one revolution of the helix, it would

look like figure 1.

Figure 1: A block representing the nut being slide up (i.e. tightened) the

inclined plane of bolt thread

The friction force always opposes the motion. The inclination of the plane is called

the lead angle .

Summation of Forces in X (Horizontal) and Y (Vertical) directions

( ) (1A)sincosNF

sinNcosNFsinNcosfF0FX

+=

===

( )

(1B)

sincos

PN

PsinNcosNPsinfcosN0FY

=

===

Combining equation (1A) and (1B)

( )( )

)1C(sincos

sincosPF

+=

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Torque required to raise the nut

( )

( ))1D(

sincos

sincos

2

dP

2

dFT

pp

1

+==

It is more convenient to express the above equation in terms of Lead L rather than

lead angle .

( ))1E(

Ld

Ld

2

dPT

p

pp

1

+=

Above expression holds good for square thread, where the normal thread loads are

parallel to the axis of the screw. In the case of other threads (such as Acme or V) the

normal thread load is inclined to the axis because of the thread angle 2 and the lead

angle . Since lead angles are small, this inclination can be neglected and only the

effect of thread angle is considered. The effect of the angle is to increase the

frictional force by the wedging action of the threads. Therefore the frictional terms

in equation (1E) must be divided by cos .

( ) )1F(secLdLsecd

2

dP

Tp

pp

1

+

=

Above expression accounts for the screw-nut interface of a thread, but it is also

necessary to add thrust collar (i.e. bolt under head or nut face and joint surface) also

contributes a friction torque, which must be added.

(1G)2

dPT bb2 =

Total torque required to raise the load or tighten the bolt

( )(2)

2

dP

secLd

Lsecd

2

dPTTT bb

p

pp

21 +

+=+=

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Since

pd

Ltan

= we divide the numerator and denominator of the first

term by pd and get

( )

( )(3)

2

dP

sectan1

sectan

2

dPT bb

p +

+=

Approximating the equation (4) for finding out the torque to develop desired preload

d1.25

2

d)1.5(ddanddd bp =

+==

( )

( )

( )

( )

+

+

+

+

b

i

bi

0.625sectan1

sectan0.5K

(6)dFKT

(5)0.625sectan1

sectan0.5dFT

K = Torque coefficient

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rFcos

rF

2

pFT

rF

cos

rF

2

pF

T

(7))KK(KdFT

bbbtt

bi

bbi

tti

i

321i

BalanceEnergyforNow

FrictionheadUnderbydoneWork

FrictionThreadbydoneWork

TensionbydoneWork

TorqebydoneWork

byNutofRotationaIn

++

=

=

=

=

=

++=

d

r

cosd

rK

d2

pK

(8)and(7)equationComparing

bb3

tt21

bbtti

bbtti

K

(8)d

r

cosd

r

d2

pdFT

d

r

cosd

r

d2

pdFT

=

==

+

+

=

+

+

=

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CHAPTER 3

DESIGN AND

FABRICATION OF

SETUP

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INTRODUCTION

Design consists of application of scientific principles, technical information

and imagination for development of new or improvised machine or mechanism to

perform a specific function with maximum economy & efficiency .

Hence a careful design approach has to be adopted . The total design work ,

has been split up into two parts;

System design

Mechanical Design.

System design mainly concerns the various physical constraints and ergonomics,

space requirements, arrangement of various components on main frame at system,

man + machine interactions, No. of controls, position of controls, workingenvironment of machine, chances of failure, safety measures to be provided,

servicing aids, ease of maintenance, scope of improvement, weight of machine from

ground level, total weight of machine and a lot more.

In mechanical design the components are listed down and stored on the basis of their

procurement, design in two categories namely,

Designed Parts

Parts to be purchased

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For designed parts detached design is done & distinctions thus obtained are

compared to next highest dimensions which are readily available in market. This

amplifies the assembly as well as postproduction servicing work. The various

tolerances on the works are specified. The process charts are prepared and passedon to the manufacturing stage.

The parts which are to be purchased directly are selected from various catalogues &

specified so that any body can purchase the same from the retail shop with given

specifications.

SYSTEM DESIGN

In system design we are mainly concentrated on the following parameters: -

1. System Selection Based on Physical Constraints

While selecting any machine it must be checked whether it is going to be used in a

large-scale industry or a small-scale industry. In our case it is to be used by a small-

scale industry. So space is a major constrain. The system is to be very compact so

that it can be adjusted to corner of a room.

The mechanical design has direct norms with the system design. Hence the

foremost job is to control the physical parameters, so that the distinctions obtainedafter mechanical design can be well fitted into that.

2. Arrangement of Various Components

Keeping into view the space restrictions the components should be laid such that

their easy removal or servicing is possible. More over every component should beeasily seen none should be hidden. Every possible space is utilized in component

arrangements.

3. Components of System

As already stated the system should be compact enough so that it can beaccommodated at a corner of a room. All the moving parts should be well closed &

compact. A compact system design gives a high weighted structure which is desired.

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Man Machine Interaction

The friendliness of a machine with the operator that is operating is an important

criteria of design. It is the application of anatomical & psychological principles tosolve problems arising from Man Machine relationship. Following are some ofthe topics included in this section.

Design of foot lever

Energy expenditure in foot & hand operation

Lighting condition of machine.

2. Chances of Failure

The losses incurred by owner in case of any failure is an important criteria of design.Factor safety while doing mechanical design is kept high so that there are less

chances of failure. Moreover periodic maintenance is required to keep unit healthy.

3. Servicing Facility

The layout of components should be such that easy servicing is possible. Especially

those components which require frequents servicing can be easily disassembled.

Scope of Future Improvement

Arrangement should be provided to expand the scope of work in future. Such as to

convert the machine motor operated; the system can be easily configured to requiredone. The die & punch can be changed if required for other shapes of notches etc.

4. Height of Machine from Ground

For ease and comfort of operator the height of machine should be properly decided

so that he may not get tired during operation. The machine should be slightly higher

than the waist level, also enough clearance should be provided from the ground for

cleaning purpose.

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Table 1

22

PART NO : W-1

PART NAME : MAIN BLOCK

Sr.

No

Description of

Operation

Tools Time in minutes

Jigs &

Fixture

M/c Cutting

Tools

Measuring

Instrument

Setting

Time

M/c

Time

Total

Time

1. Clamp stock M/C Vice Milling - - 15 - 15

2. Facing All Sides

to 120 X80X70---- ---- Timex Vernier 20 90 110

3. Slot of 60X20(2 no)

---- ---- End mill

cutter

Vernier 20 45 65

4. Slot of 80X40 ---- ---- Endmillcutter

Vernier 15 35 50

5. Boring 22

through 20

---- ---- Boring bar Vernier 15 15 30

6. Step bore of 30

Through 5

---- ---- Boring bar vernier - 10 10

7. Drilling 8.2

through 20(7 no)

m/c vice drilling Drill ---- 10 20 30

8. Milling of 7X5

slot

---- Milling End mill

cutter

Vernier 10 20 30

9. Milling by 2mm

on one side for

tapper

---- Milling End mill

cutter

Vernier 10 20 30

MATERIAL SPECIFICATION: EN 24

RAWMATERIAL SIZE: 120X90X90

QUANTITY: - 01 NOS.

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Table 2

TOTAL TIME TAKEN FOR 4 PLATES = 80

23

PART NO : W-2

PART NAME : TOP PLATE

Sr.

No

Description of

Operation


Jigs &

Fixture

M/c Cutting

Tools

Measuring

Instrument

Setting

Time

M/c

Time

Total

Time

1)

Clamp stock M/C Vice Milling - 15 - 15

2

)

Facing all side

120X60X20

---- ---- Timex Vernier 5 50 55

3

)

Drilling 12 though

20 mm

m/c vice Drilling drill ---- 5 10

4

)

Drilling 8

through

20mm(no.2)

m/c vice Drilling Drill ---- 5 10

MATERIAL SPECIFICATION : EN 24

RAW MATERIAL SIZE: 120X70X25

QUANTITY :- 04 NO(S).

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Table 3

TOTAL TIME TAKEN FOR 2 SIDE PLATES = 75X2=150

24

PART NO : W-3

PART NAME : SIDE PLATE

Sr.

No

Description of

Operation


Jigs &

Fixture

M/c Cutting

Tools

Measuring

Instrument

Setting

Time

M/c

Time

Total

Time

1 Clamp stock M/C Vice milling - - 15 - 15

2 Facing all sides

80 X70 X10

---- ---- timex Vernier 30 30

3 Drilling 8.2

through 10 mm

(3 nos)

m/c vice drilling Twist drill ---- 15 30


RAW MATERIAL SIZE: 90X90X15QUANTITY :- 02 NO(S).

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Table 4

TOTAL TIME TAKEN FOR 2 SIDE PLATES = 68 X 4=27

25

PART NO : W-4

PART NAME : BUSH

Sr.

No

Description of

Operation


Jigs &Fixture

M/cTools

CuttingTools

MeasuringInstrument

SettingTime

M/cTime

TotalTime

1 Clamp stock Three jaw

chuck

Lathe - - 15 - 15

2 Facing B/S to total

length 18

---- ---- Facing tool Vernier 5 14 19

3 Drilling through 20 ---- ---- Centre drill ---- 3 5 8

4 Clamp stock

between center

Center

support &

carrier

---- - ---- 10 10

5 Turning OD 30

mm through out

length

---- ---- Turning tool ---- - 9 9

6 Step turning 22

through 15 length

---- ---- Turning tool ---- - 7 7


RAW MATERIAL SIZE: 33X25QUANTITY :- 04 NO(S).

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TABLE 5

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PART NO : W-5

PART NAME : CUBIC BUSH

Sr.

No

Description of

Operation


Jigs &

Fixture

M/c Cutting

Tools

Measuring

Instrument

Setting

Time

M/c

Time

Total

Time


2 Milling cube by

32x32x32

---- Milling End cutting

tool

Vernier 10 20 30

3 Drilling 12.5

through 32mm

m/c vice drilling Twist drill ---- 15 15 30


RAW MATERIAL SIZE: 34X34X34QUANTITY :- 01 NO(S).

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TABLE 6

27

PART NO : W-6

PART NAME : SIDE PLATE

Sr.

No

Description of

Operation


Jigs &

Fixture

M/c Cutting

Tools

Measuring

Instrument

Setting

Time

M/c

Time

Total

Time


2 Facing all sides

40 X60 X15

---- ---- timex Vernier 30 30

3 Drilling 8, 10,

12 through 15

mm

(3 nos)

m/c vice drilling Twist drill ---- 15 15 30


RAW MATERIAL SIZE: 90X90X15


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TABLE 7

28

PART NO : W-7

PART NAME : L-SHAPE BASE PLATE

Sr.

No

Description of

Operation


Jigs &

Fixture

M/c Cutting

Tools

Measuring

Instrument

Setting

Time

M/c

Time

Total

Time


2 Milling by

120x150x25


tool

Vernier 10 20 30

3 Milling by

75x150x25


tool

Vernier 15 15 30

4 Welding 1 and 290 degree edge

---- Weldingm/c

Rod welding ---- 10 10 20


RAW MATERIAL SIZE: 200x200x30

RAW MATERIAL SIZE:200x100x30


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TABLE 8

FIG 2 - MAIN BLOCK (FRONT VIEW)

FIG 3 - SIDE VIEW

FIG 4 TOP VIEW

TABLE 9

29

PART NO : W-8

PART NAME : EXPERIMANTAL SETUP

Sr.

No

Description of

Operation


Jigs &

Fixture

M/c Cutting

Tools

Measuring

Instrument

Setting

Time

M/c

Time

Total

Time

1 Welding of w1 and

w7

M/C Vice Welding

m/c

Rod welding - - 15 15


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FIG 5 DIGITAL TORQUE WRENCH

FIG 6 - DIGITAL TORQUE WRENCH

FIG 7 LOAD CELL

30

PART NO : W-9, 10,11

Sr.

No

NAME OF THE

PART

DISCRIPTION OF

PART

MODEL NO. COMPANY

1 Digital torque

wrench

To measure the

torque with high

accuracy

------------- ATCO LMT.

2 Load cell To measure load on

the cubic bush

-------------- CONCEPT ELECTRONICS

3 Display To display reading

in kilogram

WSMDPCB CONCEPT ELECTRONICS


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FIG 8 LOAD CELL DISPLAY

COST ANALYSIS

TABLE 10

BILL OF MATERIALS:-

Sr no Part code Description Qty. material

1 W-1 MAIN BLOCK 1 En 24

2 W-2 TOP PLATE 4 En 24

3 W-3 SIDE PLATE 2 En 24

4 W-4 BUSH 4 En 24

5 W-5 M-8 BOLT&NUT100 mm

3 STD


3 STD


3 STD

8 W-8 M 14 BOLT&NUT100 mm

3 STD

9 W-9 M-8 ALLEN BOLT 4 STD

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20 mm

10 W-10 L-SHAPE BASE PLATE 1 STD

RAW MATERIAL COST

The total raw material cost as per the individual materials and their

corresponding rates per kg is as follows,

Cost per kg = RS 60

Total weight of raw material = 30 kg

Total cost of raw material = 30*60

= 1800

this includes the cost of cutting as per desired length through automatic

hack saw

MACHINING COST

Table 11

OPERATION RATE

(Rs /HR)

TOTAL TIME

(HRS)

TOTAL

COST (Rs)

LATHE 95 6 570

MILLING 110 15 1650

DRILLING 50 3 150

TAPPING 10 Rs./hole 40 min 150

TOTAL 2520

TOTAL MACHINING COST =2520-200(discount procured)

=2320

COST OF PURCHASED PARTS :-

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TOTAL COST = Raw Material Cost +Machine Cost + Miscellaneous Cost

+ Cost of Purchased Parts +Overheads

= RS (1800+2320+18826+1000 )

HENCE, THE TOTAL COST OF EXPERIMENTAL SETUP = RS 23946/-

CHAPTER 4

TEST PROCEDUREAND RESULTS

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ANALYTICAL PROCEDURE TO MEASURE BOLTPRELOAD

Bolt pretension, also called preload or prestress, comes from the installation

torque T you apply when you install the bolt. The inclined plane of the bolt

thread helix converts torque to bolt pretension. Bolt preload is computed as

follows.

Pi = T/(K D) (Eq. 1)

where Pi = bolt preload (called Fi in Shigley).

T = bolt installation torque.

K = torque coefficient.

D = bolt nominal shank diameter (i.e., bolt nominal size).

Torque coefficient K is a function of thread geometry, thread coefficient of

friction t, and collar coefficient of friction c. Look up K for your specific

thread interface and collar (bolt head or nut annulus) interface materials,surface condition, and lubricant (if any). If you cannot find or obtain K from

credible references or sources for your specific interfaces, then you would

need to research to try to find the coefficients of friction for your specific

interfaces, then calculate K yourself using one of the following two formulas

listed below (Shigley, Mechanical Engineering Design, 5 ed., McGraw-Hill,

1989, p. 346, Eq. 8-19, and MIL-HDBK-60, 1990, Sect. 100.5.1, p. 26,

Eq. 100.5.1, respectively), the latter being far simpler.

K = {[(0.5 dp)(tan + t sec )/(1 t tan sec )] + [0.625 c D]}/D

(Eq. 2)

K = {[0.5p/] + [0.5 t (D 0.75p sin )/sin ] + [0.625 c D]}/D

(Eq. 3)

where D = bolt nominal shank diameter.

p = thread pitch (bolt longitudinal distance per thread).

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= thread profile angle = 60 (for M, MJ, UN, UNR, and UNJ thread

profiles).

= thread profile half angle = 60/2 = 30.

tan = thread helix angle tan =p/(dp).

dp = bolt pitch diameter.

t = thread coefficient of friction.

c = collar coefficient of friction.

D andp can be obtained from bolt tables such as Standard Metric and USA

Bolt Shank Dimensions.

The three terms in Eq. 3 are axial load component (coefficient) of torque

resistance due to (1) thread helix inclined plane normal force, (2) thread

helix inclined plane tangential (thread friction) force, and (3) bolt head or nutwasher face friction force, respectively.

However, whether you look up K in references or calculate it yourself, the

engineer must understand that using theoretical equations and typical values

for K and coefficients of friction merely gives a preload estimate.

Coefficient of friction data in published tables vary widely, are often

tenuous, and are often not specific to your specific interface combinations

and lubricants. Such things as unacknowledged surface condition variations

and ignored dirt in the internal thread can skew the results and produce a

false indication of preload.

The engineer and technician must understand that published K values apply

to perfectly clean interfaces and lubricants (if any). If, for example, the

threads of a steel, zinc-plated, K = 0.22, "dry" installation fastener were not

clean, this might cause K to increase to a value of 0.32 or even higher. One

should also note that published K values are intended to be used when

applying the torque to the nut. The K values will change in relation to

fastener length and assembly running torque if the torque is being read from

the bolt head.

One should measure the nut or assembly "running" torque with an accurate,

small-scale torque wrench. ("Running" torque, also called prevailing torque,

is defined as the torque when all threads are fully engaged, fastener is in

motion, and washer face has not yet made contact.) The only torque that

generates bolt preload is the torque you apply above running torque.

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A few more things to be aware of are as follows. Bolt proof strength Sp is

the maximum tensile stress the bolt material can withstand without

encountering permanent deformation. Published bolt yield strengths are

determined at room temperature. Heat will lower the yield strength (and

proof strength) of a fastener. Especially in critical situations, you should

never reuse a fastener unless you are certain the fastener has never been

yielded.

BOLT PRELOAD MEASUREMENT

If a more accurate answer for bolt preload is needed than discussed above,

the specific combination and lubricant would have to be measuredinstead of

calculated. Measurement methods are generally involved, time-consuming,and expensive. But perhaps one of the simplest and least expensive

methods, to test specific combinations and lubricants, is to measure the

installed fastener with a micrometer, if possible, and compute torque

coefficient K as follows, per Shigley, op. cit., p. 345, para. 2.

K = T L/(E A delta D) (Eq. 4)

where T = bolt installation torque, L = bolt grip length, E = bolt modulus of

elasticity, A = bolt cross-sectional area, D = bolt nominal shank diameter,

and delta = measured bolt elongation in units of length.

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EXPERIMENTAL PROCEDURE

Apparatus used :

Digital torque wrench , load cell, display , dial gauge, setup block, adjustable

spanner , m/c vice, 3 side plate of 15x60x40 with hole dia 8,10,12 and 4 top

plates of 120x60x20 with hole dia of 8,10,12,14 and bolt size of M6 , M8,

M10.

FIG 9

PROCEDURE: First clamp the FIXTURE on the m/c vice

Select the side plate fit to the block to constraint the motion of joint

member

Then select the appropriate bolt corresponding to the above plate

Hold the load cell in the cavity

Then keep the plate on the top side of the load cell and clamp with the

help of bolt and nut

FIG 10

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The bolt is then tightened with the help of digital torque wrench with

desired amount of torque, which is displayed on it.

Then with the same angle load is noted from the display attached to

the load cell

The stretch can be measured with the help of dial gauge or LVDT.

Repeat the same procedure for different bolt sizes

FIG 11

SAMPLE OBSERVATIONS

Table 13

Sr no. Bolt size Torque (N-m) Load (N)

1 M6 21 20000

2 M8 29 20000

3 M10 36 20000

CHAPTER 9

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FUTURE SCOPE

FUTURE SCOPE

To make sure that bolted joints don't fail, you have to accurately tighten

them, achieving correct preload.

When tightening a bolted joint, you must pay attention to the precision of the

preload. If the tightening method doesn't achieve accurate preload, there's a

good chance that the bolted joint won't last, as insufficient preload

commonly causes failure. You can steer clear of this mistakealthough you

won't be able to avoid a degree of bolt preload scatterby learning about the

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main methods of tightening bolts and their distinct features and

characteristics.

Pretension setup when coupled with load cells, LVDT, Optical angle

measurement, strain gauge analogue to digital converters and computers canbe very useful in determining the preload required on the bolt more

efficiently and accurately. Graphs can be plotted in real time and actions can

be taken to prevent the failure of the bolt

With the use of computers the interface between the user and the machine

can be made more user friendly and thus can be useful in detecting the

problems efficiently and effectively. Thus, in future it can be made more

useful.

Different readings can be taken by varying the the types of threads ,length of

the bolt,length of engagement, size of bolts .

CHAPTER 10

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CONCLUSION

CONCLUSION

The concept of project was included in our engineering syllabus with the

view to inculcate within us the application ability of the theoretical concept

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of design and production engineering to practical problems. Also it helped us

to work more as a team rather than an individual.

In completing our project titled DESIGN AND DEVELOPMENT OF

TEST SETUP FOR MEASURING BOLTED JOINT CLAMPING FORCE

we learned while clamping using bolts and nuts how much force or torque

is required at the point of application so that it does not get loosed and also

the compression and tension which is created at the bush and the bolt

respectively while tightening the bolt

REFERANCES

BOOKS

An Introduction to Design and Behavior of Bolted Joint

: JOHN H. BICKFORD

Engineering Mechanism

:ERDMAN AND SANDOR

Machine Design

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: R. S. KHURMI

PSG Design Data

Mechanical Engineering Design

:JOSEPH SHINGLEY, CHARLES MISCHKE

WEBSITES

http:// www.boltscience.com/

http:// www.wikipedia.com/

APPENDIX-A

Load cell

Load cell

A load cell is an electronic device (transducer) that is used to convert a force

into an electrical signal. This conversion is indirect and happens in two

stages. Through a mechanical arrangement, the force being sensed deforms a

strain gauge. The strain gauge converts the deformation (strain) to electrical

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APPENDIX-B

TORQUE WRENCH

A torque wrench is a tool used to precisely set the torque of a fastener such

as a nut or bolt. It is usually in the form of a socket wrench with special

internal mechanisms. A torque wrench is used where the tightness of screws

and bolts is crucial. It allows the operator to measure the torque (rotational

force) applied to the bolt so it can be matched to the specifications. This

permits proper tension and loading of all parts. A torque wrench indirectly

measures torque as a proxy for bolt tension. The technique suffers frominaccuracy due to inconsistent or uncalibrated friction between the fastener

and its mating hole. Measuring bolt tension (bolt stretch) is more accurate

but often torque is the only practical means of measurement.

Electronic torque wrenches

With electronic (indicating) torque wrenches, measurement is by means of a

strain gauge attached to the torsion rod. The signal generated is converted bythe transducer to the required unit of force (N m, lbf.ft etc.) and shown on

the digital display. A number of different joints (measurement details or

limit values) can be stored. These programmed limit values are then

permanently displayed during the tightening process by means of LEDs or

the display. At the same time, this generation of torque wrenches can store

all the measurements made in an internal readings memory. This readings

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memory can then be easily transferred to a PC via the interface (RS232) or

printed straight to a printer. A popular application of this kind of torque

wrench is for in-process documentation or quality assurance purposes.

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