Design of RSW Machine and Investigating weldability of mild steel. B-TECH (Mechanical Engineering)

1. DESIGN OF RESISTANCE SPOT WELDING MACHINE AND
INVESTIGATING WELDABILITY OF MILD STEEL
MAJOR PROJECT REPORT
SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
AWARD OF THE DEGREE OF
BACHELOR OF TECHNOLOGY
(Mechanical Engineering)
SUBMITTED BY
TOSIF MIR (2010EME43)
UMAR ALTAF SHIEKH (2010EME41)
AMAN MAHAJAN (2010EME56)
JUNAID JAHANGIR MIR (2010EME57)
TRIBHUVAN KHAJURIA (2010EME59)
RAJINDER SINGH PARIHAR (2010EME60)
UNDER THE SUPERVISION OF
Dr. Ankush Anand
ASSISTANT PROFESSOR
School of Mechanical Engineering
SHRI MATA VAISHNO DEVI UNIVERSITY
KATRA (J&K), INDIA
MAY 2014

2. CANDIDATES’ DECLARATION
We hereby certify that the project titled “DESIGN OF RESISTANCE SPOT
WELDING MACHINE AND INVESTIGATING WELDABILITY OF MILD
STEEL” submitted to the School of Mechanical Engineering of SHRI MATA VAISHNO
DEVI UNIVERSITY, KATRA is an authentic record of our own work carried out during a
period from Jan. 2014 to May 2014 under the guidance of Dr. Ankush Anand
The matter presented in this major project report has not been submitted by us to
any other University/ Institute for the award of any Degree/ Diploma.
Signature of the Students
UMAR ALTAF SHEIKH (2010EME41)
TOSIF MIR (2010EME43)
AMAN MAHAJAN (2010EME56)
JUNAID JAHANGIR MIR (2010EME57)
TRIBHUVAN KHAJURIA (2010EME59)
RAJINDER SINGH PARIHAR (2010EME60)
This is to certify that the above statement made by the candidate is correct to the best
of my knowledge
Signature of the Supervisor

3. BONAFIDE CERTIFICATE
This is to certify that the project titled DESIGN OF RESISTANCE SPOT
WELDING MACHINE AND INVESTIGATING WELDABILITY OF MILD STEEL is
a bonafide record of the work done by
UMAR ALTAF SHIEKH (2010EME41), TOSIF MIR (2010EME43), AMAN MAHAJAN
(2010EME56), JUNAID JAHANGIR MIR (2010EME57), TRIBHUVAN KHAJURIA
(2010EME59), RAJINDER SINGH PARIHAR (2010EME60) in partial fulfillment
of the requirements for the award of the degree of Bachelor of Technology
in Mechanical Engineering of the SHRI MATA VAISHO DEVI
UNIVERSITY ,KATRA during the year 2013-2014.
Guide Director
Dr. Ankush Anand Dr. Ankush Anand
Asst. Professor School of Mechanical Engineering
SMVDU SMVDU
External Examiner

5. [I]
ACKNOWLEDGEMENT
I take this opportunity to express my profound gratitude and deep regards to our
Guide Dr. Ankush Anand, for his exemplary guidance, monitoring and constant
encouragement throughout the course of this thesis. The blessing, help and guidance
given by him time to time shall carry me a long way in the journey of life on which I
am about to embark.
I also take this opportunity to express a deep sense of gratitude to Mr. Sanjay
Mohan Sharma, Asst. Professor (School of Mechanical Engineering), for his cordial
support, valuable information and guidance, which helped me in completing this task
through various stages.
I am obliged to Mr. Mir Irfan Ul Haq, for the valuable information and technical
help provided by them in their respective fields. I am grateful for their cooperation
during the period of my assignment.
Lastly, I thank almighty, my parents, family and friends for their constant
encouragement without which this assignment would not be possible.
Dated: UMAR ALTAF SHIEKH
TOSIF MIR
AMAN MAHAJAN
JUNAID JAHANGIR MIR
TRIBHUVAN KHAJURIA
RAJINDER SINGH PARIHAR

6. [II]
ABSTRACT
It is necessary that welding doesn’t change properties like geometry, corrosion
protection etc. This may result in complications in case of welding methods
like oxy-acetylene welding. Spot welding overcomes this limitations with less
fume production and less power consumption. There is no need to use any
fluxes or filler metal to create a join by spot welding, and there is no dangerous
open flame. Spot welding can be performed without any special skill.
The designed machine featuring motor operated electrodes offer features like
repeatability, accuracy and constant pressure. It is estimated to give better
results than existing machines like rocker- arm type and press type machine.
Also flexibility in using different thickness combination is studied so as to
increase the use of mild steel sheets combination which is cheap, easily
available and most widely used.
Study deals with finding the most optimized and best combination of welding
current & welding force so that we can find minimum distance to be kept
between welds which gives best shear strength. Also study involve comparison
with existing spot welding machine.

7. [III]
LIST OF TABLES
Table
Title Page
3.1 Step-down Transformer………………………………………………….….44
3.2 Material Comparison ……………………………………………………….45
4.3.1 Testing weld specimen on Designed spot welding machine………………..52
4.4.2 Testing weld specimen on Existing welding machine………………….......54
4.4.3 Test on different sheet combination performed on Designed machine……..55
4.4.4 Test on different sheet combination performed on Existing machine………56

8. [IV]
LIST OF FIGURES
Figure
Title Page
1.1 Construction of dc motor ...................................................................................2
1.2 Schematic diagram of step- down transformer……………………………..….4
1.3 Step Down Transformer…...…………………………………...………..…….5
1.4 Welding Electrodes………………………………………...……….....………6
1.5 Bridge Rectifier Circuit……………………………..……………………........6
1.6 Rectifier Positive Half Cycle…………………………………………………..7
1.7 Rectifier Negative Half Cycle ………………………………..…………….....7
1.8 Speed Reduction Gear- Box…………………….…………...…………….......8
1.9 Typical resistance welding sequence………………………………..………...9
3.1 Components of Mechanism……………………………..……………………14
3.2 Force Calculations…………………………………………..………………..15
3.3 Force Diagram………………………...………………………..…………….16
3.4 Assembly Diagram of Components……………………………..………..….17
3.5 Lower Lever Geometry…................................................................................18
3.6 Upper Lever Geometry…………………….………………………………...19
3.7 T- section Geometry…………………….……………………...……………19
3.8 Mild Steel Vertical Column……………...…………..……………………....21
3.9 Plastic Analysis of Column under Axial Load…………….....……………...23
3.10 Real Beams……………………...…………………………………………...23
3.11 Comparison of Euler & Rankine Gordon formulae………………………….26
3.12 Lateral Buckling of Column……………………………………………..…...22
3.13 Model of T- section…………………………………………………………..28
3.14 Equivalent Stress in Column………………………………………………....29
3.15 Equivalent Stress in case of inverted T- section of Upper Lever………….…30
3.16 Equivalent Principal Stress in case of inverted T- section of Upper Lever …31

9. [V]
3.17 Maximum Principal Stress in Vertical Column……………………..…….....32
3.18 Maximum Shear Stress in case of inverted T- section of Upper Lever...…....33
3.19 Mesh of inverted T- section of Upper Lever………………………………....34
3.20 Mesh in case of Vertical Column …………………………………………....35
3.21 Total Deformation in case of inverted T- section of Upper Lever…….……..36
3.22 Total Deformation in case of Vertical Column……………………………....37
3.23 Design of DC Motor……………..…………………………………………...40
3.24 Performance of DC Motor…………………………………………..………..41
3.25 Gear and Belt Arrangement…………………………………………...……...41
3.26 Motor and Gear Speed Reduction Box.....................................……….……..42
4.1 Mild Steel Samples…………………………………………………………..49
4.2 Tensile Shear Test……………………..……………………………………..50
4.3 Button Pull-out……………………………………………………………….62
4.4 Interfacial fracture Failure……………………………………………………62

10. [VI]
NOMENCLATURE
English Symbols
Pm Maximum Short-Circuit Power
Pc Maximum Conventional Power at 50 Percent Duty Cycle
Ø Field flux
E Electromagnetic force developed at armature terminal (volt)
N Speed (RPM)
Ia Armature current
Mb Maximum bending moment
f Allowable stress of the material of lever
Z Modulus section of the lever
Fc Critical load for failure
σl Stress at which first yield occurs
σm Nominal maximum stress at failure
σc Crushing stress
Pr Rankine- Gordon buckling load

11. [VII]
ABBREVIATIONS
RWMA Resistance Welding Manual
SSRSW Small Scale Resistance Spot Welding
AWS American Welding Society
SAE Society of Automotive Engineers
SSRSW Small Scale Resistance Spot Welding
NEC National Electrical Code
DC Direct Current
RPM Revolutions per minute
F.O.S Factor of safety
M.O.I Moment of Inertia

12. [VIII]
TABLE OF CONTENTS
Title Page No.
ACKNOWLEDGEMENTS........................................................................................... i
ABSTRACT................................................................................................................ ii
LIST OF TABLES....................................................................................................... iii
LIST OF FIGURES...................................................................................................... iv
LIST OF NOMENCLATURE. ……………………..……………………….…..vi
LIST OF ABBREVIATIONS..................................................................................vii
CHAPTER 1 INTRODUCTION
1.1 Overview.................................................................................................................……1
1.2 Application…………………………………………………………………………......1
1.3 Processing………………………………………………………………………………2
1.4 A brief over view of the components…………………………………………………..2
1.4.1 DC Motor……………………………………………………………………...2
1.4.2 Step down Transformer………………………………………………………..4
1.4.3 Welding electrodes…………………………………………………………….5
1.4.4 Bridge rectifier circuit…………………………………………………………6
1.4.5 DC Motor Speed reduction Gear-box………………………………………....7
1.5 Spot welding sequence………………………………………………………………...8
1.6 Spot welding variables ………………………………………………………………..9

13. [IX]
CHAPTER 2 IDENTIFICATION OF NEED
2.1 The Idea.........................................................................................................................11
2.2 Factors for Project Selection… ................................................................................... 12
2.3 Expected Outcome of Project........................................................................... ……...13
CHAPTER 3 DESIGN AND FABRICATION
3.1 Force Analysis............................................................................................................. 14
3.1.1 Components..................................................................................................... 14
3.1.2 Force Calculations.......................................................................................... 15
3.2 Design Procedure and Material Selection....................................................................16
3.2.1 Principle of Lever Design..........................................................................................16
3.3 Material Selection for the Lever...................................................................................17
3.3.1 Material selection for Lower Lever…………..…………………………….18
3.3.2 Material selection for Upper Lever…………………………………….......19
3.3.3 Design of Compression Member…………………………………...………20
3.3.4 Analytical method ………………………………………….…………….21
3.3.5 Rod with bi-axial loading…………………………………………………..22
3.3.6 Rankine- Gordon loading…………………………………………………..24
3.3.7 Study of flexural strength of T-section………………………………….....26
3.3.8 Calculation Based on ANSYS…………………………………………………..28
a) Equivalent Stress in column……………………………………………..29
b) Equivalent Stress in case of inverted T-section………………………....30
c) Maximum Principal Stress in inverted T-section………………………..31
d) Maximum Principal Stress in Vertical Column……………………..…..32
e) Maximum Shear Stress in inverted T-section……………………….......33
f) Mesh of inverted T-section………………………………………………34
g) Mesh in case of Vertical Column……………………….…………….....35
h) Total Deformation in case of inverted T-section……………………......36
i) Total Deformation in case of Vertical Column…………………………..37
j) Analysis of Rectangular Section…………………………………………38

14. [X]
3.4 DC Motor Specifications……………………………………………………………...40
3.4.1 Speed reduction Gear box…………………………………………………………..41
3.4.2 Belt used…………………………………………………………………………….42
3.5 Step down transformer………………………………………………………………..44
3.6 Material Selection………………………………………………………………….…45
CHAPTER 4 EXPERIMENTS AND RESULTS
4.1 Abstract of Experiments................................................................................................48
4.2 Introduction……….......................................................................................................48
4.3 Experimental Procedure……….. .................................................................................49
4.3.1 Testing on Designed Machine…………………………………………………...….49
4.3.2 Testing on Existing Machine…………………………………………………...…...50
4.4 Tables………………………………………………………………………………....51
4.5 Graphs…………………………………………………………………………….......57
4.5.1 Shear testing on Designed machine………………………………………………...57
4.5.2 Shear testing on Existing machine……………………………………………….....58
4.5.3 Shear testing on Designed machine……………………………………………..….59
4.5.4 Shear testing on Existing machine……………………………………………….....59
4.5.5 Strength Comparison on the basis of Force variation….…………………………...60
4.5.6 Strength Comparison on the basis of Force variation….…………………………...60
4.5.7 Strength Comparison on the basis of sheet combination on Designed machine……61
4.6 Experimental Results and Discussions………………………………………….….....62
CHAPTER 5 CONCLUSIONS
5.1 CONCLUSIONS ........................................................................................................ 63
REFRENCES…………………………………………………………………………......64

15. [XI]

16. [XII]

17. [XIII]

18. [XIV]

19. Page | 1
CHAPTER 1
INTRODUCTION
1.1 OVERVIEW
Resistive spot welding (RSW) is a process in which contacting metal surfaces are joined
by the heat obtained from resistance to electric current. Work-pieces are held together
under pressure exerted by electrodes. Typically the sheets are in the 0.5 to 3 mm (0.020
to 0.118 in) thickness range. The process uses two shaped copper alloy electrodes to
concentrate welding current into a small "spot" and to simultaneously clamp the sheets
together. Forcing a large current through the spot will melt the metal and form the weld.
The attractive feature of spot welding is that a lot of energy can be delivered to the spot
in a very short time (approximately 10 - 100 milliseconds).That permits the welding to
occur without excessive heating of the remainder of the sheet.
The amount of heat (energy) delivered to the spot is determined by the
resistance between the electrodes and the magnitude and duration of the current. The
amount of energy is chosen to match the sheet's material properties, its thickness, and
type of electrodes. Applying too little energy will not melt the metal or will make a
poor weld. Applying too much energy will melt too much metal, eject molten material,
and make a hole rather than a weld.
1.2 APPLICATIONS
Spot welding is typically used when welding particular types of sheet metal, welded
wire mesh or wire mesh. Thicker stock is more difficult to spot weld because the heat
flows into the surrounding metal more easily. Spot welding can be easily identified on
many sheet metal goods, such as metal buckets. Aluminium alloys can be spot welded,
but their much higher thermal conductivity and electrical conductivity requires higher
welding currents. This requires larger, more powerful, and more expensive
welding transformers.
Spot welding of BMW 3 series car bodies with KUKA Industrial Robots
Perhaps the most common application of spot welding is in
the automobile manufacturing industry, where it is used almost universally to weld the
sheet metal to form a car. Spot welders can also be completely automated, and many of
the industrial robots found on assembly lines are spot welders (the other major use for

20. Page | 2
robots being painting). In the North American automobile industry there are
approximately 100 billion spot welds, which are done every year.
Spot welding is also used in the orthodontist's clinic, where small scale spot welding
equipment is used when resizing metal "molar bands" used in orthodontics.
Another application is spot welding straps to nickel-cadmium or nickel-metal-hydride
cells to make batteries. The cells are joined by spot welding thin nickel straps to the
battery terminals. Spot welding can keep the battery from getting too hot, as might
happen if conventional soldering were done.
1.3 PROCESSING
Spot welding involves three stages; the first of which involves the electrodes being
brought to the surface of the metal and applying a slight amount of pressure. The current
from the electrodes is then applied briefly after which the current is removed but the
electrodes remain in place for the material to cool. Weld times range from 0.01 sec to
0.63 sec depending on the thickness of the metal, the electrode force and the diameter
of the electrodes themselves.
1.4 A Brief Overview of the Components:
1.4.1) DC Motor:
Direct-current motors, as the name implies, use direct uni-directional current. DC
motors are used in special applications where high torque starting smooth acceleration
over a broad speed range is required.
Fig. 1.1 Construction of dc motor

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A dc motor has three main components:-
Field Pole:- Simply put, the interaction of two magnetic fields causes the rotation in a
DC motor. The DC motor has filed poles that are stationary and an armature that turns
on bearings in the space between the field poles. A simple DC motor has two field
poles: a north pole and a south pole. The magnetic lines of forces extend across the
opening between the poles from north to south.
Armature:- When current goes through the armature, it becomes an electro-magnet.
The armature, cylindrical in shape, is linked to a drive shaft in order to drive the load.
For the case of a small dc motor, the armature rotates in the magnetic field established
by the poles, until the north and south poles of the magnets change locations with
respect to the armature. Once this happens, the current is reversed to switch the south
and north poles of the armature.
Commutator:- This component is found mainly in dc motor. Its purpose is to overturn
the direction of the electric current in the armature. The commutator also aids in the
transmission of current between the armature and the power source. The main
advantage of dc motor is speed control, which does not affect the quality of power
supply. It can be controlled by adjusting armature voltage- increasing the armature
voltage will increase the speed of the field current- reducing the field current will
increase the speed
Back electromagnetic force: E=ØKN
Torque T=KØIa
Where Ø= field flux which is directly proportional to field current
E= Electromagnetic force developed at armature terminal (volt)
N= Speed (RPM)
Ia= Armature current
K= an equation constant

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1.4.2) Step- down Transformer
Working Principle of transformer:
Fig 1.2 Schematic diagram of Step- down Transformer
An important property of electricity is that a magnetic field is produced around a wire
when electric current is flowing. The more current flowing, stronger the magnetic field.
An uniformly stronger magnetic field can be produced by winding the magnetic field
into a coil. Now the magnetic field of adjacent wires add together to form one strong
magnetic field.
The electric current flowing in a transformer is alternating current. As a result, current
first flows in one direction, stops then, reverses and flow in the other direction. So, the
magnetic field around the winding is constantly in motion. When a magnetic field
moves around a wire, a voltage is induced into the wire.
If a second coil of wire is placed in a moving magnetic field, then the voltage can be
induced in the second coil. Electric energy is converted into a magnetic field and then
converted back into a electric energy in the second winding. The trick is to do this with
little or no loss of energy.

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Fig 1.3 Step Down Transformer
The magnetic field loses strength quickly in air, therefore, a special steel core is
used.The core is composed of thin sheet of a silicon- steel alloy. The magnetic field is
concentrated in the core and the energy loss is reduced to a minimum.
1.4.3 Welding Electrodes:
To achieve the desired current density within a small region, electrodes are used. It is
important to have a proper electrode shape for which three main types of electrodes are
used; these are pointed, domed, and flat electrodes.
Pointed Tips: Pointed tips are most widely used particulars for ferrous materials; with
continued wear they mushroom uniformly. The pointed electrodes are basically
truncated cone electrodes with an angle of 120 degree to 140 degree.
Domed Electrodes: Domed electrodes are characterized by their ability to withstand
heavier pressure and serve heating without mushrooming which makes them
particularly useful for welding non-ferrous metals.
Off-set Electrodes: Offset electrodes can be used to make spot welds in places that are
inaccessible to weld by conventional type electrodes e.g. for making corner welds, and
for welding parts with overhanging flanges.

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Fig.1.4 Welding Electrode
1.4.4 Bridge Rectifier Circuit:
The four diodes labelled D1 to D4 are arranged in “series pairs” with only two diodes
conducting current during each half cycle. During the positive half cycle of the supply,
diodes D1 and D2 conduct in series while diodes D3 and D4 are reverse biased and the
current flows through the load as shown below.
Fig 1.5 Bridge Rectifier Circuit

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The Positive Half-Cycle
Fig. 1.6- Rectifier Positive Half Cycle
During the negative half cycle of the supply, diodes D3 and D4 conduct in series, but
diodes D1 and D2switch “OFF” as they are now reverse biased. The current flowing
through the load is the same direction as before.
The Negative Half-Cycle
Fig. 1.7- Rectifier Negative Half Cycle
As the current flowing through the load is unidirectional, so the voltage developed
across the load is also unidirectional the same as for the previous two diode full-wave
rectifier, therefore the average DC voltage across the load is 0.637Vmax.
1.4.5 DC Motor Speed Reduction Gear Box:
Power transmission box attached to d.c motor for changing velocity ratio and axis of
rotation. It consists of four pulleys and two belts. It is a compound belt drive as shown
in figure.

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Fig.1.8 Speed Reduction Gear Box.
1.5 Spot Welding Sequence:
All resistance welding operations are automatic and therefore all process variables are
pre-set maintained constant. Once a welding operation has been initiated there is no
way in which its progress can be controlled and thus the weld cycle is completed as per
the pre-set times.
Welding Cycle: The welding cycle for spot welding machine, seam welding machine
and projection welding machine consists basically of four elements viz., squeeze time,
weld time, hold time, and off time. These timings are pre-set for a particular metal and
a thickness range and the shop operator normally cannot change them on his own. Each
one of these four time phases has its own role to play in achieving a sound weld of the
required size.
Squeeze Time: The time interval between the application of electrode pressure to the
work and switching on the welding current is called the squeeze time. This time interval
is provided to assure contact between the electrode and the work and to initiate the
application of force on it.
Weld Time: It is the time for which the welding current actually flows to melt the metal
at the interface.

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Hold Time: It is the time for which the electrodes are kept in position, after the welding
current is switched off, to assure the application of pressure so as to consolidate the
molten metal into a nugget which is then cooled by the dissipation of heat to the
surrounding work material. If the applied force is excessive it may result in expulsion
of molten metal from in-between he sheets.
Off Time: The time allowed to shift the work to the next location before the cycle is
repeated is referred to as the off time. The electrodes are kept off the work during this
time interval.
1.6) Spot welding variables
Welding current, time of current flow and the electrode pressure are recognized as the
fundamental variables of resistance spot welding. For achieving quality weld is most
metals, these variables are required to be kept within very close limit.
Welding Current: In spot welding machine size of the weld nugget, and the in fact
whether it will form or not depends upon the heat being generated faster than it is
dissipated by conduction. Welding current is, thus the most critical variable.
Most application use single phase a.c. of mains frequency i.e. 50 hertz. However, d.c.
is used for applications that need heavy current and the load for which can be balanced
on a 3-phase power line.

28. Page | 10
Pressure Control: Application of pressure through the electrode onto the work piece
ensures the completion of the electrical circuit. The force is applied by hydraulic,
pneumatic, magnetic, or mechanical means. The pressure exerted depends upon the area
of contact between the electrode and the work.
The application of pressure serves a number of functions e.g.
a) Brings the work pieces in close contact,
b) Reduces the initial contact resistance at the interfaces,
c) Suppresses metal expulsion between the work pieces,
d) Consolidates the molten metal into sound weld nugget.

29. Page | 11
CHAPTER 2
IDENTIFICATION OF PROJECT
2.1) The Idea
Rocker arm type is one of the most widely used type of spot welding involving applying
pressure by foot. To get desired mechanical strength it is necessary to get repeatability
in weld size i.e. constant pressure, constant weld time, constant strength, nugget
diameter, hardness etc which is almost impossible in this case. In rocker-arm type,
inability to have constant time makes it difficult to avoid expulsion and interfacial
failure. Another alternative is press type spot welding machine involving use of air
vessel which suffers from disadvantages like maintenance cost, cylinder rebuilding,
non-repeatability and poor efficiency (high power consumption). So use of motor which
offer features like accuracy, repeatability in position for end of strokes, high efficiency
(+85%), time adjustment and energy consumption only during operation, can serve the
purpose.
Use of mild steel in applications like barrels, drums etc
involves multiple welds, so it is important to know minimum distance between two spot
welds to get desired shear strength. Test method like shear testing on universal testing
machine enable us to know the spacing between welds so as to avoid failures. Also it is
important to know weld strength when combination involving different thickness of
sheet is used.
To test whether motor enables us to get desired strength,
comparison of results with rocker-arm type spot welding machine for lower current
range is to be carried to find whether it is efficient or not.

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2.2) Factors for Project Selection:
Limitations of various Existing Spot Welding Machine:
1) Force applied is not constant which doesn’t gives a proper weld.
2) Inability of the welder to know the proper force required for spot weld.
3) There is a lot of exhaustion for the welder as work has to be done against stiffer spring.
Due to spring failure if any take place, the whole machine will not work.
4) In case of pneumatic welding machine, it is difficult to maintain the repeatability, tip
contact the part at high speed generating high impact on part. A spare part inventory
has to be maintained due to different mounting requirements.
Due to the following limitations of the existing spot welding machine, we have
designed a motor operated RSW machine keeping in view the above mentioned
problems. We have overcome these problems. The advantage of our designed machine
are as under:-
1) Due to the incorporation of dc motor the exhaustion factor of welder is completely
eliminated which is the main advantage.
2) Proper force is maintained required for desired spot weld.
3) Constant weld force application and constant time consumption.
4) Due to spring elimination, the motor has the ability to bring back the electrodes at
desired position, thus eliminating the spring failure.
5) Minimum environmental impact such as noise, contamination, energy/power
efficiency.
6) Reduced or no spare parts inventory required.
7) Motor requires energy supply when only in action.
8) Taking in consideration the load carrying capacity with F.O.S of mild steel in various
members, minimum material is used. Thus, weight is reduced.
9) The cost factor is taken into study by using mild steel which is cheap and has good
mechanical properties compared to aluminium and stainless steel.

31. Page | 13
2.3) Expected Outcome of Project:
1) A new idea has been generated which will result in less time consumption, less labour
effort and cheaper way of spot welding equipment or machine is designed.
2) Proper investigations of welds is done on mild steel on varying thicknesses which
increases the utilization of spot welding in various applications.
3) Welding distance plays an important role which can be proved by shear testing.
4) Taking in consideration the ability of designed machine having controlled parameters
like weld force, weld current, accuracy and repeatability, the strength is better than
existing machines.

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CHAPTER 3
DESIGN AND FABRICATION
3.1) Force Analysis:
3.1.1) COMPONENTS
Fig 3.1 Components
a) Lower Lever: Rectangular section is pin- jointed with vertical column
b) Vertical column: Solid circular section which is hinged at bottom and fixed at
top with t- section.

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c) Upper Lever: T-section is attached with electrode holder and is pivoted at
fulcrum point
3.1.2 Force Calculation:
Fig 3.2 Force Calculations
Since normal force a human can apply by foot is around 850N.
Taking this into consideration we have designed our machine accordingly. The
range of force at electrodes should be between 0.9-1.1KN.
By taking into account the diameter of vertical column, geometry of t- section and
length of electrode holder, and applying the designed equation for levers
which is

34. Page | 16
P*l2=F*l1
we have calculated the value of force at electrode which comes out to be 0.9KN
which is well within the range.
3.2) Design Procedure and Material Selection
Fig.3.3 Machine Design
Designing a lever means determining the physical dimensions of the lever when forces
acting on the lever are specified. In a machine we have to design two levers.
1)Upper lever
2)Lower lever
3.2.1) PRINCIPLE OF LEVER DESIGN
a) The lever may be straight or curved.
b) The forces applied by the lever or on the lever may be parallel or may be inclined to
one another. The principle of lever is same as that of moments.

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3.3) MATERIAL SELECTION FOR THE LEVER
For any kind of lever the section at which the maximum bending moment occurs
can be determined by strength equation.
Mb=f*z
where
Mb is the maximum bending moment
f is the allowable stress of the material of lever
z is the modulus section of the lever
Fig 3.4 Assembly diagram of components.

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3.3.1) MATERIAL SELECTION FOR LOWER LEVER
Fig 3.5 Lower lever geometry
For lower lever maximum bending moment is,
B.M=136N-m
Modulus section for rectangular section,
z=1/6*t*h*h
where
t is the thickness
h is the height
t=10mm=.01m
h=3.8cm=.038m
z=2.407*10-6
m3
B.M=f*z
f=B.M/z
f=56.51Mpa
The yield strength of Mild Steel is 250Mpa
Maximum allowable stress=yield strength/F.O.S
If we will take factor of safety 2
Maximum allowable stress for Mild Steel will be 125Mpa. It comes well within our
range, so the material used for making lower lever is Mild Steel.

37. Page | 19
3.3.2) MATERIAL SELECTION FOR UPPER LEVER
Fig 3.6 Upper lever geometry
Maximum Bending Moment B.M=238N-m
The section for on the left side of the fulcrum point of the upper lever is a T-section.
z=I/Y, where
I is the Moment of Inertia
and Y is the deflection
z= I/Y=.02874/.005=5.75m
f=B.M/z=238/5.75=42Mpa
Fig 3.7 T-section geometry

38. Page | 20
The yield strength of mild steel is 250Mpa
Maximum allowable stress=yield strength/F.O.S
If the F.O.S is taken 2, the maximum allowable stress for mild steel is well within
range.
3.3.3 Design of Compression Member:
Software based calculations:
Column Length= 0.66m
Cross-section area= 1.075cm2
Second Moment of area= 0.0919 cm4
Distance of neutral axis= 0.00585cm
Yield Strength= 250MPa
Compressive Yield Strength= 160MPa
RESULTS
Effective length constant= 0.8
Radius of gyration of column= 2.92mm
Slenderness ratio of column= 225.73
Effective slenderness ratio of column = Seff= 180.58
Critical load for Failure Fc= 6832.3N
Allowable load including design factor= 3416.5N
Column Category= Long column with central loading

39. Page | 21
Fig 3.8 Mild steel vertical column
3.3.4 ANALYTICAL METHOD
Calculation of Euler’s load for different materials:
Ø= Diameter= 0.0117m
I= ᴨ d4
/64 for solid shaft
L= length= 66cm
For one end hinged and one end fixed

40. Page | 22
1. Mild Steel: 3. Stainless Steel:
Pe=8.964KN Pe=6.9KN
2. Aluminium: 4. Cast iron:
Pe= 3.07KN Pe= 2.817KN
Here
Ø= Diameter= 0.0117m
As l > 30d
So it is an example of long column.
3.3.5 Rod with Bi-axial Loading:
If axial load is applied with an eccentricity, in a plane of symmetry, a column will
deflect but remains un-twisted at loads less than the buckling load. But if column is
loaded with bi-axial loading with eccentricity, it will usually deflect and twist at any
load. So circular section column which is symmetrical is preferred.
Basic Concept:
The differentiating feature is the relation between stress and strain. The extreme
difficulty in obtaining an exact plastic analysis of column under axial loading, even
with the aid of digital computers, is due to the fact that stress-strain relation in the plastic
range is far more complicated than Hooke’s law for linear elastic material. Further
complicity that the plastic boundary is moving and relation is different.

41. Page | 23
Fig 3.9 Plastic Analysis of Column under Axial Load
Buckling of Real Beam:
When the beam is bent in its stiffer principal plane, it usually deflects in that plane. If
not stiff then will bent. Load must always be less than its load carrying capacity. Lateral
buckling involves lateral bending and axial torsion.
I and T section resistance to lateral bending and torsion is low. Slender beam will only
bend after yielding. For intermediate, will bent even before buckling.
In reality, columns deflects as soon as loading is commenced and deformation increases
rapidly as the critical buckling load is approached. In such cases there is a limiting stress
σl at which first first yield occurs.
σm = nominal maximum stress at failure.
Fig 3.10 Real Beams

42. Page | 24
3.3.6 Rankine-Gordon formula
Predictions of buckling loads by the Euler formula is only reasonable for very long and
slender struts that have very small geometrical imperfections. In practice, however,
most struts suffer plastic knockdown and the experimentally obtained buckling loads
are much less than the Euler predictions. For struts in this category, a suitable formula
is the Rankine4ordon formula which is a semi-empirical formula, and takes into account
the crushing strength of the material, its Young's modulus and its slenderness ratio,
namely l/k, where
L = length of the strut
k = least radius of gyration of the strut's cross-section
Pc = σc A
where A = cross-sectional area
σc = crushing stress
For Mild steel
Ø= Diameter= 0.0117m
σc= 300MPa
Pr= 7.042KN which is safe
For Cast Iron
σc= 572MPa

43. Page | 25
Pr=2693KN
With higher F.O.S it is more prone to failure.
Fig 3.11 Comparison of Euler & Rankine Gordon formulae
3.3.7 Study of Flexural Strength of T-section:
Flexure strength of t-section
a) Lateral buckling of a narrow beam:
Problems of structural instability are not entirely to compression members. In case of
deep beams, lateral buckling may occur involving torsion and bending perpendicular to
the plane of depth of beam.
As we know

44. Page | 26
Fig 3.12 Lateral buckling of columns
a) Using Mx= 230N-m in above equation
σcr =34MPa
which is well within range of mild steel. So we have safe structure.
b) G=80GPa & J=4.5699*10-8
m4
=> GIy= 3655.92
E= 210GPa & Iy= 3.793*10-8
=> EIy= 7965.3
Mcr= 48.42KN-m
σcr =71.7MPa

45. Page | 27
value comes out to be within limit as yield stress is 300MPa for mild steel.
b) Stress generated in T- section at the time of contact:
At the time of contact of electrodes, the fulcrum is restricted to move further by frame
of the machine.
σx = M*y/Iy
Y= 0.0064m
Iy= 3.793*10-8
σx= 39.15MPa

46. Page | 28
3.3.8 Calculation Based on ANSYS:
Fig 3.13 Model of t-section

47. Page | 29
a) Equivalent Stress in Column:
Fig. 3.14 Equivalent Stress in Column
Maximum Stress= 3.4 MPa (around pin- joint)
Minimum Stress= Almost negligible at fixed end of column

48. Page | 30
b) Equivalent Stress in case of inverted T-section:
Fig. 3.15 Equivalent Stress in case of inverted T-section
Maximum Equivalent Stress= 71MPa (near free surface of web of t- section close to
fulcrum point)
Minimum Equivalent Stress= 21KPa
Maximum Equivalent Stress is less than yield stress of mild steel which is 300MPa

49. Page | 31
c) Maximum Principal Stress in inverted T-section:
Fig 3.16 Maximum Principal Stress in inverted T-section
Maximum principal stress= 46MPa (in flange of inverted t- section)

50. Page | 32
d) Maximum Principal Stress in Vertical Column:
Fig 3.17 Maximum Principal Stress in Vertical Column
Maximum Principal Stress= 3.8MPa
Minimum Principal Stress= 0.39MPa

51. Page | 33
e) Maximum Shear Stress in inverted T-section
Fig 3.18 Maximum Shear Stress in inverted T-section
Maximum Shear Stress= 36MPa (near free surface of web of t- section close to
fulcrum point)
Minimum Shear Stress= 11KPa

52. Page | 34
f) Mesh of inverted t- section
Fig 3.19 Mesh of inverted t- section

53. Page | 35
g) Mesh in case of Vertical Column
Fig 3.20 Mesh in case of Vertical Column

54. Page | 36
h) Total Deformation in case of inverted t-section
Fig 3.21 Total Deformation in case of inverted t-section of upper lever
Maximum Deformation= 0.87mm

55. Page | 37
i) Total Deformation in case of Vertical Column
Fig 3.22 Total deformation in case of vertical column

56. Page | 38
j) Analysis of Rectangular Section:
Total Deformation:
Equivalent Stress:

57. Page | 39
Maximum Principal Stress:
Maximum Shear Stress:
l)
Clearly, no deformation until load reaches the critical value as per Euler load

58. Page | 40
3.4) DC Motor Specifications
Made= Globe Motors
Part no. = 403A441
Series= E2400 IM 15 MOTORS
Number Prefix= 403A- IM15 Motor
Power Rating= 0.03hp= 22.4W
Voltage= 12VDC
Shaft= Hardened Stainless steel
Options= flats, pinions, gears etc.
Magnet= high energy ceramic to provide greater torque and high pulse current.
Bearings= Ball bearings- Pre-loaded to have higher side loads.
Cables/leads= #20AWG, 2 leads UL style 1180 (polyester or polyurethane)
Cover= Steel housings, zinc plate
End Bells= Die-Cast zinc
Winding insulation rating= 1800
C (H-class)
RPM= 6000
Current (mA) = 0.250
Rated torque= 0.028N-m
Fig 3.23 Design of DC Motor

59. Page | 41
Temp. = 8.50
C/watt
Resistance= 2.25Ώ
Typical Motor Performance:
Fig 3.24 Performance of dc motor
3.4.1 Speed Reduction Gear Box
Intermediate or Counter-shaft
Gear Material: Plastic
Fig. 3.25 Gear and Belt Arrangement

60. Page | 42
Fig. 3.26 Motor and Gear Reduction Box
Dia. of first pulley (input pulley) = 8.2mm
Dia. of second pulley (intermediate or counter shaft pulley) = 40mm
Dia. of third pulley (intermediate or counter shaft pulley) =8.2mm
Dia. of fourth pulley (output pulley) =40mm
Thickness of the belt=1.22mm
V.R=N2/N1= D1/D2
Velocity ratio=0.0522
Therefore, RPM of output shaft is reduced and the value of
RPM comes out 313.2.
3.4.2 Belt Used
Timing Belt-A timing belt is a belt that usually features teeth on the inside surface.
Timing belts are part of synchronous drives which represents an important category of
drive. These drive employs the positive engagement of two sets of meshing teeth.
Hence, they don’t slip and there is no relative motion between elements of mesh. Hence,
parts will maintain a constant speed ratio or even the permanent relative position.
Motors which are usually the largest heat source, can be placed away from the
mechanism. Achieving this with a gear train would represent an expensive solution.

61. Page | 43
There is no slippage nor creep as with flat belt. These belts don’t require lubrication.
Speed is transmitted uniformly as there is no chordal rise and fall of the pitch line. The
tooth profile of most commonly used synchronous belts is of trapezoidal shape with
sides being straight lines which generate an involute, similar to that of a spur gear tooth.
As a result, profile of a pulley teeth is involute.
Backlash between pulley and belt is negligible.
Material: Timing belts are made of rubberized fabric and steel wire and have teeth that
fits into grooves cut on the periphery of the sprocket.
DESIGN
Design is similar to V-belts
GATES 2MR-152-08 566-2576 106MC
Where 152= 15.2cm= Length of belt
2MR represent 2 is the Belt pitch
08 represents the width
566-2576 represents the Part no.
MC represents the modified Curvilinear
Weight= 4.5g
No. of teeth = 76

62. Page | 44
3.5 STEP DOWN TRANSFORMER
Power Rating= 10KVA
Cool Style= Air Cooled
Phase =Single
Electrode Material = Copper
Electrode Face Diameter= 4mm
Maximum Sheet thickness= 1mm+1mm
Material Selection= Mild Steel, Galvanized Iron
STEP CURRENT(A)
Step1 600A
Step2 800A
Step3 1000A
Step 4 1300A
Step 5 1600A
Step 6 2000A
Table 3.1 Step down Transformer

63. Page | 45
3.6 Material Selection
Before we select the right material, it is important to know the properties of all the
possible choices.
PROPERTY Cast Iron Stainless Steel Aluminium Mild Steel
1 Bulk modulus 43-130 GPA 163GPA 0.017 to 72GPA 159GPA
2 Elastic modulus 66-176GPA 163-204GPA 0.02-74GPA 210GPA
3 Density 7.1-7.2g/cm3 7.5-8.1g/cm3 0.1-2.84g/cm3 7.8g/cm3
4 Hardness(Brinell) 130-480 200 30-95 85-105
5 Elongation at break 0.6-18% 1-60% 0.01-43% 19-30%
6 Poisson's ratio 0.26-0.275 0.29 0.31-0.34 0.3
7 Fracture toughness 14-160(MPa · m1/2) 50(MPa · m1/2) 24(MPa · m1/2) 50(MPa · m1/2)
Stiffness to weight ratio)
8 Tensile(MN-m/kg) 9.4-24 20-26 0.2-26 26-47
9 Bulk(MN-m/kg) 6.8-18 0.17-26
10 Shear(MN-m/kg) 4.6-12 0.1-13
Strength to weight ratio
11 Tensile(kN-m/kg) (Yield) 13-150 21-160 0.4-180 21-39
12 Tensile strength (Ultimate) 152-1400MPA 415-1970MPA 124-310MPA 380-440MPA
13 Yield strength 13-150MPA 170-1900MPA 0.04-505MPA 370MPA
14 Electrical conductivity 1.02MS/m 27.26MS/m 6.96MS/m
15 Fatigue Strength 250MPA 0.02-160MPA 193MPA
16 Resilience(Impact absorption) 30kg/cm2 24.6kg/cm2 11.5kg/cm2 30kg/cm2
17 Crushing Strength 572-2200MPA
Table 3.2 Material Comparison
Results:
1) Bulk Modulus: A measure of a material's resistance to reduction in volume due to
compression from all sides.
Mild Steel and Stainless steel has good compression resistance which acts on column
beam after completion of weld cycle.
2) Elastic Modulus: A measure of a material's stiffness, expressed as the stress required
to produce a unit of elastic strain in the same direction. So it is resistance to tension.

64. Page | 46
Aluminium has poor elasticity
3) Density: More the density, more will be increase in weight.
Clearly, stainless steel will have more weight compared to mild steel. So, dc motor
selection have to be done on the basis on weight to be lifted.
4) Hardness: A test-specific measure of a material's resistance to mechanical penetration
(indentation) of its surface. All hardness values are reported as belonging to
some hardness scale. Some of the most popular scales are Brinell, Knoop, Rockwell,
Shore, and Vickers.
Cast iron is very hard so chances of cracks are always which can propagate further with
time. Aluminium is highly ductile in nature. Mild steel is within range.
5) Elongation at break: Elongation between zero stress and final rupture, as a percent of
original specimen length. For example, a 1 meter specimen that stretches to 1.1 meters
before breaking in two has 10% elongation at break.
A material must have lower elongation as higher the elongation more will be skidding
problem during weld. Mild Steel provides good value.
6) Fracture toughness: A measure of a material's resistance to the propagation of an
existing crack. Useful for evaluating the material's ability to resist the effects of
fabrication defects and operational damage on mechanical service.
Stainless steel on bending loses its properties to great extent so lower will be its fracture
toughness. Alternative is Mild Steel.
7) Fatigue Strength:The maximum amount of tensile stress that can be applied to a
material over somewhere near 107
cycles without causing failure. The fatigue strength
for a Test with just one cycle is equal to the ultimate tensile strength (UTS). As the
number of cycles increases, the value decreases. Some metals (most steels, some
brasses, and a few others) will eventually floor out, so that, past a certain number of
cycles, the maximum allowed stress per cycle will no longer decrease. This is called
the endurance limit.
Fatigue Strength of mild steel and stainless steel is good.

65. Page | 47
A) Material Selection for Rod:
1) Mild Steel and Stainless Steel has almost the same deflection as elastic modulus of all
the grade of steel is almost the same.
2) If worried about wear, hardness and thus heat treatment of metal is to be taken into
account. If resilience is not proper, wear occurs and causes failure.
3) Most common grades of steel are softer than stainless steel. Look for hard steel
(hardened shafting steel). Mild steel gives good result as far as deflection is concerned.
4) Member can undergo bending and the industry responded with conventional wisdom-
just increase the wall thickness of the entire rod to make it stronger.
B) Circular Rod Selection:
1) Screw threads with spring is required to vary the horn clearance (spacing) between two
electrodes. As electrodes wear, spacing between them is to be altered so that tips of
electrodes can generate required contact resistance. So I-section or T-section cannot be
used.
2) It has well within range load carrying capacity.
3) Less weight.
4) Less space required.
5) I-section which has better strength is difficult to manufacture of same area as circular
beam.
6) I section suffers the problem of eccentric loading, so bending with torsion occurs.

66. Page | 48
CHAPTER 4
EXPERIMENTS AND RESULTS
4.1) Abstract of Experiment:
The resistance weldability of 0.8mm and 1mm thick sheet of mild steel is to be found.
The shear strength is checked in case of multi- spot weld. Experiment involves variation
of distance between two spot welds at different current levels with constant force and
time. Optimized distance to be kept between two spot welds is found which yields
maximum shear strength. Results are obtained on both the designed machine and
existing machine. As designed machine offers features like repeatability, accuracy,
constant time, constant pressure, it is estimated to give better results than existing
machine. Also flexibility in using different thicknesses is studied so as to increase the
use of mild steel sheet combination in different applications. Strength obtained due to
different electrode diameters is studied.
4.2) Introduction
It is necessary that welding doesn’t change characteristics like geometry, corrosion
protection, mechanical properties etc. This complications may occur in case of TIG,
oxy acetylene welding. Spot welding overcomes these limitations with less fumes
production, less power consumption and high efficiency. An important feature of spot
welding is that there is no increase in weight as filler metal is not used in this case.
It becomes important to know best combination of welding current, weld time,
electrode force and distance to be kept between welds to get best shear strength result.
Study of modes of failure is also critical in spot welding. By controlling the welding
parameters some of the unacceptable failure modes can be avoided.

67. Page | 49
Fig 4.1 Mild Steel Samples
4.3) Experimental Procedure:
4.3.1) Testing on Designed Machine:
Welding set-up includes designed new motor operated mechanism with 5KVA
transformer, motor with 12VDC input which generates a weld force of 0.9-1.1KN.
Sheet range is suitable for 1.0mm+1.0mm and material includes mild steel and
galvanized iron.
1) Mild steel sheets (0.8mm+0.8mm) are welded by varying distance between two welds.
Results are obtained for different current values, by keeping force and time constant.
2) Mild steel sheets (1.0mm+ 1.0mm) are welded by varying distance between two welds.
Results are obtained for different current values, by keeping force and time constant.
3) Mild steel sheets (1.0mm+0.8mm) are welded by varying distance between two welds.
Results are obtained for different current values, by keeping force and time constant.

68. Page | 50
4.3.2 Testing on Existing Machine
10KVA step down transformer with gun metal electrodes (88% Cu) with uncontrollable
weld time and weld force is used.
1) Mild steel sheets (0.8mm+0.8mm) are welded by varying distance between two welds.
Results are obtained for different current values, by keeping force and time constant.
2) Mild steel sheets (1.0mm+ 1.0mm) are welded by varying distance between two welds.
Results are obtained for different current values, by keeping force and time constant.
3) Mild steel sheets (1.0mm+0.8mm) are welded by varying distance between two welds.
Results are obtained for different current values, by keeping force and time constant.
Result obtained for different current range, distance between welds and sheet
thicknesses are obtained and are compared. Also best combination of welding
parameters in designed machine is obtained to get maximum strength.
Tensile Shear Test
Fig 4.2 Tensile Shear Test

69. Page | 51
TABLES

70. Page | 52
4.3.3 Tables:
4.3.1 Testing weld specimen on Designed spot welding machine
Experiment no. 1
Weld Id Current Thickness Force Distance between welds Shear Strength
1 800A 1mm 0.9KN 1.5cm 3608 N
2 800A 1mm 0.9KN 2.0cm 6080 N
3 800A 1mm 0.9KN 2.5cm 2196 N
4 1300A 1mm 0.9KN 1.5cm 3800 N
5 1300A 1mm 0.9KN 2.0cm 7600 N
6 1300A 1mm 0.9KN 2.5cm 7596 N
6.1 1600A 1mm 0.9KN 1.5cm 4736 N
6.2 1600A 1mm 0.9KN 2.0cm 9600 N
6.3 1600A 1mm 0.9KN 2.5cm 7981 N
7 1000A 1mm 0.9KN 1.5cm 3750 N
8 1000A 1mm 0.9KN 2.0cm 5200 N
9 1000A 1mm 0.9KN 2.5cm 4300 N
10 800A 0.8mm 0.9KN 1.5cm 5511 N
11 800A 0.8mm 0.9KN 2.0cm 5844 N
12 800A 0.8mm 0.9KN 2.5cm 3882 N
13 1300A 0.8mm 0.9KN 1.5cm 5600 N
14 1300A 0.8mm 0.9KN 2.0cm 5860 N
15 1300A 0.8mm 0.9KN 2.5cm 5550 N
15.1 1600A 0.8mm 0.9KN 1.5cm 6879 N
15.2 1600A 0.8mm 0.9KN 2.0cm 5844 N
15.3 1600A 0.8mm 0.9KN 2.5cm 4600 N
16 1000A 0.8mm 0.9KN 1.5cm 5374 N

71. Page | 53
17 1000A 0.8mm 0.9KN 2.0cm 6491 N
18 1000A 0.8mm 0.9KN 2.5cm 4766 N

72. Page | 54
Experiment no. 2
Weld Id Current Thickness Force Distance between welds Shear Strength
19 1000A 1mm 780N 1.5cm 3020 N
20 1000A 1mm 780N 2.0cm 5000 N
21 1000A 1mm 780N 2.5cm 4800 N
22 1600A 1mm 780N 1.5cm 4300 N
23 1600A 1mm 780N 2.0cm 9708 N
24 1600A 1mm 780N 2.5cm 8649 N
24.1 1800A 1mm 780N 1.5cm 5393 N
24.2 1800A 1mm 780N 2.0cm 8217 N
24.3 1800A 1mm 780N 2.5cm 7393 N
25 1400A 1mm 780N 1.5cm 4100 N
26 1400A 1mm 780N 2.0cm 8010 N
27 1400A 1mm 780N 2.5cm 7943 N
28 1000A 0.8mm 780N 1.5cm 4667 N
29 1000A 0.8mm 780N 2.0cm 4942 N
30 1000A 0.8mm 780N 2.5cm 3687 N
31 1600A 0.8mm 780N 1.5cm 6884 N
32 1600A 0.8mm 780N 2.0cm 5903 N
33 1600A 0.8mm 780N 2.5cm 5200 N
31.1 1800A 0.8mm 780N 1.5cm 7237 N
32.2 1800A 0.8mm 780N 2.0cm 7400 N
33.3 1800A 0.8mm 780N 2.5cm 6099 N
34 1400A 0.8mm 780N 1.5cm 5785 N
35 1400A 0.8mm 780N 2.0cm 5766 N
36 1400A 0.8mm 780N 2.5cm 4900 N
4.4.2 Testing Weld specimen on Existing Welding machine

73. Page | 55
4.4.3 Test on different sheet combination performed on Designed machine
Experiment no. 3
Weld Id Current(A) Sheet thickness Force(KN) Distance between welds Shear strength
37 800A 1mm+0.8mm 0.9KN 1.5cm 3334 N
38 800A 1mm+0.8mm 0.9KN 2.0cm 4785 N
39 800A 1mm+0.8mm 0.9KN 2.5cm 5060 N
40 1300A 1mm+0.8mm 0.9KN 1.5cm 5413 N
41 1300A 1mm+0.8mm 0.9KN 2.0cm 5600 N
42 1300A 1mm+0.8mm 0.9KN 2.5cm 4452 N
43 1600A 1mm+0.8mm 0.9KN 1.5cm 4801 N
44 1600A 1mm+0.8mm 0.9KN 2.0cm 8177 N
45 1600A 1mm+0.8mm 0.9KN 2.5cm 5099 N
46 1000A 1mm+0.8mm 0.9KN 1.5cm 5491 N
47 1000A 1mm+0.8mm 0.9KN 2.0cm 5600 N
48 1000A 1mm+0.8mm 0.9KN 2.5cm 5727 N

74. Page | 56
4.4.4 Test on different sheet combination performed on Existing machine
Experiment 4
Weld
Id Current(A)
Sheet
thickness Force(KN)
Distance
between welds
Shear strength
49 1000A 1mm+0.8mm 780N 1.5cm 2800 N
50 1000A 1mm+0.8mm 780N 2.0cm 4000 N
51 1000A 1mm+0.8mm 780N 2.5cm 3216 N
52 1600A 1mm+0.8mm 780N 1.5cm 4200 N
53 1600A 1mm+0.8mm 780N 2.0cm 7139 N
54 1600A 1mm+0.8mm 780N 2.5cm 4400 N
55 1800A 1mm+0.8mm 780N 1.5cm 5687 N
56 1800A 1mm+0.8mm 780N 2.0cm 6452 N
57 1800A 1mm+0.8mm 780N 2.5cm 5413 N
58 1400A 1mm+0.8mm 780N 1.5cm 4197 N
59 1400A 1mm+0.8mm 780N 2.0cm 6040 N
60 1400A 1mm+0.8mm 780N 2.5cm 5217 N

75. Page | 57
4.5 Graphs:
Graph 4.5.1 Shear testing on Designed machine
a) 1mm+1mm
b) 0.8mm + 0.8mm
0
2
4
6
8
10
12
1.5cm 2.0cm 2.5cm
ShearForce(KN)
Distance between welds
Force= 900N
800A 1000A 1300A 1600A
0
1
2
3
4
5
6
7
8
1.5cm 2.0cm 2.5cm
ShearForce(KN)
Distance between welds
Force= 900N
800A 1000A 1300A 1600A

76. Page | 58
Graph 4.5.2 Shear testing on Existing machine
a) 1mm+1mm
b) 0.8mm+0.8mm
0
2
4
6
8
10
12
1.5cm 2.0cm 2.5cm
ShearForce(KN)
distance between welds
Force=780N
1000(A) 1400(A) 1600(A) 1800(A)
0
1
2
3
4
5
6
7
8
1.5cm 2.0cm 2.5cm
ShearForce(KN)
Distance between welds
Force= 780N
1000A 1400A 1600A 1800A

77. Page | 59
Graph 4.5.3 Shear testing on Designed machine
a) 1mm+0.8mm
Graph 4.5.4 Shear testing on Existing machine
a) 1mm+0.8mm
0
1
2
3
4
5
6
7
8
9
1.5cm 2.0cm 2.5cm
ShearForce(KN)
Distance between welds
Force= 900N
800A 1000A 1300A 1600A
0
1
2
3
4
5
6
7
8
1.5cm 2.0cm 2.5cm
ShearForce(KN)
Distance between welds
Force 780N
1000A 1400A 1600A 1800A

78. Page | 60
Graph 4.5.5 Strength Comparison on the basis of force variation
Graph 4.5.6 Strength Comparison on the basis of force variation
0
2
4
6
8
10
12
800 1000 1200 1400 1600 1800
ShearForce(KN)
Current(A)
780N(1mm) 900N(1mm) 900N(0.8mm) 780N(0.8mm)
0
1
2
3
4
5
6
7
8
9
800 1000 1200 1400 1600 1800
ShearForce(KN)
Current(A)
780(N) 900(N)

79. Page | 61
Graph 4.5.7 Strength Comparison on the basis of sheet combination on Designed
machine
0
2
4
6
8
10
12
800 1000 1300 1600
ShearForce(KN)
Current(A)
1mm+1mm 0.8mm+0.8mm 1mm+0.8mm

80. Page | 62
4.6 Experimental Results and Discussions
a) Shear Strength:
Shear strength in both of the machine gives maximum strength at 2mm weld distance.
However, the value of designed machine always gives better strength than existing
machine for same current value.
b) Failure Modes: No case of interfacial fracture observed. Button pullout is common
mode of failure observed.
Fig. 4.2 Button Pull-out
Fig. 4.3 Interfacial fracture Failure

81. Page | 63
CHAPTER 5
CONCLUSIONS
1) All the members of mechanism, in designed machine works safely with hardly
any chance of failure. Stresses generated within members are well within range.
2) Repeatability, accuracy and constant pressure in every weld in case of designed
machine are obtained.
3) DC motor consumes energy only when in operation, produces less noise and
generate very less heat.
4) Results in case of mild steel for low a.c power supply and different sheet
combinations are obtained.
5) Pressure plays a significant role in strength of weld. Change in pressure causes
change in strength of weld.
6) Variation in distance between two spot welds changes the shear strength.
7) In case of designed machine, shear strength continuously increases with
increase in current.
8) Higher the thickness of sheet combination more will be bulk resistance.
Therefore, more heat will be producing, giving stronger weld.

82. Page | 64
REFERENCES:
1) Weldability of Thin Sheet Metals during Small-Scale Resistance Spot
Welding using an Alternating-Current Power Supply-Y. ZHOU, P.
GORMAN,W. TAN and K.J. ELY.
2) Making Resistance Spot Welding Safer by ROGER B. HIRSCH.
3) An experimental investigation on critical specimen sizes of high strength
steels DP600 in resistance spot welding- Hong Gang Yang, Yan Song Zhang,
Xin Min Lai, Guanlong Chen.
4) Using resistance spot welding for joining aluminium elements in
automotive industry A. AMBROZIAK, M.KORZENIOWSKI.
5) Optimization of resistance spot welding parameters using Taguchi Method-
A. K. Pandey, M.I.Khan, K. M. Moeed.
6) The influence of Resistance Spot Welding weld joint quality and service
life of electrodes-Marie KOLAŘÍKOVÁ, Ladislav KOLAŘÍK.
7) Investigating spot weld growth on 304-austenitic stainless steel (2mm)
sheets- NACHIMANI CHARDE, RAJPRASAAD RAJ KUMAR.
8) Resistance Spot Welding by ENTRON Control, Inc (RWMA-700081A
Revised 11/98).
9) Indian Standard SPECIFICATION FOR RESISTANCE WELDING
EQUIPMENT PART I SINGLE-PHASE TRANSFORMERS (Third Reprint
FEBRUARY 1989). 10)
Design of belts-Power Grip GT2 Belts-GATES BELTS.
11) Design of Motor- DC Motor & Gear motors, Globe Motors.
12) Estimation of the weldability of single-sided resistance spot welding-Jae
Hyung Kima, Yongjoon Chob, Yong Hoon Janga.

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13) Effect of welding current on mechanical properties of galvanized chromided
steel sheets in electrical resistance spot welding S. Aslanlara, A. Ogurb,
U.Ozsaraca, E.Ilhana, Z.Demir.
14) Contact conditions on nugget development during resistance spot welding of
Zn coated steel sheets using rounded tip electrodes- R. Raoelisona, A. Fuentesa,
Ph. Rogeona, P. Carréa, T. Louloua, D. Carrona, F. Dechalottec
15) Numerical study on the effect of electrode force in small-scale resistance
spot welding B.H.Chang,Y.Zhou.