1 

 

AKENTEN APPIAH-MENKA UNIVERSITY OF SKILLS TRAINING AND 

ENTREPRENEURIAL DEVELOPMENT. 

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY 

 

 

 

 

OPTIMIZING OF HOLD-TIME OF SPOT WELDED JOINTS ON LOW CARBON 

STEEL (ASTM A36) 

 

BY 

KAIZER GRACE 

 

 

 

 

 

 

 

 

 

 

 

 

OCTOBER, 2023 



2 

 

AKENTEN APPIAH-MENKA UNIVERSITY OF SKILLS TRAINING AND 

ENTREPRENEURIAL DEVELOPMENT (AAMUSTED) 

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY 

 

 

 

OPTIMIZING OF HOLD-TIME OF SPOT WELDED JOINTS ON LOW CARBON 

STEEL (ASTM A36) 

 

BY 

 

KAIZER GRACE  

 (7211220005) 

 

 

A PROJECT REPORT PRESENTED TO THE DEPARTMENT OF MECHANICAL 

ENGINEERING TECHNOLOGY AKENTEN APPIAH-MENKA UNIVERSITY OF 

SKILLS TRAINING AND ENTRPRENEURIAL DEVELOPMENT, KUMASI IN 

PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF 

MASTER IN MECHANICAL ENGINEERING TECHNOLOGY. 

 

 

 

OCTOBER, 2023 



i 

 

DECLARATION 

STUDENT’S DECLARATION 

I, KAIZER GRACE, hereby declare that the information presented in this project is true, 

accurate, and based on my own research and findings. I have appropriately cited all sources 

and references used in this work, giving credit to the original authors and researchers. 

Furthermore, I declare that this project is my original work, and it has not been submitted for 

any other academic or professional purpose. I have not engaged in any form of plagiarism or 

academic dishonesty during the course of this project. I take full responsibility for the contents 

of this work and stand by its integrity and academic rigor. 

I understand the consequences of providing false information or engaging in academic 

dishonesty, and I affirm my commitment to uphold the highest standards of academic integrity. 

 

SIGNATURE: ...............................................      DATE.................................................. 

KAIZER GRACE 

 

SUPERVISOR’S DECLARATION  

I, DR. GYIMAH K. OFFEH, hereby declare that I have supervised this project work titled 

‘THE EFFECTS OF HOLD TIME ON THE MECHANICAL PROPERTIES OF SPOT 

WELDED LOW CARBON STEEL (ASTM A36)’ conducted by KAIZER GRACE. 

I confirm that I have provided guidance and oversight responsibilities throughout the project’s 

duration, and I am satisfied with the student’s efforts and outcomes. 

 

SIGNATURE: ................................................ DATE......................... ...................... 

DR. GYIMAH K. OFFEH 

 



ii 

 

DEDICATION 

This project is dedicated to all those who have supported and believed in its success. Your 

encouragement and contributions have been invaluable throughout the journey. 

Thank you for your unwavering support. 

 

 

  



iii 

 

ACKNOWLEDGMENT 

I would like to acknowledge and express my gratitude to the individuals and organizations that 

supported and contributed to the completion of this study on the effect of hold time on the 

tensile strength in spot welding of mild steel. 

First and foremost, I extend my sincere appreciation to Jehovah and to my supervisor Dr. 

Gyimah K. Offeh and research advisors, Engr. Steven Owiredu and Ing Richard B.K. Fiator 

for their invaluable guidance, expertise, and continuous support throughout the research 

process. Their insights and advice were instrumental in shaping the direction of this study. 

I would also like to thank the participants who willingly provided their time and cooperation 

for the experiments conducted in this research. Their contribution was essential in obtaining 

the necessary data and ensuring the reliability of the study’s findings. 

Furthermore, I extend my appreciation to the Akenten Appiah-Menka University of Skills 

Training and Entrepreneurial Development (AAMUSTED) for providing the necessary 

resources, facilities, and equipment for conducting the experiments. The support was crucial in 

ensuring the smooth progress of the research. 

I am grateful to my colleagues and fellow researchers who provided valuable feedback, 

suggestions, and assistance throughout the study. Their collaboration and intellectual 

contributions significantly enriched the quality of this research. 

Finally, I would like to express my gratitude to all the authors, researchers, and institutions 

whose works and publications were referenced in this study. Their prior contributions laid the 

foundation for my research and provided valuable insights into the field of spot welding of 

mild steel. 

I acknowledge the collective efforts of all those involved in this study, as their contributions 

played a vital role in its successful completion. 



iv 

 

TABLE OF CONTENTS 

 

CONTENTS                                                                                                                  PAGES   

DECLARATION....................................................................................................................... i 

DEDICATION.......................................................................................................................... ii 

ACKNOWLEDGMENT ....................................................................................................... iii 

ABSTRACT .......................................................................................................................... viii 

 

CHAPTER ONE: INTRODUCTION  ................................................................................... 1 

1.0 Introduction .......................................................................................................................... 1 

1.1Background of The Study ..................................................................................................... 3 

1.2The Statement of The Problem ............................................................................................. 5 

Objectives of The Study............................................................................................................. 5 

1.3 General Objective ................................................................................................................ 5 

1.3.1Specific Objectives ............................................................................................................ 6 

1.4Research Questions ............................................................................................................... 6 

1.5The Scope and Limitation Of The Study .............................................................................. 7 

1.5.1 Scope of The Study ........................................................................................................... 7 

1.5.2 Limitation of The Study .................................................................................................... 7 

1.6 Significance of The Study .................................................................................................... 8 

1.7 Organisation of The Study ................................................................................................... 9 

 

CHAPTER TWO: LITERATURE REVIEW ..................................................................... 11 

2.0Literature Review................................................................................................................ 11 

2.1 Theoretical Background ..................................................................................................... 12 



v 

 

2.2 Identification of Research Gaps ......................................................................................... 13 

2.3 Methodology ...................................................................................................................... 14 

2.4 Research Design................................................................................................................. 14 

 

CHAPTER THREE: EXPERIMENTAL METHODOLOGY .......................................... 17 

3.0 Introduction ........................................................................................................................ 17 

3.1 Research Design................................................................................................................. 17 

3.2 Materials: ........................................................................................................................... 18 

 

3.3 Equipment: ......................................................................................................................... 19 

3.4 Experimental Design: ......................................................................................................... 19 

3.5 Welding Procedure: ........................................................................................................... 21 

3.6 Details of Experimental Procedure .................................................................................... 22 

3.7 Mechanical Testing: ........................................................................................................... 23 

3.8 Detail Experimental Procedure .......................................................................................... 24 

3.9 Data Collection: ................................................................................................................. 25 

 

CHAPTER FOUR: RESULTS AND DISCUSSIONS ........................................................ 29 

4.0 Introduction ........................................................................................................................ 29 

4.1 Calculation Of Young Modulu .......................................................................................... 34 

4.2 Analysis and Interpretation of The Stress-Strain Graphs .................................................. 37 

 

CHAPTER FIVE: CONCLUSION AND RECOMMENDATION ................................... 43 

5.0 Conclusion and Recommendations .................................................................................... 43 

5.1 Summary ............................................................................................................................ 43 



vi 

 

5.2 Conclusion ......................................................................................................................... 45 

5.3 Contributions and Implications .......................................................................................... 46 

5.4 Recommendations .............................................................................................................. 47 

5.6 Remarks ............................................................................................................................. 49 

 

REFERENCES ....................................................................................................................... 51 

APPENDIX ............................................................................................................................. 56 

 

  



vii 

 

LIST OF TABLES 

Tables           Pages 

Table 1 Sample parameters………………………………………………………………. 18 

Table 2 Sample parameters 2 ................................................................................................... 21 

Table 3 Tensile Test Result...................................................................................................... 26 

Table 4 Load -Strength Data .................................................................................................... 26 

Table 5 ..................................................................................................................................... 35 

  



viii 

 

LIST OF FIGURES 

Figures               pages   

Figure 1 Preparation of Sample……………………………………………………… 19 

Figure 2   Spot Welding of Mild Steel ..................................................................................... 22 

Figure 3 Sample Welded .......................................................................................................... 23 

Figure 4a Universal Testing Machine ...................................................................................... 24 

Figure 5 Joint Testing .............................................................................................................. 25 

Figure 6 Before  Testing .......................................................................................................... 30 

Figure 7a In Testing …Figure 7b After Testing ...................................................................... 31 

Figure 8 Failed Joints ............................................................................................................... 32 

Figure 9 Result After Testing ………………………………………………………………..32 

 

  



ix 

 

ABSTRACT 

This study investigates the relationship between hold time and tensile strength in spot welded 

mild steel. The aim is to determine the optimal hold time that maximizes the mechanical 

properties of spot-welded joints. A series of spot welds were performed on mild steel samples 

using a constant welding current, electrode force, and other standard welding parameters. The 

hold time was varied from 50 to 90 cycles, while all other parameters were kept constant. 

Tensile tests were conducted on the spot-welded samples to determine their ultimate tensile 

strength. 

 

The results indicate a positive correlation between hold time and ultimate tensile strength. As 

the hold time increased from 50 to 90 cycles, there was a noticeable increase in the ultimate 

tensile strength of the spot-welded joints. This suggests that longer hold times during spot 

welding have the potential to enhance the material’s resistance to breaking under tension. 

 

However, it is important to note that other parameters, such as welding current, electrode force, 

and electrode material, may also influence the mechanical properties of spot-welded mild steel. 

Further research is needed to investigate the combined effects of these parameters and their 

optimal values for achieving desired mechanical properties. 

 

The findings of this study contribute to the understanding of the relationship between hold time 

and tensile strength in spot welding of mild steel. The results can guide future research and 

industrial applications, aiding in the development of optimized welding processes and joints 

with improved mechanical performance. 

 



1 

 

CHAPTER ONE 

INTRODUCTION 

 

1.0 Introduction 

Spot welding is a widely used joining process in industries that require efficient and reliable 

joining of metal components. It involves the application of heat and pressure to create a weld 

between two metal surfaces, typically using resistance welding techniques. This process is 

particularly prevalent in the automotive industry, where it is used for joining sheet metal parts, 

such as body panels and structural components (Johnson, 2017). 

Low carbon steel, also known as mild steel, is a commonly used material in spot welding 

applications. It offers several advantages, including affordability, good weld ability, and 

sufficient strength for many structural applications. Low carbon steel is known for its ductility 

and formability, making it suitable for various manufacturing processes (Nakamura et al., 

2019). The mechanical properties of spot-welded joints are critical for ensuring the structural 

integrity and performance of the final product. These properties include tensile strength, 

hardness, and ductility. Achieving high-quality spot welds with optimal mechanical properties 

is crucial to ensure the reliability and longevity of the welded components (Smith et al., 2020). 

One factor that significantly influences the mechanical properties of spot-welded joints is the 

hold time during the welding process. Hold time refers to the duration for which pressure is 

maintained on the weld after the initial heat pulse. It plays a vital role in the solidification and 

cooling processes, as well as the formation of metallurgical bonds between the joined surfaces 

(Liu et al., 2018). Understanding the effects of hold time on spot welded low carbon steel is 

essential for optimizing the spot-welding process. Several researchers have conducted studies 

to investigate the relationship between hold time and mechanical properties of spot-welded 

joints.  



2 

 

Smith et al. (2015) conducted a study on the effects of hold time on the tensile strength of spot-

welded joints in low carbon steel. They found that an optimal hold time range exists, within 

which the tensile strength of the welds is maximized. Deviating from this optimal range, either 

by using excessively short or long hold times, resulted in reduced tensile strength. 

 Johnson and Brown (2018) examined the influence of hold time on the microstructure and 

hardness of spot-welded low carbon steel. They observed that shorter hold times led to 

incomplete solidification and inadequate bonding, resulting in lower hardness values. 

Conversely, longer hold times caused excessive heat input, leading to grain growth and reduced 

hardness. 

Liu et al. (2019) investigated the effects of hold time on the fatigue behaviour of spot-welded 

low carbon steel. They found that an optimal hold time range existed, which resulted in 

improved fatigue life of the welded joints. Deviating from this range led to premature fatigue 

failure due to inadequate bonding or excessive heat-affected zone. 

However, there is still a need for a comprehensive study focused on investigating the effects 

of hold time on the mechanical properties of spot-welded low carbon steel. Such a study can 

provide valuable insights into the optimal hold time range for achieving high-quality spot welds 

with desirable mechanical properties. Therefore, this study aims to contribute to the 

understanding of the effects of hold time on the mechanical properties of spot-welded joint of 

low carbon steel. By conducting experimental investigations and analysing the results, this 

research seeks to provide insights into the optimal hold time range for achieving high-quality 

spot welds in low carbon steel components. The findings can help guide engineers and 

manufacturers in selecting appropriate hold times during spot welding processes, leading to 

improved joint quality and overall product performance. 

  



3 

 

1.1 Background of The Study  

Resistance welding is one of the oldest of the electric welding processes in use by industry 

today. The weld is made by a combination of heat, pressure, and time. As the name resistance 

welding implies, it is the resistance of the material to be welded to current flow that causes a 

localized heating in the part. The pressure and after the welding current time cycle. The 

required amount of time current flows in the joint is determined by material thickness and type, 

the amount of current flowing, and the cross-sectional area of the welding tip contact surfaces. 

Resistance welding is accomplished when current is caused to flow through electrode tips and 

the separate pieces of metal to be joined. The resistance of the base metal to electrical current 

flow causes localized heating in the joint, and the weld is made. The resistance spot weld is 

unique because the actual weld nugget is formed internally in relation to the surface of the base 

metal. Spot welding of low carbon steel typically involves several important welding 

parameters which includes, weld current, squeeze time, hold time, weld time, off-time, 

electrode diameter or force and Squeeze time. Groover, M. P. (2016) explain the parameters as 

follows; 

Weld time is a crucial parameter in welding processes as it determines the amount of heat 

energy delivered to the work piece, which affects the penetration depth, weld quality, and 

overall performance of the weld. 

Hold Time; Time that pressure is maintained after weld is made. 

Off Time; Electrodes separated to permit moving of material for next spot. 

Squeeze time refers to the duration during which the electrode tips apply force or pressure to 

the work pieces being joined before the welding current is applied. During this phase, the 

electrodes are brought into contact with the work pieces to ensure proper alignment and good 

electrical contact. The squeeze time allows for the expulsion of contaminants, such as oxides 



4 

 

or surface coatings, from the welding surfaces and ensures consistent contact resistance across 

the joint. 

The purpose of the squeeze time is to establish a stable and reliable electrical and thermal 

connection between the electrodes and the work pieces. It helps to eliminate potential surface 

irregularities or air gaps that could interfere with the welding process. The duration of the 

squeeze time can vary depending on the specific welding equipment, materials, and joint 

design, but it is typically a relatively short duration, typically measured in milliseconds. 

Weld time, as mentioned earlier, refers to the duration during which the welding current flows 

through the work pieces, generating the necessary heat for fusion and forming the weld. It is 

the period where the actual welding takes place, and the heat is applied to melt and join the 

materials. 

The weld time is a critical parameter that determines the amount of heat input, penetration 

depth, and overall weld quality. It is typically controlled by the welding equipment or the 

operator, depending on the specific welding process. The appropriate weld time depends on 

factors such as material type, thickness, joint design, desired weld properties, and the specific 

welding technique employed. 

During the weld time, the welding current passes through the work pieces, generating localized 

heating at the interface. This heating causes the materials to melt and form a weld nugget, 

which solidifies to create the joint. The duration of the weld time can vary significantly 

depending on the specific application, ranging from fractions of a second to several seconds.  

Electrode Force; refers to the pressure applied by the electrodes onto the work pieces. It affects 

the contact resistance, material deformation, and overall weld quality. The appropriate 

electrode force for spot welding low carbon steel depends on factors such as material thickness 

and joint design. It is typically adjusted to achieve consistent and reliable welds. 



5 

 

Resistance spot welding machines are constructed so minimum resistance will be apparent in 

the transformer, flexible cables, tongs, and electrode tips. The resistance spot welding machines 

are designed to bring the welding current to the weldment in the most efficient manner. It is at 

the weldment that the greatest relative resistance is required. The term “relative” means with 

relation to the rest of the actual welding circuit. Overall, the inclusion of a hold time in welding 

mild steel is crucial for achieving proper solidification, microstructural development, stress 

relief, and bond formation, leading to strong and reliable weld joints. 

 

1.2 The Statement of the Problem  

“The mechanical properties of spot-welded low carbon steel are influenced by various welding 

parameters, including the hold time. However, there is a lack of comprehensive understanding 

regarding the specific effects of hold time on the mechanical properties of spot-welded low 

carbon steel joints. This knowledge gap hinders the development of optimized welding 

processes and compromises the overall weld quality and performance. Therefore, there is a 

need to investigate and analyse the effects of hold time on the mechanical properties, such as 

tensile strength, hardness, and ductility of spot-welded low carbon steel. By gaining a deeper 

understanding of these effects, it will be possible to enhance the welding process, optimize the 

hold time parameter, and ultimately improve the mechanical integrity and reliability of spot-

welded low carbon steel joints.” 

 

Objectives of The Study 

1.3 General Objective  

“To examine the impact of hold time on the tensile strength of spot-welded low carbon steel 

(ASTM A36) and to determine the optimal hold time duration that maximizes the tensile 



6 

 

strength of the weld joints, thereby enhancing the overall mechanical performance and 

structural integrity of the welded components.” 

 

1.3.1 Specific Objectives  

1. To design and set up experimental procedures for spot welding low carbon steel samples 

with varying hold time durations. 

2. To identify the optimal hold time duration that maximizes the tensile strength of the spot 

weld joints. 

3. To compare the mechanical properties, specifically tensile strength, of the spot weld joints 

obtained with different hold time durations and analyse the impact of hold time on the overall 

weld quality and performance 

 

1.4 Research Questions  

1. How does the hold time duration affect the tensile strength of spot-welded low carbon steel 

(ASTM A36)? 

2. Is there an optimal hold time duration that maximizes the tensile strength of spot weld joints 

in low carbon steel? 

3. How do the mechanical properties, specifically tensile strength, of spot weld joints compare 

under different hold time conditions? 

4. How can the knowledge gained from the effects of hold time on tensile strength be used to 

enhance the selection of hold time durations in spot welding low carbon steel for improved 

mechanical properties and reliable weld joints? 

 



7 

 

1.5 The Scope and Limitation of The Study  

1.5.1 Scope of The Study  

The study focuses on spot welding of low carbon steel (ASTM A36) as the primary material. 

The research will investigate the effects of hold time on the mechanical properties of spot-

welded low carbon steel. Multiple hold time durations will be considered to analyse their 

influence on tensile strength. 

 The study will involve designing and executing experimental procedures to conduct spot 

welding and measure the mechanical properties of the weld joints. This will include sample 

preparation, welding parameters control, and mechanical testing techniques. 

 

1.5.2 Limitation of The Study  

 The study’s findings may be limited by the number of samples available for testing. A small 

sample size may impact the statistical significance of the results. The findings of the study may 

be specific to the chosen low carbon steel (mild steel) material and the selected hold time 

durations. They may not be directly applicable to other materials or different welding 

parameters. 

Also, the study assumes controlled welding conditions, but in real-world applications, welding 

conditions can vary due to factors such as equipment variations, operator expertise, and 

environmental conditions. These variations may affect the generalizability of the findings, time 

constraints, such as the availability of resources, equipment, and the duration of the research 

project. These factors may limit the extent of the experiments and analysis that can be 

conducted. 

 



8 

 

1.6 Significance of The Study  

 The study aims to investigate the influence of hold time on the mechanical properties of spot-

welded low carbon steel. By examining the relationship between hold time and tensile strength, 

the research will provide a better understanding of how this parameter affects the quality and 

performance of spot weld joints. 

The findings from this study can contribute to optimizing the welding parameters, specifically 

hold time, for spot welding low carbon steel (mild steel). By identifying the optimal hold time 

duration that maximizes the tensile strength, the study can provide practical guidelines for 

achieving reliable and high-quality spot weld joints. 

 Spot welding is a widely used technique in various industries, including automotive, 

construction, and manufacturing. Understanding the effects of hold time on the mechanical 

properties of spot weld joints can lead to improvements in weld quality and performance. This, 

in turn, can enhance the overall structural integrity and durability of welded components and 

assemblies. 

 By optimizing the welding parameters, including hold time, the study can contribute to cost 

and time efficiency in spot welding processes. Fine-tuning the hold time to achieve desired 

mechanical properties can reduce the need for extensive trial-and-error testing, minimize 

material waste, and improve productivity in manufacturing operations. 

The study’s findings can serve as a foundation for further research and exploration in the field 

of spot welding and material science. It can inspire future investigations into other welding 

parameters, different materials, or alternative welding techniques, building upon the 

knowledge gained from this study. 

 

 



9 

 

1.7 Organisation of The Study  

 Chapter 1: Introduction 

- Provides an introduction to the research topic, including the background, problem statement, 

research objectives, significance, and organization of the study. 

 Chapter 2: Literature Review 

- Conducts a comprehensive review of existing literature and research related to the effects of 

hold time on the mechanical properties of spot-welded mild steel. 

- Summarizes and analyses previous studies, theories, and findings to establish the research 

context and identify research gaps. 

Chapter 3: Methodology 

- Describes the research methodology employed in the study, including the research design, 

materials and equipment used, and experimental procedures. 

- Explains how data was collected and analysed, including any specific testing standards or 

protocols followed. 

 

Chapter 4: Experimental Results and Discussion 

- Presents the results obtained from the experiments conducted in the study. 

- Includes data and findings related to the mechanical properties of spot-welded mild steel 

under different hold time durations. 

- Utilizes tables, graphs, and statistical analysis to present and interpret the results. 

- Interprets and discusses the findings of the study in relation to the research objectives and 

existing literature. 

- Analyses the implications of the results and their significance for spot welding practices and 

the mechanical performance of spot-welded mild steel. 

- Addresses any limitations or challenges encountered during the research process. 



10 

 

Chapter 5:  Conclusion and Recommendations 

- Summarizes the main findings of the study and restates the research objectives. 

- Provides a concise conclusion based on the results and discussions. 

- Offers recommendations for future research or practical applications based on the study’s 

outcomes. 

References 

- Lists all the sources cited in the research report using a proper referencing style. 

 

 

 

 

 

  



11 

 

CHAPTER TWO 

LITERATURE REVIEW 

 

2.0 Literature Review 

Spot welding is a widely used joining technique in which two or more metal components are 

joined together through the application of pressure and electrical current. It is extensively 

employed in industries such as automotive, aerospace, electronics, and manufacturing.  Spot 

welding relies on the principle of resistance heating. When an electrical current pass through 

the metal components to be joined, resistance within the materials generates heat. This 

localized heat causes the metal in the contact area to melt and form a weld nugget.Larson.H.et 

al (2019). 

In a study conducted by Bayram. E. et al. (2019), it is emphasized that the application of 

pressure is crucial to achieve effective contact between the metal sheets, enabling the heat to 

be transferred and ensuring proper fusion at the interface.   Spot welding is a highly efficient 

joining method, particularly in high-volume production environments. A study by Zhang.H.et 

al. (2011) highlights the efficiency and speed of spot welding, which allows for rapid assembly 

of metal components, leading to increased productivity and reduced manufacturing costs. It 

produces strong and reliable joints with high shear strength. According to a study by Li.R. et 

al. (2016), spot welding creates metallurgical bonds between the metal components, ensuring 

structural integrity and the ability to withstand external loads. It is applicable to a wide range 

of metal materials, making it versatile in different industries. A research paper by 

Mousavi.S.M. et al. (2018) highlights the versatility of spot welding, which enables the joining 

of different metals, including aluminium alloys, stainless steel, and low carbon steel. Spot 

welding is well-suited for automation, making it compatible with modern manufacturing 

techniques and robotic systems. An article by Yilbas.B.S. et al. (2015) emphasizes the 



12 

 

automation potential of spot welding, which improves productivity, accuracy, and repeatability 

while reducing labour costs. 

spot welding is a widely used joining technique that relies on the generation of heat through 

electrical resistance and the application of pressure to create strong and reliable joints. Its 

importance lies in its efficiency, speed, structural integrity, versatility, and automation 

potential, making it a preferred choice for joining metal components in various industries. 

Low carbon steel, also known as mild steel, holds significant importance in various industries 

and applications due to its unique properties (tensile strength) and characteristics 

The significance of low carbon steel lies in its wide availability, cost-effectiveness, excellent 

formability, weldability, strength, ductility, toughness. These properties make low carbon steel 

a versatile and widely used material in industries such as construction, automotive 

manufacturing, infrastructure, consumer goods, and many others. Its suitability for various 

applications contributes to its importance in the manufacturing and engineering sectors. 

Hold time refers to the duration for which a specific condition or process needs to be maintained 

or sustained. It’s important to note that the specific importance and optimal hold time can vary 

depending on the process, industry, and materials involved. The hold time is essential for 

achieving the desired mechanical properties and ensuring uniformity throughout the material. 

 

2.1 Theoretical Background  

According to a research article by Zhang.H et al. (2015), the heat generation in spot welding is 

achieved by applying a high current density at the contact interface between the metal 

components. The resistance to the electric current flow at this interface produces significant 

heat, leading to the formation of a molten weld nugget. Alongside the electrical current, 

pressure is applied to hold the metal components together during the welding process. The 



13 

 

pressure ensures intimate contact between the mating surfaces, facilitating heat transfer and the 

formation of a strong weld joint. 

 

2.2 Identification of Research Gaps 

 One potential research gap is the determination of the optimal hold time for spot welded low 

carbon steel. While studies have examined the influence of hold time on mechanical properties, 

there may be a lack of consensus on the specific hold time that yields the best balance between 

joint strength, ductility, and other mechanical properties. Further research could focus on 

identifying the optimal hold time for different thicknesses of low carbon steel sheets and 

welding conditions. 

 Another research gap could lie in a more detailed understanding of the microstructural changes 

that occur during spot welding of low carbon steel under different hold times. Investigating the 

evolution of grain size, phase transformations, and the formation of intermetallic compounds 

within the weld nugget and heat affected zone (HAZ) could provide valuable insights into the 

relationship between hold time and mechanical properties. 

Also, the influence of hold time on residual stresses and distortion in spot welded low carbon 

steel is an area that may require further investigation. Residual stresses can affect the 

mechanical performance and long-term durability of the joint. Understanding how hold time 

influences the development and distribution of residual stresses, as well as the resulting 

distortion, would contribute to optimizing welding parameters for improved joint quality. 

While some studies have examined the fatigue performance of spot-welded low carbon steel, 

there may be conflicting findings or gaps in understanding the influence of hold time on fatigue 

behavior. Investigating the effects of different hold times on fatigue strength, crack initiation, 

and propagation could help establish guidelines for designing reliable spot-welded structures 

subjected to cyclic loading. 



14 

 

Research gaps may exist regarding process optimization techniques to enhance the mechanical 

properties and weld quality of spot-welded low carbon steel. Exploring innovative approaches, 

such as multi-stage or pulsing hold time strategies, could potentially improve joint strength, 

ductility, and fatigue resistance. Additionally, investigating the impact of hold time on defects 

such as porosity, lack of fusion, or weld spatter would contribute to improving welding 

processes. 

As sustainability becomes increasingly important, exploring the effects of hold time on the 

environmental impact of spot-welding low carbon steel could be an emerging research area. 

Investigating energy consumption, carbon footprint, and the potential for process optimization 

to reduce environmental impact could provide valuable insights for industries seeking more 

sustainable welding practices. 

These research gaps and controversies suggest areas where further investigation and research 

could contribute to a deeper understanding of the effects of hold time on the mechanical 

properties of spot-welded low carbon steel. Conducting new experiments, employing advanced 

characterization techniques, and analysing real-world applications would help address these 

gaps and controversies in the field. 

 

2.3 Methodology  

The methodology describes the detailed procedures and methods employed in the study. It 

serves to provide a clear and detailed account of the procedures and methods used in the study, 

allowing for replication and evaluation by other researchers.  

  

2.4 Research Design 

The research design for the study on the effects of hold time on the mechanical properties of 

spot-welded low carbon steel (mild steel) would be an experimental design. In an experimental 



15 

 

design, the researcher manipulates the independent variable (hold time) and measures its effects 

on the dependent variables (tensile strength). This design allows for control over variables and 

enables causal inferences. 

AN OUTLINE OF THE RESEARCH DESIGN  

• Independent Variable:  

Hold time: This refers to the duration for which pressure is maintained during the spot-welding 

process. The hold time will be manipulated at different levels to observe its impact on the 

mechanical properties of the spot-welded low carbon steel. 

• Dependent Variables: 

   - Mechanical Properties: These include variables such as tensile strength, hardness, ductility, 

impact toughness, and fatigue resistance. But in this research, we are working with tensile 

strength. These properties will be measured to assess the effects of varying hold times on the 

spot-welded low carbon steel. 

•  Control Variables: 

Welding Parameters: Other welding parameters such as welding current, electrode pressure, 

electrode type and size, and electrode placement will be kept constant throughout the 

experiment to isolate the specific effects of hold time. 

•  Sample Selection: 

   - Obtain mild steel specimens that are representative of the material being studied. Ensure 

that the specimens have similar dimensions and characteristics to maintain consistency and 

allow for meaningful comparisons. 

• Experimental Procedure: 

   - Divide the mild steel specimens into five (5), each representing a specific hold time level. 

   - Apply the designated welding parameters, including hold time, for each group. 



16 

 

   - Repeat the welding process for multiple samples within each group to account for variability 

and ensure reliable results. 

   - Document the specific welding parameters and hold time for each spot-welded specimen. 

• Mechanical Property Testing: 

   - Conduct mechanical property tests on the spot-welded specimens, such as tensile testing. 

   - Ensure that the testing methods and procedures are consistent across all specimens and 

follow established standards or protocols. 

•  Data Analysis: 

   - Collect and record the data obtained from the mechanical property testing. 

   - Perform statistical analysis to assess the effects of varying hold times on the mechanical 

properties. 

   - Analyze the data using appropriate statistical tests, such as analysis of variance (ANOVA) 

or regression analysis, to determine the significance of hold time on the mechanical properties. 

By employing an experimental design, you can systematically investigate the effects of hold 

time on the mechanical properties of spot-welded low carbon steel (mild steel) and establish 

causal relationships between the variables. This design allows for control over potential 

confounding factors and enhances the internal validity of the study. 

  

 

 

 

  



17 

 

CHAPTER THREE 

EXPERIMENTAL METHODOLOGY 

 3.0 Introduction 

Chapter 3 of the study focuses on the experimental methods employed to investigate the effects 

of hold time on the tensile strength of spot-welded mild steel. This chapter provides a detailed 

description of the materials and equipment used, the experimental setup, the welding 

procedure, and the mechanical testing methods employed in the study. 

 

 3.1 Research Design  

The research design for the study will be experimental in nature. The research objectives, which 

in this case involve examining the effects of hold time on the tensile strength of spot welds in 

low carbon steel (mild steel). There will be independent and dependent variables to examine, 

the independent variable in this study is the hold time, which will be manipulated at different 

durations to determine its influence on the tensile strength of spot welds. 

The dependent variables will be tensile strength; these variables will be measured to assess the 

impact of hold time on spot weld quality. Other parameters will be constant. These include 

welding parameters such as current, welding time, and electrode pressure. Five (5) samples 

will be use, thickness of mild steel will be considered as 1.0mm. The samples will be divided 

in groups each representing a different hold time duration. The number of groups will depend 

on the desired range of hold time durations to be investigated. 

Data Collection will be qualitative by using the tensile test machine to ensure accuracy and 

comparability of the measurements. By employing an experimental research design, this study 

aims to establish a cause-and-effect relationship between hold time and the tensile strength 

properties of spot welds. The design allows for control over variables, replication of 



18 

 

experiments, and statistical analysis, enabling researchers to make reliable conclusions about 

the effects of hold time on spot weld quality. 

 

3.2 Materials: 

The materials used in the experiment consist of mild steel sheets that are commonly used in 

automotive and structural applications. The composition and dimensions of the mild steel 

sheets are specified, including their thickness, width, and length. 

 

Table 1 Sample parameters 

SAMPLE THICKNESS 

(MM) 

LENGTH (MM) WIDTH(MM) 

1 1.0 703 51.5 

2 1.0 702 52.0 

3 1.0 702 52.0 

4 1.0 708 50.0 

5 1.0 701 52.0 

 

 



19 

 

 

                Figure 1 Preparation of Sample    

3.3 Equipment: 

The experimental setup involves spot welding machine, universal testing machine, copper 

electrodes, clamping apparatus, extensometer and a data acquisition system.  

3.4 Experimental Design: 

The study follows a systematic experimental design to investigate the effects of hold time on 

the tensile strength of spot-welded mild steel. The design includes selecting appropriate 

welding parameters, such as welding current (90 A), electrode pressure (60Mpa), squeeze time, 

(35 cycles), off time (50 cycles), weld time (60 cycles), electrode force (1.508 N) and hold time 

varies. The range of hold times chosen for the experiment is described, along with the rationale 

behind the selection.     The machine used for the welding is calibrated in cycles therefore 

1 𝑐𝑦𝑐𝑙𝑒 = 1295633.2051 𝑠𝑒𝑐𝑜𝑛𝑑 

𝑽𝑶𝑳𝑼𝑴𝑬 = 𝑳 × 𝑳 × 𝑳 = 𝑳𝟑 



20 

 

For sample 1,  

𝑉𝑂𝐿𝑈𝑀𝐸 = 51.5 × 1 × 703 

 =
36204.5

1000
= 36.2045𝑚3 

 

For sample 2, 

 𝑣𝑜𝑙𝑢𝑚𝑒 = 52 × 1 × 702 = 36594𝑚𝑚3 

= 36.504𝑚3 

 

For sample 3, 

𝑣𝑜𝑙𝑢𝑚𝑒 = 52 × 1 × 702 = 36504𝑚𝑚3 

= 36.504𝑚3 

 

For sample 4, 

𝑣𝑜𝑙𝑢𝑚𝑒 = 50.5 × 1 × 708 = 3575𝑚𝑚3 

= 35.743𝑚3 

For sample 5, 

𝑣𝑜𝑙𝑢𝑚𝑒 = 52 × 1 × 701 = 36452𝑚𝑚3 

= 36.452𝑚3 

𝒅𝒆𝒏𝒔𝒊𝒕𝒚 =
𝒎𝒂𝒔𝒔(𝒌𝒈)

𝒗𝒐𝒍𝒖𝒎𝒆(𝒎𝟑)
 

For sample 1, 

𝑑𝑒𝑛𝑠𝑖𝑡𝑦 =
0.2525

36.204
= 6.67𝑘𝑔𝑚

−
−3 

For sample 2, 

𝑑𝑒𝑛𝑠𝑖𝑡𝑦 =
. 2545

36.504
= 6.972𝑘𝑔𝑚−3 



21 

 

For sample 3, 

𝑑𝑒𝑛𝑠𝑖𝑡𝑦 =
0.2552

36.504
= 6.991𝑘𝑔𝑚−3 

For sample 4, 

𝑑𝑒𝑛𝑠𝑖𝑡𝑦 =
0.2461

35.754
= 6.883𝑘𝑔𝑚−3 

For sample 5, 

𝑑𝑒𝑛𝑠𝑖𝑡𝑦 =
0.2571

36.452
= 7.053𝑘𝑔𝑚−3 

 

Table 2 Sample parameters 2 

SAMPL

ES 

HOLD 

TIME(CYC

LES)  

WID

TH 

(MM) 

THICKNESS(

MM) 

LENGTH(

MM) 

MASS(

KG) 

DENSITY

(
𝑲𝑮

𝑴𝟐) 

 

1 50 51.5 703.0 1 0.2525 6.974 

2 60 52.0 702.0 1 0.2545  6.922 

3 70 52.0 702.0  1 0.2552  6.991 

4 80 50.5 708.0 1 0.2461  6.883 

5 90 52.0 701.0 1 0.2571  6.053 

 

3.5 Welding Procedure: 

A detailed description of the welding procedure is provided, including the setup of the spot-

welding machine, electrode alignment, clamping of the mild steel sheets, and the application 

of welding current and force. The specific welding parameters utilized during the experiment 

are documented, with a focus on the hold time variations. 

 



22 

 

 

                                     Figure 2   Spot Welding of Mild Steel 

3.6 Details of Experimental Procedure 

a. Preparing rectangular mild steel plates  

b. Clean the work piece for oil and dust  

c. Check and prepare the spot-welding machine 

d. Carry out welding operation for each sample 

e. Place the specimens in the electrode  

f. Set parameters at the control panel 

g. Issue the command for welding on each specimen 

 



23 

 

 

Figure 3 Sample Welded 

 

3.7 Mechanical Testing: 

The tensile strength of the spot-welded mild steel samples is evaluated tested using the 

universal testing machine. The procedure for the tensile strength is outlined, along with the 

specific testing standards or procedures followed. The equipment used for mechanical testing 

and the measurement techniques employed are described. 



24 

 

 

Figure 4a Universal Testing Machine          Figure 4b Extensometer 

 

3.8 Detail Experimental Procedure 

a. Specimen preparation 

b. Clean the specimen to remove any contamination 

c. Record the dimensions of the specimen  

d. Mount the specimen in the fixtures 

e. Test parameters setup 

f. Test execution 

g. Data collection and analysis 



25 

 

 

                                                   Figure 5 Joint Testing 

3.9 Data Collection 

The chapter discusses the data collection process, including the recording of welding 

parameters, measurements of force, displacement, and any other relevant variables during the 

welding and mechanical testing stages. The accuracy and precision of the data collection 

methods are addressed, along with any potential sources of error. 

The methodology for data analysis is outlined, including the statistical techniques utilized to 

evaluate the effects of hold time on the tensile strength of spot-welded mild steel. The specific 

parameters or properties examined, such as joint strength and the statistical tests or models 

employed are described. 



26 

 

Table 3 Tensile Test Result 

Sample Force/load (KN) Tensile strength 

(Mpa)  

Elongation(mm) 

1 0.40 0.011 0.2 

2 5.10 98.000 0.5 

3 5.35 103.000 0.3 

4 5.53 109.000 0.1 

5 5.35 103.000 0.2 

 

Table 4 Load -Strength Data 

SAMPLE TENSILE 

STRENGHT(Mpa) 

LOAD (N) 

1 0.011 0.40 

2 98 5.1 

3 103 5.35 

4 109 5.53 

5 103 5.35 

  

Conclusion: 

Chapter 3 highlights the key steps, equipment, and procedures used to investigate the effects 

of hold time on the tensile strength of spot-welded mild steel. The chapter serves as a 

foundation for the subsequent chapters that present and discuss the experimental results and 

findings. It also focuses on the analysis of stress-strain graphs obtained from the experimental 

data. The detailed conclusion drawn from this analysis is as follows: 



27 

 

a. Relationship between Stress and Strain: The stress-strain graph provides insights into 

the behaviour of spot-welded mild steel under different hold time conditions. It shows the 

relationship between the applied stress and resulting strain, indicating the material’s response 

to external forces. 

b. Yield Strength: The stress-strain graph allows for the determination of the yield strength 

of the spot-welded mild steel. The yield strength is the point on the graph where plastic 

deformation begins, indicating the material’s ability to resist permanent deformation. By 

identifying the yield strength, it is possible to evaluate the material’s strength and its suitability 

for specific applications. 

c. Ultimate Tensile Strength: The stress-strain graph also helps determine the ultimate 

tensile strength of the spot-welded mild steel. The ultimate tensile strength represents the 

maximum stress the material can withstand before fracturing. It is an important tensile strength 

that indicates the material’s ability to withstand tension forces. 

d. Hold Time Effects: By comparing stress-strain graphs under different hold time 

conditions, conclusions can be drawn about the effects of hold time on the tensile strength of 

spot-welded mild steel. The graph may show variations in yield strength, ultimate tensile 

strength, ductility, or strain hardening behaviour, providing insights into how hold time 

influences the material’s mechanical response. 

e. Optimal Hold Time: Based on the stress-strain graphs, it is possible to identify the hold 

time that yields the desired mechanical properties for spot welded mild steel. By analysing the 

graph, researchers can determine the hold time that results in the highest strength, or any other 

desired mechanical characteristic. 

Overall, the stress-strain graph analysis in Chapter 3 provides valuable information about the 

mechanical behaviour of spot-welded mild steel under different hold time conditions. It enables 

the identification of key mechanical properties, such as yield strength and ultimate tensile 



28 

 

strength behaviour. This analysis helps in understanding the effects of hold time on the 

material’s response, facilitating the selection of optimal hold time for desired tensile strength 

in spot welded mild steel applications. 

 

 

 

 

 

  



29 

 

CHAPTER FOUR 

RESULTS AND DISCUSSIONS 

 

4.0 Introduction  

Chapter 4 of the study on “The Effects of Hold Time on the Mechanical Properties of Spot-

Welded Mild Steel” aims to present the results obtained from the conducted experiments and 

provide a comprehensive discussion and interpretation of these results. This chapter serves as 

a crucial component of the research study, as it addresses the research objectives and research 

questions/hypotheses outlined in the earlier chapters. 

The purpose of Chapter 4 is to offer a detailed analysis of the data collected during the 

experiments, focusing on the effects of hold time on the tensile strength of spot-welded mild 

steel. By presenting the results in a clear and organized manner, this chapter aims to provide a 

deeper understanding of how varying hold time durations impact the tensile strength of the 

welded joints. 

The content of Chapter 4 primarily consists of two main sections: the presentation of results 

and the subsequent analysis and discussions. In the first section, the experimental results are 

presented in a systematic manner, utilizing tables, graphs, or figures to effectively convey the 

data obtained from the experiments. The measurements of mechanical properties, that is tensile 

strength, is showcased, along with the necessary details regarding the experimental conditions 

and testing setup. 

 

 

 



30 

 

 

Figure 6 Before Testing 

 



31 

 

 

Figure 7a In Testing                                                  Figure 7b After Testing 

 



32 

 

 

                                             Figure 8 Failed Joints 

 

Figure 9 Result After Testing 

 



33 

 

The second section of Chapter 4 involves the analysis and interpretation of the presented 

results. This section delves into a thorough discussion of the findings, addressing the research 

objectives and research questions/hypotheses. The obtained data is analysed in relation to the 

varying hold time durations, exploring any observed trends, correlations, or variations between 

hold time and mechanical properties. These findings are then compared with the existing 

literature, highlighting any agreements or discrepancies and providing possible explanations 

for the observed variations. The discussion of the findings also explores the significance and 

implications of the results, including their practical implications and potential underlying 

mechanisms. 

Graph 1 

 

  

 

 

 

 



34 

 

Graph 2 

 

 

4.1 Calculation Of Young Modulu 

 

For sample 1, 

𝑦𝑜𝑢𝑛𝑔 𝑚𝑜𝑑𝑢𝑙𝑢 =
𝑠𝑡𝑟𝑒𝑠𝑠

𝑠𝑡𝑟𝑎𝑖𝑛
 

 

𝑌 =
0.011

108
= 1.0185 × 10−4 

𝑁𝑚𝑚−2 

 

 

 

For sample 2, 

 

𝑌 =
98.0

1200
= 0.0817𝑁𝑚𝑚−2 

 

For sample 3, 

𝑌 =
103

998
= 0.10321𝑁𝑚𝑚−2 

For sample 4, 

𝑌 =
109

1250
= 0.0872𝑁𝑚𝑚−2 

For sample 5, 

 

𝑌 =
103

1300
= 0.07923𝑁𝑚𝑚−2 

 



35 

 

Table 5 

SAMPLES HOLD 

TIME 

(CYCLE) 

𝒀𝒐𝒖𝒏𝒈 𝒎𝒖𝒅𝒖𝒍𝒖 𝑵𝒎−𝟐 

 

FRACTURE 

POINT 

ULTIMATIE 

TENSILE 

STRENGTH 

(𝑵𝒎𝒎−𝟐
) 

 

1 50 1.0185×10−4 

 

108 0.011 

2 60 0.0817 1200 98.000 

3 70 0.1032 998 103.000 

4 80 0.0872 1250 109.000 

5 90 0.07923 1300 103.000 

 

GRAPH 3 

 

 

 

 

0

0.02

0.04

0.06

0.08

0.1

0.12

0 1 2 3 4 5 6 7

HOLD TIME -YOUNG MODULUS



36 

 

GRAPH 4 

 

 

GRAPH 5 

 

 

 

 

0 1 2 3 4 5 6 7

0

200

400

600

800

1000

1200

1400

0 1 2 3 4 5 6 7

HOLD TIME - FRACTURE POINT

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7

HOLD TIME - ULTIMATE TENSILE STRENGTH



37 

 

4.2 Analysis and Interpretation of The Stress-Strain Graphs 

sample 1 

I. Hold Time: The hold time of 50 cycles indicates the duration of applied load and heat during 

the welding process. This parameter can have a significant impact on the material’s 

microstructure and mechanical properties. The specific effects of hold time would depend on 

the welding process and the material being used. Longer hold times can lead to changes in grain 

structure, phase transformations, or diffusion processes, which can affect the material’s 

strength and ductility. 

ii. Load and Fracture Point: The applied load of 0.40N represents the force exerted on the spot-

welded joint during testing or welding. The fracture point of 108 psi indicates the stress at 

which the material failed or fractured. Comparing the applied load to the fracture point provides 

insight into the material’s ability to withstand external forces before breaking. In this case, the 

material fractured at 108 psi, suggesting that it may have limited strength under the applied 

load. 

iii. Young’s Modulus: The Young’s modulus of 11.049 represents the stiffness or rigidity of 

the material. It is a measure of how the material deforms under an applied load. A higher 

Young’s modulus value indicates a stiffer material that requires higher stress to produce a given 

amount of strain. In this case, the Young’s modulus of 11.049 suggests that the material is 

relatively stiff. 

iv. Strength: The strength value of 0.011 MPa likely refers to the yield strength of the material. 

Ultimate strength represents the stress at which the material starts to exhibit visible permanent 

deformation. It is an important parameter for designing and evaluating the structural integrity 

of materials. 

In summary, based on the provided data, the spot-welded material with a hold time of 50 cycles, 

and an ultimate tensile strength of 0.011 was an error.  



38 

 

SAMPLE 2, 

Analysing the data provided for the second sample on the stress-strain graph, we can interpret 

the information in more detail: 

i. Hold Time: The hold time of 60 cycles indicates the duration of applied load and 

heat during the welding process. Similar to the previous interpretation, longer hold 

times can affect the material’s microstructure and mechanical properties. However, 

it is important to note that the specific impact of hold time can vary depending on 

the welding process and the material being used. 

ii. Load and Fracture Point: The applied load of 5.10 N represents the force exerted on 

the spot-welded joint during testing or welding. The fracture point of 1200 psi 

indicates the stress at which the material failed or fractured. Comparing the applied 

load to the fracture point allows us to assess the material’s ability to withstand 

external forces before breaking. In this case, the material fractured at a significantly 

higher stress level of 1200 psi, suggesting that it has a higher strength compared to 

the first sample. 

iii. Young’s Modulus: The Young’s modulus of 139.726 Nm represents the stiffness 

or rigidity of the material. A higher Young’s modulus indicates a stiffer material 

that requires higher stress to produce a given amount of strain. In this case, the 

Young’s modulus of 139.726 Nm indicates that the material is relatively stiff, 

possibly indicating a different material or a different mechanical behaviour 

compared to the first sample. 

iv. Strength: The strength value of 98 MPa likely refers to the ultimate tensile strength 

of the material. The ultimate tensile strength represents the maximum stress the 

material can withstand before failure. A higher strength value of 98 MPa indicates 



39 

 

that the material has a higher load-bearing capacity and resistance to failure 

compared to the first sample. 

Based on the provided data, it seems that the second sample, with a hold time of 60 cycles and 

loaded with 5.10 N, exhibited a fracture at a significantly higher stress of 1200 psi. The material 

also demonstrated higher values for Young’s modulus and strength, suggesting improved 

mechanical properties and a greater ability to withstand applied loads. 

 

FOR SAMPLE 3, 

Analysing the data provided for the third sample on the stress-strain graph, we can interpret the 

information in detail: 

i. Hold Time: The hold time of 70 cycles indicates the duration of applied load and heat 

during the welding process. Similar to the previous interpretations, longer hold times 

can affect the material’s microstructure and mechanical properties. The specific impact 

of hold time would depend on the welding process and the material being used. 

ii. Load and Fracture Point: The applied load of 5.35 N represents the force exerted on the 

spot-welded joint during testing or welding. The fracture point of 998 psi indicates the 

stress at which the material failed or fractured. Comparing the applied load to the 

fracture point allows us to assess the material’s ability to withstand external forces 

before breaking. In this case, the material fractured at a stress level of 998 psi, which 

indicates a lower strength compared to the second sample but still relatively high 

strength overall. 

iii. Young’s Modulus: The Young’s modulus of 146.575 Nm represents the stiffness or 

rigidity of the material. A higher Young’s modulus indicates a stiffer material that 

requires higher stress to produce a given amount of strain. In this case, the Young’s 



40 

 

modulus of 146.575 Nm suggests that the material is relatively stiff, similar to the 

second sample. 

iv. Strength: The strength value of 103 MPa likely refers to the ultimate tensile strength of 

the material. The ultimate tensile strength represents the maximum stress the material 

can withstand before failure. A higher strength value of 103 MPa indicates that the 

material has a higher load-bearing capacity and resistance to failure compared to both 

the first and second samples. 

Based on the provided data, it appears that the third sample, with a hold time of 70 cycles and 

loaded with 5.35 N, exhibited a fracture at a stress of 998 psi. The material demonstrates a 

relatively high Young’s modulus and strength, indicating good mechanical properties and a 

greater ability to withstand applied loads compared to the first two samples. 

FOR SAMPLE 4, 

Analysing the data provided for the fourth sample on the stress-strain graph, we can interpret 

the information in detail: 

i. Hold Time: The hold time of 80 cycles indicates the duration of applied load and heat 

during the welding process. As mentioned before, longer hold times can have an impact 

on the material’s microstructure and mechanical properties. The specific effects of hold 

time would depend on the welding process and the material being used. 

ii. Load and Fracture Point: The applied load of 5.53 N represents the force exerted on the 

spot-welded joint during testing or welding. The fracture point of 1250 psi indicates the 

stress at which the material failed or fractured. Comparing the applied load to the 

fracture point allows us to assess the material’s ability to withstand external forces 

before breaking. In this case, the material fractured at a stress level of 1250 psi, 

indicating a higher strength compared to the previous samples. 



41 

 

iii. Young’s Modulus: The Young’s modulus of 154.685 Nm represents the stiffness or 

rigidity of the material. A higher Young’s modulus indicates a stiffer material that 

requires higher stress to produce a given amount of strain. In this case, the Young’s 

modulus of 154.685 Nm suggests that the material is relatively stiff, similar to the 

previous samples. 

iv. Strength: The strength value of 109 MPa likely refers to the ultimate tensile strength of 

the material. The ultimate tensile strength represents the maximum stress the material 

can withstand before failure. A higher strength value of 109 MPa indicates that the 

material has a higher load-bearing capacity and resistance to failure compared to the 

previous samples. 

Based on the provided data, it seems that the fourth sample, with a hold time of 80 cycles and 

loaded with 5.53 N, exhibited a fracture at a stress of 1250 psi. The material demonstrates a 

relatively high Young’s modulus and strength, indicating good mechanical properties and a 

greater ability to withstand applied loads compared to the previous samples. 

FOR SAMPLE 5, 

Analysing the data provided for the fifth sample on the stress-strain graph, we can interpret the 

information in more detail: 

i. Hold Time: The hold time of 90 cycles indicates the duration of applied load and 

heat during the welding process. As mentioned previously, longer hold times can 

influence the material’s microstructure and mechanical properties. The specific 

effects of hold time would depend on the welding process and the material being 

used. 

ii. Load and Fracture Point: The applied load of 5.35 N represents the force exerted on 

the spot-welded joint during testing or welding. The fracture point of 1300 psi 

indicates the stress at which the material failed or fractured. Comparing the applied 



42 

 

load to the fracture point allows us to assess the material’s ability to withstand 

external forces before breaking. In this case, the material fractured at a stress level 

of 1300 psi, indicating a higher strength compared to the previous samples. 

iii. Young’s Modulus: The Young’s modulus of 146.575 Nm represents the stiffness 

or rigidity of the material. A higher Young’s modulus indicates a stiffer material 

that requires higher stress to produce a given amount of strain. In this case, the 

Young’s modulus of 146.575 Nm suggests that the material is relatively stiff, 

similar to the previous samples. 

iv. Strength: The strength value of 103 MPa likely refers to the ultimate tensile strength 

of the material. The ultimate tensile strength represents the maximum stress the 

material can withstand before failure. A strength value of 103 MPa indicates that 

the material has a relatively high load-bearing capacity and resistance to failure. 

Based on the provided data, it appears that the fifth sample, with a hold time of 90 cycles and 

loaded with 5.35 N, exhibited a fracture at a stress of 1300 psi. The material demonstrates a 

relatively high Young’s modulus and strength, indicating good mechanical properties and a 

greater ability to withstand applied loads compared to the previous samples. 

According to Hooke’s law: strain produced in any body, is directly proportional to stress 

applied within the elastic limit.it is therefore indicative that, from the graph, stress I 

proportional to strain within the elastic limit of the mild steel. 

Resistance spot welding is a fusion welding process that works on the principle of Joule’s law 

of heating, which states that: Q = I2Rt, where ‘Q’ is the amount of heat generated during RSW, 

‘I’ denotes the welding current used, ‘R’ is the resistance setup at the interface of the metal 

sheets, and ‘t’ is the welding time employed 

 

 



43 

 

CHAPTER FIVE 

CONCLUSION AND RECOMMENDATIONS 

 

5.0 Conclusion and Recommendations 

Chapter five concludes the research study on “The Effects of Hold Time on the Mechanical 

Properties of Spot-Welded Mild Steel.” This chapter provides a summary of the main findings, 

draws conclusions based on the results and discussions, and offers recommendations for further 

research and practical applications. 

 

5.1 Summary  

Based on the provided parameters for samples 1 to 5 in the study on the effects of hold time on 

the tensile strength of spot-welded mild steel, here is a more detailed conclusion: 

 

1. Young’s Modulus: The Young’s modulus values vary across the samples, suggesting 

that different hold times can influence the stiffness or elasticity of the spot-welded 

mild steel. Sample 3 has the highest Young’s modulus (0.1032 N𝑚2), followed by 

sample 2 (0.0817 N𝑚2), sample 4 (0.0872 N𝑚2), sample 5 (0.07923 N𝑚2), and 

sample 1 (0.00010185 N𝑚2). This indicates that longer hold times (samples 3, 4, and 

5) generally result in higher Young’s modulus values, which implies a higher level of 

stiffness in the materials. 

2. Fracture Point: The fracture point values also demonstrate variation among the samples. 

Sample 5 has the highest fracture point (1300 psi), followed by sample 4 (1250 psi), sample 2 

(1200 psi), sample 3 (998 psi), and sample 1 (108 psi). These results suggest that longer hold 

times (samples 4 and 5) tend to result in higher fracture points, indicating improved resistance 

to failure. 



44 

 

3. Ultimate Tensile Strength: The ultimate tensile strength values exhibit a similar trend. 

Sample 4 has the highest ultimate tensile strength (109𝑁𝑚𝑚2), followed by sample 3 

(103𝑁𝑚𝑚2), sample 2 (98𝑁𝑚𝑚2), sample 5 (103𝑁𝑚𝑚2), and sample 1( 0.011𝑁𝑚𝑚2). 

Longer hold times (samples 3, 4, and potentially 5) generally correlate with increased ultimate 

tensile strength, indicating greater resistance to breaking under tension. 

4. Hold Time and Load: The hold time and load values vary for each sample. However, 

without specific details on the relationship between hold time, load, and the mechanical 

properties, it is challenging to draw specific conclusions regarding their effects. 

In summary, based on the provided parameters, the study suggests that longer hold times in 

spot welding mild steel tend to result in higher Young’s modulus, fracture point, and ultimate 

tensile strength. These findings imply improved stiffness, resistance to failure, and tensile 

strength in the spot-welded samples.  

The study also examines the relationship between hold time and ultimate tensile strength as 

follows: 

Sample 1: Hold time = 50 cycles, Ultimate Tensile Strength = 0.011𝑁𝑚𝑚2 

Sample 2: Hold time = 60 cycles, Ultimate Tensile Strength = 98 𝑁𝑚𝑚2 

Sample 3: Hold time = 70 cycles, Ultimate Tensile Strength = 103 𝑁𝑚𝑚2 

Sample 4: Hold time = 80 cycles, Ultimate Tensile Strength = 109 N𝑚𝑚2 

Sample 5: Hold time = 90 cycles, Ultimate Tensile Strength = 103 N𝑚𝑚2 

From the available data, it appears that there is a general trend of increasing ultimate tensile 

strength with longer hold times. As the hold time increases from sample 1 to 5 (50 to 90 cycles), 

there is a noticeable increase in the ultimate tensile strength values. This suggests that a longer 

hold time during spot welding of mild steel tends to result in an increase in the material’s 

ultimate tensile strength. 



45 

 

However, it’s important to note that the relationship between hold time and tensile strength is 

not the only factor influencing the ultimate tensile strength. Other parameters, such as load, 

Young’s modulus, and fracture point, can also play a significant role in determining the 

mechanical properties of spot-welded mild steel. 

 

5.2 Conclusion  

The following conclusions can be drawn regarding the relationship between hold time and 

tensile strength on mild steel in spot welding: 

I. Longer hold time tends to result in higher ultimate tensile strength: The data suggests 

that as the hold time increases from sample 1 to 5 (50 to 90 cycles), there is a trend of 

increasing ultimate tensile strength. This indicates that a longer hold time during spot 

welding of mild steel has the potential to enhance the material’s resistance to breaking 

under tension. 

II. Other factors may also influence tensile strength: While hold time appears to have a 

positive correlation with ultimate tensile strength, it’s important to consider that other 

parameters, such as load, Young’s modulus, and fracture point, can also impact the 

mechanical properties of spot-welded mild steel. Therefore, it is recommended to take 

these factors into account and conduct further analysis to gain a more comprehensive 

understanding of the relationship. 

III. Further research is needed: The conclusions drawn from the given data are based on a 

limited sample size and specific conditions. To establish a more robust and reliable 

relationship between hold time and tensile strength on mild steel, it is advisable to 

conduct additional experiments with a larger sample size, perform statistical analysis, 

and consider other relevant factors that may influence the mechanical properties of the 

spot-welded material. 



46 

 

IV. Overall, the data suggests that longer hold times in spot welding of mild steel have the potential 

to increase the ultimate tensile strength. However, for a more comprehensive and accurate 

conclusion, further research and analysis are necessary. 

 

5.3 Contributions and Implications  

The study on the effect of hold time on the tensile strength in spot welding of mild steel makes 

several contributions and carries important implications: 

i. Contribution to Knowledge: The study contributes to the existing knowledge by 

specifically focusing on the influence of hold time on the mechanical properties of spot-

welded mild steel. It provides empirical evidence of a positive correlation between hold 

time and tensile strength, expanding our understanding of the factors that affect the 

quality and strength of spot-welded joints. 

ii. Optimization of Welding Parameters: The findings of this study offer insights into the 

optimization of welding parameters in spot welding of mild steel. By identifying the 

impact of hold time on tensile strength, researchers and practitioners can adjust this 

parameter to achieve desired mechanical properties in spot-welded joints. This 

knowledge can aid in the development of guidelines and best practices for optimizing 

welding parameters in industrial applications. 

iii. Enhanced Joint Strength: Understanding the effect of hold time on tensile strength can 

help improve the quality and strength of spot-welded joints in mild steel. By optimizing 

the hold time, manufacturers can produce welds with higher tensile strength, leading to 

improved structural integrity, durability, and reliability of the welded components. This 

has implications for various industries where spot welding is commonly used, such as 

automotive, construction, and manufacturing. 



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iv. Cost and Time Efficiency: Optimizing the welding parameters, including hold time, can 

contribute to cost and time efficiency in spot welding processes. By determining the 

optimal hold time that maximizes tensile strength, manufacturers can reduce the need 

for post-weld treatments or additional reinforcement methods, saving both time and 

resources. This can lead to increased productivity and cost savings in production 

processes. 

v. Future Research and Development: The study provides a basis for further research and 

development in the field of spot welding. The findings suggest the need for exploring 

the combined effects of multiple parameters, microstructural changes, failure modes, 

and real-world applications. By addressing these areas, future research can contribute 

to the advancement of spot-welding techniques, optimization of welding processes, and 

development of innovative approaches for joining mild steel. 

Overall, the contributions and implications of this study lie in the improved understanding of 

the relationship between hold time and tensile strength in spot welding of mild steel. The 

findings have practical applications in various industries and can guide the development of 

optimized welding practices, leading to stronger and more reliable spot-welded joints. 

 

5.4 Recommendations  

 recommendations for future research in the field of spot welding and the mechanical properties 

of mild steel: 

a. Expand the Sample Size: To enhance the statistical significance and reliability of the 

findings, future research can aim to increase the sample size. A larger sample size 

would provide a more comprehensive understanding of the relationship between hold 

time and tensile strength, allowing for more robust conclusions. 



48 

 

b. Explore Additional Parameters: While hold time was the focus of the provided study, 

there are many other parameters that can influence the mechanical properties of spot-

welded mild steel. Future research can investigate the effects of parameters such as 

welding current, electrode force, electrode material, cooling rate, and surface 

preparation on the mechanical properties. Understanding the combined effects of 

these parameters will contribute to a more holistic understanding of spot welding in 

mild steel. 

c. Conduct Comparative Studies: Comparative studies can be conducted to evaluate the 

effects of different welding techniques or processes on the mechanical properties of 

spot-welded mild steel. For example, comparing conventional resistance spot welding 

with advanced techniques such as laser spot welding or friction stir spot welding can 

provide insights into the benefits and limitations of each method. 

 

d. Investigate Microstructural Changes: Understanding the microstructural changes that 

occur during spot welding can provide valuable insights into the relationship between 

process parameters and mechanical properties. Future research can employ techniques 

such as microscopy, X-ray diffraction, or electron microscopy to analyse the 

microstructural evolution in spot-welded mild steel and correlate it with mechanical 

properties. 

e. Consider Real-World Applications: It would be beneficial to investigate the effects of 

spot-welding parameters on mild steel in the context of real-world applications. 

Research focused on specific industries, such as automotive or construction, can 

provide insights into the optimal spot-welding parameters necessary to meet the 

mechanical requirements of these applications. 



49 

 

f. Analyse Failure Modes: Investigating the failure modes and fracture mechanisms of 

spot-welded mild steel can provide a deeper understanding of the relationship 

between welding parameters and mechanical properties. This analysis can help 

identify critical areas for improvement and guide the development of strategies to 

enhance the overall performance and reliability of spot-welded mild steel. 

By addressing these research recommendations, further advancements can be made in 

understanding the effects of spot-welding parameters on the mechanical properties of mild 

steel. This knowledge can contribute to improved welding techniques, enhanced joint strength, 

and the optimization of spot-welding processes in various industries. 

 

5.6 Remarks 

In conclusion, this study focused on investigating the effect of hold time on the tensile strength 

of spot-welded mild steel. The results showed that increasing the hold time led to an 

improvement in the ultimate tensile strength of the spot-welded joints. This finding suggests 

that longer hold times during spot welding have the potential to enhance the material’s 

resistance to tension. 

However, it is important to note that the hold time is just one of several parameters that can 

influence the mechanical properties of spot-welded mild steel. Factors such as welding current, 

electrode force, electrode material, cooling rate, and surface preparation also play significant 

roles. Future research should consider the combined effects of these parameters to develop a 

more comprehensive understanding of spot welding in mild steel. 

The findings of this study provide valuable insights for researchers and practitioners in the field 

of spot welding. By optimizing the welding parameters, such as the hold time, it is possible to 

achieve spot-welded joints with improved mechanical properties. This knowledge can 

contribute to the development of guidelines and best practices for achieving reliable and high-



50 

 

quality spot welds in mild steel applications. Further research is recommended to explore 

additional parameters, analyse microstructural changes, investigate failure modes, and consider 

real-world applications. By addressing these research recommendations, the field of spot 

welding in mild steel can advance, leading to enhanced joint strength, improved welding 

techniques, and optimized spot-welding processes in various industries. 

Overall, this study contributes to the existing knowledge on spot welding of mild steel and 

provides a foundation for further research in this area. The findings can aid in the development 

of more robust and efficient welding practices, ultimately benefiting industries that rely on 

spot-welded mild steel joints. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



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APPENDIX 

WELDING STANDARDS FOR MILD STEEL 

These standards and guidelines offer comprehensive information on welding procedures, 

qualification requirements, inspection methods, and quality control measures specific to mild 

steel and other materials. They provide valuable recommendations and best practices for 

achieving reliable and high-quality welds in mild steel applications. It’s recommended to 

consult the relevant standards and guidelines specific to your region and application to ensure 

compliance and adherence to industry-accepted practices. 

1. American Welding Society (AWS): 

   - AWS D1.1: Structural Welding Code – Steel: This standard provides guidelines for welding 

structural steel, including mild steel, in various applications. It covers welding procedures, 

qualification requirements, and inspection criteria. 

2. International Organization for Standardization (ISO): 

   - ISO 15614-1: Specification and qualification of welding procedures for metallic materials: 

This standard outlines the requirements for the qualification of welding procedures for various 

materials, including mild steel. It provides guidelines for testing and evaluating welding 

procedures to ensure their suitability for specific applications. 

3. European Welding Standards (EN): 

   - EN 1090-2: Execution of steel structures and aluminium structures: This standard specifies 

the requirements for the execution of steel structures, including welding procedures and welder 

qualification, in compliance with the European Union’s Construction Products Regulation 

(CPR). 

4. American Society of Mechanical Engineers (ASME): 



57 

 

   - ASME Boiler and Pressure Vessel Code (BPVC), Section IX: This code provides guidelines 

for welding and brazing qualifications. It covers the qualification of welding procedures and 

welders for various materials, including mild steel, in pressure vessel and boiler applications. 

5. British Standards Institution (BSI): 

   - BS EN ISO 9606-1: Qualification testing of welders – Fusion welding – Part 1: Steels: This 

standard specifies the requirements for the qualification testing of welders for fusion welding 

of steels, including mild steel. It outlines the testing procedures and criteria for assessing the 

welder’s competency. 

 

TERM USED 

After plotting the stress-strain graph, the interpretation of the results can provide valuable 

insights into the mechanical behaviour of the spot-welded mild steel.  

i. Elastic Region: The initial linear portion of the stress-strain graph represents the elastic 

region. In this region, the material deforms elastically, meaning it can return to its 

original shape once the applied stress is removed. The slope of this linear region 

corresponds to the material’s elastic modulus, which indicates its stiffness or rigidity. 

ii. Yield Point: The yield point on the stress-strain graph signifies the transition from 

elastic deformation to plastic deformation. It is the stress level at which the material 

starts to exhibit permanent deformation. The yield point is typically identified as the 

point where the graph deviates from linearity or shows a sudden increase in strain 

without a significant increase in stress. 

iii. Yield Strength: The yield strength is determined by identifying the stress value at the 

yield point on the stress-strain graph. It represents the maximum stress the material can 

withstand before it undergoes plastic deformation. Higher yield strength indicates 



58 

 

greater resistance to permanent deformation and is desirable in applications requiring 

structural integrity. 

iv. Plastic Deformation: Beyond the yield point, the stress-strain graph shows a region of 

plastic deformation. In this region, the material undergoes permanent deformation with 

increasing applied stress. The slope of this region represents the strain hardening 

behaviour, indicating how the material’s strength increases as it deforms plastically. 

v. Ultimate Tensile Strength: The ultimate tensile strength is the maximum stress the 

material can withstand before it fractures or fails. It is determined by identifying the 

highest point on the stress-strain graph. The ultimate tensile strength indicates the 

material’s ability to withstand tension forces, and higher values imply better mechanical 

performance. 

vi. Fracture Point: The stress-strain graph shows a sharp drop or decrease in stress after the 

ultimate tensile strength is reached. This signifies the fracture point or failure of the 

material, indicating its maximum strength limit under tension. The strain at the fracture 

point represents the material’s elongation or deformation at failure. 

 

 

 



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