INTRODUCTION
Put the problem
Metal 3D printing technology, a form of additive manufacturing (AM), has gained global traction but remains underutilized in Vietnam This innovative method builds objects layer by layer, unlike subtractive manufacturing (SM), which removes material to achieve the final product As the industry evolves, increasing awareness and adoption of metal 3D printing in Vietnam could enhance manufacturing capabilities and competitiveness.
The International ASTM Technical Committee on AM identifies seven prevalent additive manufacturing technologies: stereolithography (SLA), material jetting, material extrusion, binder jetting, powder bed fusion (PBF), sheet lamination, and direct energy deposition These methods typically rely on metal powders and melted plastic filaments, which can lead to material shortages and insufficient hardness in final products To address these challenges, metal 3D printing technology has been explored, utilizing laser energy to melt metal sheets, with promising applications in large components across engineering, architecture, and maritime industries.
WAAM (Wire Arc Additive Manufacturing) is an innovative metal 3D printing technology that employs arc welding energy to melt metal wire, enabling the additive layer-by-layer deposition of materials with the aid of shielding gas Unlike traditional metal sheet 3D printing, which melts materials in sheet form, WAAM integrates a robotic arm or CNC machine with GTAW welding technology to achieve precise shapes This method is cost-effective, as the primary material expenses stem from metal sheets, which are often more affordable and readily available compared to powder forms used in other additive manufacturing techniques.
The strength of additive layers is crucial in WAAM technology, and integrating it with CNC machining allows for the creation of optimal geometries that enhance the structural integrity of products This principle is explored in the research project titled "Investigation of Heat Source Movement Options in Metal Sheet 3D Printing."
Process" aims to explore the influence of heat source movement options on the mechanical strength and microstructural organization of the products using the WAAM method
This project aims to investigate and assess various heat source movement strategies for heating metal on a flat surface, with the goal of enhancing the efficiency and quality of metal production processes.
Research situation in Viet Nam
In recent years, the research and application of metal 3D printing technology, including
Additive Manufacturing (AM) is gaining traction in Vietnam, yet research on metal sheet 3D printing remains scarce There is a notable gap in studies examining the microstructural organization and mechanical strength of products created through AM technology.
Vietnam's metal sheet 3D printing sector is still in its early stages, highlighting the necessity for additional research to grasp its full potential and limitations This emerging field offers a significant opportunity for both researchers and industry professionals to play a vital role in advancing this technology within the country.
Research situation of orther contries
Additive Manufacturing (AM) technology has undergone over 20 years of research and development, leading to significant advancements and diverse applications across various industries, including aerospace, automotive, medical, energy, and space.
Additive manufacturing (AM) plays a crucial role in the aerospace and space industries by enabling the production of aircraft components, rocket engines, and intricate space structures This innovative technology facilitates the creation of lightweight designs, enhances operational efficiency, and minimizes material waste when compared to conventional manufacturing methods.
Additive manufacturing (AM) in the automotive industry enables the production of custom parts, including casting patterns, exhaust pipes, brake calipers, and interior components This innovative technology streamlines the manufacturing process, minimizes weight, and improves overall vehicle performance.
In the medical field, additive manufacturing (AM) has revolutionized the creation of custom implants, artificial hearts, dental prosthetics, bone scaffolds, and advanced body simulation systems, significantly enhancing patient care and treatment options.
Additive Manufacturing (AM) plays a crucial role in the energy sector by producing essential components for renewable energy systems, including solar panels and cast structures for power generators As AM continues to evolve and diversify, it has emerged as a vital tool in the manufacturing process, providing significant advantages over conventional manufacturing methods.
In conclusion, Additive Manufacturing (AM) technology is undergoing extensive research globally, focusing on microstructure, mechanical properties, and structural characteristics like hardness and tensile strength However, research on AM in Vietnam remains limited The study titled "Investigation of Heat Source Movement Options in the Process of Metal Deposition on a Flat Surface" aims to establish a foundational framework for advancing AM technology in Vietnam.
Graduation project goals
The research project "Investigation of heat source movement options in the process of metal deposition on a flat surface" is conducted with the following objectives:
- To survey and optimize the heat source movement options in four configurations: vertical, horizontal, curved, and diagonal directions
- To examine the tensile strength, hardness, and microstructural properties of the samples after heat source movement
This study investigates the correlation between key welding parameters, including step over distance between welding paths, deposition thickness, and the final height of the deposited material, to ensure the final dimensions meet the specified requirements of the sample.
Additive Manufacturing (AM) plays a vital role in the energy sector by producing essential components for renewable energy systems, such as solar panels and cast structures for power generators As AM technology evolves and diversifies, it has emerged as a crucial tool in manufacturing, providing significant advantages compared to traditional production methods.
Objects, research scope of the topic
Research on welding options of AM technology to assess the influence on microorganism and tensile strength of the product
1.5.2 Research scope of the topic
This research investigates the layer deposition process using the Tungsten Inert Gas (TIG) welding method with 2mm thick stainless steel plates The study aims to analyze how different heat source movement configurations affect the tensile strength and microstructural properties of the weld Mechanical properties of the weld bead will be evaluated based on existing literature regarding microstructure and tensile strength.
Research will yield valuable insights into how various heat source movement options affect the mechanical properties and microstructure of welded samples These findings will enhance the understanding of the TIG welding process for layer deposition and offer critical information for optimizing welding parameters, ultimately improving the strength and structural integrity of the fabricated products.
Research method
Combination of theoretical and experimental research
Refer to documents related to additive manufacturing (AM) technology
Using the software to evaluate the experimental results, write a program to simulate the profile for the moving plan to compare the optimality between the profiles
The article discusses the evaluation of various moving options with different profiles, ultimately selecting the four most effective running profiles for the heat source It emphasizes the use of a microscope to examine the microscopic structure and a tensile testing machine to assess product durability Additionally, statistical methods are employed to analyze the changes and interactions of factors influencing the product, allowing for comparisons with theoretical research to identify the optimal solution.
The scientific and practical significance of the graduation project topic
Research Topic: Investigation of Heat Source Movement Options in Metal Heating Process on a Flat Surface, Generating New Knowledge about the Process
The aim of this research is to explore various options for heat source movement during the process of metal heating on a flat surface The study intends to provide detailed
This research investigates the effectiveness of various heat source movement strategies in metal heating processes, aiming to identify optimal techniques for efficient heating outcomes By conducting experiments and analyzing data on heat distribution, temperature profiles, and energy consumption, the study seeks to enhance understanding and open avenues for further research and development in this field.
This research will enhance our understanding of the metal heating process on flat surfaces by analyzing different heat source movement strategies The findings will provide valuable insights for improving existing heating techniques and inspire innovative approaches in the field Additionally, this study will lay the groundwork for future research and advancements in metal heating technologies.
This research project investigates various methods for relocating the heat source during metal heating on flat surfaces The results will offer valuable insights into the efficiency and impact of different heat source movement strategies, paving the way for future advancements in this field.
Additive Manufacturing (AM) technology significantly reduces production time and costs by enabling the rapid and efficient creation of complex and customized products directly from digital design data, eliminating the need for traditional machining and assembly processes.
Additive manufacturing (AM) allows for the creation of products featuring intricate shapes and complex structures that traditional manufacturing methods cannot achieve This capability paves the way for innovative research and development in advanced products across various sectors, including healthcare, industry, and materials science.
Additive Manufacturing (AM) technology enables swift and efficient repair and component replacement, significantly enhancing the maintenance of systems and equipment This innovation reduces downtime and minimizes costs related to component replacement, making it an invaluable asset for businesses seeking to optimize their operations.
Additive Manufacturing (AM) technology provides substantial time and cost efficiencies over traditional manufacturing methods By directly creating intricate and customized products from digital designs, AM eliminates the necessity for complicated machining and assembly processes, lowers tooling expenses, facilitates on-demand production, and enhances material utilization These benefits position AM as an effective and economical solution for modern manufacturing needs.
Limitations of the research
This article investigates the techniques for relocating heat sources while heating metal on flat surfaces, emphasizing the examination of the microstructure and tensile strength of weld specimens However, it is important to note that the study does not encompass the exploration of heat source movement on curved, irregular, or specially shaped surfaces.
Structure of the thesis
The expected structure of the thesis, apart from the introduction and the prescribed table of contents, will be presented in 6 chapters as follows:
This chapter will outline the purpose of conducting the research
This chapter will present the theory of 3D metal printing, including factors and parameters influencing the process
In this chapter, the design and fabrication of the prototype will be carried out
Chapter 4: Sample testing and evaluation
The steps and methods for testing the sample will be presented before conducting the actual testing
Chapter 5: Statistical analysis and evaluation of test results
This chapter will present the test results and include force diagrams and result evaluations Chapter 6: Conclusion
OVERVIEW OF RESEARCH TOPIC
Overview of additive manufacturing technology
Additive Manufacturing (AM), commonly referred to as 3D printing, involves creating objects by layering materials according to 3D model data This innovative technology can be categorized into various types depending on the primary materials used, including plastics, polymers, concrete, metals, and ceramics The physical state of these input materials—whether liquid, molten, powder, or solid—plays a crucial role in determining the bonding methods employed in both direct and indirect processes.
The AM layering process utilizes a CAD design file along with 3D printing software to transform a product model into thin slices This method directs the material flow to stack and overlap each layer, ultimately resulting in a fully realized 3D product.
Figure 2 1 Operating principle of Additive Manufacturing (AM) technology
AM technology, commonly known as 3D printing, is increasingly utilized beyond prototyping, finding applications in diverse industries such as shipbuilding, aviation, automotive, and biomedical research This innovative technology is regarded as a promising advancement for the future.
Classification of AM technology
Figure 2 2 Methods in Additive Manufacturing (AM) technology
According to the ASTM 2013 (American Society of Testing and Materials) standard, there are 7 methods:
Material extrusion is a process that involves extruding materials through a nozzle, where plastic is melted and combined with a layer of metal powder to create the desired product shape.
Material Jetting: In this technology, the material will be sprayed onto a flat surface and solidified in layers, then these layers will be hardened by ultraviolet (UV) light
Sheet Lamination: is a type of technology that depends on two main processes: ultrasonic additive manufacturing (UAM) and multi-layer material processing (LOM)
Vat Photopolymer: is an AM additive manufacturing technology that uses photopolymer fluids to create objects It is also known as Stereolithography (SLA) or Digital Light Processing (DLP)
Binding jetting: is a bonding inkjet technology, metal powders will be bonded together with a liquid binder to create solid details
Powder Bed Fusion (PBF) encompasses several advanced technologies, including Direct Metal Laser Sintering (DMLS), Electron Beam Melting (EBM), Selective Laser Melting (SLM), Selective Laser Sintering (SLS), and Selective Heat Sintering (SHS) This innovative process utilizes lasers or electron beams to effectively melt powdered materials, enabling the creation of highly detailed and durable components.
Direct Energy Deposition (DED), also known as Laser Metal Deposition (LMD) or Electron Beam Deposition (EBD), is an advanced manufacturing technology that utilizes lasers or electron beams to generate a weld pool on a product's surface In this process, metal particles are heated and fused together, resulting in a strong bond after the welding is completed.
AM technology has a number of advantages and disadvantages compared to traditional machining methods:
Freelance Design: AM enables the creation of highly detailed and complex shaped objects that are difficult or impossible to achieve with traditional machining methods
Material savings: AM uses material only as needed to create the object, minimizing material waste compared to traditional cutting machining, where unnecessary cutting and removal of material is required
Additive Manufacturing (AM) technology significantly reduces time and costs by eliminating the need for molds and machining tools, as the production process is fully automated This efficiency is particularly beneficial for producing small or custom product batches, making it a more economical choice compared to traditional machining methods.
Diversity of materials: AM additive technology can use a wide range of materials, including plastics, metals, ceramics, composites and combinations
Production speed: AM typically has a slower production rate than traditional machining, especially for large and complex objects
Accuracy and surface finish: Some AM processes may have less accuracy and surface finish than traditional machining
Additive manufacturing (AM) typically restricts the size of objects compared to conventional machining methods The dimensions and height of printed items are constrained by the capabilities of the 3D printer and the size of the build platform.
Initial investment costs: The initial investment for 3D printers and related equipment can be significant compared to traditional machining methods This can increase costs for businesses new to AM technology
Additive Manufacturing (AM) technology, researched for nearly 40 years, is gaining significant attention for its capability to produce customized, complex, and material-efficient products By integrating various welding technologies like MIG, MAG, or TIG with robotic arms and CNC machines, AM accelerates production processes compared to traditional methods This innovative technology has notably reduced metal waste, reflected in improved Buy To Fly Ratios (BTF).
Some materials used in AM technology
Metal powders, including aluminum, stainless steel, titanium, copper, and zinc, play a crucial role in additive manufacturing (AM) processes These powders are primarily utilized in techniques such as Direct Metal Laser Sintering (DMLS) and Selective Laser Melting (SLM), enabling the creation of complex metal parts with high precision.
Metal wires, including aluminum, stainless steel, titanium, and nickel-chromium (Inconel), are essential for processes like Wire Arc Additive Manufacturing (WAAM) and Laser Metal Deposition (LMD), enabling the creation of metal layers.
Metal rods play a crucial role in additive manufacturing (AM) processes, particularly in methods such as Directed Energy Deposition (DED) and Bound Metal Deposition (BMD), where they are employed to produce high-quality metal components.
Metal alloys play a crucial role in the creation of metal layers alongside pure metal materials A notable example is the nickel-titanium alloy, known as Nitinol, which is utilized in additive manufacturing to produce items with shape memory characteristics.
Metal fibers, including stainless steel and carbon fibers, play a crucial role in enhancing the mechanical properties of metal additive manufacturing (AM) products through their incorporation in Fiber Reinforced Metal Matrix Composites (FRMMCs).
Additive Manufacturing (AM) utilizes sheet steel to produce metal products by overlapping and bonding thin layers, resulting in a finished item.
TIG electrodes welding in a protective gas environment
2.4.1 General concept of TIG welding in a protective gas environment
TIG welding, or Tungsten Inert Gas Welding, is an industrial method for joining metal materials, utilizing a non-consumable tungsten electrode This process employs a stream of inert shielding gas, typically argon, to safeguard the welding area from air and oxygen, ensuring high-quality welds.
TIG welding, performed in a shielded gas environment, is extensively utilized across various industries such as machine building, automotive, aviation, metalworking, and construction This versatile and precise welding technique enables the production of high-quality welds on a diverse range of metal materials.
TIG welding is known for creating clean and aesthetically pleasing welds, thanks to the use of a non-consumable tungsten electrode and inert shielding gas, usually argon This shielding gas effectively protects the weld pool from atmospheric contamination, leading to welds that exhibit minimal defects, porosity, and oxidation.
Figure 2.3 Diagram of TIG welding system
Reference source: U.S Army Welding Manual (2005)
TIG (Tungsten Inert Gas) welding is a welding method used in industries to join metal materials Here are some key characteristics of the TIG welding process:
TIG welding employs a non-consumable tungsten electrode, known for its high melting point, which enables the creation of a hot arc to effectively melt the welding area.
During the TIG welding process, an inert shielding gas, usually argon, creates an oxygen-free environment around the weld area, effectively preventing oxidation and ensuring a high-quality weld.
TIG welding is characterized by a slower welding speed compared to other methods, enabling precise control over the welding process and resulting in high-quality welds.
TIG welding offers exceptional control over welding current, shielding gas flow, and heat zones, allowing for precise adjustments tailored to specific materials and welding requirements.
- Accurate and aesthetically pleasing welds: The TIG welding process produces accurate and visually appealing welds The welds have high strength, uniformity, and no impurities or gas porosity
TIG welding offers exceptional material versatility, enabling the welding of a diverse array of metals such as stainless steel, aluminum, copper, and various alloys This capability makes TIG welding a highly adaptable and widely utilized process across various industries.
- Wide range of applications: TIG welding is employed in various industries such as machinery manufacturing, automotive, aerospace, metal fabrication, and construction
2.4.3 Advantages and disadvantages of Tig welding
- High Quality: TIG welding produces high quality welds with high strength and uniformity Welds are resistant to high loads and pressures
- Beautiful welds: TIG welding process creates beautiful welds, without impurities, air bubbles or cracks This makes the weld easy to clean and finish
- Versatile: TIG welding can be used on a wide variety of metal materials, including stainless steel, aluminum, copper and other alloys
TIG welding offers exceptional control over essential parameters like current, shielding gas flow, and heat zone, enabling precise adjustments tailored to specific materials and welding requirements.
TIG welding ensures a clean and high-quality weld by preventing impurities, as there is no direct contact between the electrode and the working material.
- Slow welding speed: The TIG welding process usually takes place slower than some other welding methods This can increase welding time and increase production costs
- Complex technique: TIG welding requires high skill and experience to perform effectively The adjustment and control of important parameters in the welding process requires careful attention and fine-tuning
- High cost: TIG welding machines and related accessories are often more expensive than some other welding methods
Welding in hard-to-reach areas can be challenging due to the non-consumable nature of the electrode, which necessitates maintaining a specific distance from the work surface This limitation makes it difficult to effectively weld complex shapes and intricate designs.
The table below will provide the compatibility of some gases with some common metals:
Table 2.1 Applications of Some Types of Gases in TIG Welding
Metal is welded Protective gas
Stainless Steel Argon Welding of machine parts, pipes, water supply systems, automobile manufacturing
Aluminum Argon Aluminum tube welding, electronic equipment manufacturing, fixture manufacturing
Copper Argon Brazing copper pipes, nickel copper pipes, manufacturing water tanks, exhaust pipes
Light alloy Argon Welding aluminum-magnesium alloys, manufacturing aircraft, cars, sporting goods
Heavy alloy Argon Welding titanium alloys, stainless steel alloys, manufacturing vehicles, aircraft
Zinc Argon Welding zinc pipes, assembling construction works, manufacturing drilling rigs
Welding steel pipes, factory structures, construction works
Argon Welding duplex stainless steel structures, manufacturing drilling rigs, agricultural equipment
Welding materials and equipment
In the TIG (Tungsten Inert Gas) welding process, the selection of shielding gas is crucial for achieving high-quality and durable welds Shielding gas protects the welding area from atmospheric contamination, creating a non-reactive environment that preserves the weld's properties and consistency Common types of gases and gas mixtures utilized in TIG welding play a significant role in optimizing the welding process.
Argon is a colorless, odorless, and tasteless inert gas that does not form chemical compounds under any conditions Extracted from the atmosphere through air liquefaction, it is refined to a purity of 99.9% and has a density of 1.33, making it heavier than air This non-reactive gas is the most common shielding gas used in TIG welding, valued for its excellent protective properties that prevent oxidation in the weld area without affecting the metal.
13 argon has good thermal conductivity, helping to control the welding zone temperature As a result, the weld quality is improved with high load-bearing capacity
Helium is a colorless, odorless, and tasteless inert gas with a density of 0.13 compared to air, extracted from natural gas and stored in high-pressure cylinders With a low liquefaction temperature of -272°C, helium is commonly used as a shielding gas in TIG welding, particularly for aluminum, due to its higher thermal conductivity than argon, which enhances welding zone temperature and speed Additionally, helium's excellent electrical conductivity allows for precise control of welding energy, offering flexibility in the process However, its rarity and high cost can increase production expenses, and its tendency to evaporate quickly poses challenges in flow rate control.
Nitrogen is commonly added to argon for welding copper and its alloys, while pure nitrogen is utilized for stainless steel welding As an additive to argon or argon/helium mixtures, nitrogen creates a non-reactive shielding gas that prevents chemical reactions with the metal and eliminates oxygen in the welding environment, enhancing weld stability and consistency This economical and readily available gas simplifies the TIG welding process, making it a practical choice for various applications, although it does not fully substitute argon in TIG welding.
An argon/helium mixture serves as an effective shielding gas in TIG welding, leveraging the unique properties of both gases By adjusting the ratio of argon to helium, welders can tailor the mixture to meet the specific needs of different applications and materials It is essential to optimize the phase ratio of argon and helium to achieve the desired welding results.
The addition of hydrogen gas to argon, forming an Ar-H2 mixture, enhances arc voltage and offers benefits similar to those of helium A 5% hydrogen gas mixture significantly improves the cleaning effect in manual TIG welding, while a 15% mixture is ideal for high-speed mechanized welding of stainless steel lap joints up to 1.6 mm thick This mixture is also effective for welding stainless steel beer kegs of various thicknesses, particularly with a weld root gap of 0.25-0.5 mm However, it is crucial to avoid excessive hydrogen gas, as it can lead to porosity issues in nickel alloys and stainless steel welds.
In TIG welding, the choice of shielding gas is crucial and varies based on the specific application, the materials being welded, and the desired welding characteristics Commonly used gases and gas mixtures play a significant role in achieving optimal results.
Table 2.2 The types of gases used in TIG welding according to DIN standards
Alloy and low alloy steel Argon 100%
High-alloy steels resistant to heat, acids, high-alloy steels
Aluminum and Alloys Aluminum, Copper and Alloys Copper, Nickel and Nickel
Gas sensitive materials such as titanium, tantal
Tungsten, also known as Wolfram, is favored as an electrode in TIG welding because of its exceptional heat resistance and high melting point of 3410°C It exhibits relatively good electron emission and can effectively ionize while maintaining a stable arc, alongside its impressive oxidation resistance The two primary types of electrodes used in TIG welding are crucial for achieving optimal performance.
Pure Tungsten (green tip) is composed of 99.5% pure tungsten, making it a cost-effective option for welding While it offers affordability, it has a low current carrying capacity and is susceptible to contamination This type of tungsten is primarily utilized for welding with alternating current (AC), particularly when working with aluminum and lightweight alloys.
Thoriated Tungsten electrodes, identifiable by their red tip, contain 1 to 2% thorium (ThO2), which enhances electron emission for higher welding currents and prolongs electrode life These electrodes facilitate easy arc ignition and stable burning, offering excellent resistance to contamination They are primarily used with direct current (DC) for welding steel and stainless steel.
Additionally, there are other types of tungsten electrodes:
Zirconiated tungsten electrodes, containing 0.15 to 0.4% zirconium and characterized by a brown tip, offer a balanced performance between pure tungsten and thoriated tungsten They are particularly effective for AC welding applications involving aluminum and provide the added benefit of being non-radioactive, unlike thoriated electrodes.
Ceriated tungsten, featuring a 2% cerium content and an orange tip, is a non-radioactive electrode that ignites easily and maintains a stable arc Known for its longevity, it excels in both direct current (DC) and alternating current (AC) applications, making it a versatile choice for welding tasks.
- Lanthanated Tungsten (containing lanthanum oxide, similar properties to ceriated tungsten)
Table 2.3 Classification and composition of tungsten electrodes according to AWS A5.12 standard
Tungsten electrodes are available in diameters from 0.25 to 6.35 mm and lengths between 70 to 610 mm They can feature either a clean surface, achieved by removing impurities post-drawing or extrusion with appropriate solutions, or a ground surface, where impurities are eliminated through grinding techniques.
Various grinding forms are available based on the application, material, thickness, and joint type For AC current welding, larger electrodes and rounded grinding are favored, while pointed grinding is more suitable for DCEN current welding.
Tungsten electrode used for DC current Tungsten electrode used for AC current.
Figure 2 4 The various forms of tungsten electrode grinding
Figure 2 5 Methods of grinding tungsten electrodes
Reference source: TIG welding technology by Đặng Trung Dũng
Table 2.4 Table for detailed dimensions during tungsten electrode grinding
Electrode diameter Welding rod tip diameter
Polarity DCEN mm mm Degree Continuous
The values in the table below apply to Argon gas, other current values may be used depending on the shielding gas and equipment type
The shape and grinding technique of the electrode play a crucial role in maintaining the stability and focus of the welding arc Electrode grinding is performed using a fine-grit grinding wheel in the axial direction, as illustrated in the accompanying diagram.
TIG weld formation and organization
Factors influencing the transfer of liquid metal from the electrode to the weld pool:
- Effect of gravity on liquid metal droplets: Under the influence of gravity, liquid metal tends to move towards the weld pool (significant in butt welding)
Surface tension, generated by molecular forces, minimizes the surface area of liquids, causing liquid metal droplets to take on a spherical shape This phenomenon is crucial in fillet welding, as it pulls droplets into the weld pool, allowing them to merge into a cohesive mass.
Magnetic forces are generated around the electrode when current flows through the welding wire and base metal, acting on the liquid metal and reducing its cross-sectional area As the welding current density (J) increases at the constriction, the liquid metal reaches its boiling point and detaches from the electrode Despite this, the large surface area of the weld pool leads to low magnetic field intensity and current density, allowing for a continuous transfer of liquid metal into the weld pool across all welding positions.
- Gas pressure: Due to the high temperature of the arc, strong reactions occur, and the flux coating on the welding wire melts, generating a significant amount of gas This creates a
23 pressure that pushes the liquid metal from the electrode into the weld pool (significant in overhead welding)
These factors collectively contribute to the transfer of liquid metal from the electrode to the weld pool during the welding process.
General rules in the manufacture of tensile specimens
The shape and size of the test piece may be constrained depending on the shape and dimensions of the metal product used to take the test piece
Test pieces are typically machined prototypes derived from the product, blank, or cast However, products with a uniform cross-section, such as shaped products, rods, and wires, along with cast test pieces for cast iron and non-ferrous alloys, can be tested without undergoing a machining process.
The cross-section of the test pieces may be square, round, rectangular, annular or, in special cases, several identical cross-sections of a part
The test pieces are selected with certain standard for the convenience of tensile testing
In this case the standard ASTM E8/E8M -13
According to ASTM E8/E8M -13 at Standard Test Methods for Tension Testing of Metallic Materials (Standard Test Methods for Tension Testing of Metallic Materials)
Figure 2 10 Tensile test specimen size [7]
Table 2 6 Tensile sample size according to ASTM [7]
Standards of sample Sample sub size
[0.250 in.] mm[in] mm[in] mm[in]
A –Length of reduced section, min
B –Length of grip section, min
C –Width of grip section, approximate
THEORETICAL BASIS
Tensile strength test method
3.1.1 Theoretical basis of tensile testing
Based on the impact on the material or product, we have two main testing methods: Destructive Testing (DT) and Non-Destructive Testing (NDT)
To test the quality of the tensile strength of the sample, we choose the destructive test method
Tensile testing is a fundamental method for assessing the yield strength, tensile strength, and elongation of steel plates The procedure involves securing the specimen at both ends with clamps while a load is applied, gradually increasing until the specimen fails This testing provides critical data on the strength, quality, and reliability of the material Additionally, the mechanical properties of metals and welded joints are evaluated through static, dynamic, and fatigue tensile tests While tensile testing offers valuable insights into material performance, it also has its advantages and disadvantages that should be considered.
The pull test method provides an accurate assessment of tensile strength by measuring the maximum load a material can endure before failure, offering crucial insights into its strength and performance under tensile forces.
The pull test method evaluates various mechanical properties, including yield strength, elongation, modulus of elasticity, and ultimate tensile strength, alongside tensile strength Understanding these properties is crucial for the effective design and engineering of materials and products.
Non-destructive testing (NDT) is a crucial method for evaluating tensile strength and mechanical properties without causing any permanent damage to the material or product Unlike destructive testing, the pull test method can be performed non-destructively, ensuring that the integrity of the item remains intact while still providing valuable insights into its performance characteristics.
The pull test method is a versatile technique applicable to a diverse array of materials, including metals, plastics, composites, and adhesives This method is essential across multiple industries, such as manufacturing, construction, automotive, aerospace, and quality control, ensuring reliable performance and material integrity.
The pull test method is an essential quality control tool used to validate products and materials against specified standards By identifying weaknesses, defects, or inconsistencies in performance, this method enables manufacturers to implement necessary improvements and adjustments, ensuring that the final products meet quality requirements effectively.
Standardized testing procedures, governed by established standards like ASTM and ISO, ensure consistency and comparability in pull test results across various laboratories and industries.
The pull test is a destructive testing method that permanently damages or alters the sample, rendering it unusable and unsellable as a finished product.
Sample preparation for pull testing involves creating test samples with precise dimensions and configurations This process can be time-intensive and may necessitate specialized equipment or expertise to achieve accurate and consistent results.
The pull test method may face limitations due to the size and geometry of the sample, making it difficult or even impossible to conduct tests on small or irregularly shaped components.
Pull testing is primarily designed for assessing individual components or materials, making it inadequate for evaluating the strength of assembled products or complex structures This limitation arises because the interactions between various parts are crucial in determining overall strength and performance.
The pull test method often fails to accurately simulate the real-world loading conditions and environmental factors that components or materials encounter in their intended applications, potentially resulting in discrepancies between test outcomes and actual performance.
Conducting pull tests necessitates specialized equipment and trained personnel, leading to potential additional costs This investment in both testing tools and training may be impractical for some organizations or specific testing needs.
Adjust the zero point of the force
Before effectively clamping the test piece at both ends, it is essential to adjust the force measuring system on the gage to zero after installing the test load actuator.
Once the force zero has been set, the parameters in the force measurement system shall not be changed in any way during the test
To ensure accurate results during tensile testing, it is crucial to securely clamp the test specimen using effective methods like hydraulic clamping systems, threaded clamp jaws, parallel-faced grips, or notched grips The clamping jaws must possess adequate hardness and grip strength to prevent any slippage of the specimen throughout the test.
Methods of checking microorganism
A metallographic microscope is a specialized optical instrument utilized to examine the microscopic structure of metals The technique employed to assess and analyze this microscopic organization is known as metallurgical analysis.
Metallographic microscopes have magnifications from 80 to 2000 times The team wanted to observe with higher magnification, so they had to use an electron microscope
Through microscopic observation we can see the organization of the phases, their distribution, shape and size In addition, we can see material defects such as microcracks and impurities
The method employed for particle size determination under the microscope allows for the analysis of phase composition and organization, as well as the identification of key material characteristics, including the depth of the permeability layer and the presence of air bubbles.
Quantitative metallographic analysis helps determine the mechanical properties of metals, it supports methods such as chemistry, spectroscopy, etc
Austenite grains, also known as gamma iron, are an allotropic that has a great influence on the mechanical properties of metals Coarse austenite grain will have low ductility
To identify austenite grains, an oxide grid is created through the oxidation of a polished sample, leading to pronounced oxidation of grain boundaries after cooling and polishing, making the oxide grid distinctly visible at the austenite grain edges Various techniques exist for measuring grain size and quantifying phases during microscopic observation.
The grid method is a technique used to assess grain size by overlaying a grid of square lines on a microstructure image By counting the number of grains that intersect with the grid lines, this method provides a quantitative measure of grain size, ensuring accurate and reliable results in material analysis.
The line intercept method involves randomly placing straight lines on a microstructure image and counting how many times these lines intersect with the grains This data is then utilized to statistically estimate the grain size, providing valuable insights into the material's characteristics.
The standard comparison method is a technique used to determine grain size by analyzing a microstructure image and comparing it to a collection of standard images or charts that depict various grain sizes The grain size is identified by selecting the closest match from these references.
The point counting method involves overlaying a grid of points on a microstructure image to quantify the phase fractions By counting the number of points that fall within each phase, such as austenite and other phases, researchers can accurately determine the distribution of different microstructural components.
First it is necessary to determine the value of the ruler at the magnification used of X10
To accurately measure using a micrometer, place the instrument on the sample measuring table and utilize a polished metal plate marked with a 1 mm ruler divided into 100 increments of 0.01 mm as a standard reference Ensure that the microscope is adjusted for clear visibility of all divisions on the ruler.
The CMEX DC 5000-C camera model supports microscopic observation through the ImageFocus 4 software, allowing users to capture the objective lens gauge at specific magnifications By connecting the scale with a mouse and assigning a value, the software automatically saves measurements, enabling easy and accurate particle size analysis by clicking on grain boundaries.
Method to calculate particle size after having data
The average grain area is calculated: 𝑆 𝑡𝑏 = 𝜋.𝐼 𝑡𝑏 2
Based on the average area of the particle, we can look up the table to find the particle level [10]
Smaller grain sizes lead to a larger total grain boundary area, resulting in enhanced resistance to sliding and increased durability This relationship is quantitatively expressed by the Hall-Petch equation, which states that the yield strength (σ0.2) is related to grain size (d) as follows: σ0.2 = σ + kd^1/2.
Including: σ is the stress required to deflect the motion when d → ∞ (corresponding to the single crystal case)
31 k is a constant denoting the structure of the grain boundary
Table 3.1 The relationship between grain grade and grain area
Particle area (mm 2 ) Number of particle in 1mm 2
Smallest Medium Biggest Smallest Medium Biggest
Method of Scanning Electron Microscopy (SEM)
Scanning Electron Microscopy (SEM) is a crucial technique utilized in material science, biology, and various other disciplines for high-resolution imaging and analysis of samples Understanding SEM requires a grasp of its operating principles and the structural components of the scanning electron microscope.
The scanning electron microscope (SEM) utilizes a powerful electron beam produced by an electron gun, which is then directed across the sample's surface This interaction leads to various phenomena, allowing for detailed analysis of the sample's topography and composition.
Backscattered Electrons (BSE) are electrons that reflect off a sample when they interact with heavier atoms or those with different atomic weights These electrons typically possess higher energy, enabling the analysis of areas within the sample that have greater atomic mass.
Secondary electrons (SE) are emitted from a sample's surface when struck by a primary electron beam These electrons typically possess lower energy levels and are instrumental in generating high-resolution images of the sample's surface.
- Cathodoluminescence (CL): Some samples exhibit luminescence when impacted by the electron beam This luminescence can provide information about the sample's composition and structure
3.3.3 Structure of the Scanning Electron Microscope (SEM)
The scanning electron microscope consists of the following main components:
- Electron Gun: The electron source, typically a tungsten filament or a field emission electron source, generates the electron beam
- Imaging System: This includes the scanning system and sensors to collect signals from the electron beam interacting with the sample
- Observation Chamber: To display the sample's image and control the imaging process
- Control System: It controls the electron beam scanning, imaging system, and processes and displays the images on the screen
RESEARCH, DESIGN, AND FABRICATION OF TENSILE TEST
Testing weld profiles for optimal welding parameters
Testing weld line profiles aims to determine optimal parameters, including the distance between the electrode tip and the work surface, as well as the spacing between weld lines This testing is essential for reducing common welding issues such as material shortages, gas porosity, and electrode adhesion to the sample surface.
We use a single parameter for all movement options: Voltage 220V, Current Intensity (A) 165A, Gas Flow Rate 11 liters per minute, Welding Speed 30 mm per minute
4.1.2 Results of testing for welding movement option a) Straight profile - D b) Short profile - N
In the experimental study of welding seam movement, two distinct profiles were analyzed: a straight profile, where the heat source is moved to melt the steel plate in a continuous line of 150 mm, and a short profile, with the heat source moving in a straight line for only 25 mm.
34 c) Cross profile - HC d) Curved profile - DT
This article illustrates the movement of welding seams through experimental images captured from a top-down perspective Specifically, it details two distinct profiles: a cross profile, where the heat source is directed diagonally to melt the steel plate, and a curved profile, where the heat source is maneuvered in a curve with a radius of 40mm to achieve the desired melting effect.
For samples designated as D, we maintain a distance of 9 mm between welds to achieve a height ranging from 8 mm to 10 mm, while selecting an arc length of 2 mm for this configuration.
The sample profile is designated as N, with a specified distance of 10mm between welds to create a sample height ranging from 8mm to 10mm For this scenario, we select an arc length of 2mm.
In cross profile analysis, we refer to samples as HC, maintaining a distance of 14mm between welds to produce samples with a height ranging from 8mm to 10mm For this application, we select an arc length of 2mm.
The curved profile, referred to as DT in arc welding, is a unique design Based on our experiments, we determined that a distance of 9 mm between welds is optimal for creating samples with a height ranging from 8 mm to 10 mm For this specific case, we selected an arc length of 2 mm.
Each profile we complete 3 tensile test pieces, each test piece is fully machined and carefully measured according to the standard dimensions below.
Tentile test sample design
Based on ASTM E8/E8M-13 standards, we choose and design tensile test pieces with dimensions as shown below:with dimensions as shown below:
Figure 4.3 Tensile test specimen Table 4.1 Dimensions of tensile specimens according to ASTM [7]
Width 6mm [0.250 in.] mm[in]
A –Length of reduced section, min 32 [1,25]
B – Length of grip section, min 30 [1,25]
C –Width of grip section, approximate 10 [0,375]
4.2.2 The case of taking a test sample
Each profile we complete 3 tensile test pieces, each test piece is fully machined and carefully measured according to the standard dimensions below
STT U(V) I (A) V (mm/min) Agron (l/min) Option
To investigate heat source migration, 12 samples were welded using constant parameters, with each of the 4 profiles yielding 3 test pieces Each weld sample was processed into blocks, sized 100x10x6mm, for tensile testing From these blocks, smaller samples measuring 15x10x6mm were cut for microscopy, and additional samples of 10x4x6mm were prepared for scanning electron microscopy (SEM) The welding was conducted in specific patterns as illustrated.
Figure 4.4 Initial weld pattern parameters
Process tensile test sample
Figure 4.5 Tools and equipment for specimen fabrication a) CNC machine; b) TIG welding machine; c) Vertical milling machine; d) Bandsaw machine; e) Wire-cutting machine; f) Vernier caliper; g) Vise
4.3.2 Machining of tensile test samples
Step 1: Set parameters of TIG welding machine
TIG welding, or Gas Tungsten Arc Welding (GTAW), utilizes a non-melting electrode in a shielded gas environment, primarily employing argon as the shielding gas This method is also referred to as WIG, which stands for Wolfram Inert Gas welding.
Distance from the tungsten electrode tip to the welding surface
Percentage of main ingredients Wolfram (W): 99.5 - 99.9%
Possible impurities Titanium (Ti), Mercury (Hg) (In very small amounts) Welding material thickness 1 - 6 mm
Auxiliary gas Argon or argon/helium gas mixture
Welding materials Stainless steel, aluminum, copper, Other alloys
Step 2: Clean and prepare the soldering C45 steel base for melting after attaching to the machine
Step 3: Carry out welding for the samples for sample
Figure 4.7 Manufacturing process of tensile test piece b) d) e) c)
The welding sample fabrication process involves several key operations: first, establishing the origin of the welding process; second, programming the CNC command for the movement of the TIG welding gun; third, initiating the welding process; fourth, completing a line of welding for the sample; and finally, applying multiple layers of welding to create a finished sample.
Step 4: After having the welded sample, we begin the process of testing the tensile sample
The process of creating a tensile sample involves several key operations First, the surface is flattened through mechanical milling (Operation 1) Next, a molybdenum wire cutting machine is employed to cut the sample according to specific drawings (Operation 2) Following this, a sawing machine is utilized to reduce the sample's thickness to 5-6 mm (Operation 3) Finally, the surface is milled again to achieve the required thickness of 4 mm, as specified in the design (Operation 4).
SAMPLE INSPECTION AND EVALUATION
Tensile Testing Process
- Drawer (for interval) on the samples
Figure 5.1 Tools and Equipment for Tensile Testing a) Vernier caliper; b) SANS Hydraulic Compression Testing Machine
The SANS Hydraulic Compression Testing Machine offers the capability to display data on a computer screen via specialized software, enabling users to generate graphs and access critical parameters, including yield point, upper and lower yield points, maximum load, fracture point, tensile strength, elongation, and elongation coefficient.
- Distance between two columns of the machine: 600 mm
- The machine uses an electric motor and weighs 3550 kg
- Mesure width bo và thickness ao at the begin
- Predict the ultimate strength of the material (the tensile force at which the sample breaks) to determine the appropriate load capacity
- Select the appropriate grips and load capacity of the machine based on the diameter of the test specimen
- Place the test specimen into the grips, start the tensile testing machine, observe the graph, and record the parameters during the testing process
Figure 5.2 Tensile Testing in Progress a) Placing the test specimen into the tensile testing machine b) Observing the tensile force and the deformation graph
To ensure accurate testing, gradually increase the load while closely monitoring the force gauge and deformation graph Record the yield force (Pch) when the force stabilizes despite ongoing deformation, and identify the ultimate force (Pb) as the peak force before the specimen fails, as indicated by the stress-strain curve After the specimen fractures, promptly turn off the machine, relieve the pressure, and carefully remove the test sample.
Figure 5.3 Sample before and after tensile testing
The strain graph illustrated in Figure 5.4 highlights key positions, including the tensile fracture force (Fm), the upper yield point, and the elastic tensile forces P1 and P2 (E_Begin and E_End) Analyzing this graph allows for the precise determination of both the yield point and the ultimate strength of the sample.
Figure 5.5 Graph showing the relationship between tensile force and strain during tensile testing
OA: In the elastic phase, the relationship between force and deformation is a first-order relationship, the smallest and largest pulling force is called force P1 and P2
Including: 𝑃 1 , 𝑃 2 Tensile force at the beginning and end of the elastic phase
𝛥𝑙 1 , 𝛥𝑙 2 Strain length at the beginning and end of the elastic phase
L Initial gauge length, with ASTM we have L = 32mm
AC: In the plastic deformation phase, the force remains constant while the strain increases
The force value at this stage is called the yield force
CBD: Fracture phase Ultimate strength is calculated:
Microscopic observation process
Figure 5.6 Equipment for Microscopic Observation: a) Microscope; b) Grinding machine; c) Various types of sandpaper; d) Polishing machine; e) Etching solution; f) Micrometer
To effectively monitor the microstructure along each weld line, from the beginning to the end, the research team requires vertical cutting of the samples.
For the sample cutting, the group has used a specific metal cutting machine, specifically a saw They proceeded to cut the samples with dimensions of 10x10x50mm for observation
Figure 5.7 The saw machine is used for cutting samples 5.2.3 Sample preparation and observation method: a) Coarse grinding:
Sample after cutting is coarsely ground using sandpaper from coarse to fine
Different types of sandpaper are usually numbered from small to large, and the larger the number, the finer the sandpaper For example, 180, 240, 320, 400, 600, etc
Coarse grinding begins with 180-grit sandpaper positioned on a flat surface or thick glass plate, where the sample is pressed against it in a consistent direction to create parallel scratches The process is repeated by lifting the sample and applying pressure again, followed by rotating the sample 90 degrees to eliminate previous scratches and generate new ones This method is continuously repeated to achieve a refined surface.
The process involves using progressively finer sandpapers, including 240, 320, and 400 grits It is essential to clean the sample thoroughly when transitioning to a finer sandpaper to eliminate any residual coarse particles Polishing follows this step to achieve a smooth finish.
After coarse grinding, fine scratches may remain on the surface of the sample, necessitating further polishing This process involves using a machine equipped with a cloth or felt pad to effectively remove these imperfections.
Figure 5.8 MP-2B Grinder Polisher machine for sample grinding and polishing
For effective polishing, apply a small amount of polishing solution, usually containing Chromium oxide (Cr2O3), to the cloth or felt Continue the polishing process until the surface achieves a scratch-free finish.
After polishing, it is crucial to rinse and dry the sample thoroughly A microscopic examination is necessary to identify any remaining scratches If scratches are detected, the sample should undergo additional polishing.
Etching is a technique that involves corroding a metal surface with a specialized chemical solution, commonly referred to as an etching solution For effective etching, it is essential that the surface of the sample is clean and devoid of scratches, rust, and other impurities.
After etching, the surface of the sample will reveal corroded and uneven features corresponding to different phases and structures
The etching process involves quickly and evenly applying a rotating cotton swab or cotton ball to the sample surface for a few seconds To prevent deep chemical corrosion that can lead to dark black spots, the surface must be thoroughly rinsed with a water spray Finally, the sample is gently dried to complete the process.
- Step 1: Plug in the power and turn on the light switch
- Step 2: Select the objective lens, eyepiece, and adjust the interpupillary distance
- Step 3: Place the sample on the sample stage, where the light shines on
- Step 4: Adjust the coarse and fine knobs and observe on the computer screen
- Step 5: Adjust the focus knob to clearly view the microscopic structure
To accurately assess measurements at a magnification of X10, it is essential to establish the value of the measuring scale In this scenario, a metal plate featuring a polished surface is utilized, equipped with a 1mm long scale divided into 100 increments, where each division represents 0.01mm.
To ensure accurate measurements, position the standard measuring scale of 47 on the sample stage of the microscope, ensuring that the entire scale and its divisions are clearly visible.
The CMEX DC 5000-C camera model supports ImageFocus 4 software for precise microscopic observations Users can capture images of a measuring scale at a specific magnification and connect the scale divisions using the mouse to assign values This information is automatically saved by the software, simplifying the measurement of particle sizes By clicking on the boundaries of the particles, the software accurately and effortlessly performs the necessary measurements.
Figure 5.10 Microscopic observation image taken on the microscope a) Micrometer b); c); d) Micrographs at 3 samples, respectively D1, D2, D3 of the move plan D e); f); g) Micrographs at 3 samples, respectively N1, N2, N3 of the move plan N
Microscopic observations were conducted, showcasing images from samples HC1, HC2, and HC3 under the move plan HC, as well as samples DT1, DT2, and DT3 under the move plan DT The micrographs provide detailed insights into the characteristics of each sample, highlighting the differences and similarities between the two plans.
Scanning Electron Microscope (SEM)
5.3.1 Introduction to scanning electron microscopy (SEM)
Figure 5.12 General view of scanning electron microscopy (SEM)
Scanning Electron Microscopy (SEM) is an advanced imaging technique that utilizes a focused electron beam to examine the surface of specimens This method generates electronic signals that interact with the sample, yielding valuable information regarding surface morphology, compositional structure, and crystal structure.
Scanning Electron Microscopy (SEM) is widely applied across various fields, including biology and materials science In biology, SEM enables detailed observation of cell structures and tissue models, facilitating the study of their structure and function In materials science, it examines the surface and structural properties of materials, aiding in the analysis of their physical and chemical characteristics Overall, SEM is a crucial tool for exploring the microscopic world, significantly advancing scientific and technological research.
The scanning electron microscope (SEM) images presented in Figure 5.13 showcase two options: D and N Subsections a) and b) display SEM images of option D1 at magnifications of 500x and 1500x, respectively Meanwhile, subsections c) and d) illustrate SEM images of option N1 at the same magnifications.
Figure 5.14 The image captured by the scanning electron microscope (SEM) represents option of HC and DT
50 e) ; f) are SEM images of option HC1 at magnifications of 500x and 1500x, respectively g) ; h) are SEM images of option DT1 at magnifications of 500x and 1500x, respectively
Welding is essential across multiple industries, and to assess the quality and longevity of welds, we utilized Scanning Electron Microscopy (SEM) at magnifications of x500 and x1500 to examine prevalent defects like porosity and weld slag Our findings from the SEM analysis are detailed below.
SEM images at x500 magnification identified significant quality issues in the weld samples, with porosity being the most common problem This porosity manifested as unevenly distributed voids, creating weak zones that heighten the risk of cracking during service Consequently, these porosity-affected areas act as stress concentrators, resulting in a substantial decrease in the overall strength of the weld.
Weld slag, characterized by small, irregular particles with uneven distribution, poses a significant challenge by compromising both the aesthetics and mechanical properties of welds This issue can lead to the formation of voids, initiate cracks, and weaken adhesion between material layers, ultimately diminishing the weld's lifespan.
At x1500 magnification, we obtained a clearer understanding of the issues present in the welds, enabling us to pinpoint small yet significant details that could have been missed at lower magnifications Despite this enhanced visibility, quality concerns like porosity and weld slag remained prevalent even at higher magnification levels.
To enhance the quality and durability of welds, we propose the following improvement measures:
1 Control welding processes: Ensure precise control of temperature, welding time, and pressure to minimize the occurrence of porosity and weld slag
2 Use high-quality welding materials: Select the best alloy and welding materials to reduce the risk of porosity and weld slag formation
3 Perform weld quality inspections: Conduct post-weld inspections to ensure welds meet the required standards
4 Provide welding training for workers: Train welders in accurate welding techniques and quality inspection procedures
The SEM analysis at x500 and x1500 magnifications has revealed significant quality issues in the welds, particularly concerning porosity and weld slag By assessing and reviewing weld quality, we aim to implement suggested improvements that will enhance the performance and durability of future welds.
STATISTICS AND ASSESSMENT OF SUPPLY SAMPLE TEST
Sample parameters of the testing sample
Parameters of the location of the test pieces:
Figure 6.1 Shows the location of the tensile sample taken from the specimen block
Figure 6.2 The position for microscopic observation
In each case, the tensile processing and testing are conducted with multiple samples, and the results are averaged and presented in the table below
6.1.1 The parameters of the test samples for each option
Table 6.1 Average test results of each option
Elongation at break Δl max (mm)
Relative elongation at break ε max (%)
After thoroughly testing all samples and analyzing the data presented in the table, we proceeded to saw the testing textile samples into smaller pieces for microscopic examination This allowed us to conduct statistical analysis to determine the frequency of grain levels within each sample.
We conducted an analysis using a microscope with 10x magnification and a micrometer, selecting 15 particles from each of the 5 positions, resulting in a total of 75 particles per sample This methodology allowed us to gather statistical data and plot the particle frequency across 12 tensile samples, as illustrated below.
From the above calculation results, we can draw a stress diagram representing 4 options for welding profiles:
Figure 6.3 Stress diagrams of different options
Figure 6.4 Histogram showing the particle-level frequencies of the different alternatives
Figure 6.5 Tensile strength comparison chart of samples and 2mm steel plate
Figure 6.6 Comparison chart of the elongation of the samples and the original 2mm steel plate after breaking
The tensile strength of samples from four welding methods exceeds the minimum 270 MPa of the original JIS G-3141 SPCC steel However, these welded samples generally exhibit lower elongation at break than the original steel plate, primarily due to the melting process during welding.
The TIG welding torch employs a heat process that melts and cools steel plates, significantly impacting their crystal structure and microstructure This process results in a weld that features a new crystal structure, which can alter the size and shape of the steel grains, ultimately leading to reduced elongation.
In evaluating the elongation of four welding methods, each method was tested with three samples to determine average tensile strength The results revealed that the D heat source movement method achieved the highest average tensile strength, followed by the N movement method The DT movement method ranked third, while the HC movement method recorded the lowest average tensile strength among the tested methods.
The D heat source movement method effectively melts steel in a continuous straight line, allowing for uniform and consistent application of welding force along the sample's length This approach prevents welding force concentration and imbalances in the welding pool, ultimately enhancing the load-bearing capacity of the test samples.
The particle size distribution, or grain size, is a crucial factor influencing the mechanical strength of a weld Smaller grain sizes contribute to a more homogeneous weld with uniform properties, resulting in increased tensile strength Conversely, larger grain sizes may enhance ductility but also elevate the risk of crack formation, ultimately compromising the weld's overall strength.
The D movement method exhibits a particle size distribution predominantly in grades 8 and 9, with a notable concentration in grade 8 While the majority of particles fall within grade 8, a significant quantity is also present in grades 7 and 9 This distribution results in the highest tensile strength compared to the other three movement methods.
The N movement method exhibits a particle size distribution predominantly in grades 7, 8, and 9, with grade 8 showing the highest concentration, followed by grades 7 and 9 Additionally, test samples obtained from this method demonstrate commendable tensile strength.
The DT movement method produces a particle size distribution predominantly in grades 7, 8, and 9, with grade 8 showing the highest concentration Additionally, there is a significant presence of particles in grades 7 and 9 Test samples derived from this method demonstrate relatively strong tensile strength.
The HC movement method results in a particle size distribution predominantly in grades 7, 8, and 9, with grade 8 exhibiting the highest concentration Notably, the particle count in grade 7 surpasses that of grade 9, which significantly influences the tensile strength of the test samples.
In summary, the D heat source movement method demonstrates superior tensile strength due to its evenly distributed welding force and finer grain size distribution While other methods also achieve satisfactory tensile strength, the HC movement method, characterized by a higher concentration of larger grain sizes, results in slightly lower tensile strength compared to the D method.
Tensile strength parameters at the positions of the options
In a survey on heat source migration for weld sample durability testing, the movement of the heat source significantly influences the mechanical properties of the samples However, other contributing factors also play a role in these variations.
56 difference despite the same heat source migration scheme such as cooling time, surface conditionof the material, presence of impurities, etc
6.2.1 Option 1: Move the heat source in a long straight line (D)
Figure 6.7 Comparison chart of tensile strength and elongation of D profiles
Figure 6.8 Histogram showing the particle-level frequencies of the different alternatives
The D movement method, characterized by the linear movement of the heat source to melt steel plates, demonstrates significant findings regarding tensile strength, grain size, and elongation across three tested samples.
Sample 2 exhibits the highest tensile strength at 501.06 MPa and an impressive elongation exceeding 40% This remarkable performance is attributed to the high heat input and uniform grain size distribution, which enhance bonding and elasticity The presence of grain sizes 7, 8, and 9 contributes to a more homogeneous distribution, ultimately improving the material's mechanical properties and allowing it to endure significant loads before fracture.
Sample 3 exhibits a tensile strength of 430.58 MPa and an elongation of 20.88% While these values surpass those of Sample 1, they fall short compared to Sample 2 The observed heterogeneity in grain size distribution may have led to uneven bonding and weaker structural integrity, ultimately influencing the tensile strength and elongation of Sample 3.
- Sample 1 has the lowest tensile strength, only reaching 330.73 MPa, and an elongation of 15.5% This sample exhibits the poorest performance among the 3 samples in the D
57 movement method When evaluating the sample through SEM micrographs, some common TIG welding defects such as cracks and gas porosity can be observed in its internal structure
The D heat source movement method, characterized by high heat input and uniform grain size distribution, has proven to enhance tensile strength and elongation in welds Sample 2 exhibits the best mechanical properties, showcasing superior bonding, while Sample 1, with the lowest tensile strength and elongation, demonstrates significant TIG welding defects Additionally, the distribution of grain size is critical in influencing the mechanical performance of the weld, with a more homogeneous distribution resulting in better outcomes.
6.2.2 Option 2: Move the heat source in a short straight line (N)
Figure 6.9 Comparison chart of tensile strength and elongation of N profiles
Figure 6.10 Histogram showing the particle-level frequencies of the different alternatives
The N movement method, characterized by short, straight-line movements of the heat source to melt steel plates, yields significant results regarding tensile strength, grain size, and elongation across three samples.
Sample 1 exhibits exceptional tensile strength of 471.27 MPa and an impressive elongation of over 16% The more uniform grain sizes of 7, 8, and 9 enhance the material's mechanical properties Notably, the concentration of grains at size 8 significantly contributes to the sample's strong tensile strength.
Sample 2 exhibits a tensile strength of 451 MPa and an elongation of 10.94%, surpassing Sample 3 but falling short compared to Sample 1 The grain size distribution remains consistent around size 8, contributing to its respectable tensile strength and elongation properties.
Sample 3 demonstrates the lowest tensile strength at 272.22 MPa and an elongation of 6.28%, making it the least effective among the three samples tested using the N movement method Despite its poor performance, the grain size distribution remains predominantly clustered around sizes 7, 8, and 9, with size 8 being the most frequent.
In summary, the N heat source movement method utilizing short straight lines has yielded diverse results across different samples Sample 1 stands out with superior tensile strength and elongation, attributed to its uniform grain size distribution Sample 2 shows satisfactory tensile strength and elongation as well Conversely, Sample 3, while exhibiting the lowest tensile strength and elongation, still performs reasonably well due to its concentrated grain size distribution, particularly at sizes 7, 8, and 9, with size 8 being especially notable.
6.2.3 Option 3: Move the heat source in a short cross profiles (HC)
Figure 6.11 Comparison chart of tensile strength and elongation of HC profiles
Option 3: Move the heat source in a short cross profiles (HC)
Figure 6.12 Histogram showing the particle-level frequencies of the different alternatives
The HC movement method, characterized by the movement of the heat source in long straight lines to melt steel plates, yields significant results regarding tensile strength, grain size, and elongation across three samples.
Sample 2 exhibits the highest tensile strength of 433 MPa and an elongation exceeding 15%, demonstrating that the high-temperature melting process and larger grain size contribute to a strong bond and excellent elasticity This allows the specimen to endure significant loads while maintaining substantial elongation before fracturing Additionally, the more homogeneous distribution of grain sizes 7, 8, and 9 enhances the material's mechanical properties.
- Sample 3 has a tensile strength of 355 MPa and an elongation of 10.9% Although its tensile strength and elongation are higher than those of Sample 1, they are lower than those
The non-uniform grain size distribution in Sample 2 can lead to inconsistencies in grain sizes and weak intergranular bonds, ultimately impacting the specimen's tensile strength and elongation properties.
Sample 1 demonstrates the lowest tensile strength at just 207 MPa and an elongation of 5.9%, indicating the weakest performance among the three samples tested using the D movement method SEM micrographs reveal typical TIG welding defects, including cracks and gas porosity within the specimen.
The HC heat source movement method using short straight lines has produced mixed results across different samples Notably, Sample 2 achieved the highest tensile strength and elongation, attributed to its more uniform grain size distribution Sample 3 also showed satisfactory tensile strength and elongation, while Sample 1 exhibited the lowest values, with SEM analysis indicating typical TIG welding defects within the specimen These findings indicate a need for further optimization of the HC movement method to enhance the mechanical properties of welded specimens.
6.2.4 Option 4: Move the heat source in a short curved profiles (DT)
Figure 6.13 Comparison chart of tensile strength and elongation of DT profiles
Figure 6.14 Histogram showing the particle-level frequencies of the different alternatives