The research topic aims to determine the welding mode to achieve a quality weld joint when welding the materials SUS 304 and C20 using the MIG welding method.. The main purpose of this s
INTRODUCTION
Overview
Nowadays, Stainless steel and low carbon which are the two types of material are the most important and common in industrial field Thanks to their outstanding features, they have helped them become the main material in the production of cars, ships, airplanes and unique architectural works Connecting different types of steel joints together to make the steel joints stronger and economical.However, this is a huge challenge for manufacturers and researchers One of the challenges when welding two different materials is the formation of a hard and brittle intermetallic layer structure at the interface area of the two materials [1] This intermetallic layer significantly reduces the load-bearing level of the welded joint There have been many authors who have successfully welded carbon steel and stainless steel alloys using welding methods such as friction stir welding, laser welding, TIG welding, ultrasonic welding, etc The main purpose of this study is to study the welding characteristics between C20 carbon steel and SUS304 stainless steel using a semi-automatic welding process in a protective gas (MIG) environment The results of the study focused mainly on evaluating the formation and thickness of the intermetallic layer, as well as its influence on the mechanical properties of the weld joint between these two materials.
Domestic
In Vietnam, research on the welding of different materials, especially the optimization of welding parameters to enhance the mechanical properties and durability of welded joints, has been extensively conducted For example, Dang Thien Ngon and Tao Anh Tuan from the Ho Chi Minh City University of Technology and Education investigated the influence of welding parameters on the tensile properties of rotary friction welded joints between low carbon steel AISI 1020 and stainless steel AISI 304 The study identified that friction time, welding force, and rotation speed are critical factors affecting the tensile strength of the welds Optimal welding conditions—friction time of 6 seconds, welding force of 100 MPa, and rotation speed of 1450 rpm—resulted in tensile strengths ranging from 86.89% to 93.68% of the base material strength [2].
Foreign
Globally, extensive research has been done on welding dissimilar materials like C20 steel and SUS304 stainless steel Jakkrit Thamprajamjit and Prayoon Surin from the Pathumwan Institute of Technology in Thailand studied the plasma arc welding (PAW) process parameters for welding stainless steel SUS304 and carbon steel SS400 They varied welding speed, shielding gas composition, and welding current, concluding that the optimal conditions
2 included a welding speed of 400 mm/min, a welding current of 110 A, and a shielding gas mixture of Ar95% + He5%, which resulted in a maximum tensile strength of 455.99 MPa in the heat-affected zone [3]
Overall, both domestic and international research have significantly advanced the understanding and optimization of welding parameters that giving reference sources have inspired us to develop and research MIG welding between steel and stainless steel, providing valuable insights for achieving high-quality welds with improved mechanical properties and durability.
Main objectives
- Deep understanding of the function, characteristic and technical requirements of this welding process
- Grasp the fundamental principles of welding technical
1.4.2 Practicing the welding technique with 304 stainless steel
- Performing the C20 welding on material
- Ensure the quality of welding technique
1.4.3 Analysis the result of C20 technical and compare with another welding technical
- Analyze weld quality and determine their load-bearing capacity
- Evaluate factors affecting welding quality and propose improvements
- Compare the result of this technical with the another one.
Objectives and scope of researching
The goal of this topic is use for businesses in the manufacturing industry requiring C20 welding technique for their products Besides that, the topic is use for engineering managers to take the responsibility of quality in products line
1.5.2.1 C20 welding process with 304 stainless steel
- Analyze the process of C20 technique in execution and control the quality
- Evaluate the effective element during C20 welding process
- Examination of the applications of C20 welding technique with stainless steel 304 in various industries
- Evaluation of commercial potential and the application of welding methods in mass production.
Research methodology
The research methodology of the project on C20 welding with stainless steel 304 can be divided into stages and research methods as follows:
Examine and understand the fundamental principles of the C20 welding process
Research the properties and applications of stainless steel 304 in the welding industry
Conduct a technical and engineering evaluation of C20 welding with a focus on stainless steel 304
Gather and analyze relevant studies, articles, and specialized documents
Utilize quality control methods to ensure the accuracy and uniformity of weld joints
Evaluate the existing quality and propose improvements if necessary
- Discussion and Proposal of Solutions:
Discuss research results and compare them with standards and requirements
Propose solutions to enhance the welding process and product quality
Organize and write a report detailing the research methodology, implementation process, and achieved results
Present findings comprehensively and share experiences gained during the research
The research methodology will integrate both theoretical and practical aspects to ensure that the project is not only academically rigorous but also applicable in real-world situations, adding value to the field of C20 welding with stainless steel 304.
The meaning of science and practice
Investigating and finding the good options for optimal weld in MIG between the steel C20 and inox SUS304 Then, the development of way to find the best case to use it in real environment Also, this science will focus on all the method and improvement to be better As a result, we can select the best criterion for assessment the products
The idea to develop weld in MIG between the steel C20 and Inox SUS304 will help each people in field of manufacturing mechanical products or technology This tech not only impact on enterprises but also contribute to the social development
Easily to assess the weld in product that help all enterprises, and labor to find the efficient of products in real environment Avoiding the error in manufacturing and selling it to the society.
The limited of this project
This topic is going to concentrate on MIG welding technology Additionally, measuring and evaluating the microstructure and tensile strength of the welded products by using a microscope and compression machine, then we use two materials such as the steel C20 and inox SUS304 to perform the experiment.
The structure of this project
Content of this project has 6 chapters and depict it below:
Chapter 3: Research, design, manufacture of test sample
THEORETICAL BASIC
Learn about mig welding technology
Gaseous metal arc welding (GMAW), known as metal inert gases (MIG) or metallic active gases (MAG) welding in subgroups, is a process that involves the formation of an electric arc between a consumable MIG wire electrode and the metal(s) of the workpiece This arc heats the workpiece metal(s), causing them to melt and rejoin The welding gun, along with the wire electrode, directs a protective gas flow that shields the process from atmospheric contamination
When the welding electrode or welding wire is automatically fed into the arc zone through the wire feeding mechanism, while the arc shift along the weld is manipulated manually, it is called semi-automatic arc welding in a protective gas environment If all basic movement is mechanized, it is called automatic arc welding in a protective gas environment
During gaseous metal arc welding (GMAW), an arc discharge occurs between the consumable solid metal electrode and the weld pool Protective gases, either inert gas for MIG (Metal Inert Gas) welding or chemically active gas for MAG (Metal Active Gas) welding, shield the electrode wires, liquid metal transfer within the arc, and welding pools from exposure to air
These welding techniques find application across various industries for the joining of both ferrous and non-ferrous metals Commonly used gases or gas mixtures include argon, helium, and combinations thereof in MIG welding, while MAG welding utilizes mixtures of these gases with CO2, H2, O2, and N2 In MIG-MAG welding, molten electrodes typically serve as anodes, contributing to improved arc stability [4] [5]
Figure 2 1 Diagram depicting the welding torch
This process can be either semi-automatic or automatic While DC power supplies with constant voltage are most commonly used with GMAW, constant current systems and alternating current can also be utilized GMAW features four main metal transfer methods: spherical, short-circuit, injection, and pulsed injection, each with distinct characteristics, advantages, and limitations
Figure 2 2 MAG welding system diagram
Originally developed in the 1940s for welding aluminum and other non-ferrous metals, GMAW soon became popular for steel welding due to its faster welding times compared to other methods However, the high cost of inert gas initially limited its use in steel welding
7 until semi-inert gases like carbon dioxide became more widely adopted several years later Advancements in the 1950s and 1960s further increased the versatility of this process, leading to its widespread use in industrial settings
Today, GMAW is the most widely used industrial welding process, valued for its versatility, speed, and ease of integration with robotic automation systems Unlike welding processes that do not use shielding gas, such as shielded metal arc welding, GMAW is typically not used outdoors or in environments with significant air movement In contrast, conventional flux core arc welding often operates without shielding gas, relying instead on hollow, flux-filled electrode wires
The MIG/MAG welding process enables the creation of weld beads with controlled electrode metal displacement using STT (Surface Tension Transfer) technology, facilitating procedural groove filling Currently, this method enjoys widespread adoption Additionally, after laying down the base layer, welding procedures may utilize electrodes with a basic coating type in addition to the MIG/MAG process [6]
Figure 2 3 Scheme of MIG/MAG process
Gas metal arc welding requires essential equipment, including a welding gun, wire feeder, power supply, electrode wire, and a supply of shielding gas
GMAW stands out as one of the most prevalent welding techniques, particularly in industrial settings It finds extensive application in industries such as sheet metal fabrication and automotive manufacturing In these sectors, it often replaces rivet point welding or resistance point welding for arc spot welding
Furthermore, GMAW is frequently employed in automated welding processes, where robots handle both workpieces and welding guns to enhance production efficiency However, GMAW may pose challenges when used outdoors, as drafts can disperse protective gases and introduce contaminants into the weld In such outdoor scenarios, flux core arc welding is often preferred, especially in construction applications
Likewise, GMAW's use of shielding gas is not suitable for underwater welding, which is usually done through shielded metal arc welding, flux core arc welding, or gas tungsten arc welding [7]
Figure 2 4 Diagram of electric arc welding with a molten metal electrode in a protective medium with active gas
3 Rolls with additional materials, 9 Contact tube
4 Drive roller (wheel), 10 Protective atmosphere
Table 2 1 Application of shielding gas with welded metal [4]
At the welding site where melt droplets pass through the arc into the welding pool, it is necessary to take measures to protect against the oxidizing effects of the surrounding air This protection can be successfully implemented using appropriate protective gases
The density of the shielding gas significantly impacts its ability to shield the arc and welding pool from surrounding air Values denoting the relative density of protective gases compared to air are crucial Argon and carbon dioxide, boasting the highest density among gases currently known, effectively envelop the arc with a protective gas layer In contrast, hydrogen and helium have densities 10 to 20 times lower than argon, making them prone to turbulent flow due to thermal buoyancy when exiting a bellows nozzle
However, in the MIG/MAG welding process, gaseous plasma also contains metallic vapors that are relatively easily ionized and thus become a carrier As a result, the characteristics of the weld have fundamentally altered Argon, with its low ionization potential, creates a soft and stable arc, whereas helium, with its high ionization potential, produces an arc that is less stable and more difficult to ignite [8]
Figure 2 5 Influence of shielding gas in Mig/Mag welding processes
MIG welding in a protective gas environment
To determine the fabrication of tensile samples that we could do the test conveniently and smoothly So the workpiece specifications based on the mold to produce drawing pattern, which has 3 dimensional parameters such as: length, width, and height The parameters number in the workpieces that we choose for length, width, and height is 110 mm, 105 mm, and 2mm, respectively
Two type of material workpiece: Steel C20, Inox SUS 304, the quantity of each is 16, then totally combine them having 32 workpieces The picture below is the illustration
Figure 2 6 Two workpieces: C20 and Inox SUS 304 b Argon protective gas
Argon is a gas does not burn and explode By the heavy of argon higher than oxygen, which argon can ensure to weld According to standard some country SNG (GOST 10157-62) pure
11 argon has 3 types: A, B and C (Table 1-1) Moisture for 3 types of gaseous argon must not be exceeded 0.03 g/m 3 [9]
Figure 2 7 The tank of argon gases
Argon type A: Using for welding and smelting active and rare metals (Titan, Zirconi, Noibi) and their alloys, and for welding some important especially product in the end of the stage manufacturing
Argon type B: Using for welding and smelting aluminum, mage base alloys and other alloys are sensitive to impurities of gases dissolved in the metal, by melting electrode and un-melting wolfram electrode
Argon type C: Using for welding and smelting some alloys with anti-rust chromium nickel and heat resistant, clean alloy steel and aluminum [9]
Table 2 2 The argon of gas composition by percent mass (GOS 10157) [7]
Argon is preserved and transported into linked monolithic gas tanks A tank with below 150
AT pressure contains about 6m 3 gaseous argon Tank harbor argon is painted black at under and white at top “Cleaned argon” is printed above
Welding wire is a metal that added into weld, and plays a role such as electrode to cause an arc and maintain combustion
When welding in a protective gas environment, the alloying of the weld metal as well as the required properties of the weld is performed only through the welding wire Therefore, the characteristics of the welding technological process depend enormously on the condition and quality of the welding wire
Figure 2 8 The welding wire Per AWS standards, welding wire is designated in the following manner: [10]
Welding wire ranging in diameter from 0.6 to 1.6 mm: 0.6; 0.8; 0.9; 1.1; 1.2; 1.4; 1.6
R – Rod: auxiliary welding rod, introduces metal into the weld
70 – minimum tensile strength of the weld metal, measured in ksi - 1000 pounds/ inch 2
S - solid: solid welding wire, to distinguish it from welding wire with flux core
X- alloying components and deoxidizing elements contained in the welding wire
Illustrates the mechanical properties and chemical composition of various welding wires as specified by the AWS All wires listed (E70S-2, E70S-3, E70S-4, E70S-5, E70S-6, E70S-7) utilize DCEP polarity with CO₂ as the protective gas Each type exhibits a tensile strength of
72000 psi and a melting strength of welded joints at 60000 psi, with a minimum elongation percentage of 22%
The chemical composition of these wires varies slightly
E70S-2 has a carbon content of 0.6%, manganese is not specified, and silicon ranges from 0.40 to 0.70%
E70S-3 has 0.06 to 0.15% carbon, 0.90 to 1.40% manganese, and 0.45 to 0.70% silicon E70S-4 contains 0.07 to 0.15% carbon, 1.40 to 1.85% manganese, and 0.65 to 0.85% silicon E70S-5 has 0.07 to 0.19% carbon, 1.50 to 2.00% manganese, and 0.30 to 0.60% silicon, with additional elements including titanium (0.05 to 0.15%), zirconium (0.02 to 0.12%), and aluminum (0.05 to 0.15%)
E70S-6 contains 0.07 to 0.15% carbon and 0.80 to 1.15% silicon, with aluminum content ranging from 0.50 to 0.90%
E70S-7 features 0.07 to 0.15% carbon and 0.50 to 0.80% silicon d Clamping fixture for welding samples
The fixture is processed and installed to easily conduct welding experiments on two steel materials C20 and Stainless Steel 304 The fixture is bought from materials and mechanically welded with 2 clamping arms to easily clamp the two materials Conducting the welding experiment of two steel materials C20 and Inox 304, the jig has fixed with 3 positioning mechanical chip to easily position the workpiece By attached the chip, standard installation and welding experiments become easier
According to YA-1NA robot instructions This robot, whose name is TA-1400, is the model of series YA-1NA Welding robot is a robotic machine using motor to control the axis and having 4 parts such as: The operation box, Robot controller main body, Teach pendant, Robot
14 manipulator Each parts have a specific use that we can combine it to get full function of welding robot
Figure 2 10 Structure of welding robot
Rotation (RT): 2.97 rad/sec (170°/sec)
Upper Arm (UA): 3.32 rad/sec (190°/sec)
Front Arm (FA): 3.32 rad/sec (190°/sec)
Rotation (RW): 6.46 rad/sec (370°/sec)
Bending (BW): 6.54 rad/sec (375°/sec)
Twisting (TW): 10.5 rad/sec (600°/sec)
Positioning Repeatability Precision: ±0.1 mm or less
Robot manipulator has 6 arm axes due to the motor Each axis arm can rotate independently or combine 2 axes together for move along the coordinate axis Including 6 axes, for instance:
RT axis (Rotational Traverse), FA axis (Front Arm), ), TW axis (Twist Wrist) RW axis (Rotate Wrist), UA axis (Upper Arm), BW axis (Bent Wrist [11]
Robot controller main body is a power supply that provide welding current and control the machine
Operation box is a button function providing a lot of function when we control and use the welding robot a Teach pendant
Teach pendant is a tool that we can program an operation for axes move It can work based on program that we setup in a teach pendant with a programming file We can adjust parameters and speed of axes b Wire feeder
Wire feeder including a lot of parts such as motor with 2 or 4 rolls, welding wire coil are combination together [10]
We could adjust the speed of welding wire feed speed which depend on the speed we want accurately When the voltage change, control circuit will adjust and prevent some the speed of wire feed to minimum or high for following the speed of welding
Figure 2 11 Wire feeder c Protective gas supply equipment
Including pressure regulator and protective gas tank Pressure regulator has a major important information about the pressure and air flow that we can adjust the parameters by electronic valves Then the gas tank will contain argon gas and harbored with high-pressure compressed air
Figure 2 12 Argon gas pressure gauge d Welding power source
Welding power source is a tool that provide welding current It has 2 poles negative and positive, the negative will attach to the product and the opposite will attach into a welding gun It using one-way polarized DC current to maintain electric So it can change welding parameters easily
The welding current used in MIG welding has the most significant impact on deposition rate, weld size, shape, and penetration b) Voltage
Voltage is an important factor which affects the electrode melting rate In MIG welding, welding voltage affects surface’s temperature, welding border, height and width of the welding line c) Electrode’s stick-out
Stick-out of electrode is the length of the welding wire protruding from the welding nozzle The thickness of electrode’s stick-out affects the width of penetration through the welding current The distance between the air nozzle and the surface of the part impacts the effectiveness of shielding the liquid metal from air exposure If the air nozzle is too close, it will easily burn and metal debris will cover the nozzle [12] If it is too far away, the protection process will be destroyed d) Welding speed
C20 steel material theory
Steel plays a crucial role in many industrial and construction sectors Carbon Steel C20 is a type of steel that contains a specific amount of carbon in its chemical composition Typically,
"C20" is associated with a carbon content of approximately 0.20%, where "C" represents carbon and "20" denotes its percentage in the chemical composition Carbon Steel C20 is classified as low carbon steel with a carbon content (%) of less than 0.25%
Presents the chemical composition of C20 steel, expressed in weight percentages The carbon (C) content is 0.192%, manganese (Mn) is 0.68%, and silicon (Si) is 0.34% Phosphorus (P) and sulfur (S) are present in smaller amounts, at 0.027% and 0.023% respectively Copper (Cu) constitutes 0.18%, chromium (Cr) is 0.19%, and nickel (Ni) is 0.26% The remainder of the composition is balanced with iron (Fe)
In addition to carbon, C20 steel typically contains minerals such as silicate, aluminate, and ferrite The interaction between these components plays a vital role in forming the crystalline structure and affects the steel's strength and elasticity
Water, additives, and elements like manganese, phosphorus, and sulfur also contribute to the chemical composition of C20 steel These can be adjusted to enhance specific properties of the material, including strength and temperature resistance
Carbon Steel C20 is commonly used in applications that require moderate strength and hardness Its physical and mechanical properties are often adjusted through heating and mechanical treatment processes Common applications of Carbon Steel C20 include construction, mechanical engineering, and the production of medium-strength load-bearing products As a low carbon steel, it has lower strength but good machinability and is suitable for welding
With a carbon concentration of approximately 0.20%, Carbon C20 steel typically exhibits average mechanical strength This is the result of a harmonious combination of toughness and stiffness, making it suitable for a wide range of applications in construction and construction
- Tensile Strength: The tensile strength of C20 steel typically ranges from 370 MPa to 470 MPa This value measures the maximum pressure the steel can withstand before breaking or stretching
- Elasticity: C20 steel generally has high elasticity, allowing it to return to its original shape after the pressure or load is removed
- Hardness: C20 steel has good wear resistance and typically exhibits medium to high hardness, depending on the specific processing
- Ductility: C20 steel often has good ductility, allowing it to deform without cracking or significant damage
- Flexibility: C20 steel generally has good flexibility, making it suitable for various construction and structural applications
- High-Temperature Strength: C20 steel has good high-temperature strength, making it suitable for use in high-temperature conditions
- Density: The density of C20 steel typically hovers around 7.85 g/cm³, making it a high- density material among construction and structural materials
- Thermal Conductivity: C20 steel has good thermal conductivity, making it useful in applications requiring efficient heat transfer, such as manufacturing
- Electrical Conductivity: C20 steel can conduct electricity, although its conductivity is not as high as that of some good electrical conductors like copper or aluminum
- Melting Temperature: The melting temperature of C20 steel typically ranges from 1425°C to 1540°C, depending on the specific composition of the steel
- Magnetic Properties: C20 steel often has magnetic properties and can become magnetized during processing
- Environmental Compatibility: C20 steel has good corrosion resistance and oxidation resistance, making it suitable for harsh environments like marine settings or high humidity areas
C20 steel, as a medium-strength, highly elastic carbon steel, is widely used in many practical applications, particularly in construction and structural projects Here are some common applications of C20 steel:
- Construction and Structural Engineering: Production of columns, beams, and other structural components in construction projects Use in bridge, culvert, and other infrastructure constructions Creation of structural frameworks for residential and industrial buildings
- Machine Manufacturing and Mechanical Structures: Production of machine components, such as shafts, bearings, and gears Use in the structures and materials of equipment and machinery
- Tool and Instrument Manufacturing: Production of cutting, grinding, and chiseling tools Creation of tools and instruments that require durability and elasticity
- Construction Industry: Use in the production and installation of pipelines, drainage systems, and industrial structural frameworks
- Energy and Oil & Gas Industries: Applications in the production and maintenance of structures for oil and gas drilling equipment Use in renewable energy projects, such as poles and support systems for wind turbines
- Shipbuilding and Marine Industry: Use in the production and maintenance of ship structures, drilling rigs, and marine equipment
- Automotive Industry: Production of structural components for automobiles and other transportation vehicles
- Water Industry and Wastewater Treatment: Use in the production and maintenance of water pipeline systems and wastewater treatment structures
These applications are just a few examples and are not exhaustive C20 steel, as a versatile material, is used in various fields depending on the specific requirements of the application and the working environment
Material theory stainless steel SUS304
2.4.1 The composition of the material
SUS 304 stainless steel, also known as SUS 304 stainless steel, is one of the most popular stainless steels today Its composition consists of a compound of steel and metals such as Chromium (from 18% to 20%), Manganese (less than 2%), Silicon (less than 1%), Carbon (less than 0.8%), and Nickel (from 8% to 10.5%), which does not contain Iron Its anti- corrosion properties are much higher than those of conventional steels, And therefore, it is widely used in many different applications When the concentration of chromium reaches a sufficiently high level, a passivating chromium oxide film will form on its surface This film works to prevent oxidation and corrosion of the material under it It is thanks to this property
25 that stainless steel is often used in the manufacture of household appliances and in the medical field, where high durability and hygienic properties are required
Since the publication of design regulations for stainless steel structures in Europe (EN1993- 1-4 1996) and the United States (ASCE 2002), stainless steel has been utilized in significant structural components of highway and pedestrian bridge projects across various countries (Euro Stainless Steel 2004) Eurocode outlines specific design strength criteria for structural sections constructed from austenitic, ferritic, and duplex stainless steels On the other hand, design standards for construction works in Japan focus only on the use of austenitic stainless steel (Design Standard Drafting Committee for Stainless Constructions 2001) However, stainless steel is not yet widely used in bridge and civil works in Japan The reason for this may be cost issues, as stainless steel appears to be less efficient than mainly weathered and mild carbon steels Mainly due to the high price and more difficult production process, instead of anti-corrosion advantages However, in many cases, stainless steels offer the best solution to ensure long-term design performance, especially in severely corrosive environments, thanks to their excellent corrosion resistance [17]
Details the chemical composition of stainless steel 304 according to the ASTM A276/A276M standard The AISI (UNS) designation for this steel is 304 (S30400) The maximum allowable carbon (C) content is 0.08%, while silicon (Si) is limited to 1.00%, and manganese (Mn) to 2.00% The limits for phosphorus (P) and sulfur (S) are 0.045% and 0.030% respectively Chromium (Cr) content ranges between 18.0% and 20.0%, and the nickel (Ni) content varies from 8.0% to 11.0%
DThe composition, developed by W H Hatfield at Firth Brown in 1924 and marketed as
"Staybrite 18/8", is classified under SAE steel grades by SAE International
It is known by various designations including 4301-304-00-I and X5CrNi18-9 in ISO 15510, and as UNS S30400 in the unified numbering system
Outside the US, it is referred to as A2 stainless steel and adheres to the ISO 3506 standard for fasteners
In the commercial tableware and fastener industries, it is also recognized as 18/8 or 18/10 stainless steel (written as 18-8 and 18-10)
In Japan, it is equivalent to SUS304 under JIS G4303, and 1.4301 under EN 10088
In Chinese nomenclature, it is identified as 06Cr19Ni10 and ISC S30408, conforming to GB/T 20878 and GB/T 17616
SUS 304 stainless steel (304 stainless steel) has a number of mechanical properties as shown in the table below:
Physical Characteristics of SUS304 Material [19]
+ Embodied Water: 150 L/kg (17 gal/lb)
+ Embodied Energy: 43 MJ/kg (18,000 BTU/lb)
+ Stiffness to Weight (Bending): 25 points
+ Stiffness to Weight: 20 to 32 points
+ Stiffness to Weight (Axial): 14 points
+ Embodied Carbon: 3.0 kg CO₂/kg material
The mechanical properties of SUS 304 stainless steel (304 stainless steel) are detailed in the table below Thermal treatment is not applicable; instead, strength can be enhanced through cold working
It is weakest in its annealed state and strongest when fully hardened Tensile strength ranges from 30,000 to 153,000 psi (210 to 1,050 MPa)
Tensile strength ranges from 30,000 to 153,000 psi (210 to 1,050 MPa) The density is 0.286 lb/cu in (7,900 kg/m3), and its modulus of elasticity ranges from 26.6 × 10 6 to 29.0 × 10.6 psi
Table 2 3 Mechanical properties of SUS304 material [19]
Brinell Hardness 170 to 360 Fatigue Strength
Elongation at Break 8.0 to 43 % Elastic (Young's,
Poisson's Ratio 0.28 Shear Modulus 77 Gpa (11 x 10-
Table 2 4Mechanical property for stainless steels
304 stainless steel demonstrates exceptional resistance against a variety of atmospheric and corrosive environments It effectively withstands pitting and crevice corrosion in warm chloride environments, as well as stress corrosion cracking above approximately 60°C At
28 room temperature, it maintains resistance to pitting corrosion in water containing chloride levels of up to about 400 mg/L, decreasing to approximately 150 mg/L at 60°C
Additionally, 304 stainless steel is highly susceptible to thiosulfate anions released from pyrite oxidation, a common occurrence in scenarios like acid mine drainage Exposure to pyrite-rich clay materials or sulfides undergoing oxidation can lead to significant issues with pitting corrosion
304 stainless steel is used for many home and industrial applications such as:
- Food and Medical Industry: Manufacturing stoves, sinks, utensils, and medical equipment
- Construction and Decoration: Interior components, windows, door handles, and decorative lights
- Chemical and Petroleum Industries: Pipelines, tanks, and pressure equipment
- Automotive Industry: Decorative parts, exhaust, and other components
304 stainless steel finds application in the architectural domain, where it is utilized to craft exterior accents like water and fire features Additionally, it serves as a popular material for vaporizer rolls Early SpaceX spacecraft were constructed using SAE 301 stainless steel, but for the SN7 and Starship SN8 test tanks in 2020, the switch was made to SAE 304L Notably,
304 stainless steel is employed in cladding the Arch in St Louis, Missouri
Stainless steel is utilized across various applications including gas tanks, front bumpers, and bus and truck chassis With ongoing advancements in austenitic, ferritic, and martensitic stainless steel technologies, the automotive industry actively explores their potential for further innovation.[20] [21] [22] [23].
General regulations in manufacturing tensile test specimens
The sample testing follows ASTM E8/E8M-13 standards and is manufactured using the stamping method Samples can have square, round, rectangular, ring, or other specialized cross-sections as needed These samples are selected based on established standards to conduct tension testing during research processes, in accordance with the Standard Test Methods for Tension Testing of Metallic Materials [24]
Figure 2 21 Tensile test sample dimensions are based on ASTM E8/E8-13 standards [24]
Dimensional parameters of table with the test sample are based on ASTM E8/E8-13 standards in below:
Table 2 5 Sample sizes follow ASTM standards [24]
Sample standards Sample sub- dimensions Plate type,
[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)
Foundations and theory of sample testing and evaluation
Theoretical basis of tensile testing:
Based on the impact on welded materials or products, testing methods are divided into two groups: destructive testing methods (KTPH) and non-destructive testing methods (KTKPH, called Non-Destructive Testing)
To check the quality and tensile strength of the sample, we choose a destructive test method Tensile testing is a basic test method to determine the yield limit, tensile strength and elongation of steel plates The sample usually has a round, rectangular, square section, depending on the requirements and materials to be tested During inspection, the deformation focuses on the narrow area in the middle, which has a uniform cross section along the length The standard diameter is 12.8 mm, 0.5 in, where this narrow segment length is not less than
4 times the standard, usually selected diameter of 60 mm, 2 1/4 in [5]
The tensile tester is designed to pull samples at a constant speed, continuously measuring instantaneous loads and corresponding elongations This test may last for several minutes until the sample is destroyed The usual mechanical testing procedure consists of: the sample is held in place at both ends with a mount and the load is placed on both ends, then gradually increasing the load until the sample is pulled off The tests allow to receive characteristic figures of strength, quality and reliability of bonding in the sample Mechanical testing of metal properties and welded bonding by tensile load characteristics conducts static, dynamic and fatigue tests [25]
2.6.1.1 Pros and cons of using the traction test method:
Test specimens are usually made by mechanical machining of samples taken from products, pressed or molded workpieces However, it is possible to try without machining products with constant cross sections (shaped steels, bars, wires, etc.) and molded samples (such as cast iron alloys and non-ferrous alloys) Determine the destructive load or shelf life until destroyed Tensile testing is a mechanical test method employed to assess the strength and ductility of materials Widely utilized across various materials such as metals, plastics, composites, and ceramics [6],
It stands as one of the most prevalent types of mechanical testing Tensile strength testers offer numerous advantages, including the ability to evaluate material quality and detect potential manufacturing or design flaws These machines also enable characterization of
31 material behavior under diverse conditions, including extremes of temperature and dynamic loads
When tested single, only a few properties of the sample can be determined, affecting the reliability of the product
Not regularly applicable in conditions of continuous work operation
The total cost of testing is high and consumes many necessary materials, especially precious materials
It can only be tested on the sample and not the actual object of use because the shape characteristics of the product are not suitable for tensile testing
The quality between parts may vary as it can only be tried on select models from within the product group
Time-consuming and high machining requirements
The impact can only be measured when used if multiple test products are selected that have worked for a certain period of time [25]
2.6.1.2 Test conditions a Adjust the zero point of the force
Once the test load actuator is installed, the force measurement system on the measuring device must be zeroed before clamping the specimen securely at both ends
After establishing the force zero point, the parameters of the force measurement system should remain unchanged throughout the test b Tight clamping method
Test specimens shall be clamped tightly by appropriate methods such as hydraulic clamping, screw-threaded clamping pins, parallel clamping spokes, or burred (shoulder) clamping mechanisms The clamping beaks must reach rigidity and semi-rigidity to keep the pull pattern from slipping as it progresses to the tensile test
The specimen must be straightened, and the alignment of both the specimen and grippers verified A preliminary force may be applied, not exceeding 5% of the specified yield strength Adjustments should consider the effects of this preliminary force
Efforts should be made to ensure that the test specimens are clamped so that the force is applied vertically along the axis to reduce bending to a minimum This requirement is especially important when testing brittle materials or when determining the plasticity limit (plasticity elongation), plasticity limit (total elongation) or yield limit [26]
Figure 2 22 Material deformation diagram [26] e: relative elongation mE: slope of the elastic part of the stress supply line – relative elongation
Rm: tensile limit Δe: the horizontal section size on the graph
A: post-rupture relative elongation [is determined from the extensometer signal or directly from the test specimen
Ag: relative plasticity at the greatest force
Agt: total relative elongation at maximum force
At total: relative elongation at the largest destruction site
Calculation of relative plasticity at maximum force, Ag by equation (1):
Le is the length of the extensometer tamarind is the slope of the elastic part of the stress curve - relative elongation
Rm is the tensile limit ΔLm is the elongation at the greatest force
The method consists in determining the elongation at the greatest force on the force curve - the elongation is obtained with an extensometer and minus elastic deformation b) Determination of total relative elongation at maximum force
Calculating the sum relative elongation at maximum force, Agt by equation (2):
Le is the length of the extensometer ΔLm is the elongation at the greatest force
The method consists in determining the elongation at the maximum force on the force curve the elongation obtained with an extensometer c) Determination of relative tightness
The relative tightness must be determined in accordance with the given definition
If necessary, the destroyed part of the test specimen should be pieced together so that their axis line is in a straight line
Calculation of relative tightness, Z from equation (3) :
So is the initial cross-sectional area of the parallelepiped section
Su is the smallest cross-sectional area after the rupture d) Determination of relative elongation after rupture
Calculation of the relative elongation after the rupture, A by equation (4):
Lu is the length of the last after the rupture
To determine elongation, the two broken pieces of the specimen must be carefully aligned along their axial line to ensure straightness The relative elongation after fracture must be measured according to specified definitions, ensuring proper contact between the broken ends of the specimen during final length measurements This requirement is particularly critical for specimens with small cross-sections and low elongation values
When using an extensometer to measure elongation at fracture, length markings are unnecessary Total elongation at fracture is measured, with elastic elongation subtracted to obtain relative post-fracture elongation To ensure values comparable to manual methods, additional adjustments may be necessary, such as dynamic settings and a sufficiently high frequency bandwidth for the extensometer
Elongation after Lu-Lo fracture must be measured to the nearest 0.25 mm or finer with high- resolution measuring instruments If the specified minimum relative elongation is less than 5%, special precautions are required Valid results are obtained only if the distance between the fracture and the nearest measurement marker is less than one-third of the original gauge length (Lo) However, measurement validity is ensured regardless of fracture location if the relative elongation after fracture meets or exceeds the specified value
Results are valid only if fracture and local dilation (necking) occur within the extensometer gauge length (Le) Measurement validity is assured irrespective of fracture location if relative elongation after fracture meets or exceeds the specified value
If the product standard requires determining relative post-fracture elongation over a specific length, the extensometer length should match this requirement
If the elongation is measured over a given fixed length, it can be converted to a proportional length using conversion formulas or tables agreed prior to the start of testing (e.g., as in ISO 2566-1 and ISO 2566-2) [26]
2.6.1.4 Durability test a Universal compression machine
Universal tensile and compression machine is used to conduct sample tensile and compression tests according to ASTM E8/E8-13 standards, which have been processed according to the stamping mold The two heads of the sample are clamped on the upper and lower clamping bars, and gradually compress the sample in two opposite directions When force is applied, it will cause the test specimen to deform, leading to the test specimen increasing in length and decreasing its cross-sectional area Experimental data recorded in real time during pulling includes: Applied force, elongation, or corresponding deformation through the chart on the computer screen
Optimized Method
2.7.1 Statement of the problem about optimization
TAGUCHI method is one of the statistical tools applied in the parameter optimization model
In empirical research, model building has important technical and economic implications Implementation processes are often complex, with many input factors acting independently or co-influencing the outcomes (outputs) In order to solve this problem, the Factorial Model (FM), which describes the simultaneous influence of many inputs on outputs, was proposed by Fisher in 1926 and developed by Plackett and Burman 20 years later (1946) However, along with the development of the times, the essential requirement of experimental models is to describe the process as close to reality, with the most complete input factors, but minimizing the number of experiments Therefore, the TAGUCHI model, proposed by a Japanese engineer Genichi Taguchi (1924 – 2012), is considered a satisfactory solution to this problem The TAGUCHI method is primarily utilized during the parameter design phase to analyze and assess how input factors influence output parameters, aiming to determine the optimal set of process parameters Unlike global multi-factor models, which are suitable for up to three factors, the TAGUCHI method can effectively handle between 3 and 50 factors Its objective is to identify process factors that maximize efficiency by minimizing the effects
37 of variability Each factor (input variable) influences the outcome in two ways: directing the outcome closer to the target is considered a beneficial signal, known as "signal", while deviations from the target are termed "noise" The Signal-to-Noise (S/N) ratio serves as an efficiency metric, used to evaluate and select parameters, with larger S/N values indicating the most optimal parameter set
Design of experiment (DOE) is a tool which could be used in a series of situation’s experiments DOE allow to control many input elements to determine the effects to output elements that we want DOE helps us to determine the important interaction between the elements which can be shortcomed in testing with one element at the moment
Using the design of experiment when we want to survey more than one elenment which is suspected to affect to one or many output elements
- Step 1: Determine the factors can affect to the results Collecting the list of input factors usually taken from persons who join the project
- Step 2: Determine objective function to optimize
There are three types of applied math with ratio S/N:
ANOVA (Analysis of Variance) comprises a collection of statistical models and estimation methods utilized for examining variations among group variances within a sample This method was pioneered by Ronald Fisher, a prominent statistician and evolutionary biologist ANOVA is a statistical technique used when we want to compare the average of a class ≥ 3 groups This technique divides the variance of an observation into two parts:
Since variance is the relative dispersion of observations compared to the mean, the analysis of variance makes it easy to compare the averages (comparison between variances), the ANOVA analysis allows us to quantify the relative influence of the factors and their importance to the target function
- Step 1: Calculate the total sum of squares of the factors
𝑖=1 Where n is the number of experiments
- Step 2: Calculate the determination factor 𝑅 2
𝑆𝑆𝑇 𝑆𝑆𝑇 Determination coefficient R 2 (Unit: %) is a metric used to assess the appropriateness of models that display linear correlation relationships It represents the square of the correlation coefficient and serves as a decisive factor in this evaluation
The R2 value is typically calculated as a percentage, and the method to assess the relationship based on this coefficient is as follows:
Table 2 9 Sample sizes follow ASTM standards [24]
25% ≤ R2 ≤ 50% The correlation is quite close
- Step 3: Calculate the degrees of freedom for the experiment and the degrees of freedom for the elements (Df):
𝐷𝑓𝑗: The degree of freedom of the corresponding elements
Where: l is the number of levels of the factor j n is the total number of experiments
- Step 4: Mean of Squares (Variance of Factors) MS (Mean of Square): Mean of Squares
- Step 6: Calculate the F-value of the rate of variation between the sample averages and the variation within the samples
MS e Calculate the contribution percentage of the factors
- Step 7: Summarize the results in the ANOVA table
RESEARCH, DESIGN, MANUFACTURE OF TEST SAMPLE
Experimental procedure
The purpose of designing experimental procedure is based on the specification of parameter that the data of inputs and outputs must be targeted
41 Figure 3.1 Diagram of the experimental work
Experimental equipment
Figure 3 8 Hydraulic punch pressing machine
Prepare workpices
Based on researching in different jounals, we had estimated and determited the demensions, and the thickness workpieces according to the specimens in ASTM E8/E8M-13 [24] and ASTM E290-22 [25] Thus, we want 2 workpices of C20 and SUS-304 will gain each 3 in specimens of tension and bending Therefor, the dimension of one workpice has demesions to produce 3 specimens shows below:
Figure 3.11 The dimension of workpieces
Preparing the workpieces by buying sheet metal with these dimensions: length is 110 mm, width is 105 mm, and thickness is 2 mm The total quantity of workpieces being bought is 80 pieces Dividing them into 2 types of materials: 40 pieces for C20 and 40 pieces for SUS-304 However, 72 pieces are needed for welding a total of 32 specimens for both tensile and bending test because extra workpieces are bought to ensure the process avoids welding errors These materials will serve as the base for creating the test samples
Then these workpieces are going to make a spark testing of metals, which ensuring those workpieces are bought the right material and source
Figure 3 11 Spark testing of metals
With C20 Steel, the spark testing of metals will show on a long yellow spark stream to follow, while the SUS-304 gain a very small spark stream and straight lines.
Conditions in welding sample
When processing the welding workpieces, we must check the edges of the workpiece have swarf, which must be cleaned with a metal file to avoid bad conditions affecting the welding process
With the thickness of workpiece is 2 mm, we had to choose the type of edge weld preparation for both materials must be perpendicular [35] we could find that root gap of the weld joint between the two workpieces is from 0 to 1.6 mm [10]
The temperature in the open room is 30 degrees Celsius, the humidity is low, and there is no wind
Welding workpieces with a steel wire: GM-70S, ensuring that the robot follows the programmed instructions to create uniform and precise welds on the sheet metal
Figure 3 14 the wire of GM-70S Set up the program with the teach pendant for the automated control robot This involves configuring the robot with specific instructions needed to carry out welding and other automated tasks accurately
When using MIG welding technology to join two sheet metal parts with steel wire, the jig, which plays a crucial role, must provide tight clamping This feature is essential to prevent movement and imbalance in the plane of the welded part while welding at the selected speed
Figure 3 12 Fixturing workpieces on the jig
Select the parameters of MIG welding for robots
Based on Table 5 from the book Welding Dictionary MIG/MAG [30], with the table title:
"Guide values for MIG/MAG welding butt welds on unalloyed." For a workpiece thickness of 2mm, I looked up the welding parameters from the handbook and found the following: Wire electrode diameter 0.8 mm, Wire feed rate 7.1 m/min, Current 130 A, Arc voltage 19 V Using these parameters from the handbook, I conducted an experimental survey on the test sample and verified that the feasibility met the standards From this, I combined scientific
48 research reports and conducted a survey of wider limit ranges based on the initial reference parameters I found With the workpices material is 3 mm thickness, They performed welding experiments with welding currents from 70A - 100A, the stable welding voltage is 13V, welding speeds 130-190 (mm/min) and shielding gas used was 100% Ar with a flow rate of
15 L/min applied on butt joints welded by MIG/TIG welding [31] In the same view, experiments shows that 3mm thickness worpices were used welding currents from 80A - 120A, welding speeds 250-400 (mm/min), and gas flow rate of 12 L/min [3] Moreover, a 8 mm thickness of butt joint was used welding currents from 220A - 260A, the welding voltages 22V-26V, welding speeds 150 (mm/min) [32]
With these references, we research and find out the first parameters for welding, which concluding 4 input factors, each with 4 levels of values Therefore, choosing the Taguchi L16(4^4) orthogonal array with 16 experiments is appropriate [33].": This resulted in the establishment of the first set of limit parameters as follows:
Table 3.1: First paramters for welding
Welding Parameters (Factors) Level 1 Level 2 Level 3 Level 4
With flow rate is 14L/min
Although the parameters were good looking, we certainly failed by the test in real time with the external quality inspection in all test for each workpieces on the first parameters This example below has the solder joint is damaged due to overheating by checking the welding inspection standard according to: AWS C6.1-89 [34] So we going to scale it
Figure 3 2 The testing results of first parameters
Because of failing many times, we tried out and alternated different parameters with try max – min ranges, and we have identified the regions and scaled them down in small range Finally, we found the final parameters Then we are going to test on the external quality inspection in all test for each workpieces and evaluate it good for all the weld sush as below:
Welding Parameters (Factors) Level 1 Level 2 Level 3 Level 4
Figure 3 3 The testing results of final parameters
Aiming to investigate 4 factors (U, I, v, d), each of which includes 4 levels, we design with taguchi method to export the table show below
3.5.2 Calculate Degree-of-freedom (DOF) rules to select an orthogonal design table
Based on the Taguchi Experimental Design [36] We have the formula that design the orthogonal table With 4 factors and 4 levels, without the two-factor interaction have in those parameters belows:
Degrees of Freedom of the Overall Mean: Always DF mean = 1
Degrees of Freedom of Each Factor: For a factor with 𝑛 n levels, the degrees of freedom is
Total Degrees of Freedom of All Main Factors: Sum of the degrees of freedom for all factors
Degrees of Freedom of Interactions: For an interaction between two factors with aaa and bbb levels respectively, the degrees of freedom is: (a−1) × (b−1)
Apply on the experiment with have 4 factors, 4 level, and without interactions:
Degrees of Freedom of the Overall Mean: DF mean=1
Degrees of Freedom of each factor: For 4 levels, n=4: DF= 4−1=3
Total Degrees of Freedom of the 4 Factors: 4×3
Total Degrees of Freedom: DF total=1+12
The minimum number of experiments required must be greater than or equal to the total degrees of freedom: Nmin ≥ DFtotal => Nmin ≥ 13
So that we Choosing an orthogonal array:
L9 (9 experiments): Not sufficient as it only provides 9 experiments to work
L16 (16 experiments): Sufficient as it provides 15 degrees of freedom
L27 (27 experiments): Therefor, sufficient as it provides 27 expermients but in the table of desgining Taguchi 4 levels and 4 factors do not have L27
In conclusion, combining degree-of-freedom with the table of taguchi design table 4 factors and 4 levels will be chosen as L16 array
Table 3.3: Taguchi experimental plan for Array L16 specimens with GM70S welding wire
No Voltage (V) Current (A) Stick-out (mm) Speed
Designing test sample
3.6.1 The size of tensile testing sample
Based on the standard ASTM E8/E8M-13, we chose and design the tension testing sample like the photo below [24]:
Table 3 4 Sample sizes follow ASTM standards Dimension
Width 12.5 mm [0.50 in.] mm[in]
A – (Length of reduced section, min) 82 [3.22]
B – (Length of grip section, min) 50 [1.96]
C – (Width of grip section, approximate) 20 [0,787]
3.6.2 The size of bending test sample:
Based on the standard ASTM E290-22, we chose and design the bend testing sample like the photo below [25]:
EXPERIMENTAL PROCESS
Experiment of tensile and bending test
We used the WE1000B universal testing machine, which the specifications show on belows:
Figure 4 1 Universal testing machine Capacity:
Maximum tensile/compressive force: 100 Tons (1000kN)
Maximum distance between clamps: 600mm
• Main machine body size: 960 x 620 x 2150mm
Using wire-cut machines, and mechanical stamping machine to process the samples in bulk This step involves cutting the samples into the required shapes for tensile and bending tests, ensuring consistency and accuracy across all samples Basically, we used wire-cut machines to produce the specimens instead of using mechanical stamping machine, because the fail of manufacturing when we tried out the sample and it not working at we had thought
Figure 3 16 using mechanical stamping machine to produce specimens
All steps for tensile and bending tests of test samples:
+ The steps for tensile of test samples are as follows below:
Prepare the test samples according to the required dimensions and specifications
- Step 2: WE1000B universal testing machine
Turn on the power key in table control, and then pressing two green control buttons to get ready to conduct the specimen tensile test
Secure the test samples in the appropriate fixtures for tensile
Calibrate the testing machine to ensure accurate measurement and data collection, adjusting the button up, and down, or open, and close
- Step 5: Starting the tensile test:
Initial Measurement: Measure the initial dimensions of the test sample, including length, width, and thickness
Loading: Gradually apply tensile force to the sample until it fails
Figure 4 3 The result of testing
Data Collection: Record the force and elongation data during the test
Figure 4 4 The record of tesile testing by screen
+ The steps for bending of test samples are as follows below:
Prepare the test samples according to the required dimensions and specifications
- Step 2: WE1000B universal testing machine
Turn on the power key in table control, and then pressing two green control buttons to get ready to conduct the specimen bending test
Secure the test samples in the appropriate fixtures for bending
Calibrate the testing machine to ensure accurate measurement and data collection, adjusting the button up, and down, or open, and close
- Step 5: Starting the bending test:
Initial Measurement: Measure the initial dimensions of the test sample
Loading: Gradually apply bending force to the sample until it reaches the desired deflection or failure
Data Collection: Record the force and elongation data during the test
Figure 4 6 The record of bend testing by screen
Experiment of microstructure’s welds
The result of this method is to measure weld width, swallowing, and height In order for the analysis of the metal sample to be effective and highly accurate, it is necessary to go through the following steps:
This is the first and also the most important step to help reduce sample preparation time To increase the reliability of the results, the metallographic test profile is taken right next to the tensile test position The more accurate the wire cutting, the closer it is to the point to be analyzed, will help grinding and polishing be done faster, optimizing sample preparation time
- Step 2: Prepare the sample by molding it with a two-component adhesive (AB), specifically epoxy, to securely fix it, facilitating easier observation under the microscope
Figure 4 8 Molding the sample with AB glue
- Step 3: Grind the sample using sandpaper of varying grits (P180, P220, P320, and P400) sequentially from coarse to fine on a flat surface, following correct procedures Maintain surface parallelism, grind evenly, and avoid excessive force to prevent the formation of deep scratches that are challenging to polish out later
Figure 4 9 Grinding the sample on sandpaper
- Step 4: Polish the sample using a polishing machine, felt cloth, and chromium oxide powder to achieve a high gloss finish while minimizing surface scratches
- Step 5.1: Prepare HCl and HNO3 cooking solution at a ratio of 3:1 Working requirements: Dispensing must prioritize safety The dispensing area should be near a water tank for immediate access in case of emergencies Wear rubber gloves to protect
60 hands from chemicals, and wear medical masks to minimize inhalation of acid fumes
- Step 5.2: Impregnate the welding sample This step involves exposing the weld for inspection by corroding the metal surface Ensure even and adequate impregnation without causing oxidation If excess impregnation occurs, polish and re-impregnate the sample as needed
After impregnation, if the sample has not been immediately observed with a microscope, the sample surface must be protected with a layer of oil, which prevents surface oxidation
- Step 6: Observing on optical matallurgical microscope
Use a microscope equipped with AmScope software to measure the width, depth, and alignment of the weld
- Place the template securely on the table and use a clip to hold it in place
- Position the prepared sample on the table
- Select the x5 objective to observe the entire sample
- Connect the camera to a laptop using AmScope software
- Adjust the lighting for optimal visibility
- Look through the eyepiece and adjust the coarse focus knob to bring the objective into view until you see a slightly blurry image of the microfield Fine-tune using the fine focus knob for a clear image
Requirements: Ensure the microscope lenses are cleaned thoroughly before and after use, and adjust them properly for accurate measurements
Figure 4 12 Analyzing a sample under a microscope
- Step 7: Statistics of weld geometry and parameters compared with ASME IX and ASME
RESULTS AND DISCUSSION
Parameter optimization and analysis of varience for ultimate tensile strength
Based on data that we collected on using the universal testing machine, and we proceeded with processing and entering input tensile parameters
Figure 5.1 Example of tensile testing data
Graph of Tensile Test 5 with GM-70S
Table 5 1: Table all of 16 specimens of Taguchi and tensile test results
Speed (cm/min) UTS (Mpa)
The Taguchi method emphasizes analyzing response variation using the signal-to-noise (S/N) ratio This approach aims to minimize quality characteristic variation caused by uncontrollable parameters In other words, it helps optimize process parameters for better outcomes
The UTS was considered as the quality characteristic with the concept of "the larger-the- better" The S/N ratio used for this type response is given by [5.2]:
The S/N ratio for the larger-the better is: s
The S/N ratio values are calculated by taking into consideration eqn 5.2 The calculated results and analysis of the S/N by using Minitab 18 software which presented in table 4.1 and figure 4.1
Table 5 2 Response Table for Signal to Noise Ratios
The results show that the welding current has the strongest effect on the UTS value, followed by the weldingvoltage, stick-out and speed
Figure 5 2 Main effect plot for tensile strength
As show in figure 5.3, an increase in the welding current in the examined range leads to an increase in the UTS value Moreover, Figure 9 indicates that the optimal parameters for the UTS value with the “larger is better” option are stick-out of 12mm, a welding current of 110 A,a welding voltage of 15V and a welding speed of 500mm/min In the surveyed range, it
64 appears to achieve the highest UTS value, as shown in Figure 5.3, with the highest point at
110 mm in the current section
Table 5 3 Analysis of variance for tensile strength
Source DF Adj SS Adj MS F-Value P-Value
The R-squared value = 93.88% > 50% is the statistical significance
From ANOVA table above, we see P-value values of variables: Voltage, stick-out, and speed are all larger 0.05 and Amperate is approximately 0.05 so these parametes do not significantly affect the ultimate tensile strength with 95% confidence
“From the result table 5.5 of the variance analysis in the experiment, ignoring the error amount, we can calculate the percentage of the influence of parameters on the quality of the weld in a general way, as shown in figure 5.4
Figure 5 3 The influence of parameters on weld quality Comments:
From the results and the chart, we can clearly evaluate that the speed has the lowest impact, accounting for only 2.54% Meanwhile, Current is the most influential parameter, representing 69% As for Voltage and Stick-out, they account for 13.49% and 14.93%, respectively
Moreover, P-value also reflects the confidence of parameter P- value 0.05 which shows the confidence of parameters is 95% From that, we can construct the regression equaition that approaching the ideal value line And we can use this equation to apply it in reality và find a suitable set of parameters
In addition, to find the relationship between factors affecting weld tensile strength, use Minitab software to produce a linear regression function equation.:
UTS(MPa) = 413 + 5.17 I(A)- 22.1 U(V) - 11.03 d(mm) - 0.146v(mm/min)
And finally, we have a optimal parameters set for tensile strength :
Table 5 4 Parameter optimization of UTS result
I (A) U (V) Stick-out (mm) Speed (mm/min)
Percentage distribution chart of the influence of factors on the tensile strength of the weld
After we have a set of optimized parameters, we used Minitab sofware to predict S/N ratio and CI :
Table 5 5 Predicted values of UTS parameter optimization
Fit SE Fit 95% CI 95% PI S/N Ratio Mean
Parameter optimization and analysis of varience for ultimate flexural strength
Based on data that we collected on using the universal testing machine, and we proceeded with processing and entering input bending parameters
Figure 5.4 Example of bending testing data
Graph of Bending Test 11 with GM-70S
Table 5 6 L16 of Taguchi and tensile test results
I (A) U (V) Stick-out (mm) Speed (mm/min) Flexural Strength (MPa)
The flexural strength was considered as the quality characteristic with the concept of "the larger-the-better" The S/N ratio used for this type response is given by [5.2]:
The S/N ratio for the larger-the better is: s
The S/N ratio values are calculated by taking into consideration eqn 1 The calculated results and analysis of the S/N by using Minitab 18 software which presented in table 5.9 and figure 5.5
Table 5 7 Response Table for S/N of Flexural Strength
Level I (A) U (V) Stick-out (mm) Speed (mm/min)
The results show that the welding speed has the strongest effect on the UTS value, followed by the welding voltage, stick-out and current
Figure 5 1 Main effect plot for flexural strength
As show in figure 5.5, a decrease in the welding speed in the examined range leads to a decrease in the UTS value Moreover, Figure 5.5 indicates that the optimal parameters for the UTS value with the “larger is better” option are stick-out of 12mm, a welding current of 100A, a welding voltage of 15V and a welding speed of 450mm/min In the surveyed range, it appears to achieve the highest UTS value, as shown in Figure 5.5, with the highest point at 450mm/min in the speed section
Table 5 8 Analysis of variance for flexural strength
Source DF Adj SS Adj MS F-Value P-Value
The R-squared value = 99.39% > 50% is the statistical significance
From ANOVA table above, we see P-value values of variables: Current, stick-out, and speed are all smaller 0.05 these parametes do significantly affect the flexural strength with 95% confidence
“From the result table 5.9 of the variance analysis in the experiment, ignoring the error amount, we can calculate the percentage of the influence of parameters on the quality of the weld in a general way, as shown in figure 5.6
Figure 5 2 The effect of parameters on the quality of welded joint From the results and the chart, we can clearly evaluate that the current has the lowest impact, accounting for only 3.25% Meanwhile, is the most influential parameter, representing 55.20% As for speed and Stick-out, they account for 25.77% and 5.78 %, respectively.Moreover, P-value also reflects the confidence of parameter P- value 0.05 which shows the confidence of parameters is 95% From that, we can construct the regression equaition that approaching the ideal value line And we can use this equation to apply it in reality và find a suitable set of parameters
In addition, to find the relationship between factors affecting weld tensile strength, use Minitab software to produce a linear regression function equation.:
In addition, to find the relationship between factors affecting weld tensile strength, use Minitab software to produce a linear regression function equation.: d, 5.78%
Percentage distribution chart of the influence of factors on the tensile strength of the weld
And finally, we have a optimal parameters set for tensile strength
Table 5 9 Parameter optimization of UTS result
After we have a set of optimized parameters, we used Minitab sofware to predict S/N ratio and CI :
Table 5 10 Predicted value of flexural strength parameter optimization
Fit SE Fit 95% CI 95% PI S/N Ratio Mean
Confirmation test
The experimental validation step is crucial and it is recommended to be conducted to draw the final conclusion of the entire experiment
With the results of the experiment, we have a set of parameters where the weld quality achieves the best strength within the experimental range We repeat the experiment three times at those parameters to verify the results
Figure 5.7 The speciments after tensile testing The speciments are broken at the C20 steel That means C20 steel is less tensile strength than the weld bead
Table 5.11 The tensile strength results of verification experiment
Therefore, with the average result of 469.37 MPa from the verification experiment falling within the predicted value range in the 95% confidence interval Thus, the set value in the table is confirmed and recorded with a 95% confidence level
With the results of the experiment, we have a set of parameters where the weld quality achieves the best strength within the experimental range We repeat the experiment three times at those parameters to verify the results
Figure 5.8 The speciments after bending testing The result of the bending test did not show any cracks on the surface of the weld and the weld toes This means that SUS 304 stainless steel and C20 steel, which has higher ductility, is better at withstanding bending Although there may be changes in the mechanical properties in the heat-affected zone of the weld, both SUS 304 stainless steel and C20 steel still ensure safety and do not crack during the bending test
Table 5.12 The flexural strength results of verification experiment
Therefore, with the average result of 1937.45 (MPa) from the verification experiment falling within the predicted value range in the 95% confidence interval Thus, the set value in the table is confirmed and recorded with a 95% confidence level
Microstructure of welded joint
5.4.1 Geometric dimensions of welded join
The outstanding samples of steel welding wire:
The images provided illustrate the characteristics of the surface samples Each sample exhibits a weld, areas of weld penetration, and areas of non-penetration Samples L14 and L16 demonstrate the deepest weld penetration The measured parameters are as follows:
Based on the analysis, it can be concluded that samples L14 and L16 exhibit superior weld quality due to their achieving adequate weld penetration into the base material Weld penetration is a crucial factor in ensuring the strength and overall integrity of welded joints Those pictures below will show the micro structure of all surface of specime
5.4.2 Characteristic microstructure zones of weld materials
Figure 5 10 the microstructure of a dissimilar steel weld
In Figure 5.10, L14 depicts the microstructure of a dissimilar steel weld, l4 is using transmission electron microscopy (TEM) at two magnifications (5x and 20x) But those pictures usually use 20X scope of magnification The microstructure of the base metals (zones
A and D) is evident Zone A shows the ferrite and pearlite grain structure of C20 steel Zone
D reveals the austenitic microstructure of SUS304 steel, which includes twin boundaries and some ferrite grains or carbides The heat affected zone (HAZ), zones B and E, demonstrates
74 the presence of ferrite from the C20 base metal Zone C, the weld metal (WM), exhibits a martensitic microstructure The presence of martensite in the WM suggests the weld underwent rapid cooling during the welding process This rapid cooling can lead to favorable mechanical properties such as high strength and hardness, but can also increase residual stress and susceptibility to cracking:
Figure 5.10 A (C20 steel): The base metal of microstructure shows the typical two-phase structure of C20 steel, consisting of ferrite and pearlite Ferrite is a soft and ductile phase, while pearlite is a harder and more brittle phase The ratio of ferrite to pearlite affects the strength and ductility of the material
Figure 5.10 B (HAZ in C20 steel): Due to the heat input from the welding process, the microstructure of C20 steel in the HAZ changes Ferrite becomes the dominant structure in this region This change can affect the strength and ductility of the weld
Figure 5.10 C (WM): This zone shows a mixture of microstructures from both base materials, C20 steel and SUS304 steel This mixing can affect the strength and ductility of the weld A martensitic structure is observed in the WM Martensite is a very hard and brittle phase of steel, formed by cooling during the welding process
Figure 5.10 D (SUS304 steel): The microstructure shows the characteristic austenitic structure of SUS304 steel Austenite is a ductile phase of steel at room temperature This structure includes twin boundaries and some ferrite grains or carbides The carbides contribute to the hardness of the material
Figure 5.10 E (HAZ/WM): This zone shows a HAZ is located next to the welding area
This mixing can affect the strength and ductility of the weld The base metael of SUS304 is austenitic structure
In conclusion, the microstructure of weld L14, shows the diversity of microstructures in different regions of the weld These microstructural changes can affect the mechanical properties of the weld, including strength, ductility, hardness, and crack resistance Therefore, detailed microstructural analysis is crucial for assessing the quality of the weld and ensuring its performance in service
CONCLUSION AND RECOMMENDATIONS
Conclusion
This research investigates how the welding angle, speed, voltage, and stick-out impact the geometry, macrostructure, and mechanical properties of MIG welding on SUS 304 stainless steel and C20 steel From the analysis of the results using the signal-to-noise (S/N) ratio approach, analysis of variance and Taguchi’s optimization method, the following can be concluded:
Optimal parameters setting for ultimate tensile strength are, welding current = 110 amp, voltage = 15 V, welding speed = 500 mm/min, stick-out = 12mm
Optimal parameters setting for flexural strength are, welding current = 110 amp, arc voltage
= 15 V, welding speed = 450 mm/min, stick-out = 12mm
The effect of welding current on mechanical properties was found to be much higher than of the volatge, stick-out and welding speed.
Recommendations
To further improve the topic, here are some suggestions for future research studies:Inspecting the weld bead joint requires a lot of time, it needs research and design to create intelligent devices that can assess the quality of the weld bead immediately after welding stainless steel pipes without the need for weld bead inspection, it will increase work efficiency and focus more on in-depth research on the topic
It is necessary to have a variety of material thicknesses in order to more accurately assess the quality of the weld bead based on the welding process and the proposed welding parameters
Improvements are needed for the device to operate more stably, to avoid operational errors that can cause interference and affect the evaluation results, thus reducing the reliability of the parameters
Stainless steel welding wire materials can be used to continue the research process
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Appendix 1: Images of C20 steel and SUS-304 stainless steel: microstructures and rough specimens
Geometric dimensions of welded joint with GM-7S wire:
The specimen of L1 The specimen of L2
The specimen of L3 The specimen of L4
The specimen of L5 The specimen of L6
The specimen of L7 The specimen of L8
The specimen of L9 The specimen of L10
The specimen of L11 The specimen of L12
The specimen of L13 The specimen of L14
The specimen of L15 The specimen of L16
The image of the micro structure in steel welding wire specimens:
Appendix 2: Images of tension and bend testing charts
Graph of Tensile Test 1 with
Graph of Tensile Test 2 with
Graph of Tensile Test 3 with
Graph of Tensile Test 4 with
Graph of Tensile Test 5 with
Graph of Tensile Test 6 with
Graph of Tensile Test 7 with GM-70S
Graph of Tensile Test 8 with GM-70S
Graph of Tensile Test 9 with
Graph of Tensile Test 10 with GM-70S
Graph of Tensile Test 11 with GM-70S
Graph of Tensile Test 12 with GM-70S
Graph of Tensile Test 13 with GM-70S
Graph of Tensile Test 14 with GM-70S
Graph of Tensile Test 15 with GM-70S
Graph of Tensile Test 16 with GM-70S
Images of bend testing charts
Graph of Bending Test 1 with GM-70S
Graph of Bending Test 2 with
Graph of Bending Test 3 with
Graph of Bending Test 4 with GM-70S
Graph of Bending Test 5 with GM-70S
Graph of Bending Test 6 with GM-70S
Graph of Bending Test 7 with GM-70S
Graph of Bending Test 8 with GM-70S
Graph of Bending Test 9 with GM-70S
Graph of Bending Test 10 with GM-70S
Graph of Bending Test 11 with GM-70S
Graph of Bending Test 12 with GM-70S
Graph of Bending Test 13 with GM-70S
Graph of Bending Test 14 with GM-70S
Graph of Bending Test 15 with GM-70S
Graph of Bending Test 16 with GM-70S