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1. What is welding? Answer: Welding is a process in which two or more materials (of the same type or different types) are combined together through heating, pressing, or both, thereby achieving atomic bonding and forming a permanent connection. 2. What is an arc? Answer: Supplied by the welding power source, a strong and sustained gas discharge phenomenon occurs between the two electrodes—this is called an arc. 〈1〉According to the type of current, they can be divided into: AC arc, DC arc, and pulsed arc. 〈2〉Based on the state of the arc, it can be divided into free arcs and compressed arcs (such as plasma arcs). 〈3〉Based on the electrode material, they can be divided into fusion arc welding and non-fusion arc welding. 3. What is the base material? Answer: The metal that is being welded is called the base material. 4. What is a droplet? Answer: The tip of the welding wire heats up and melts, and the liquid metal droplet that transitions into the molten pool is called a droplet. 5. What is a molten pool? Answer: The liquid metal portion with a specific geometric shape that forms on the workpiece during fusion welding is called the weld pool. 6. What is a weld? Answer: The joint formed in the welded piece after welding. 7. What is weld metal? Answer: The portion of metal that is formed after the melting base material and filler metal (welding wire, electrodes, etc.) solidify. 8. What is a shielding gas? Answer: The gas used in welding to protect the metal droplets and the molten pool from harmful external gases (hydrogen, oxygen, nitrogen) is known as a shielding gas. 9. What is welding technology? Answer: Welding technology is the general term for various welding methods, welding materials, welding processes, welding equipment, and their underlying theories. 10. What is welding technology? What does it contain? Answer: The entire set of process procedures and technical specifications during the welding process. The content includes: welding methods, pre-welding preparation and processing, assembly, welding materials, welding equipment, welding sequence, welding operations, welding process parameters, and post-welding treatment. 11. What is CO2 welding? Answer: Melted electrode gas shielded welding using CO2 with a purity of > 99.98% as the shielding gas is called CO2 welding. 12. What is MAG welding? Answer: Gaseous metal arc welding using a shielding gas of a mixture of 75–95% Ar + 25–5% CO2 (the standard ratio being 80% Ar + 20% CO2) is known as MAG welding. 13. What is MIG welding? Answer: <1>For gas metal arc welding of non-ferrous metals such as aluminum and its alloys, as well as copper and its alloys, high-purity argon with a purity of ≥ 99.99% is used as the shielding gas ； 〈2〉The process method for gas metal arc welding solid stainless steel wires using 98% Ar + 2% O2 or 95% Ar + 5% CO2 as the shielding gas—is known as MIG welding. 〈3〉GMAW with an inert helium+argon gas mixture as shielding gas. 14. What is TIG (Tungsten Inert Gas) welding? Answer: TIG welding is arc welding under inert gas protection using pure tungsten or activated tungsten (thorium-tungsten, cerium-tungsten, zirconium-tungsten, lanthanum-tungsten) as the non-melting electrode. 15. What is SMAW (Shielded Metal Arc Welding) welding? Answer: An arc welding method in which the weld rod is manually manipulated for welding. 16. What is carbon arc gas gouging? Answer: A surface treatment method that uses carbon rods as electrodes to generate an arc with the workpiece, and then uses compressed air (at a pressure of 0.5–0.7 Mpa) to blow away the molten metal. It is commonly used for root cleaning of welds, groove preparation, and repairing defects. 17. Why is CO2 welding more efficient than shielded metal arc welding? Answer: <1>CO2 welding has a melting speed and melting rate 1-3 times higher than those of shielded metal arc welding ； 〈2〉The groove cross-section is 50% smaller than that of the electrode, resulting in a reduction of the deposited metal volume by 1/2 ； 〈3〉The auxiliary time is 50% of that in shielded metal arc welding. Total of the three: The work efficiency of CO2 welding is 2.02–3.88 times higher compared to shielded metal arc welding. 18. Why are the quality of CO2 welding joints better than that of shielded metal arc welding joints? Answer: CO2 welding results in a small heat-affected zone and minimal welding deformation ； CO2 welds have a low hydrogen content (≤1.6 ML/100g), with little tendency to form pores or cracks ； CO2 welding produces well-formed welds with few surface and internal defects, resulting in a higher defect detection pass rate compared to shielded metal arc welding. 19. Why is the overall cost of CO2 welding lower than that of shielded metal arc welding? Answer: <1> The cross-sectional area of the groove is reduced by 36-54%, resulting in less filler metal being required ； 〈2〉Reduce power consumption by 65.4% ； 〈3〉The cost per machine-shift for this method is 67-80% lower than that of shielded metal arc welding, resulting in a cost reduction of 20-40% ； 〈4〉Reduce labor costs and working hours, cutting costs by 10-16% ； 〈5〉Save auxiliary labor time, consumables usage, and costs associated with correcting deformities ； Taking all five factors into account, CO2 welding can reduce the total welding cost by 39.6–78.7%, with an average reduction of 59%. 20. What is a low-frequency pulse? Which welds are applicable? Answer: Pulse arc with a pulse frequency of 0.5–30 Hz is called low-frequency pulse welding. It is mainly used for TIG welding of non-ferrous metals such as stainless steel, steel, and titanium. 21. What is a medium-frequency pulse? Which welds are applicable? Answer: Pulse arc welding with a pulse frequency of 30–500 Hz is called medium-frequency pulse welding. Due to the arc compression effect, the arc is concentrated and the stiffness is high; it is mainly used for TIG welding of thin stainless steel, steel, and non-ferrous metals such as titanium, as well as for MIG welding of stainless steel, aluminum, and aluminum alloys. 22. Why is there spatter in CO2 welding? Answer: The droplet at the end of the welding wire makes short-circuit contact with the molten pool (short-circuit transition), and due to intense overheating and magnetic contraction, the droplet breaks apart, resulting in spatter. The output reactor and waveform control of the CO2 welder can minimize spatter. 23. Why can jet transition and no spatter be achieved only in MIG/MAG welding with high current? Answer: During MIG/MAG welding, all metals have a critical current value at which the short-circuit transition changes to a jet transition (for example, for φ1.2 carbon steel and stainless steel wires, the current I should be ≥260–280 A); at this point the arc is in a jet transition state, enabling splatter-free welding. 24. Why is a pulsed power supply required for low-current MIG/MAG welding in order to achieve a jet transition with no spatter? Answer: In MIG/MAG welding, when the welding current is below the critical value, a pulsed power supply is used; the pulse current being higher than the critical value allows the arc to be in a jet transition state, thereby enabling splatter-free welding. (For example, with a pulsed MIG/MAG welder, welding of φ1.2 carbon steel, stainless steel, aluminum, and aluminum alloys can achieve pulse droplet transition at a current of I≥80A, with the pulse current Ip≥350A.) 25. What are welding conditions? What does it contain? Answer: The conditions surrounding the welding process include: the material of the base metal, plate thickness, groove shape, type of joint, degree of restraint, ambient temperature and humidity, level of cleanliness; as well as the type and diameter of wire (or electrode) determined based on these factors, welding current and voltage, welding speed, welding sequence, deposition method, and the method of moving the welding tool (or electrode). 26. What is penetration depth? Answer: The depth to which the base material is melted in the cross-section of the welded joint. 27. What is the welding position? How many forms are there? Answer: During fusion welding, it refers to the spatial position of the joint between the welded parts. There are forms such as flat welding, vertical welding, horizontal welding, and overhead welding. 28. What are vertical down welding and vertical up welding? Answer: <1>When welding in the vertical position, the arc moves from top to bottom – this is called vertical down welding. For example: cellulose electrode for vertical down welding ； CO2 vertical down welding, etc. 〈2〉When welding in the vertical position, the arc moves from bottom to top – this is called upward vertical welding. 29. What is a welded structure? Answer: A steel structure connected by welding is called a welded structure. 30. Why are bevels required for welded joints? Answer: Groove – A groove formed by shaping the part of the weldment to be welded into a specific geometric shape according to design or process requirements, after assembly. To achieve full penetration of the weld joint cross-section and reduce the fusion ratio ； Common groove shapes include: I, V, Y, X, U, K, J, etc. 31 What are the classification methods and basic types of welded joints? Answer: (1) Classification methods of welded joints A welded joint consists of the weld seam, fusion zone, heat-affected zone, and the adjacent base material. Welded joints serve two main functions: one is to connect components, and the other is to transmit forces. (2) What are the basic types of weld joints? Depending on the welding method, weld joints can be divided into three main categories: fusion weld joints, pressure weld joints, and brazed weld joints. The basic types of welded joints can be classified into 5 categories, namely butt joints, T-joints (cross joints), lap joints, corner joints, and end joints. All five basic types of joints mentioned above are suitable for fusion welding; for general pressure welding (with the exception of high-frequency resistance welding), lap joints are used, while butted joints are employed only in certain cases ； High-frequency resistance welding generally uses butt joints, with lap joints being used only in certain cases. There are also various types of joints formed by brazing. One classification method divides them into four categories: lap joints, T-joints, socket joints, and tongue-and-groove joints. 32 What are the types of fusion weld joints and grooves? Answer: The butt joint is an ideal joint type in fusion welding in terms of stress distribution. To ensure welding quality, reduce welding deformation, and minimize the consumption of welding materials, the edges of the workpieces to be welded must be prepared into grooves of various shapes, followed by groove welding. The grooves of fusion welded joints can be classified into three types based on their shape: basic, mixed, and special. The basic types of grooves include the following: I-shaped groove ； V-groove ； Unilateral V-groove ； U-shaped groove ； J-groove welds, etc. Special types of grooves mainly include crimped grooves ； Groove with shims ； Sealed groove ； Seam, groove weld grooves, etc. 33 What are the selection principles for welding joints? Answer: To properly and reasonably select the type of welding joint, as well as the shape and dimensions of the groove, the following factors should be taken into consideration: (1) Design requirements: Ensuring that the joint meets the operational requirements ； (2) Ease of welding and welding deformation: Welding is easy to carry out, and deformation can be controlled ； (3) Welding cost: The costs associated with joint preparation and actual welding are low ； (4) Construction conditions: The manufacturing and construction unit possesses the technical expertise, personnel, and equipment necessary to meet the construction requirements. 34. Why is preheating necessary for certain materials before welding? Answer: To slow down the cooling rate of the welded parts after welding and prevent the formation of cold cracks. 35. Why is heat treatment required for certain welded components after welding? Answer: To eliminate welding residual stresses and improve the microstructure and properties of the welded joint. 36. Why is it necessary to formulate a welding procedure specification before welding? Answer: Ensuring welding quality relies on five key control aspects: people, machinery, materials, methods, and environment. Person – the operator’s skills and experience; Machine – the high performance and stability of welding equipment; Material – the high quality of welding materials; Method – the correct welding procedures and standardized operations; Environment – a favorable welding work environment. The welding procedures established based on welding tests and welding procedure qualifications prior to welding are considered “regulations,” and they are an important factor in ensuring welding quality. 37. Why is it necessary to treat the surface of the base material before welding? Answer: If there are impurities such as oil (paint), water, or rust on the groove and surface of the weldment, they will dissolve into the weld, causing defects such as pores, inclusions, slag inclusions, and cracks, which pose risks and hazards to the welded joint. 38. What is the melting coefficient of welding wire? Answer: The melting coefficient of welding wire refers to the amount of welding wire that melts per unit time under a unit current (in g/Ah). The finer the welding wire, the higher its melting coefficient, which means higher efficiency. 39. What are welding process parameters? Answer: During welding, it refers to the collective term for various physical parameters selected to ensure welding quality (such as welding current, arc voltage, welding speed, wire energy, etc.). 40. What is welding current? Answer: During welding, the current flowing through the welding circuit is generally expressed in amperes (A). 41. What is arc voltage? Answer: The voltage drop between the two ends of an arc (the two electrodes) is generally expressed in volts (V). 42. What is welding speed? Answer: The length of weld completed per unit of time is generally expressed in centimeters per minute (cm/min). 43. What is the dry elongation? Answer: During welding, it is the distance between the end of the welding wire and the tip of the electrode tip. 44. What is welding line energy? Answer: In fusion welding, it refers to the energy supplied per unit length of weld by the welding heat source, also known as “heat input”. It is generally expressed in joules per centimeter (J/cm). 45. What is the fusion ratio of weld metal? Answer: In fusion welding, it is the proportion of the melted base metal in the weld metal. 46. What is the weld shape factor? Answer: In fusion welding, it is the ratio of the weld width to the weld thickness in the cross-section of a single weld bead. 47. What is leftward welding? Answer: In fusion welding, it is a welding method in which the welding torch moves from the right end to the left end of the joint between the workpieces. It provides good gas protection and results in aesthetically pleasing welds. For both CO2 and TIG welding, the left-hand welding method is used ； MIG welding of aluminum must be done using the left-hand welding method. 48. What is the rightward welding method? Answer: In fusion welding, it is a welding method in which the welding torch moves from the left end to the right end of the joint between the workpieces. 49. Why is the welded joint considered the weak link in welded structures? Answer: This is because welding joints exhibit non-uniformity in structure and properties, and often contain various welding defects, as well as high tensile residual stresses ； Therefore, the weld joint is the weak link in welded structures. 50. Why is it said that high-quality welded joints can be obtained through appropriate processing methods? Answer: To improve the quality of welded joints, the following approaches can be adopted: selecting appropriate welding materials, using reasonable welding processes, controlling the fusion ratio, adjusting the characteristics of the welding heat cycle, employing proper operating methods and groove designs, along with measures such as preheating, interpass insulation and slow cooling, post-weld heating, or post-weld heat treatment, to obtain high-quality welded joints. 51. What is welding material? What does it include? Answer: It includes electrodes, welding wire, flux, gas, electrodes, gaskets, etc. 52. What is welding wire? Answer: The metal wire used as filler material during welding and also for conducting electricity is called welding wire. It is divided into solid wire and flux-cored wire. Common solid wire grades: ER50-6 (grade: H08Mn2SiA). 53. Why do MAG welded joints have higher impact toughness than CO2 welded joints? Answer: During MAG welding, the proportion of active gas is only 20%. The transfer coefficient of alloying elements in the welding wire is high, resulting in high impact toughness of the weld. The active gas for CO2 welding is 100%; manganese and silicon, which are alloying elements in the wire, work together to remove oxygen from the metal. The transition coefficient of these alloying elements is slightly lower, resulting in welds that have lower impact toughness compared to those produced by MAG welding. For example, the Tangshan Shinko MG-51T welding wire (equivalent to ER50-6) has the following impact toughness value at room temperature: MAG: 160J ； CO2: 110J. 54. What is flux-cored wire? Answer: It is a type of welding wire made by rolling thin steel strips into circular steel tubes and then filling them with powder of a specific composition, followed by drawing. 55. Why is CO2 gas used for shielding flux-cored wires? Answer: Based on the protection method, there are two types of flux-cored wires: flux-cored gas-shielded welding wires and flux-cored self-shielded welding wires. Flux-cored gas shielded welding wires generally use CO2 gas for protection, belonging to the combined gas-slag shielding method; they yield welds with good shape and high overall mechanical properties. 56. Why do dentation pores appear on the surface of wire rod welds? Answer: Since flux-cored wire is a tubular wire made by rolling thin steel strips, it belongs to seamed wire ； Moisture in the air can penetrate the flux core through gaps; the flux becomes moist (unable to be dried), resulting in indentations and pores in the weld. 57. Why are there technical requirements for the purity of CO2 gas? Answer: Generally, CO2 gas is a by-product of chemical production. Its purity is only about 99.6%, and it contains trace amounts of impurities and moisture, which can lead to defects such as pores in the weld. When welding important products, it is essential to use gas with a CO2 purity of ≥99.8% – this results in fewer weld porosities, a lower hydrogen content, and better crack resistance. 58. Why are there high technical requirements for the purity of argon? Answer: There are currently three types of argon available on the market: ordinary argon (with a purity of around 99.6%), pure argon (with a purity of around 99.9%), and high-purity argon (with a purity of 99.99%). The first two types can be used for welding carbon steel and stainless steel ； When welding non-ferrous metals such as aluminum and aluminum alloys, as well as titanium and titanium alloys, high-purity argon must be used ； Prevent the welds and heat-affected zones from oxidizing, which could prevent welding. 59 What is the classification method for welding electrodes? Answer: (l) Classified by the purpose of the welding rod: l) Welding rods for low-carbon steel and low-alloy high-strength steel (abbreviated as structural steel welding rods). 2) Stainless steel welding electrodes. 3) Surfacing electrodes. 4) Low-temperature steel electrodes. 5) Cast iron welding electrodes. 6) Nickel and nickel alloy electrodes. 7) Copper and copper alloy welding electrodes. 8) Aluminum and aluminum alloy welding electrodes. (2) Classified by the characteristics of the slag formed after the melting of the electrode coating: l) Acidic electrodes. It is generally used for welding low-carbon steel and less critical steel structures. 2) Alkaline electrodes. The deoxidation of alkaline slag is relatively complete; it can also effectively remove sulfur from the weld metal. There is minimal loss of alloying elements, resulting in good mechanical properties and crack resistance of the weld metal. Therefore, it can be used for welding alloy steels and important carbon steel structures. 60 How to select welding electrodes? Answer: Generally, it is necessary to consider the chemical composition and mechanical properties of the steel used in the welded structure. Requirements such as weldability and working environment (presence of corrosive agents, high or low temperatures), as well as the shape of the welded structure. A comprehensive consideration of factors such as the stress conditions and welding equipment (whether there is a DC welder) is needed to determine which type of electrode to use. The following principles should be considered when selecting welding electrodes: (l) the mechanical properties and chemical composition of the welded material. For low-carbon steel, medium-carbon steel, and low-alloy steel, welding electrodes of corresponding strength can be selected based on their strength grades. After the strength of the welding rod has been determined, the choice between acidic and alkaline welding rods depends mainly on the complexity of the shape of the welded structure, the thickness of the steel, the type of load acting on the welded parts (static or dynamic), the crack resistance of the steel, and the ease of obtaining a direct current power supply. Generally, alkaline electrodes should be used for welds that require high levels of plasticity, impact toughness, and crack resistance, and that operate under low-temperature conditions ； When it is not possible to remove rust from the groove of low-carbon steel weldments due to certain constraints. When dealing with dirt such as oil stains and scale, it is advisable to use acidic welding electrodes that are less sensitive to rust, oil stains, and scale, and have good resistance to porosity. For welding of dissimilar steels, such as welding of low-carbon steel to low-alloy steel or low-alloy steels with different strength grades, electrodes matching the steel with the lower strength grade are generally selected. (2) Operating conditions and service performance of the welded parts. For pearlitic heat-resistant steel, welding electrodes with a chemical composition similar to that of the steel are generally used, or choices are made based on the operating temperature of the welded component. (3) Simplify processes, improve productivity, and reduce costs. 61 How to select welding parameters when performing manual welding? Answer: The welding parameters for arc welding mainly include electrode diameter, welding current, arc voltage, number of welding layers, type and polarity of the power source, etc. (1) Selection of electrode diameter. The selection of electrode diameter mainly depends on factors such as the thickness of the workpiece, joint type, weld position, and welding layer. Without compromising the welding quality, in order to improve labor productivity, it is generally preferable to choose electrodes with a larger diameter. (2) Selection of welding current. It is primarily determined by factors such as electrode type, electrode diameter, thickness of the workpiece, joint type, spatial position of the weld, and welding pass sequence; among these, the most important factors are electrode diameter and the spatial position of the weld. (3) Selection of arc voltage. The arc voltage is determined by the arc length. The longer the arc, the higher the arc voltage ； If the arc is short, the arc voltage is low. (4) Selection of the number of weld layers. In shielded metal arc welding of medium and thick plates, multi-pass welding is often employed. (5) Selection of power supply type and polarity. DC power supply: stable arc, minimal spatter, and good welding quality; it is generally used for welding important structural components or thick plates with high stiffness. In other cases, an AC welder should be considered first. Under normal circumstances, for welding with alkaline electrodes or thin sheets, direct current with reverse polarity is used ； For acidic electrodes, direct polarity is usually chosen. 62 What is an acidic welding rod? Answer: Welding electrodes whose coating contains a large amount of acidic oxides, such as the AC/DC welding electrodes J422 (E4303), etc. 63 What is an alkaline welding electrode? Answer: Welding electrodes whose coating contains a large amount of basic oxides as well as fluorides, such as the E5015 (J507) welding electrode. 64 What is a cellulose-type electrode (specific for vertical down welding)? Answer: Welding rods with a flux coating containing large amounts of organic substances, designed specifically for vertical welding in pipeline and thin plate structures. <1> For example, E6010 (equivalent to E4310 and J425G) is suitable for root welding, hot welding, and filler welding. <2> E8010 (equivalent to E5511, J555) is suitable for hot welding, filler welding, and cover welding layers. Generally, low-hydrogen downward welding electrodes are used for surfacing welds ； The weld appearance of E7048 (equivalent to J506X) is neat and aesthetically pleasing. 65 Why must welding rods be dried thoroughly before welding? Answer: Electrodes often suffer from deteriorated process performance due to moisture absorption, resulting in unstable arcs, increased spatter, and a higher likelihood of defects such as pores and cracks. Therefore, welding electrodes must be carefully dried before use. The drying temperature for general acidic welding electrodes is 150–200°C, with a duration of 1 hour ； The drying temperature for basic electrodes is 350–400°C, with a duration of 1–2 hours. After drying, they should be stored in an oven maintained at 100–150°C for easy access when needed.