Basic principles for selecting welding materials

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Basic principles for selecting welding materials I. Definition Welding materials: A general term for the materials consumed during welding (including electrodes, welding wires, fluxes, shielding gases, electrodes, fluxes, etc.). Welding electrode: A consumable electrode used for arc welding, coated with flux. Welding wire: A metal wire used as filler metal during welding, or simultaneously to conduct electricity. Flux: A granular substance used during welding that can melt to form slag (and sometimes gas), serving to protect the molten metal and to facilitate its metallurgical processing. Protective gas: A gas used during welding to protect the metal droplets, the welding pool, and the hot metal in the welding area, thereby preventing harmful external gases from entering that area. Electrodes: During welding, these are wires (welding wires, electrodes), rods (graphite rods, tungsten rods), tubes, plates, etc., used to conduct electricity and melt the filler material and the base metal, or that may also melt as part of the filler material. In resistance welding, it refers to the metal electrodes used to conduct the electrical circuit and apply pressure. Flux: A powdery substance used in gas welding to remove the oxides formed during welding and to improve the wetting of the weld pool. General principles for selecting welding materials 1. Electrodes The basic requirements for electrodes are as follows: (1) The weld metal produced by the electrode should have good mechanical properties. (2) The weld metal should have the specified chemical composition to ensure it meets the required performance standards. (3) The electrode should have good processability. (4) It is necessary that the electrode has good resistance to porosity and cracking. (5) The electrode should also have good appearance quality (of its surface layer). Image: Composition of an electrode: An electrode consists of a core and a coating. The metal core wrapped in flux within the welding rod is the welding core; its main function is to conduct electricity and generate an arc at the end of the welding rod. Meanwhile, as the welding core melts due to the heat of the arc, it cools down to form weld metal with specific composition. The coating applied on the surface of the welding core in a welding rod is called the flux coat. Its main functions are mechanical protection, metallurgical treatment, and improvement of welding process properties. Classification of welding electrodes: Based on the alkalinity of the slag, they are divided into acidic welding electrodes and basic welding electrodes ； Classified by the main components of the coating, they are divided into titanium type, titancalcium type, ilmenite type, and iron oxide type ； Classified by purpose, they are divided into structural steel welding electrodes (J), molybdenum and chromomolybdenum heat-resistant steel welding electrodes (R), stainless steel welding electrodes (chromium stainless steel G, chromium-nickel stainless steel A), surfacing welding electrodes (D), low-temperature welding electrodes (W), cast iron welding electrodes (Z), nickel and nickel alloy welding electrodes (Ni), copper and copper alloy welding electrodes (T), aluminum and aluminum alloy welding electrodes (L), and special-purpose welding electrodes (Ts). Type and grade of welding electrode: The grade of the welding electrode should include the following information: the type of welding electrode, its category, its characteristics (such as the tensile strength of the deposited metal, the operating temperature, the type of core metal, the chemical composition of the deposited metal, etc.), the type of flux, and the welding power supply. In accordance with the provisions of GB/T 5117-1995 \"Carbon Steel Welding Electrodes\" and GB/T 5118-1995 \"Alloy Steel Welding Electrodes\", the basic structure of a welding electrode model consists of the letter \"E\" followed by four digits. Its structure and meaning are as follows: E X1X2X3X4. E: denotes the welding electrode; X1X2: represents the electrode series, i.e., the minimum tensile strength of the deposited metal; X3: indicates the welding position for which the electrode is suitable; X4: specifies the type of flux coating on the electrode and the type of welding power supply. For example: E 5015. E: welding electrode; 50: tensile strength of the deposited metal σb ≥ 409 MPa; 1: suitable for all welding positions (0, 1 – all positions) ； 2 Butt Welding and Fillet Welding ； 4: Flat welding, vertical welding, overhead welding, and downward vertical welding are applicable only to carbon steel electrodes.) Low-alloy steel electrodes: E X1X2 X3 X4-□-□ E: Electrode; X1X2: Minimum tensile strength of the deposited metal; X3: Welding position of the electrode (0, 1: all positions ； 2 for flat welding and fillet welding) X4: The type of welding current and the type of flux are indicated by numbers. □1: The classification code for the chemical composition of the deposited metal, indicated by letters. □2: Additional chemical elements, indicated by their chemical symbols. Stainless steel electrodes: E 308L-16; E denotes the electrode type. 308L refers to the chemical composition of the deposited metal, with L indicating ultra-low carbon content; 308 denotes the type of chemical composition of the electrode’s deposited metal. Other types of electrodes are not discussed here. 2. Welding wire: The basic requirements for welding wire are that it serves to conduct current, supply filler metal, and act as an alloying agent during welding. Self-shielded flux-cored welding wires also play a role in protection, as well as in deoxidation and denitration during welding. Therefore, the welding wire is required to have the specified chemical composition and mechanical properties, and clear technical requirements are also imposed on its dimensions and surface quality. Classification of welding wires: Based on their structural format, they are divided into flux-cored wires and solid-core wires. Flux-cored wires, in turn, can be further categorized into various types depending on their structure and filler material ； Classified by steel type, they include low-carbon steel welding wires, low-alloy steel welding wires (wiring for high-strength steel, Cr-Mo heat-resistant steel welding wires, wiring for low-temperature steel), stainless steel welding wires, cemented carbide surfacing welding wires, copper and copper alloy welding wires, aluminum and aluminum alloy welding wires, cast iron welding wires, etc ； Classified by welding method, they include submerged arc welding wires, electroslag welding wires, CO2 gas shielded welding wires, TIG welding wires, MIG welding wires, MAG welding wires, self-shielded welding wires, surfacing welding wires, and oxyacetylene welding wires. Image: Type or grade of welding wire. (1) Welding wires made of carbon steel, low-alloy steel, and stainless steel – Except as specified in GB/T8110-95, the type or grade of such welding wires is indicated by the letter H; the method for designating their grades is to use the letter H to represent the welding wire ； The one or two digits following H indicate the carbon content (average value) ； The chemical element symbol, followed by a number, indicates the approximate mass fraction of that element; when the mass fraction of the main alloying element is ≤1%, the number can be omitted and only the element symbol is used ； When A or E is marked at the end of the wire grade, it indicates high-quality or ultra-high-quality products, meaning lower levels of impurities such as S and P. For example: H08Mn2SiA – H: wire; 08: carbon content, with a mass fraction of approximately 0.08%; Mn2: manganese content, with a mass fraction of approximately 2%; Si: silicon content, with a mass fraction of ≤1%; A: high-quality grade, with sulfur and phosphorus contents of approximately ≤0.03%. (2) Carbon steel and low-alloy steel wires for gas shielded welding: According to GB/T8110-95, the designation format for wire types is ERXX-X. The letter ER denotes a wire, the two digits following ER indicate the minimum tensile strength of the deposited metal, while the letter or digit following the hyphen represents the classification code for the chemical composition of the wire. When other chemical elements are added, they can be represented directly by their element symbols, separated from the preceding number by a hyphen –. For example: ER55-B2-Mn – ER refers to welding wire; 55 indicates that the minimum tensile strength of the deposited metal is 550 Mpa; B2 is the code used to classify the chemical composition of the welding wire; Mn denotes the presence of manganese in the welding wire. 2. Flux – Basic requirements for flux: (1) It should have good metallurgical properties; (2) It should possess good weldability; (3) It should have a low water content and good moisture resistance; (4) The mass fraction of mechanical impurities in the flux should not exceed 0.3%; (5) The flux should have low levels of S and P, with S ≤ 0.06% ； ≤0.08% (6) The flux should have a certain particle size; the usual range is 8–40 mesh, while finer grades have a particle size of 14–60 mesh. (7) For electroslag welding, in order to obtain good weld joints, certain requirements are placed on the flux: the electrical conductivity of the slag must be within an appropriate range ； The viscosity of the slag should be appropriate ； Control the evaporation temperature of the flux. In addition, the flux should also have good slag removal properties, crack resistance, and porosity resistance. Classification of fluxes: Fluxes are commonly divided into melting fluxes and non-melting fluxes (bonding fluxes, sintered fluxes), etc. For example: HJ431 – HJ: Welding fluxes for submerged arc welding and electroslag welding; 4: The type of flux is manganese-rich; 3: The type of flux is high-silicon and low-fluorine; 1: The grade number, with different numbers within the same category arranged from 0, 1…9. II. Selection of welding materials: To obtain high-quality welded joints, it is necessary to select the welding materials appropriately first. 1. Meet the requirements for the performance of welded joints, including strength at room temperature and at high temperatures for short periods, bending properties, impact toughness, hardness, chemical composition, etc. Additionally, there are special requirements for joint performance specified in various technical standards and design drawings, such as endurance strength, creep limit, oxidation resistance at high temperatures, and corrosion resistance. 2. Requirements for the mechanical properties of welded joints and welding processes: Components formed by welding inevitably undergo various forming and cutting operations during manufacturing, such as stamping, rolling, bending, turning, planing, and other processes. This requires that welded joints possess certain plastic deformation capabilities, machinability, as well as high-temperature performance. The welding process requires that, depending on the differences in weldability of the base metal, the welding materials possess good process properties and the ability to resist defects such as cracks. 3. Reasonable cost-effectiveness: While meeting the minimum requirements for the aforementioned performance characteristics and manufacturing properties, it is necessary to choose welding materials that are inexpensive in order to reduce manufacturing costs and improve economic efficiency. For example, when performing GMAW on low-carbon steel for critical components, alkaline flux-cored electrodes should be preferred, as they provide thorough deoxidation and desulfurization, have a low hydrogen content, and thus confer good crack resistance and impact toughness to the weld metal. For some less critical components, acidic electrodes can be used, as they offer good workability, meet the performance requirements of such components, and are inexpensive, thereby helping to reduce manufacturing costs. III. Selection of welding materials for plain steel and low-alloy steel (1) Principle of equal strength: As part of the component, the tensile strength of the weld joint should be no less than the lower limit of the specified standard tensile strength of the base material. At the same time, it should be noted that the tensile strength of the weld metal produced from the welding materials should not be much higher than that of the base material; otherwise, it will lead to reduced plasticity and increased hardness in the weld, which is not conducive to subsequent manufacturing and shaping. When selecting the welding material for welded joints under high-temperature operation, it should also be considered that their high-temperature short-term tensile strength or endurance strength is not lower than the corresponding values of the base material. When welding ordinary carbon steel and standard low-alloy steel, the selection of welding materials is primarily based on their tensile strength; there is no need to consider whether the chemical composition of the deposited metal matches that of the base material ； However, when welding Cr-Mo heat-resistant steel materials, the selection of welding materials requires considering not only the chemical composition of the deposited metal to match that of the base material, but also the matching of alloying elements, in order to ensure that the overall properties of the welded joint are consistent with those of the base material. In special cases where components are designed using the allowable stress calculated from the yield strength of the material, the equivalence of yield strengths must be taken as an important consideration. (2) Principle of equivalent toughness: When selecting welding materials, it is necessary to ensure that the impact toughness of the weld meets the requirements of relevant standards. Due to the different operating conditions of components, brittle failure often occurs during operation as a result of insufficient toughness; this is especially true for components that operate at low temperatures or those that are thick-walled and high-strength. Therefore, the relevant standards set clear requirements for the impact toughness indicators of welded joints. However, different standards result in varying requirements for the impact toughness of joints. According to the “Regulations on the Safety Supervision of Steam Boilers”, the impact toughness of welded joints shall not be lower than the specified lower limit for the impact toughness of the base material. When there are no requirements regarding the impact toughness of the base material, this value shall not be lower than 27 J. According to GB 150 “Steel Pressure Vessels”, the required impact toughness value for joints shall be determined based on the minimum tensile strength of the steel. The minimum impact toughness requirements for joints in carbon steel and low-alloy steel are shown in Table 3-40. The impact toughness value of cryogenic vessels shall not be lower than the specified minimum value for the base material. Meanwhile, ASME Code VIII-1 determines whether impact toughness requirements must be met for joints, based on factors such as the material’s strength grade, thickness, operating temperature, design stress, and the ratio of design stress to allowable stress. If there are requirements regarding impact toughness for the joint, then the minimum guaranteed value of impact toughness is specified based on the material’s strength grade and thickness. (3) Consideration of manufacturing process requirements and impacts: After welding, the components often undergo various forming processes such as rolling, pressing, bending, and straightening. Therefore, both the welded joint and the base material must possess a certain capacity for mechanical deformation, with cold deformation being the most important form of such capacity. The method used to assess this is through bend tests on the joints. 4. Selection of welding materials for austenitic stainless steel: The principle of matching the strength of welding materials to that of the base material does not apply entirely to austenitic stainless steel. For austenitic stainless steels used in corrosion-resistant applications, no specific requirements are imposed on strength; the main focus is on the corrosion resistance of the welds. When used in high-temperature and high-pressure conditions, short-term operation requires a certain degree of high-temperature short-term strength, while long-term operation demands that the weld metal possess sufficient endurance strength and creep resistance. For example, when SA213-TP304H pipes are used in such conditions and welded by arc welding, an E308H electrode with a higher carbon content should be selected. a) Considering the chemical composition of the deposited metal: When welding austenitic stainless steel, when selecting welding materials, it is crucial to ensure that the chemical composition of the deposited metal is similar to that of the base material. As long as the chemical composition of the deposited metal from the welding materials matches that of the base material, the mechanical properties and corrosion resistance of the weld metal will be comparable to those of the base material. In addition, special attention must be paid to any specific requirements regarding corrosion resistance specified in the manufacturing procedures or drawings. To prevent intergranular cracks during welding, it is best to use low-carbon (ultra-low carbon) stainless steel welding materials containing Ti and Nb. If the content of SO2 in the welding rod coating or flux is too high, it is not suitable for welding austenitic steels with high nickel content. To prevent weld hot cracks (solidification cracks), it is necessary to control the levels of impurities such as P, S, Sb, and Sn, and to avoid the formation of a single-phase austenite structure in the weld metal as much as possible. b) Consider the ferrite content in the weld: Although many sources indicate that a higher ferrite content in the weld metal of austenitic stainless steels helps to reduce the tendency for cracks in such welds, large quantities of pure austenitic weld metal have been used in practical applications for many years, with satisfactory performance of the joints. Furthermore, an appropriate ferrite content in certain media is beneficial for corrosion resistance, but it is detrimental to the impact toughness of weld metal under low-temperature conditions. Overall, a ferrite content of 4-12% in typical austenitic stainless steels is considered appropriate, as a ferrite content of 5% already provides satisfactory resistance to intergranular corrosion. c) Consider the effect of the welding method. When selecting welding materials for austenitic stainless steel, attention should be paid to the effect of the welding method on the chemical composition of the deposited metal. Tungsten inert gas welding has the least impact on the chemical composition of the weld metal; aside from C and N, little change occurs in the undiluted weld metal, with C experiencing the greatest loss. In wire with a carbon content of 0.06%, the carbon content in the undiluted weld metal produced by TIG welding is 0.04%, while the nitrogen content in the weld metal increases by about 0.02%. In GMAW, the contents of Mn, Si, Cr, Ni, and Mo may experience slight changes; the loss of C is only 1/4 that in TIG welding. The content of N increases significantly, with the amount of increase varying depending on the welding process, and can reach up to 0.15%. In shielded metal arc welding and submerged arc welding, the alloying elements in the weld metal are influenced by both the flux coating and the welding electrode core/wire; especially in those welding materials in which alloying elements are transferred through the flux coating or flux, it is not possible to estimate the chemistry of the weld metal based on the chemical composition of the electrode core or wire. Of course, the ferrite content in the weld can be estimated based on the alloy content in the weld metal, but this estimated value differs somewhat from the actual value, as the cooling rate during welding also affects the ferrite content. It is generally agreed that if the alloy element content in the weld metal is exactly the same, different welding methods will result in different ferrite contents. The ferrite content in the welds is highest in strip welding, followed by submerged arc welding, shielded metal arc welding, CO2 gas shielded welding, MAG welding, MIG welding, and TIG welding, with the lowest ferrite content in TIG welded welds. However, even with the same strip welding, the ferrite content in the welds varies in different areas. Measurements showed that the ferrite content at the arc-end and arc-start areas is about 2-3% lower than that in the middle section. With the standardization of stainless steel materials and welding materials, it has become simpler to choose welding materials for austenitic stainless steels; the appropriate welding material can be selected based on the grade of the stainless steel. For example, when welding SA-240-316 stainless steel, E316 welding rods can be used directly. V. Selection of welding materials for stainless steel: When welding martensitic stainless steel, it is best to use welding materials of the same composition as the base material. For example, when welding 1Cr13 steel, welding materials from the E410 series should be used, with the electrode wire for shielded metal arc welding having the grade G217. However, the welding materials corresponding to ordinary 1Cr13 result in a weld metal structure composed of coarse martensite and ferrite; this structure is hard and brittle, prone to cracking. Moreover, the welded parts must be preheated to 250–350°C. To improve the properties, it is necessary to limit the contents of S and P in the welding materials, control the Si content at ≤0.30%, reduce the C content, and add small amounts of Ti, Al, and Ni to refine the grains and reduce hardenability. Studies show that increasing the Nb content in the welding materials to around 0.8% can yield a single-phase ferritic structure. In CO2 gas shielded welding, the wire is enriched with Ti and Mn elements to achieve deoxidation. Maraging stainless steels can also be welded using austenitic stainless steel welding materials; in such cases, the effect of base metal dilution on the composition of the weld metal must be taken into account. By adjusting the levels of Cr and Ni, it is possible to prevent the formation of martensitic structure in the weld metal. For example, when using shielded metal arc welding, A312 (E309Mo) electrodes can be employed to weld 1Cr13 maraging steel. VI. Selection of welding materials for ferritic stainless steels. Generally, welding materials homogeneous to the base metal are used for ferritic stainless steels. However, the ferritic structure in the weld zone is coarse and has poor toughness. Increasing the Nb content in the welding material can help refine this ferritic structure. Additionally, heat treatment can be employed to improve the toughness of the weld metal. VII. Selection of welding materials for dissimilar steel grades Welding between low-carbon steel and low-alloy steel, as well as between low-alloy steels of different grades, falls under the category of welding dissimilar steel grades. For welding between such steels, welding materials can be selected based on lower-grade materials, or those with lower strength levels or lower contents of alloying elements. Using lower-grade materials results in better weldability compared to higher-grade materials, and they are also cheaper, which helps to reduce manufacturing costs. 1. Definition of welding materials – what materials are included? Answer: A general term for the materials consumed during welding. Welding materials include electrodes, welding wires, fluxes, shielding gases, electrodes, solvents, etc. 2. What are the selection principles for welding materials of carbon steel and low-alloy steel? Answer: 1) Principle of equal strength; 2) Principle of equal toughness; 3) Consider the requirements and effects of manufacturing processes. 3. In general, when welding low-carbon steel and low-alloy steel, should the welding materials be selected based on lower-grade or higher-grade materials? What electrode should be used for GMAW with 20g and DIWA353 electrodes? Answer: Select welding material according to the lower-grade material. Select the J507 welding rod. (GB E5015 or AWS E7015 are both acceptable.) 4. What does the “E” in GB E5515-B2 stand for? “What does 55” mean? Seeing this grade, can you tell what type of steel it is used for welding? Answer: “E” stands for electrode, and “55” indicates that the minimum tensile strength of the deposited metal is 540 Mp. Used for welding Cr-Mo heat-resistant steel. 13CrMo44, 15CrMo, 15CrMoR, 15CrMog, SA-335P12, SA213T12, SA213T11, SA387Gr12CL1, SA387Gr11CL1, SA387Gr11CL2, etc., can also be used as answers. 5. In H08Mn2SiA, what do “H”, “08”, “Mn2”, “Si”, and “A” represent respectively? Answer: “H” stands for welding wire; “08” indicates a carbon content of approximately 0.08%; “Mn2” means a manganese content of about 2%; “Si” denotes a silicon content of ≤1%; “A” indicates high-quality product. 6. In GB E5015 and AWS 5.1 E7015, what do “50” and “70” represent? Answer: “50” indicates that the minimum tensile strength of the deposited metal is 490 Mpa, while “70” means that the minimum tensile strength is 70 ksi, which is equivalent to 485 Mpa. Adjustment of process parameters for carbon dioxide gas shielded welding: There are many process parameters that affect carbon dioxide gas shielded welding, but the welder can adjust only the welding voltage, welding current, wire diameter, gas flow rate, and wire extension length ；   Reference values for welding process parameters: The commonly used wire diameters are 1.2 mm and 1.0 mm; in addition, there are also 1.6 mm, 0.9 mm, and 0.8 mm. Wires of other diameters are hard to find. CO2 gas shielded welding uses short-circuit transition, so the welding parameter range for wires of each diameter is quite wide; within this range, the welding current and voltage must be matched. Procedure for adjusting welding parameters: The current and voltage of the welder are adjusted according to the following procedure ；   Open the valve of the shielding gas cylinder and verify that the cylinder pressure is normal ； Turn on the power of the welder and verify that the heating and pressure-reduction flow meter is working ； Heat for 5 minutes ；   Open the welding wire package, install the wire coil on the shaft of the wire feeding mechanism, release the clamping handle, and use pliers to cut the end of the welding wire into a flat shape; the end of the wire should be inserted horizontally into the groove of the wire feeding roller from below the wire coil ； Insert the wire feeding hose ；   Close the clamping handle, lay the welding torch flat on the ground with it fully extended, press the white quick wire feed button on the remote control box to feed the welding wire until it appears at the tip of the electrode; if it is an old welding torch, the electrode can be removed first, then the microswitch is pressed to feed the wire, and the electrode is reinstalled after it appears ；  Use pliers to cut the end of the welding wire into a 45-degree sharp corner ；   Prepare the test steel plate, observe the voltage and current meters on the welder; use your left hand to deliberately lower the voltage on the remote control unit, hold the welding torch in your right hand, and initiate welding by creating an arc on the test steel plate ；   If the voltage is indeed low, the right hand holding the gun will feel a strong vibration in the tip of the welding torch, and a cracking sound from the arc can be heard. This is the sound produced when the voltage is too low, the wire feeding speed is much higher than the melting speed, and the arc is ignited only to be extinguished by the welding wire ；   If the voltage is actually too high, an arc can be generated; however, if the arc length is too long, a large molten ball forms at the end of the welding wire. If the melting rate exceeds the wire feeding speed by too much, the arc will keep burning back toward the electrode tip, melting together the welding wire and the electrode tip, which results in the cessation of wire feeding and the extinction of the arc. This can cause damage to both the conductive nozzle and the wire feeding mechanism; therefore, it is necessary to ensure that the voltage is not too high when starting arcing ；   Adjust the welding voltage knob and gradually increase it; as the welding voltage rises, the melting speed of the wire increases, and the crackling sound associated with wire breakage gradually turns into a steady humming sound ；   Observe the voltmeter and ammeter; if the current is below the predetermined value, first increase the welding current, and then increase the welding voltage ； If the current is higher than the preset value, first reduce the welding voltage, then reduce the welding current ；  Wire protrusion length: also known as the dry protrusion length of the welding wire. It is a very important parameter for gas shielded welding. An appropriate length of wire protrusion allows the wire to be sufficiently heated by resistance, which facilitates the formation and transition of droplets at the wire’s end. When the length of the welding wire protruding is too short, spatter is often severe; if it is too long, not only do large droplets cause spatter, but protection quality also deteriorates.   When the welding voltage is matched to the welding current, the arc burns steadily, emitting a faint humming sound; the tip of the welding gun experiences slight vibration, with a proper balance between hardness and softness. The voltage meter’s reading does not exceed 5V, and the ammeter’s reading does not exceed 30A. No vibration should be felt at the handle of the welding gun ； If the tip of the welding gun feels too soft with almost no vibration, and the gun can be moved freely, and when viewed through the mask it can be seen that the welding wire floats above the molten pool, forming a large molten ball at its end, with large droplets occasionally splashing off, this indicates that the voltage is too high ； If the tip of the welding gun feels hard, vibrates significantly, an audible cracking sound is heard, and there is resistance when moving the gun, and upon observation through the mask it can be seen that the welding wire enters the molten pool with plenty of spatter, this indicates that the voltage is too low ； To prevent lack of fusion, it is advantageous to keep the voltage appropriately high.    In gas metal arc welding, adjusting the welding current means regulating the wire feeding speed, while adjusting the welding voltage means regulating the melting speed of the wire. When the wire feeding speed is equal to the melting speed, the arc burns stably. Here is a set of formulas. For Japanese-style welding machines, the relationship between current and voltage is as follows: when the welding current is less than 200 A, the voltage equals 16 plus 0.04 times the current, with an increase of 1.5 V or a decrease of 1.5 V; when the current is greater than 200 A, the voltage equals 20 plus 0.04 times the current, with an increase of 2 V or a decrease of 2 V. For example, if the welding current is set at 150 A, then the welding voltage = 16 + 0.04 × 150 = 22 V. The maximum voltage is 22 + 1.5 = 23.5 V, while the minimum voltage is 22 – 1.5 = 20.5 V. When the current is less than 200A, the voltage = 14 + 0.05; it increases by 1.5 and decreases by 1.5 as the current rises. When the current is greater than 200A, the voltage = 18 + 0.05; it increases by 2 and decreases by 2 as the current rises. For example: with a current of 150A, the voltage is 14 + 0.05 × 150 = 21.5V; the maximum value is 21.5 + 1.5 = 23V, and the minimum value is 21.5 – 1.5 = 20V. When debugging, be sure to ensure the dry stretch length; this length is generally equal to (10~15) times the diameter of the welding wire.     The arc length in carbon dioxide arc welding is determined by the arc voltage; in other words, once you select the arc voltage, the arc length is also determined. It’s not like in shielded metal arc welding, where you can stretch or lower the arc as you wish. Whether you intentionally lengthen or shorten the arc, it is only a temporary effect; the arc’s self-regulation mechanism will immediately return to the arc length corresponding to the welding voltage you initially selected. It should be emphasized here that the welding voltage equals the arc voltage plus the voltage drop in the cable. Therefore, the welding voltage is slightly higher than the arc voltage; if the cable length is very short, the welding voltage is approximately equal to the arc voltage.