[Material Class] Have you mastered these basic welding knowledge?

【Summary Description】 1. What is welding? Answer: Two or more materials (the same or different), by heating or pressurizing or both, to achieve the combination between atoms and form a permanent connection process called welding. 2. What is arc? Answer: by the welding power supply, between the two poles to produce a strong and lasting gas discharge phenomenon called arc. (1) according to the type of current can be divided into: AC arc, DC arc and pulse arc. (2) According to the state of the arc, it can be divided into: free arc and compressed arc (such as plasma arc). (3) According to the electrode material can be divided into: melting pole arc and non-melting pole arc. 3. What is the base material? A: The metal being welded is called the base metal. 4. What is a droplet? Answer: The liquid metal drop that melts at the tip of the welding wire and transitions to the molten pool is called a molten drop. 5. What is a molten pool? Answer: The liquid metal part with a certain geometric shape formed on the weldment during welding is called the molten pool. 6. What is a weld? A: The joint part formed in the weldment after welding. 7. What is weld metal? A: The part of the metal formed by the solidification of the molten base metal and filler metal (welding wire, electrode, etc.). 8. What is the protective gas? Answer: The gas used to protect the metal droplets and the molten pool from the intrusion of harmful gases (hydrogen, oxygen and nitrogen) in welding-the protective gas. 9. What is welding technology? Answer: A variety of welding methods, Welding materials, welding technology and welding equipment and other basic theory of the general term-called welding technology. 10. What is the welding process and what is its content? Answer: A set of technological procedures and technical regulations in the welding process. The content includes: welding method, pre-welding preparation, assembly, Welding materials, welding equipment, welding sequence, welding operation, welding process parameters and post-welding treatment. 11. What is CO2 welding? Answer: Melt electrode gas shielded welding with CO2 purity> 99.98 is called CO2 welding. 12. What is MAG welding? Answer: mixed gas 75% ~ 95% Ar + 25% ~ 5% CO2 (standard ratio: 80% Ar + 20% CO2) is used for molten electrode gas shielded welding of shielding gas-called MAG welding. 13. What is MIG welding? Answer:(1) Non-ferrous metals such as aluminum and aluminum alloy, copper and copper alloy are welded under the protection of the melting electrode gas with high purity argon Ar≥ 99.99%; (2) The process of welding solid stainless steel welding wire with 98% Ar + 2% O2 or 95% Ar + 5% CO2 as shielding gas is called MIG welding. (3) with helium + argon inert gas mixture to do the protection of the MIG welding. 14. What is TIG (TIG) welding? Answer: Inert gas shielded arc welding with pure tungsten or activated tungsten (thorium tungsten, cerium tungsten, zirconium tungsten, lanthanum tungsten) as a non-melting electrode, referred to as TIG welding. 15. What is SMAW (electrode arc welding) welding? Answer: The arc welding method of welding with a manually operated electrode. 16. What is carbon arc gouging? Answer: It is a surface processing method that uses carbon rod as electrode to generate arc with workpiece and blows molten metal away with compressed air (pressure 0.5~0.7MPa). Commonly used for weld root cleaning, groove gouging, repair defects, etc. 17. Why is CO2 welding more efficient than electrode arc welding? Answer:(1)CO2 welding is 1 to 3 times higher than the melting speed and melting coefficient of electrode arc welding; (2) The groove section is reduced by 50% compared with the welding rod, and the amount of deposited metal is reduced by 1/2; (3) The auxiliary time is 50% of the electrode arc welding. Total of the three items: the efficiency of CO2 welding is increased by 2.02 to 3.88 times compared with that of electrode arc welding. 18. Why is the quality of CO2 welded joints better than that of electrode arc welding? Answer: The heat affected zone of CO2 weld is small and the welding deformation is small. The hydrogen content of CO2 weld is low (≤ 1.6mL/100g), and the tendency of pores and cracks is small. CO2 weld is well formed, with few surface and internal defects, and the qualified rate of flaw detection is higher than that of electrode arc welding. 19. Why is the comprehensive cost of CO2 welding lower than that of electrode arc welding? Answer:(1) The cross-sectional area of the groove is reduced by 36-54%, saving the amount of filler metal; (2) reduce power consumption by 65.4; (3) The cost of equipment shifts is 67-80% lower than that of electrode arc welding, and the cost is 20-40% lower; (4) Reduce labor costs, labor costs, reduce costs by 10-16%; (5) Save the auxiliary working hours, the consumption of auxiliary materials and the cost of correcting deformation; Combined with the five items, CO2 welding can reduce the total cost of welding by 39.6 to 78.7, with an average reduction of 59%. 20. What is a low frequency pulse and what welding is suitable? Answer: pulse frequency in 0.5~30Hz pulse arc 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 an intermediate frequency pulse and what welding is applicable? A: Pulse frequency in the 30-500Hz pulse arc called medium frequency pulse welding. Due to the arc compression effect, arc concentration and good stiffness, it is mainly used for TIG welding of thin stainless steel, steel and titanium and MIG welding of stainless steel and aluminum and aluminum alloy. 22. Why is there spatter in CO2 welding? Answer: The molten droplet at the end of the welding wire is in short-circuit contact with the molten pool (short-circuit transition). Due to strong overheating and magnetic contraction, the molten droplet bursts and splashes. The output reactor and waveform control of the CO2 welder can reduce spatter to a minimum. 23. Why can MIG/MAG high current welding realize jet transition without spatter? Answer: During MIG/MAG welding, all kinds of metals have a critical current value for short-circuit transition to jet transition (e.g. Φ 1.2 carbon steel and stainless steel welding wire, current I≥ 260 ~ 280A). At this time, the arc is in a jet transition state, realizing spatter-free welding. 24. Why does MIG/MAG small current welding use a pulsed power supply to achieve jet transition without spatter? Answer: For MIG/MAG welding, when the welding current is lower than the critical current value, a pulsed power supply is used, the pulse current is greater than the critical current value, and the arc can also be in a jet transition state to realize spatter-free welding (e.g. using Panasonic AG2/GE2 pulsed MIG/MAG welding machine, Φ 1.2 carbon steel, stainless steel, aluminum and aluminum alloy welding wires have realized pulse drop transition when the current I≥ 80A, its pulse current Ip≥ 350A). 2. Welding materials 1. What is Welding materials and what is included? Answer: Welding materials include welding rod, welding wire, flux, gas, electrode, gasket, etc. 2. What is the welding wire? Answer: When welding, it is used as filler metal and at the same time as conductive metal wire-called welding wire. There are two kinds of solid welding wire and flux cored wire. Commonly used solid welding wire model: ER50-6 (brand: H08Mn2SiA). 3. Why is the impact toughness of MAG welded joints higher than that of CO2 welded joints? Answer: When MAG welding, the active gas is only 20%, the alloy element transition coefficient in the welding wire is high, and the impact toughness of the weld is high. The CO2 welding active gas is 100%, the manganese and silicon alloy elements in the welding wire are deoxidized together, the alloy element transition coefficient is slightly lower, and the impact toughness of the weld is not as high as that of MAG welding. For example, Tangshan Shengang MG-51T welding wire (equivalent to ER50-6) has a normal temperature impact toughness value of MAG: 160J;CO2: 110J. 4. What is flux cored wire? Answer: A kind of welding wire made of thin steel strip rolled into a round steel pipe, filled with a certain composition of powder at the same time. 5. Why is flux-cored wire shielded with CO2 gas? Answer: There are two types of flux-cored wire according to the protection method: flux-cored gas shielded wire and flux-cored self-shielded wire. Flux-cored gas shielded welding wire is generally protected by CO2 gas, which belongs to the form of gas-slag joint protection, with good weld formation and high comprehensive mechanical properties. 6. Why is there indentation porosity on the weld surface of flux-cored wire? Answer: Because flux-cored welding wire is a tubular welding wire made of thin steel strips, it belongs to seamed welding wire. Moisture in the air will invade the flux core through the gap, and the welding flux will be wet (unable to dry), resulting in indentation pores in the weld. 7. Why is there a technical requirement for CO2 gas purity? A: Generally, CO2 gas is a by-product of chemical production with a purity of only about 99.6. It contains trace impurities and moisture, which will bring defects such as pores to welds. Important welding products must be selected CO2 purity ≥ 99.8% of the gas, weld porosity, low hydrogen content, good crack resistance. 8. Why are there higher technical requirements for argon purity? Answer: At present, there are three kinds of argon on the market: ordinary argon (purity of about 99.6), pure argon (purity of about 99.9) and high purity argon (purity of 99.99). The first two kinds can weld carbon steel and stainless steel. High purity argon must be used for welding non-ferrous metals such as aluminum and aluminum alloy, titanium and titanium alloy. Avoid oxidation of welds and heat affected zones and cannot be welded. 9. Why TIG welding nozzles have many sizes and specifications? Answer: There are 4-8# five specifications of the nozzle, welding carbon steel can choose 4-5# nozzle, welding stainless steel and aluminum and aluminum alloy should choose 6-7# large nozzle, in order to strengthen the weld and heat affected zone protection range. Welding titanium and titanium alloy and other non-ferrous metals should be selected 7-8# larger nozzle, in order to prevent the weld and heat affected zone is oxidized. 10. What is acid electrode? Answer: Welding rods containing a large amount of acidic oxides in the drug skin, such as AC/DC dual-purpose welding rods such as junction 422(E4303) and junction 502(E5003). 11. What is alkaline electrode? Answer: The drug skin contains a large amount of alkaline oxide and fluoride electrodes, such as 507(E5015), 506(E5016) and other electrodes. 12. What is cellulose type (special for vertical welding) electrode? Answer: The welding rod containing a large amount of organic matter in the coating is specially used for vertical welding of pipes and sheet structures. (1) For example, E6010 (equivalent to E4310 and J425G) is suitable for bottoming welding, hot welding and filling welding. (2)E8010 (equivalent to E5511, J555) is suitable for thermal welding, filling welding, cover welding layer. Generally with low hydrogen downward welding strip cover welding; E7048 (equivalent to J506X) weld appearance clean and beautiful. 13. Why should the welding rod be strictly dried before welding? Answer: The welding rod often deteriorates the process performance due to moisture absorption, resulting in unstable arc, increased spatter, and prone to defects such as pores and cracks. Therefore, the electrode must be strictly dried before use. Generally, the drying temperature of acid electrode is 150~200 ℃, and the drying time is 1 hour. The drying temperature of alkaline electrode is 350~400 ℃, and the drying time is 1~2 hours. After drying, it is placed in an incubator at 100~150 ℃, and it is taken as it is used.

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