08-26

CO2 gas shielded welding operation manual, classic in the classic!

2022-08-26

1. Arc. (1) Keep the length unchanged. (2) Reverse arc ignition method, 10-20mm at the front end of the weld. (3) The joint is worn thin to prevent the joint from melting and. 2. Arc shape. (1) Keep the length unchanged. (2) Arc at the edge of the molten pool. Arc starting and arc extinguishing technology, CO2 arc starting is simple, but if you want to achieve certain quality requirements, you must master the standard operating procedures. Arc process: Press the welding torch switch before the arc, while maintaining a certain distance between the end of the welding wire and the base metal. When arcing, keep the dry elongation stable. When the temperature of the workpiece is low, the arc cannot be preheated for a long time like manual welding, so the reverse arc ignition method should be adopted to make the weld fully. Arc process: when CO2 welding arc, the dry elongation should be kept unchanged, and the ignition point should be pulled to the edge of the molten pool to stop the arc, so that the welding machine can self-complete the arc process of burning back, ball and delay gas protection. 3. Method of operation. (1) Left welding method (right→left): small height, large width, small spatter, easy observation of the weld, stable welding process, good gas protection effect (non-ferrous metals must be welded on the left), but the solution depth is shallow. (2) Right welding method (from left to right): relatively high, small width, large spatter, easy to observe the molten pool, penetration. (3) Transport gun method: sawtooth swing grab. (4) fillet welding does not swing or swing slightly. (5) vertical angle upward welding, using triangular spray gun. (6) Welding torch transition: stay on both sides of the molten pool, and the transition point is located at 1/3 of the front of the molten pool. (7) Spray gun angle: perpendicular to the weld bead, at an angle of 80-90 ° along the direction of the spray gun. (8) Test plate: the gap is 2.0-2.5mm, and the arc point is slightly smaller than the arc. No blunt edge, 1 ° deformation resistance. 4. Welding parameters. (1) Current and voltage. U = 14 0.05I(U is the voltage I am current). The welding current should be selected correctly according to the thickness of the base metal, the type of joint and the diameter of the welding wire. During short-circuit transition, under the premise of ensuring welding penetration, try to choose a small current, because when the current is too large, it is easy to cause the pool to roll, not only the spatter is large, but also the formability is very poor. The welding voltage must be well matched to the current. Welding voltage is too high or too low will cause spatter, welding voltage should be increased with the increase of welding current, should be reduced with the decrease of welding current, the best welding voltage is generally between 1-2V, so. Welding voltage should be carefully adjusted. Excessive current: arc length, large splash, the feeling of top hand, the ratio is too high, and the two sides are not well integrated. High voltage: the arc is long, the spatter is a bit large, the current is unstable, how high is too small, every time the welding is too wide, the arc ignition is easy to burn the conductive nozzle. (2) dry elongation. The length of the wire out of the contact nozzle is the dry elongation, the general empirical formula is I =(10~20)d, try to keep it within the range of 10~20mm. When the norm is large, it is slightly larger. Standard hours, slightly smaller. Dry stretching is too long: When the length of the welding wire is too long, the greater the resistance of the welding wire, the faster the welding wire melting speed, which is easy to cause the welding wire to fuse, splash, large melting depth, and unstable arc combustion. At the same time, the gas protection effect is not good. Dry stretching too short: easy to burn the conductive nozzle. At the same time, the conductive nozzle is easy to clamp when heated. The spatter can easily clog the nozzle. Deep melt. (3) Gas flow. Filament welding is (5-15) L/min, thick wire welding L =(20-25)I/min Excessive: turbulence is generated, air intrusion is caused, and air holes are generated. Too small: gas protection is not good. Wind speed ≤ 2 m/s is not affected. Measures shall be taken when the wind speed is ≥ 2 m/s. Increase gas flow. Take wind measures. Note: When air leakage occurs, it will cause pores in the weld. The air leakage point must be treated and cannot be supplemented by increasing the flow rate. (4) Arc force. When different thickness, different position, different specifications, different welding wire, choose different arc force. Big: hard arc, big splash. Too small: soft arc, small splash. (5) The pressure. Over-tightening: the wire is deformed and the wire feeding is unstable. Too loose: the steel wire slips and the steel wire is delivered slowly. (6) Power supply polarity. DC reverse polarity: large penetration, small spatter, good arc stability of weld formation, low hydrogen content of weld. DC positive: under the same conditions, the welding wire melting speed. It is 1.6 times the opposite polarity, the melting depth is large, how high, and the splash is large. For surfacing, cast iron repair welding, high-speed welding. (7) welding speed. When the current and voltage are constant, the welding speed has an important influence on the internal and external quality of the weld. Too fast welding speed: penetration, width, residual height reduction, projection welding or humping bead, weld toe bite. When the welding speed is too fast, it will destroy the gas protection effect and easily produce pores. At the same time, the cooling rate will be accelerated, so the plasticity and toughness of the weld metal will be reduced. And it will make the middle of the welding encounter an edge, resulting in poor forming. The welding speed is too slow: the molten pool becomes larger, the weld seam becomes wider, and the weld toe is full. The welding speed is slow, and it is easy to discharge the gas in the molten pool. Overheating can cause the weld metal structure to be rough or burn through. The welding parameters shall be selected according to the following conditions: the weld is beautiful in appearance and free of defects such as burn through, undercut, pores and cracks. The penetration depth is controlled within an appropriate range. The welding process is stable and the spatter is small. The sound of sand when welding. At the same time, it should have the highest productivity.

08-25

External factors influencing the root crack of 6 series aluminum alloy fillet welding

2022-08-25

08-25

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

2022-08-25

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.

08-14

Unprecedented sharing of welding experience, you have certainly never seen such a complete one!

2022-08-14

In the welding process, there are many things that need to be paid attention to. Once neglected, it may make a big mistake. So for SQE, if you audit the welding process, you must pay attention to these points. If you deal with welding quality accidents, you should still pay attention to these problems! 1, welding construction does not pay attention to choose the best voltage [Phenomenon] During welding, the same arc voltage is selected regardless of the size of the groove, whether it is bottoming, filling or covering. In this way, the required penetration depth and width may not be reached, and defects such as undercut, pores and splash may occur. [Measures] Generally, the corresponding long arc or short arc should be selected for different situations to obtain better welding quality and work efficiency. For example, short arc operation should be adopted in order to obtain better penetration during bottoming welding, and arc voltage can be appropriately increased in order to obtain higher efficiency and melting width during filling welding or cover welding. 2. Welding does not control welding current [Phenomenon] During welding, in order to catch up with the progress, the butt weld of medium and heavy plate shall not be beveled. The strength index decreases, even fails to meet the standard requirements, and cracks appear during bending test, which will make the performance of weld joints can not be guaranteed and pose potential hazards to structural safety. [Measures] The welding shall be controlled according to the welding current in the process qualification, and 10 ~ 15% floating is allowed. The size of the blunt edge of the groove should not exceed 6mm. When butt joint, when the plate thickness exceeds 6mm, the groove shall be opened for welding. 3, do not pay attention to the welding speed and welding current, the diameter of the electrode is used in coordination [Phenomenon] When welding, do not pay attention to controlling the welding speed and welding current, and the diameter of the electrode and the welding position are used in coordination. For example, when backing welding the full penetration corner seam, due to the narrow root size, if the welding speed is too fast, the root gas and slag inclusion do not have enough time to discharge, which is easy to cause defects such as incomplete penetration, slag inclusion and porosity at the root. When welding the cover surface, if the welding speed is too fast, it is also easy to produce porosity. If the welding speed is too slow, the weld surplus height will be too high and the appearance is not neat; when welding thin plates or small welds with blunt edges, the welding speed is too slow and burn through is easy to occur. [Measures] Welding speed has a significant impact on welding quality and welding production efficiency. When selecting, appropriate welding speed is selected according to welding current, weld position (backing welding, filling welding, cover surface welding), weld thickness and groove size. On the premise of ensuring penetration, easy discharge of gas and welding slag, no burning through and good forming, larger welding speed is selected to improve productivity and efficiency. 4. Do not pay attention to control arc length during welding [Phenomenon] During welding, the arc length shall not be properly adjusted according to the groove form, welding layer number, welding form, electrode type, etc. Due to the improper use of welding arc length, it is difficult to obtain high-quality welds. [Measures] In order to ensure the weld quality, short arc operation is generally adopted during welding, but appropriate arc length can be selected according to different situations to obtain the optimal welding quality. For example, shorter arc should be used for the first layer of V-shaped groove butt joint and angle joint to ensure penetration and avoid undercut. The second layer can be slightly longer to fill the weld. Short arc should be used when the weld gap is small, and the arc can be slightly longer when the gap is large, and the welding speed is accelerated. The overhead welding arc should be the shortest to prevent the molten iron from flowing down; in order to control the temperature of the molten pool during vertical welding and horizontal welding, small current and short arc welding should also be used. In addition, no matter what welding is adopted, attention should be paid to keeping the arc length basically unchanged during the movement, so as to ensure that the melting width and penetration depth of the whole weld are consistent. 5, welding does not pay attention to control welding deformation [Phenomenon] During welding, no attention is paid to controlling deformation from the aspects of welding sequence, personnel arrangement, groove form, selection of welding specifications and operation methods, which leads to large deformation after welding, difficulty in correction and increased cost, especially for thick plates and large workpieces, which are difficult to correct and easy to cause cracks or laminar tearing with mechanical correction. The cost of flame correction is high and the operation is not good, which is easy to cause the workpiece to overheat. For workpieces with high precision requirements, if effective deformation control measures are not taken, the installation size of the workpiece will not meet the use requirements, and even cause rework or scrap. [Measures] Adopt reasonable welding sequence and select appropriate welding specifications and operation methods, and also adopt anti-deformation and rigid fixing measures. 6, multi-layer welding discontinuous welding, do not pay attention to control the inter-layer temperature. [Phenomenon] When welding thick plates in multiple layers, do not pay attention to the temperature control between layers. If the interval between layers is too long, cold cracks will easily occur between layers if welding is not preheated again. If the interval is too short and the interlayer temperature is too high (over 900 ℃), it will also affect the performance of the weld and heat affected zone, causing coarse grains, resulting in decreased toughness and plasticity, and leaving potential hidden dangers to the joint. [Measures] During multi-layer welding of thick plates, the control of interlayer temperature should be strengthened. In the continuous welding process, the temperature of the welded base metal should be checked so that the interlayer temperature can be consistent with the preheating temperature as much as possible, and the highest interlayer temperature should also be controlled. The welding time should not be too long. In case of welding interruption, appropriate post-heating and heat preservation measures should be taken. When welding again, the re-preheating temperature should be appropriately higher than the initial preheating temperature. 7, multi-layer weld without removing welding slag and weld surface defects for lower welding [Phenomenon] When thick plates are welded in multiple layers, the lower layer is directly welded without removing welding slag and defects after each layer is welded, which is easy to cause defects such as slag inclusion, pores and cracks in the weld, reduce the connection strength, and cause spatter during lower layer welding. [Measures] When thick plates are welded in multiple layers, each layer shall be welded continuously. After each layer of weld is welded, welding slag, weld surface defects and spatter shall be removed in time. If slag inclusion, pores, cracks and other defects affecting the welding quality are found, welding shall be carried out after thorough removal. 8. The joint butt or fillet butt combined weld required for penetration is not enough. [Phenomenon] For butt or fillet butt combined welds requiring penetration such as T-shaped joints, cross joints, fillet joints, etc., the size of the welding leg is not enough, or the size of the welding leg of the connection weld between the web plate of crane beam or similar components and the upper flange plate flange designed with fatigue checking requirements is not enough, which will make the welding strength and rigidity fail to meet the design requirements. [Measures] Butt combined welds requiring penetration such as T-shaped joints, cross joints and corner joints shall have sufficient weld leg requirements according to the design requirements. Generally, the size of weld leg shall not be less than 0.25t(t is the thinner plate thickness at the joint). The weld leg size of the connection weld between the crane beam or similar web and the upper flange designed with fatigue checking requirements is 0.5t and shall not be greater than 10mm. The allowable deviation of welding size is 0~4mm. 9, welding in the joint gap plug welding rod head or iron block [Phenomenon] As it is difficult to fuse the welding rod head or iron block with the welded part during welding, it will cause welding defects such as incomplete fusion and incomplete penetration, and reduce the connection strength. If it is filled with rusty electrode head and iron block, it is difficult to ensure the material consistency with the base metal. If it is filled with electrode head and iron block with oil stains and impurities, defects such as pores, slag inclusion and cracks will occur in the weld. These conditions will greatly reduce the weld quality of the joint and fail to meet the quality requirements of the design and specifications for the weld. [Measures] <1> When the assembly gap of the workpiece is large, but does not exceed the allowable range specified, and the assembly gap exceeds 2 times the thickness of the thin plate or is greater than 20mm, the surfacing method shall be used to fill the recessed part or reduce the assembly gap. It is forbidden to use the method of filling electrode head or iron block repair welding in the joint gap. <2> when processing and marking parts, attention should be paid to leaving enough cutting allowance and welding shrinkage allowance after cutting, controlling the size of parts, and not increasing the gap to ensure the external dimensions. 10. When using different thickness and width of the plate butt joint, not smooth transition [Phenomenon] When using plates with different thickness and width, do not pay attention to whether the thickness difference of the plates is within the allowable range of the standard. If it is not within the allowable range and is not treated with smooth transition, welding defects such as stress concentration and incomplete fusion are easily caused at the position where the weld is higher than the thickness of the sheet, which will affect the welding quality. [Measures] When the relevant regulations are exceeded, the weld seam shall be welded into a slope shape, and the maximum allowable slope value shall be 1:2.5; Or one or both sides of the thickness shall be processed into slopes before welding, and the maximum allowable slope value is 1:2.5. When the structural slope directly bears dynamic load and needs fatigue checking calculation, the slope shall not be greater than 1:4. When the plates of different widths are jointed, thermal cutting, mechanical processing or grinding with grinding wheel shall be adopted according to the conditions of the factory and the construction site to make the transition smoothly, and the maximum allowable slope value of the joint is 1:2.5. 11. Do not pay attention to the welding sequence for components with cross welds [Phenomenon] For components with cross welds, the welding sequence is not reasonably arranged by analyzing the release of welding stress and the influence of welding stress on the deformation of components. Instead, the vertical and horizontal welds are randomly welded. As a result, the vertical and horizontal welds will be constrained to each other, resulting in large temperature shrinkage stress, plate deformation, uneven plate surface and possible cracks in welds. [Measures] For components with cross welds, a reasonable welding sequence should be established. When several kinds of vertical and horizontal cross welds are welded, the transverse seam with large shrinkage deformation should be welded first, and the longitudinal weld should be welded later, so that the transverse weld will not be constrained by the longitudinal weld, so that the shrinkage stress of the transverse seam will be released without constraint, which can reduce the welding deformation and ensure the quality of the weld, or weld the butt weld first and then weld the fillet weld. 12. When lap joint of section steel bar adopts surrounding welding, continuous welding shall be applied at the corner. [Phenomenon] When surrounding welding is adopted for the lap joint between the section steel bar and the continuous plate, the weld on both sides of the bar shall be welded first, and the weld at the end shall be welded later, and discontinuous welding shall be carried out. Although this is beneficial to reduce welding deformation, it is easy to produce stress concentration and welding defects at the corner of the rod, which affects the quality of the welded joint. [Measures] When the lap joint of section steel bar is welded around, it should be welded continuously at the corner. Do not weld to the corner and run to the other side to weld. 13, require equal strong docking, crane beam wing plate and web plate at both ends without arc plate and lead plate [Phenomenon] When welding butt welds, full penetration fillet welds, and welds between crane beam flange plates and web plates, no arc plate and lead-out plate are added to the arc striking and lead-out. In this way, when welding the starting and ending ends, due to the unstable current and voltage and the unstable temperature of the starting and ending points, defects such as incomplete fusion, incomplete penetration, cracks, slag inclusion, pores, etc. are easy to occur, reduce the weld strength, can not meet the design requirements. [Measures] When welding butt welds, full penetration fillet welds and welds between crane beam wing plates and web plates, arc lead plates and lead-out plates shall be set at both ends of the welds. Its function is to lead the defective parts at both ends to the outside of the workpiece, and then cut off the defective parts to ensure the quality of the welds.

08-13

Welding knowledge sharing, control and prevention in welding process

2022-08-13

1. Welding arc length control and prevention During welding, the arc length shall not be properly adjusted according to the groove form, welding layer number, welding form, welding rod type, etc. Due to the improper use of welding arc length, it is difficult to obtain high-quality welds. prevention and control measures In order to ensure the quality of the weld, short arc operation is generally used during welding, but the appropriate arc length can be selected according to different conditions to obtain the best welding quality. For example, the first layer of V-shaped groove butt joint and angle joint should use shorter arc to ensure penetration and no undercut. The second layer can be slightly longer to fill the weld. When the weld gap is small, short arc should be used. When the gap is large, the arc can be slightly longer, and the welding speed is accelerated. The overhead welding arc should be the shortest to prevent the molten iron from flowing down; in order to control the temperature of the molten pool during vertical welding and horizontal welding, small current and short arc welding should also be used. In addition, no matter what welding is taken during the movement, attention should be paid to keeping the arc length basically unchanged, so as to ensure that the melting width and penetration depth of the whole weld are consistent. 2. Weld leg size control and prevention For butt or fillet combined welds requiring penetration, such as T-joints, cross joints, fillet joints, etc., the size of the weld leg is not enough, or the size of the weld leg for the connection between the web plate and the upper wing plate edge of the crane beam or similar components designed with fatigue checking requirements is not enough, which will make the welding strength and rigidity fail to meet the design requirements. prevention and control measures Butt combined welds requiring penetration, such as T-joint, cross joint and fillet joint, shall be in accordance with the design requirements, and must have sufficient weld leg requirements. Generally, the size of weld leg shall not be less than 0.25t(t is the thinner plate thickness at the connection). The weld leg size of the connection weld between the crane beam or similar web and the upper flange designed with fatigue checking requirements is 0.5t and shall not be greater than 10mm. The allowable deviation of welding size is 0~4mm. 3. Common defects and prevention in multilayer welding When thick plates are welded in multiple layers, the lower layer is directly welded without removing welding slag and defects after each layer is welded, which is easy to cause defects such as slag inclusion, pores and cracks in the weld, reduce the connection strength, and cause spatter during lower layer welding. prevention and control measures When thick plates are welded in multiple layers, each layer shall be welded continuously. After each layer of weld is welded, welding slag, weld surface defects and spatter shall be removed in time. If slag inclusion, pores, cracks and other defects affecting the welding quality are found, welding shall be carried out after thorough removal. 4. Welding voltage and its selection basis During welding, the same arc voltage is selected regardless of the size of the groove, whether it is bottoming, filling or covering. In this way, the required penetration depth and width may not be reached, resulting in defects such as undercut, pores and splash. Selection basis Generally, according to different situations, the corresponding long arc or short arc should be selected respectively to obtain better welding quality and working efficiency. For example, short arc operation should be adopted in order to obtain better penetration during backing welding. The arc voltage can be appropriately increased in order to obtain higher efficiency and melting width during filling welding or cover welding. 5. Optimal welding current and its selection basis During welding, in order to catch up with the progress, the butt weld of medium and heavy plate shall not be beveled. The strength index decreases, even fails to meet the standard requirements, and cracks appear during bending test, which will make the performance of weld joints can not be guaranteed and pose potential hazards to structural safety. Selection basis The welding shall be controlled according to the welding current in the process qualification, and 10 ~ 15% floating is allowed. The size of the blunt edge of the groove should not exceed 6mm. When butt joint, when the plate thickness exceeds 6mm, the groove shall be opened for welding. 6. Welding speed, welding current and electrode diameter and selection basis Do not pay attention to control the welding speed and welding current during welding; the diameter of the electrode and the welding position are coordinated. For example, when backing welding the full penetration corner seam, due to the narrow root size, such as too fast welding speed, the root gas and slag inclusion do not have enough time to discharge, which is easy to cause defects such as incomplete penetration, slag inclusion and porosity at the root; when welding the cover surface, if the welding speed is too fast, it is also easy to produce porosity; if the welding speed is too slow, the weld excess height will be too high and the appearance is not neat; when welding thin plates or small welds with blunt edges, the welding speed is too slow and burn through is easy to occur. Selection basis The welding speed has a great influence on the welding quality and welding productivity. When selecting, the welding current, the welding seam position (backing welding, filling welding, cover surface welding), the thickness of the welding seam and the groove size shall be selected with appropriate welding speed. On the premise of ensuring penetration, easy discharge of gas and welding slag, no burning through and good forming, the larger welding speed shall be selected to improve the productivity. 7. Control interlayer temperature and prevention measures When welding thick plates in multiple layers, do not pay attention to the temperature control between layers. If the interval between layers is too long, cold cracks will easily occur between layers without preheating again. If the interval is too short and the interlayer temperature is too high (over 900 degrees Celsius), the performance of the weld and heat affected zone will also be affected, resulting in coarse grains, resulting in decreased toughness and plasticity, and potential hidden dangers to the joint. prevention and control measures During multi-layer welding of thick plates, the control of interlayer temperature should be strengthened. In the continuous welding process, the temperature of the welded base metal should be checked to make the interlayer temperature as consistent as possible with the preheating temperature, and the maximum temperature between the layers should also be controlled. The welding time should not be too long. In case of welding interruption, appropriate post-heating and heat preservation measures should be taken. When welding again, the re-preheating temperature should be appropriately higher than the initial preheating temperature. 8. Influence and prevention of welding deformation During welding, the deformation is not controlled from the aspects of welding sequence, personnel arrangement, groove form, welding specification selection and operation method, etc., which leads to large deformation after welding, difficulty in correction and increased cost, especially for thick plates and large workpieces, which are difficult to correct and easy to cause cracks or lamellar tearing by mechanical correction. The cost of flame correction is high and the operation is not good, which is easy to cause the workpiece to overheat. For workpieces with high precision requirements, effective deformation control measures are not taken, and the installation dimensions cannot meet the use requirements, and even cause rework or scrap. prevention and control measures Adopt a reasonable welding sequence and select the appropriate welding specifications and operating methods, but also the use of anti-deformation and rigid fixation measures. 9. Influence and prevention of plug electrode head or iron block in joint clearance Since it is difficult to fuse the electrode head or iron block with the welded part during welding, it will cause welding defects such as incomplete fusion and incomplete penetration, and reduce the connection strength. If it is filled with rusty electrode head or iron block, it is difficult to ensure the material consistency with the base metal. If there are oil stains and impurities on the electrode head and iron block, the weld will have defects such as pores, slag inclusion and cracks. These conditions will greatly reduce the weld quality of the joint and fail to meet the quality requirements of the design and specifications for the weld. prevention and control measures 1) When the workpiece assembly gap is large, but does not exceed the allowable range specified, and the assembly gap exceeds 2 times the thickness of the thin plate or is greater than 20mm, the welding method shall be used to fill the recessed part or reduce the assembly gap. It is forbidden to use the method of filling electrode head or iron block repair welding in the joint gap. 2) When processing and marking parts, attention should be paid to leaving enough cutting allowance and welding shrinkage allowance after cutting, controlling the size of parts, and not increasing the gap to ensure the external dimensions. 10. The influence and prevention of different thickness and width plate butt joint When butt joint of plates with different thickness and width is adopted, it is not necessary to pay attention to whether the thickness difference of the plates is within the allowable range of the standard. If it is not within the allowable range and no smooth transition treatment is done, such welding seam is easy to cause stress concentration and incomplete fusion and other welding defects when it is higher than the thickness of the plates, thus affecting the welding quality. prevention and control measures When exceeding the relevant regulations, the weld shall be welded into a slope shape, and the maximum allowable slope value shall be 1:2.5; Or one or both sides of the thickness shall be processed into a slope before welding, and the maximum allowable slope value is 1:2.5. When the structural slope directly bears dynamic load and needs fatigue checking calculation, the slope shall not be greater than 1:4. When the plates of different widths are jointed, thermal cutting, mechanical processing or grinding with grinding wheel shall be adopted according to the conditions of the factory and the construction site to make the transition smoothly, and the maximum allowable slope value of the joint is 1:2.5.

08-12

Nickel alloy welding, what are the matters needing attention!

2022-08-12

08-11

Two kinds of small skills of welding pipe, and three kinds of welding posture to explain.

2022-08-11

Two Tips for Welding Pipes Spot welding: small pipes are usually welded from small to upward, pressing a little bit, and pressing the molten pool tightly. Otherwise, there will be trachoma, the welding hand should be stable, the welding bead should be clearly seen, and every point should be kept at the same speed and consistent, (you can't eat a fat man in one bite!!). Arc welding: This method is usually used for large pipes, because spot welding of large pipes is very time-consuming, and the welding process is also welding from bottom to top. First of all, spot welding should be done to the bottom. Remember that the bottom must not be too thick, so as to facilitate the cover. The current of continuous arc welding should be adjusted to about 40 to 50 less than that of spot welding. Tips for three welding postures: flat, upright and upright Flat: When welding, place the welding rod on the mouth in the middle of the welding handle and walk evenly at 90 degrees, so that the flat seam welded is 100% beautiful. Lean: Spot weld a little, press a little, walk slowly. Pay attention to the molten pool, don't be afraid of hot, hot to will not be avoided. (Pay attention to your feet when welding. Welding slag may burn your shoes or burn your clothes. Safety comes first!) Li: Personally, I think vertical welding is the most difficult, because it can connect arc and spot welding just like welded pipe. If you are a novice, it is recommended to use spot welding, a little pressure, don't hurry to slow down. When one welding rod is finished and the next one is connected, the medicine skin can only be knocked on the joint part.

08-10

Do you understand the relevant knowledge of flux-cored arc welding?

2022-08-10

Flux-cored wire first appeared in the United States and Germany in the 1920 s, but it was actually widely used in industrial production in the 1950 s. Especially after the 1960 s and 1970 s, with the emergence of all-position flux-cored wire with a fine diameter below Φ2.0, the flux-cored wire has entered a stage of rapid development, followed by the development of metal powder-cored wire and seamless flux-cored wire. Flux-cored wire can be divided into seamed and seamless flux-cored wire according to the manufacturing process and cross-section type. Seamless flux-cored wire has good anti-moisture absorption ability and can be convenient for long-term storage, but due to its complex manufacturing process, the general price is higher. core in the role of welding: 1. Deoxidation to prevent weld metal oxidation; 2. Provide alloying elements to ensure weld performance; 3. Stabilize the arc and ensure good operability; 4. Protect the molten pool and facilitate weld formation. the working principle of FCAW-G: The basic working principle of the FCAW-G is the same as that of the ordinary gas shielded arc welding. It uses the meltable flux-cored wire as the positive electrode and the base material as the negative electrode. Pure CO2 or CO2 + Ar mixture is usually used as the protective gas. The main difference with ordinary MIG welding is that the welding wire is filled with flux mixture. During welding, the flux material, welding wire metal, base metal metal and shielding gas in the molten state under the action of arc heat have metallurgical interaction with each other, and at the same time, a thin layer of liquid slag is formed to cover the molten droplets and cover the molten pool, forming protection for the molten metal, which is essentially a welding method of gas-slag joint protection. Advantages and disadvantages of FCAW-G in welding production: Advantages: 1. High deposition rate and production efficiency; 2. Suitable for all position and outdoor welding; 3. Good manufacturability, beautiful welding forming; 4. Suitable for semi-automatic and mechanical welding. Disadvantages: 1. The welding wire manufacturing process is complicated; 2. Seamed flux-cored wire is easy to absorb moisture; 3. Welding fume is large. In view of the above characteristics, FCAW-G has been widely used in structural welding in the marine industry, accounting for about 70%. For process pipeline and pressure vessel welding, due to the high quality requirements of welding materials, some projects have the requirement of prohibiting the use of flux-cored wire, but with the continuous improvement of the quality of flux-cored wire, the FCAW-G is gradually being accepted, its application scope is wider and wider, and the degree of welding automation is also gradually improving.

08-09

Reveal the importance of positioning welding, what are the positioning and role?

2022-08-09

During the welding process, it is very important to ensure that the position of the weldment is fixed and to avoid misalignment or movement by tack welding. However, because it is usually not used as a formal weld, the subsequent removal or melting into the formal weld, welding quality is often not taken seriously. We will take you to understand the relevant knowledge of positioning welding and reveal the importance of positioning welding. Q1 What is tack welding? Tack welding refers to welding for assembling and fixing the position of weldment joints. The English name is Tack Weld. The definition of tack welding in AWS A3.0 is as follows: "A weld made to hold the parts of a weldment in proper alignment until the final welds are made." Q2 Tack welding function · Fixed weldment position, control welding deformation; · Keep the root clearance of weldment; · Replace the fixture, convenient welding; Easy to remove, easy to group again. Q3 Tack welding requirements In the offshore industry, different project requirements will be slightly different, the general requirements are as follows: · Qualified WPS, qualified welder; · Preheat in accordance with the applicable WPS; The weld length is 100mm or 4 times the plate thickness; · Sufficient thickness to avoid cracking. Q4 Common Tack Welding Problems If there are defects in the welding quality of tack welding, it will often have a serious impact on the subsequent formal welds, so the welding quality of tack welding also needs everyone's attention. According to current project statistics, common tack welding problems are as follows: · Groove cleaning, preheating and welding are not performed according to WPS; Insufficient tack length or thickness; There are defects such as slag inclusion, undercut and cracks.

08-08

The size of a subway car asks how the experimental cabin was built?

2022-08-08

The subway car is so big, the question is how the laboratory was built. The test chamber integrates the functions of platform and test load. The total length of the engine room is 17.9 meters and the diameter is 4.2 meters. The launch weighed 23 tons, and the relevant indicators were higher than those of the Tianhe core cabin, and the size and weight of the carriage were equivalent to those of a carriage on Beijing Metro Line 13. How was the world's heaviest single-cabin active-duty on-orbit aircraft built? China Aerospace Science and Technology Corporation No. 529 plant is an important satellite and spacecraft research base in China. It is also the main research unit of the space station module structure. The mission of the Tianhe Core Module is completed here. The construction of the Wentian experimental module is more challenging and more difficult. The process technicians broke through the process bottleneck and developed a series of key technologies to ensure the high-quality delivery of capsules. From single to double, the difficulty more than doubles. The experimental cabin consists of a working cabin, an airlock cabin and a resource cabin. Among them, the airlock bears the mission of long life and installing a variety of equipment, and the requirements for important load-bearing structural parts are very high. After the demonstration, the researchers decided to use the internal and external double-rib plate structure with higher carrying capacity. Different from the conventional outer rib wall plate, the inner and outer rib walls need to add inner ribs on the inner cylindrical surface. The forming operation is very difficult to implement, and the forming defects and forming accuracy are also difficult to control, and mistakes will be made if you are not careful. From single to double, the difficulty is more than doubled. The outer ribs are visible and easy to operate. The inner rib is in the cylindrical surface, which is not only difficult to operate, but also requires seamless and high requirements. The design of the mold is very important: what kind of mold can effectively avoid the internal ribs. How to ensure the forming accuracy of the inner and outer sides of the double-rib plate? In addition, what is the bending forming trajectory of the inner ribs. How to set process parameters. These problems have never been encountered before. After repeated analysis and testing, the craftsmen put forward such a mold design scheme: first spell, then assemble, avoid the position of the internal ribs, and then bend the product. Finally, the optimized bending forming path is obtained, and the reasonable forming path and bending process parameters are set. The precision forming of inner and outer double-ribbed panels was successfully realized, which met the design requirements. The welding difficulty increases exponentially with the interval curve. The door frame of the door is connected by welding process, which is a typical space curve weld. The welding deformation is small and the quality is high. From plane to space, from straight line to curve, the difficulty of welding also increases exponentially. The welding of this spatial curve was done manually in the past, and the welding thickness was increased to 5mm. When welding by hand, researchers need to weld layer by layer. The heat input is large, the product size is not easy to grasp, and the structural stress after welding is large, which cannot meet the reliability requirements of the long-term operation of the space station in orbit. The only way out is to overcome the inter-curve automatic welding technology. After research and testing, the researchers designed a flexible welding device. The welding of the sealed compartment door frame has been successfully completed, and all indexes meet the design requirements. Reliable curve connection between sealed compartments. The bulkhead heating tube of the experimental cabin can be said to be a kind of space protective clothing. The increase of the experimental module structure means that the number of heating tubes will increase. And the overall direction of the pipeline layout is a three-dimensional space structure, so the heating pipe section design is "Ω-shaped", similar to a circle plus a plane, highly attached to the interior of the cabin, convenient for temperature sensitive control. To this end, the researchers innovatively put forward the "flexible partition, integral forming" technology, that is, the pipeline is made of high-precision three-dimensional curved surface and attached to the inner surface of the cabin.