Views: 11 Author: DURMAPRESS Publish Time: 2020-12-30 Origin: DURMAPRESS
Important structures such as boilers and pressure vessels require safe penetration of joints. However, due to restrictions on the size and shape of the structure, double-sided welding is sometimes impossible. The special operation method that can only open single-sided grooves, single-sided welding and double-sided forming technology, is a difficult operation skill in manual arc welding. When DPW-1000W Fiber Laser Welding Machine vertical welding, due to the high temperature of the molten pool, under the action of gravity, the droplets formed by the melting of the electrode and the molten iron in the molten pool are easy to drip down to form weld bead and undercut on both sides of the weld. When the temperature is too low, slag inclusion is easy to occur, and defects such as incomplete penetration and weld bead are formed on the reverse side, which makes the formation of the weld difficult. The temperature of the molten pool is not easy to determine directly, but it is related to the shape and size of the molten pool. Therefore, as long as you carefully observe and control the shape and size of the molten pool during welding, you can achieve the purpose of controlling the temperature of the molten pool and ensuring the welding quality. Mastering the following points can improve the level of welding operation technology.
1. The angle of the welding rod is very important, and the welding specification is indispensable
During vertical welding, the droplets formed by the melting of the welding rod and the molten iron in the molten pool are easy to drip down to form a weld bead, and undercuts are formed on both sides of the weld, which deteriorates the formation of the weld. Master the correct DPW-1500W Fiber Laser Welding Machine specifications and adjust the electrode angle and the speed of the welding rod according to the changes in welding conditions. The angle between the electrode and the surface of the weldment is 90° in the left-to-right direction, and the angle to the weld is 70°-80° at the start of welding, 45°-60° in the middle, and 20°-30° at the end. The assembly gap is 3～4mm, the smaller electrode diameter Φ3.2mm and smaller welding current should be selected, 110～115A for bottom welding, 115～120A for middle transition layer, 105～110A for cover layer . The current is generally 12% to 15% smaller than that of flat welding to reduce the volume of the molten pool and reduce the influence of gravity, which is conducive to excessive droplets. Short arc welding is used to shorten the distance of the droplet to the molten pool, resulting in excessive short circuit.
2. Watch the molten pool, listen to the arc sound, keep the shape of the molten hole in mind
The bottom welding at the root of the weld is a key to ensuring welding quality. The arc extinguishing method is adopted for Fiber Laser Welding Machine. The arc extinguishing rhythm of vertical welding is slightly slower than that of flat welding, 30-40 times per minute, and the arc burns slightly longer during each point welding, so the welding meat of vertical welding is thicker than that of flat welding. When welding, start welding from the lower end. The angle of the bottom electrode is about 70°～80°. Two-click penetration welding is used. The arc is ignited on the side of the groove and the spot welding point is preheated and melted to the root, and the arc penetration is heard. With the "fluttering" sound from the groove, the molten hole is seen and the molten pool seat is formed, and the welding rod is immediately lifted to extinguish the arc. Then re-ignite the other side of the groove, and the second molten pool should press 1/2 to 2/3 of the first molten pool that begins to solidify, so that the entire weld can be obtained with left and right arc extinguishing breakdown. The arc extinguishing requires the flexibility of the wrist, and the arc is extinguished cleanly every time, so that the molten pool has an instantaneous solidification opportunity.
When the arc is extinguished, the molten hole formed by the pierced blunt edge is clearly seen. The molten hole of vertical welding is about 0.8mm. The size of the molten hole is closely related to the back forming. If the molten hole is too large, it is easy to form a weld on the back. The back of the weld hole is often incomplete, and it is required to keep the size of the weld hole uniform during operation, so as to ensure uniform penetration at the root of the groove, full weld bead on the back, uniform width and height. When changing the welding rod joint, clean up the coating of the joint part every time, re-ignite the arc in the groove, and change the angle of the welding rod continuously at about 10mm along the formed weld, and extend into the weld at 90° The center swings slightly from side to side and presses down the arc at the same time. When the arc sound is heard, a molten hole is formed, and the arc is immediately extinguished, so that the electrode arc extends into the root of the weld to form a molten hole and immediately extinguish the arc. Then it is the same as the first welding rod bottom welding method. The left and right alternately circulate arc extinguishing and breakdown. Every action must be concentrated. Pay attention to the contour of the molten hole and the notch that is melted on both sides, and the notch that is melted at the root of the groove. When the arc is moved to the other side, it can be seen. It is found that the blunt edge is not fused well and the arc is slightly lowered to achieve good fusion. Each time the arc extinguishing time is controlled so that one third of the molten pool is not solidified. Start the arc again.
When closing the arc, it should be noted that when each electrode is only 80-100mm long, the electrode will melt faster due to overheating. At this time, the arc extinguishing time should be increased to make the molten pool instantaneously solidify to prevent the high temperature molten pool from falling down and forming a weld . When the welding rod is only 30-40mm left, prepare to do the arc extinguishing action, drop one side of the molten pool two or three times continuously, so that the molten pool can slowly cool down, which can prevent shrinkage holes and crater cracks on the front and back of the weld bead defect.
3. The temperature of the molten pool is well controlled and the weld quality can be improved
The middle layer welding wave is required to be flat. The middle two layers are according to the electrode diameter φ3.2mm, the welding current is 115～120A, the electrode angle is about 70°～80°, the zigzag method is adopted, the electrode angle, the length of the arc, the welding speed and both sides of the groove stay Time to control the temperature of the molten pool. Make both sides fuse well, and ensure the shape of oblate molten pool.
When welding the third layer, do not damage the edge of the groove, and leave a depth of about 1mm to make the entire filler bead smooth. The edge of the groove above the depth is used as the reference line to lay the foundation for the cover surface. In general, use left and right swings to stop a little more on both sides of the groove to melt the edge of the groove by 1～2mm, and ensure the temperature of the molten pool and both sides of the groove. Balance, mainly observe the shape of the molten pool, control the molten pool to a crescent shape, stay less on the side with more molten pool, stay more on the side with less, and calculate the height and width of the weld while welding. Because the weld meat of vertical welding is thicker than that of flat welding, pay attention to the shape of the weld pool and the thickness of the weld. Extinguishing time to reduce the temperature of the molten pool. The crater must be filled before replacing the electrode to prevent crater cracks.
4.the method of transporting the strips is correct, and the weld can be formed
When welding the cover surface, the zigzag or crescent strip method can be used when welding, the strip should be stable, the speed should be slightly faster in the middle of the welding bead, and the edges on both sides of the groove should be stopped slightly. The process specification is that the electrode diameter is φ3.2mm, the welding current is 105～110A, and the electrode angle should be kept at about 80°. The electrode swings from side to side to melt the edge of the groove by 1～2mm. When both sides stop, they will vibrate slightly. But when the electrode moves from side to side, the arc in the middle is slightly lifted to observe the shape of the entire molten pool. If the molten pool is in a flat oval shape, it indicates that the temperature of the molten pool is appropriate, normal welding is performed, and the weld surface is well formed. If you find that the bottom of the molten pool is rounded, it means that the temperature of the molten pool is slightly higher. The method of transporting the rod should be adjusted immediately, that is, the electrode staying time on both sides of the groove is increased, the intermediate transition speed is increased, and the arc length is shortened as much as possible. If the molten pool cannot be restored to a flat elliptical state and the bulge increases, it means that the temperature of the molten pool has been too high, and the arc should be extinguished immediately, and the molten pool should be cooled down for some time. Continue welding after the temperature of the molten pool drops.
When covering the surface, make sure that the edge of the weld is good. It is found that the undercut electrode moves slightly, or stays longer to compensate for the defects, and the surface is excessively smooth. When the cover joint is welded, the temperature of the weldment is relatively low, which is easy to produce defects such as poor fusion, slag inclusion, joint disjoint, and excessive height. Therefore, the quality of the cover directly affects the surface forming of the weld. Therefore, the preheating method is used to weld the joints. The arc is ignited from top to bottom by the scratching method about 15 mm above the welding end, and the arc is extended by 3 to 6 mm. heat. Then lower the arc, swing 2 to 3 times at 2/3 of the original arc pit to achieve a good fusion and then switch to normal welding.
Although the positions of the welds are different, they also have common rules. Practice has proved that selecting the appropriate welding process parameters, maintaining the correct welding rod angle and mastering the three actions of the good luck rod, strictly controlling the temperature of the molten pool, welding In vertical welding, excellent weld quality and beautiful weld formation can be obtained.
The heat treatment in the welding process mainly includes three aspects: preheating before welding and slow cooling after welding; controlling the interlayer temperature and post-heating temperature; and post-welding heat treatment.
1. Preheat before welding and slow cooling after welding
The role of preheating is: preheating can reduce the cooling rate after welding, and for a given composition of steel, the structure and performance of the weld and heat-affected zone depend on the cooling rate. For steels with high hardening tendency, the degree of hardening can be reduced by preheating to prevent welding cracks. In addition, preheating can reduce the temperature difference in the heat-affected zone, obtain a relatively uniform temperature distribution in a wider range, and help reduce the welding stress caused by the temperature difference. Therefore, preheating measures are often used for steels that tend to be hard. For chromium-nickel austenitic steel, preheating increases the residence time of the heat-affected zone in the dangerous temperature zone, thereby increasing the corrosion tendency. Therefore, when welding chromium-nickel austenitic stainless steel, preheating is not allowed.
The selection of preheating temperature should be comprehensively considered according to the composition of the weldment, structural rigidity, welding method and other factors, and determined by weldability test. Preheating is generally uniform heating within a range of about 80mm on both sides of the groove, and the heating width should be greater than 5 times the plate thickness. Flame heating, power frequency induction heating and infrared heating are often used. After welding, heat preservation and slow cooling of the weldment can slow down the cooling rate of the weld and heat-affected zone, and play a similar role to preheating.
2. Control the interlayer temperature and post-heating temperature
Interlayer temperature refers to the lowest temperature at which the weld of the next layer (pass) joins the weld of the previous layer (pass) during multi-layer and multi-pass welding. However, the general interlayer temperature that requires preheat welding should be equal to or slightly higher than pre-heat temperature. Controlling the interlayer temperature is also to reduce the cooling rate and promote the escape of diffused hydrogen, which is beneficial to prevent cracks. However, for some steels, such as austenitic steel, in order to prevent intergranular corrosion, the interlayer temperature should not exceed 60. .
The role of post-heating: After welding, the heat preservation and slow cooling of the weldment can slow down the cooling rate of the weld and the heat-affected zone, and play a similar role to preheating. For materials such as low-alloy high-strength steel with large cold crack tropism, there is also a special post heat treatment, also called hydrogen treatment, that is, the weldment is heated to the temperature range of 250-350 immediately after welding, and after holding for 2-6 hours Air cooling. The purpose of the elimination treatment is to accelerate the escape of the diffused hydrogen in the weld metal, reduce the hydrogen content in the weld and the heat-affected zone, and prevent cold cracks. For weldments that require heat treatment after welding, because the purpose of hydrogen removal can be achieved during the heat treatment process, there is no need for additional hydrogen elimination treatment. However, if the weldment cannot be heat treated immediately after welding and the weldment must be removed in time, it needs to be timely Perform hydrogen elimination treatment, otherwise the weldment may crack during the placement period before heat treatment.
The post-heating method, except that the heating temperature is different from the temperature selected for pre-heating, the post-heating heating method, heating zone width, heating area, etc. are the same as pre-heating.
3. Post-weld heat treatment
Post-weld heat treatment is a treatment method that heats the weldment as a whole or partly, and then performs furnace cooling or air cooling. Post heat treatment can reduce the welding residual stress, soften the hardened parts, improve the structure and performance of the weld and heat-affected zone, improve the plasticity and toughness of the welded joint, and stabilize the size of the structure. The most commonly used post-weld heat treatment is stress relief annealing in the range of 600-650, and high temperature tempering below Ac1 point temperature. In addition, there is stabilization treatment to improve the corrosion resistance of chromium-nickel austenitic stainless steel.
Technical Parameters And Specification:
|Working mode||Continuous/ Pulse|
|Adviced welding thickness||SS/CS: 0.5-2mm|
|Aiming and positioning||Red light positioning|