12-04

Effect of welding structure on weldability of weld metal

2022-12-04

Structural factors. Structural factors include the form, stiffness, and stress state of welded structures and welded joints,. These will affect the mechanical properties of the joint, resulting in welding defects. For the size and weight of the required welding structure, the design should choose higher than the strength of the material (such as light alloy material), in order to achieve the purpose of reducing the volume and weight. For welded structures with no special requirements for volume and weight, the selection of materials with higher strength level also has technical and economic significance, which can reduce the weight of the structure, save the base material and Welding materials, avoid the difficulty of hoisting and transportation of large structures, and improve the bearing capacity. The structural design of the welded joint affects the stress state and thus the weldability. In the design, the stress at the joint should be kept in a small state and can shrink freely, which is conducive to reducing stress concentration and preventing welding cracks. Try to avoid gaps at the joint, sudden changes in cross-section, excessive height, cross-welds, etc. This easily causes stress concentration. It is also necessary to avoid unnecessarily increasing the thickness of the base metal or the volume of the weld to produce multidirectional stresses. Welding heat source characteristics, power density, line energy and other process parameters will directly determine the temperature field and thermal cycle of the joint, which will have a significant impact on the size of the weld and heat affected zone, tissue changes, defect sensitivity and so on. For example, preheating before welding and slow cooling after welding can reduce the cooling rate of the joint, which can reduce the hardening tendency and cold crack sensitivity of the joint. Choosing a reasonable welding sequence can improve the constraint degree and profitability of the structure. Using argon arc welding and other welding methods, the welding area can be closely protected, reduce the burning loss of alloy elements, and obtain satisfactory joint performance.

12-03

Discussion on the Influence of Material Factors on the Weldability of Metal Materials

2022-12-03

What are the factors that affect the weldability of metal materials? There are many factors that affect the weldability of metal materials, including four aspects: metal materials, structural design, process measures and the use of the environment. The weldability depends on the chemical composition of the base metal and the weld metal, the design of the welded structure and the welded joint, the welding method, and the comprehensive performance of the welding process. Material factors. Material factors refer to the wood itself and Welding materials. including the chemical composition of the material, smelting and rolling state, heat treatment, microstructure and mechanical properties. Welding rods for arc welding, welding wires and fluxes for submerged arc welding, welding rods and shielding gases for ladle arc welding, and other Welding materials. During the welding process, wood and Welding materials directly participate in the metallurgical reaction of the molten pool or fusion zone, which has an important influence on weldability and welding quality. When the base metal or Welding materials is not selected, the composition of the weld will be unqualified, the mechanical properties and other properties will be reduced, and even cracks, pores, slag and other welding defects will appear, which will worsen the welding process, so it must be selected correctly. On the substrate side, the chemical composition has the greatest impact. If the steel only relies on alloying elements to achieve solid solution strengthening, it is generally easier to make the weld metal, heat affected zone, and base metal have good matching performance during the welding process. If the steel is a relatively complex alloy system and is strengthened by heat treatment, deformation processing, etc., it is not easy to obtain a weld metal that completely matches the base metal, or even the entire welded joint. For steel, the elements that affect the weldability are C, P, H, S, O, N, etc. Among the alloying elements, Mn, Si, Cr, Ni, Mo, Ti, V, Nb, Cu, B and other elements will increase the hardening tendency and crack sensitivity of welded joints to varying degrees. In general, the weldability of steel deteriorates with increasing carbon content and alloying element content. Smelting method, rolling process and heat treatment state also affect weldability to varying degrees. At present, CF steel (crack-resistant steel), Z-direction steel, TMCP steel (controlled rolling steel), etc., all improve the weldability of materials by means of refining and purification, controlled rolling process, etc.

12-02

Knowledge of welding of metal materials

2022-12-02

Definition: Welding is through heating, pressure, or both, with or without welding materials, so that the two workpieces produce interatomic diffusion, the formation of metallurgical bonding processing technology and connection. Features: Save metal material, light weight structure. To make heavy and complex machine parts, simplify casting, forging and cutting processes, and obtain the best technical and economic results. The welded joints have good mechanical properties and sealing properties. Able to manufacture bimetallic structures so that the properties of the material are fully utilized 2. Classification of welding methods According to the characteristics of the welding process and the state of the wood metal, the welding method can be divided into three categories: welding, pressure welding and brazing.

12-01

Laser technology for copper welding with flexibility and automation

2022-12-01

Manufacturers are looking for efficient, feasible and easily automated solutions to fully meet the increasingly stringent requirements in terms of quality and quantity of power electronic components for electric mobility. In addition, construction and connection techniques are included. The commonly used copper joining process has limitations due to long cycle times and insufficient solder quality. The interference factors such as spatter and heat input will cause damage to the surrounding components, so laser technology is very important for the welding of power electronic components. In addition, fluctuations in weld depth can cause problems. Laser technology has the characteristics of flexibility and automation, and has become a good alternative to traditional welding technology. And fully able to meet customer demand for production capacity and quality. However, it is difficult to weld copper, a highly reflective material, due to the current infrared laser. Especially in the field of small parts with small welding depth (<1mm), near-infrared laser cannot accurately control the welding depth and quality. However, new developments in beam sources are changing this: lasers, which can be better coupled to green wavelengths, are now available in industry, with enough power to increase productivity while achieving virtually spatter-free processing. For applications where green power is still limited (e. g., large part sizes and weld depths> 1mm),BrightLine Weld enables infrared laser technology with better laser-material coupling performance, which greatly improves productivity and quality. Power electronics manufacturers in the field of electric vehicles are facing the challenge of adopting automation and more efficient production processes to meet the growing demand. The traditional process can not meet the requirements of resistance welding and ultrasonic welding. For example, the welding of internal direct brazing (DCB) and the welding of the external bus bars of the inverter and control unit.

11-30

Welding knowledge: how to improve the technical level of welding operation

2022-11-30

Important structures such as boilers and pressure vessels require safe welding joints, but due to the limitation of structural size and shape, double-sided welding is sometimes impossible. A special method of operation that can only be slotted on one side. Single-sided welding and double-sided forming technology. In manual arc welding is a more difficult operation skills. During vertical welding, due to the high temperature of the molten pool, under the action of gravity, the molten metal droplets formed by the melting of the electrode and the molten iron in the molten pool are easy to drip downward, forming welding bumps and undercuts on both sides of the weld. When the temperature is too low, slag inclusion is easy to occur, defects such as incomplete penetration and solder joints are easy to form on the back, and it is difficult to form a weld. 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 the shape and size of the molten pool are carefully observed and controlled during welding, the temperature of the molten pool can be controlled to ensure the quality of welding. 1. The angle of welding rod is very important, and welding specification is essential. During vertical welding, the molten droplets formed by melting the electrode and molten iron in the molten pool can easily drop down to form welding bumps, forming undercuts on both sides of the weld, deteriorating the shape of the weld. Master the correct welding specification and adjust the angle of the welding rod and the speed of the welding rod according to the change of the welding situation. The angle between the welding rod and the surface of the welding piece is 90 &deg; in the left and right direction, which is consistent with the welding seam. The welding angle is 70 &deg; to 80 &deg; at the beginning of welding, 45 &deg; to 60 &deg; in the middle, and 20 &deg; to 30 &deg; at the end of welding. The assembly gap is 3-4mm, and the smaller electrode diameter &Phi;3.2mm and the smaller welding current should be selected. The bottom weld is 110-115A, the intermediate transition layer is 115-120A, and the cover layer is 105-110A. Current is generally smaller than flat welding. 12% ~ 15%, in order to reduce the volume of the molten pool, so that it is less affected by gravity, which is conducive to the excess of droplets. Short arc welding is to shorten the distance from the droplet to the molten pool, thereby forming an excessive short circuit. 2. Observe the molten pool, listen to the sound of the arc, and keep in mind the shape of the molten hole. Bottom welding at the root of the weld is the key to ensure welding quality. Arc extinguishing method is adopted for welding. The arc extinguishing rhythm of vertical welding is slightly slower than that of flat welding, 30~40 times per minute. The arc burning time is slightly longer when welding each point, 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 &deg; to 80 &deg;. Two-point penetration welding is adopted. The arc is ignited on the side of the groove and preheated along the spot weld to melt to the root. When the arc penetrates, there is a "chatter" sound from the inclined plane. When the molten hole and the molten pool seat are formed, the electrode is immediately lifted to extinguish the arc. Then ignite the other side of the groove, and the second molten pool should be 1/2 to 2/3 of that when the first molten pool starts to solidify, so that the whole weld can be broken down by extinguishing the left and right arcs. To use the flexibility of the wrist to extinguish the arc, each time to cleanly extinguish the arc, so that the molten pool has the opportunity to solidify instantly. When the arc is extinguished, the fused hole formed by the pierced blunt edge can be clearly seen. The fusion hole of vertical welding is about 0.8mm, and the size of the fusion hole is closely related to the formation of the back surface. The back of the fusion hole is often not penetrated. During the operation, the size of the fusion hole must be consistent, so as to ensure uniform penetration at the root of the groove, forming a full back weld, and uniform width and height. When bottoming and replacing the welding rod joint, clean up the coating at the joint every time, ignite the arc again in the groove, continuously weld the welding rod angle along the welding seam formed by about 10mm, extend into the center of the welding seam at 90 degrees, swing around slightly, press the arc downward at the same time, hear the arc sound, form a melting hole, and immediately extinguish the arc, so that the welding rod arc extends into the root of the welding seam, formation of dissolved pores immediately extinguish the arc. Then it is the same as the bottom welding method of the first electrode, alternating cycles of arc extinguishing and breakdown from left to right, pay attention to each action, pay attention to the contours of the molten holes and molten seams on both sides, and the molten seams at the root of the groove, only when the arc It can be seen when moving to the other side. It was found that the blunt edge did not fuse well, and the arc was slightly reduced to achieve good fusion. The arc extinguishing time is controlled until the 1/3 of the molten pool does not solidify. Restart the arc. When extinguishing 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 solidify instantly to prevent the high temperature molten pool from falling off and forming weld tumor. When the electrode is only 30-40mm, ready to do arc extinguishing action. Falling two or three times on one side of the molten pool to slowly cool the molten pool can prevent shrinkage cavities and crater cracks on the front and back of the weld. Defects 3. The temperature of the molten pool is well controlled and the quality of the weld is improved. The welding wave of the intermediate layer is required to be smooth. The diameter of the middle two layers of welding rod is φ3.2 ㎜, the welding current is 115-120A, and the angle of the welding rod is about 70-80. The zigzag method is adopted to control the temperature of the molten pool by using the angle, arc length, welding speed and the retention time on both sides of the groove of the welding rod. Make good fusion on both sides and keep the shape of oblate molten pool. When welding the third layer, do not damage the edge of the groove, leave a depth of about 1mm, so that the entire filling bead is smooth. The edge of the groove above the depth is used as a reference line to lay the foundation for the coverage. Generally, the left and right swing method is adopted, and the stay time on both sides of the groove is slightly longer, so that the edge of the groove is melted by 1-2mm, and the temperature on both sides of the molten pool and the groove is guaranteed. Balance is mainly to observe the shape of the molten pool, control the molten pool into a crescent shape, leave less on the side with more molten pool and more on the side with less molten pool, and calculate the height and width of the weld while welding. Since the welding meat of vertical welding is thicker than that of flat welding, the shape of the molten pool and the thickness of the welding meat should be observed. If the lower edge of the molten pool protrudes from the gentle side, it means that the temperature of the molten pool is too high. At this time, the arc time and arc extinguishing time should be shortened to reduce the temperature of the molten pool. The crater must be filled before the electrode is replaced to prevent the crater from cracking.

11-29

"Shake" welding operation method and characteristics

2022-11-29

The essence of the crank welding technology is that the welding nozzle of the welding torch ignites the arc on the side of the groove of the base material, and the thumb rubs the wire feeding along the tip of the index finger to form molten droplets and molten pool. Then use the wrist swing to make the welding nozzle fan-shaped rolling swing, the use of the surface tension of the droplet to fill the groove of a manual tungsten argon arc welding method.

11-28

Welding rod arc welding operation technology

2022-11-28

Electrode arc welding operation technology. In all kinds of welder training materials or welder manual, the operation technology of welding rod arc welding is introduced in detail, and the main points are briefly described here. 1 Arc striking, transportation and closing. (1) Arc strike The arc is ignited by the end of the electrode near the starting point of the weld. Usually used to ignite by scratching and tapping. The scraping method is to scrape the end of the electrode on the surface of the weldment. Similar to strike a match. Scraping must be carried out in the groove, and the arc starting point is preferably selected on the welding part about 10mm away from the arc starting point of the welding seam. Immediately after ignition, normal welding is carried out in the welding direction. The welding passes through the origin fire point and is remelted, thereby eliminating the arc scar or ball drop weld metal that may remain at this point. The tapping method is to make the electrode perpendicular to the arcing point on the weldment, gently touch the arcing point at the end, and immediately lift it. The operation method after ignition is the same as the scraping method described above. The impact force should not be too strong, otherwise the coating will fall off into pieces, causing arc instability and affecting the welding quality. Once the arc is extinguished during the welding process, the arc must be reignited. It is best to hit the weldment again immediately before the end of electrode cooling, which is conducive to reburning, because the hot drug skin is easy to become a conductor, especially for electrodes containing a large amount of metal powder. The starting point of the reignition arc shall be on or near the crater to be welded. The arc must be restarted when the electrode is replaced. Arc starting point should be selected on the front weld crater or before the front weld. After ignition, move the arc backward to fill the crater, and then continue to weld forward. Arc striking at non-welding parts is not allowed, otherwise defects such as pits, welding beading or cracks will be left during arc striking. (II) transport conditions; When welding, the shape and size of the molten pool can be controlled by correct conveying, so as to obtain good fusion and weld formation. There are three basic movements in the process of conveyor belt, namely, forward movement, swing movement and feeding movement. 1) The forward action is the action of moving the electrode end forward along the axis of the weld. Its speed represents the welding speed and can affect the welding heat input and the cross-sectional area of the weld metal. 2) The swing action is to make the electrode terminal swing horizontally in the vertical direction. The way, amplitude and speed of the swing directly affect the width and penetration of the weld, as well as the fusion on both sides of the groove. 3) The feeding action is the action of continuously feeding the electrode to the molten pool along its own axis. When the electrode feed speed is the same as its melting speed, the arc length is stable. If the wire feeding speed is slower than the melting speed, the arc length becomes longer, the melting depth becomes shallower, the melting width increases, the arc drift is unstable, the protection effect becomes worse, and the spatter is large. Therefore, in general, it is desirable to weld at a feed rate equal to or slightly greater than the melting rate and at an arc length equal to or less than the electrode diameter. Skilled welders can continuously change and coordinate these three actions according to the form of welded joint, weld position, weldment thickness, electrode diameter and welding current, as well as changes in the shape and size of the molten pool during the welding process, so as to control the molten pool within the required shape and size range. Table 3 lists the commonly used modes of transport and their scope of application. (3) End the arc. At the end of welding, if the arc is broken immediately, a crater will be formed at the end of the weld, which will reduce the working section of the weld, thereby reducing the strength of the joint, generating crater cracks, and also causing stress concentration. Therefore, the crater must be closed after it is filled. Commonly used arc closure methods are:. 1) Arc closure method When the arc moves to the end of the weld, the end of the electrode moves in a circular motion until the crater is filled, and then the arc is disconnected. This method is suitable for thick plate welding. 2) Return welding arc closing method When the arc moves to the end of the weld, stop for a while, and change the angle of the electrode to make it flow back for a short period of time, and then pull the arc off. This method is suitable for the welding of alkaline electrodes. 3) Repeated arc extinguishing reignition method The arc is extinguished and restarted several times at the end of the welding until the arc pit is filled. Suitable for high current or thin plate welding occasions.

11-27

Welding knowledge: basic knowledge of welded steel pipe

2022-11-27

According to different welding methods, it can be divided into arc welded pipe, high frequency or low frequency resistance welded pipe, gas welded pipe, furnace welded pipe, Bondi pipe, etc. Welded steel pipe: used in oil drilling and machinery manufacturing, etc. Furnace welded pipe: can be used as water gas pipe, etc., large diameter straight seam welded pipe for high pressure oil and gas transportation, etc. Spiral welded pipes are used for oil and gas transportation, pipe piles, piers, etc. According to the shape of the weld can be divided into straight seam welded pipe and spiral welded pipe. Longitudinal welded pipe: simple production process, high production efficiency, low cost and rapid development. Spiral welded pipe: the strength is generally higher than the straight seam welded pipe, can use a narrow billet to produce larger diameter welded pipe, can also use the same width of the blank to produce different diameter welded pipe. However, compared with the same length of the straight seam welded pipe, the weld length increased by 30~100%, the production speed is low. Therefore, most of the small diameter welded pipes are welded by straight seam welding, and most of the large diameter welded pipes are welded by spiral welding. Spiral seam welded steel pipes are divided into automatic submerged arc welded steel pipes and high frequency welded steel pipes. a. Spiral seam automatic submerged arc welded steel pipes are divided into Class A pipes and Class B pipes according to the pressure of the conveying medium. Grade pipes are generally welded with ordinary carbon steel Q235, Q235F and ordinary low-alloy structural steel 16Mn, and grade B pipes are welded with Q235, Q235F, Q195 and other steels for low-pressure fluid delivery pipes. B. spiral seam high frequency welded steel pipe spiral seam high frequency welded steel pipe there is no uniform product standard, generally made of ordinary carbon steel Q235, Q235F and other steel materials. According to the use is divided into ordinary welded pipe, galvanized welded pipe, blown oxygen welded pipe; steel wire casing, metric welded pipe. Idler tube, deep well water pump tube, automobile tube, transformer tube, electric welding thin-walled tube, electric welding special-shaped tube, spiral welded tube, etc. General welded pipe: General welded pipe is used to transport low pressure fluid. Made of Q195A, Q215A, Q235A steel. It can also be made of other low carbon steel that is easy to weld. Steel pipes must undergo water pressure, bending, flattening and other tests, which have certain requirements for surface quality. Typically, the delivery length is 4-10 meters, usually requiring a fixed length (or double length) delivery. The specification of welded pipe is expressed in nominal diameter (mm or inch). The nominal diameter is different from the actual diameter. Welded pipe according to the provisions of the wall thickness of ordinary steel pipe and thick steel pipe two. Steel pipes are divided into threaded and non-threaded types according to the form of pipe ends. Galvanized steel pipe: In order to improve the corrosion resistance of the steel pipe, the general steel pipe (black pipe) is galvanized. There are two types of galvanized steel pipes: hot-dip galvanized and electro-galvanized. The hot-dip galvanizing layer is thick and the electroplating cost is low. Oxygen blowing welded pipe: used for steel-making oxygen blowing pipe, generally with small diameter welded steel pipe, specifications from 3/8 inch -2 inch eight. Made of 08,10,15,20 or Q195-Q235 steel. To prevent corrosion, some are aluminized. Wire casing: It is also a kind of ordinary carbon steel welded steel pipe, which is used in concrete and various structural power distribution projects. Commonly used nominal diameter is 13-76mm. The wall of the wire casing is relatively thin, and it is mostly used after coating or galvanizing, and cold bending test is required. Metric welded pipe: its specification is expressed in the form of seamless pipe. The welded steel pipe is expressed by outer diameter * wall thickness mm. It is welded with ordinary carbon steel, high-quality carbon steel or ordinary low alloy steel with hot or cold belt, or with hot spot after welding and then made by cold drawing method. Metric welded pipes are divided into ordinary energy pipes and thin-walled pipes, which are generally used for structural parts, such as transmission shafts, or conveying fluids, while thin-walled pipes are used in the production of furniture, lamps, etc. to ensure the strength and bending test of steel pipes. Roller tube: used for welded steel pipes for belt conveyor rollers, generally made of Q215, Q235A, B steel and No. 20 steel, with a diameter of 63.5 -219.0mm. There are certain requirements for the bending of the pipe. The end face should be perpendicular to the center line and have ovality. Generally, water pressure and flattening tests should be carried out. Transformer tube: used to make transformer cooling tubes and other heat exchangers, made of ordinary carbon steel, requiring flattening, flaring, bending and hydraulic testing. The steel pipe has fixed length or multi-section transportation, and there are certain requirements for the bending degree of the steel pipe. Special-shaped pipe: square pipe, rectangular pipe, hat-shaped pipe, hollow plastic steel door and window steel pipe welded by ordinary carbon-bonded structural steel and 16Mn steel strip, mainly used for agricultural machinery components, steel doors and windows, etc. Welded thin-walled tubes: mainly used for making furniture, toys, lamps, etc. At present, thin-walled pipes made of stainless steel belts are widely used, such as high-end furniture, decoration, fences, etc. Spiral welded pipe: It is a low-carbon carbon structural steel or low-alloy structural steel strip based on a certain helix angle.

11-26

Summary of welding techniques for resistance welding and TIG welding processes

2022-11-26

Argon tungsten arc welding: 1. Very suitable for thin plate welding-a clean welding process that can obtain a good appearance of the weld. 2. Argon is used as a shielding gas when welding steel and aluminum. 3. DC positive polarity (DCEN) welded steel and stainless steel, AC welded aluminum. 4. In TIG welding, push gun technology has been used. 5. Match the size of the tungsten electrode with the size of the nozzle. 6. Welding aluminum-pure tungsten electrode should be used. In this way, the tungsten can be easily formed into a spherical tip during AC welding. 7. Welded steel and stainless steel-a tungsten electrode containing 2% thorium should be used. The tungsten electrode should be sharpened during DC positive welding. electrode arc welding: 1. Most of the time with tow gun technology. 2. Be prepared to prevent splashing. 3. Keep electrode clean and dry-follow manufacturer's recommendations. 4. Permeability: negative polarity direct current-maximum penetration, alternating current-medium penetration (there may also be more splash), positive polarity direct current-minimum penetration. Resistance welding: 1. Resistance welding is not suitable for welding aluminum, copper or copper alloys. And only for welding steel and stainless steel. 2. For greater heat (current output), shorter electrode arms should be used. 3. If it is a welding machine without thermal control function, it should be controlled according to the length of the electrode arm. For example, when welding thin plates that require low heat, longer electrode arms are used. 4. Please note that the longer electrode arm may bend, and you may also lose pressure on the weld. 5. Ensure that there is no gap between the welding workpieces, otherwise the welding effect will be greatly affected. 6. Keep the two electrode arms aligned so that the electrodes are aligned with each other. Also, to constantly adjust the appropriate pressure, not too much or too little. 7. If one side of the workpiece needs a good finish after welding, one side of the (machine) electrode can be ground. 8. Clean the electrode frequently, otherwise the output (current) will decrease. The electrodes shall also be fitted with suitable protective covers.

11-25

Summary of welding techniques for aluminum welding and self-shielded flux-cored wire welding processes

2022-11-25

Aluminum welding: 1. The most suitable for welding aluminum is the wire drawing welding torch. If you can't use this welding torch, try to use the shortest welding torch to keep the welding torch straight. Only argon can be used as a protective gas. When welding aluminum, only push gun method can be used. 2. If you find a wire feeding problem, you can try to use a conductive tip that is one size larger than the wire. 3. The most commonly used welding wire for welding aluminum is the softer standard wire. The other is harder (easier to feed wire) and is mainly used for welding operations that require hardness and strength. 4. Before welding, remove the oxide layer on the aluminum surface and use a special stainless steel brush to remove the oxide layer. 5. Fill the pits at the end of welding to prevent cracks. One method is to place the welding gun in the molten pool for a few seconds after welding. Self-shielded flux cored wire welding: summary of welding techniques for welding processes 1. Use pull (or drag) gun technology when welding. 2. Keep the welding wire clean and dry to achieve the best welding effect. 3. This type of welding is similar to stick welding, and the slag layer on the surface of the weld must be removed after welding. Slagging hammer and wire brush can be used for slag removal. 4. Self-shielded flux cored welding does not require an additional shielding gas container. (The protective agent is inside the wire). This feature makes it very suitable for outdoor work, because when used outdoors, the protective gas is easily blown away. 5. In the welding of thin plates, self-shielded flux-cored wire welding is more difficult than MIG welding.