Gas shielded arc welding is referred to as gas shielded welding or gas welding, it is the use of the arc as a heat source, the gas as a protective medium of fusion welding. In the welding process, the shielding gas around the arc to create a protective layer of gas, the arc, the molten pool and air separation, to prevent the influence of harmful gases, and to ensure that the arc burns stably.
Gas shielded welding can be categorized according to the state of the electrode, mode of operation, type of shielding gas, electrical characteristics, polarity, scope of application and so on.
According to the specific circumstances of different, gas shielded welding can be used in different gases, commonly used shielding gases are carbon dioxide, argon, helium, hydrogen and mixed gases.
The advantages of gas shielded welding are: good arc linearity, easy alignment, easy to realize all-position welding and automatic welding; arc heat concentration, small molten pool, welding speed, heat affected zone is narrower, weldment deformation is small, anti-cracking ability, weld quality is good. The disadvantage is that it is not suitable for welding in the windy site, the arc light radiation is strong.
Today Welding Town focuses on argon arc welding.
Principles of Argon Arc Welding
Argon arc welding uses the inert gas argon as a protective gas of a gas-electric shielded welding welding method.
Argon Arc Welding Features
(1) high welding seam quality, because argon is an inert gas, not a chemical reaction with the metal, the alloying elements will not be burned, and argon is not fused to the metal, the welding process is basically the process of metal melting and crystallization, so the protection of the better, to obtain a more pure and high-quality welds
(2)Welding deformation stress is small, due to the arc by the argon gas flow compression and cooling effect, the arc heat concentration, and the argon arc temperature is very high, so the heat-affected zone is small, so the welding stress and deformation is small, especially for thin welding and pipeline bottoming welding.
(3)Welding range is wide, almost all metal materials can be welded, especially suitable for welding the chemical composition of active metals and alloys.
Classification of Argon Arc Welding
Argon arc welding according to the different electrode materials can be divided into tungsten argon arc welding (non-melting pole) and melting pole argon arc welding. According to its operating method can be divided into manual, semi-automatic and automatic tig welding. According to the power supply can be divided into DC TIG welding, AC TIG welding and pulse TIG welding.
Weld before preparation
(1) read the welding process card, understand the material of the welding workpiece, the equipment needed, tools and related process parameters, including the selection of the correct welding machine, (such as welding aluminum alloy needs to use AC welder), the correct choice of tungsten electrode and gas flow, first of all, from the welding process card to know the size of the welding current and other process parameters. Then choose the tungsten electrode (generally speaking, the diameter of 2.4mm used more, its current should be 150A-250A, aluminum exceptions).
Then according to the diameter of the tungsten electrode selection of how big the nozzle, tungsten electrode diameter of 2.5-3.5 times the inner diameter of the nozzle D = (2.5-3.5) dw which D indicates the inner diameter of the nozzle (mm), dw indicates the diameter of the tungsten electrode (mm). Finally, according to the inner diameter of the nozzle selection of gas flow, nozzle inner diameter of 0.8-1.2 times is the flow of gas. q = (0.8-1.2)D, where Q indicates the gas flow (L/min) tungsten electrode Shen out length must not exceed the diameter of the inner diameter of the nozzle, otherwise it is prone to produce air holes.
(2) Check whether the welding machine, gas supply system, water supply system, grounding is intact.
(3) Check whether the workpiece is qualified:
1. Whether there is oil, rust and other dirt (welds must be clean and dry within 20mm)
2. Bevel angle, clearance, blunt edge is appropriate. Bevel angle, clearance, then had a large amount of welding, easy to produce weld tumor. Bevel angle is small, small gap, thick blunt edge is easy to produce unfused and weld opacity. Generally speaking, the bevel angle of 30-32 degrees, clearance of 0-4mm, blunt edge of 0-1mm.
3. The wrong side can not be too large, generally within 1mm.
4. The length and number of points of position welding meet the requirements, and the position welding itself should be free of defects.
5, argon arc welding practice: argon arc is a left and right hand action at the same time the operation, and our usual life of the left hand to draw a circle right hand to draw the same square, so it is recommended that in the beginning of the study of argon arc welding personnel to carry out similar training, to learn argon arc welding has some help.
(1) Wire feeding: divided into internal filler and external filler. External filler wire can be used for bottoming and filling, is a larger current, its wire head in the front of the bevel, the left hand pinch wire, constantly feeding into the molten pool for welding, its bevel clearance requirements are small or no gap. Its advantages because of the current, and small gap, so high productivity, easy to master the operating skills. The disadvantage is used for bottoming words because the operator can not see the blunt edge of the melting and the reverse side of the residual high situation, so easy to produce not fused and do not get the ideal reverse side of the molding. Filling wire can only be used for bottoming welding, is the left thumb, index or middle finger with the wire feeding action, pinky and ring finger clamp the wire to control the direction of the wire, the wire is close to the inside of the bevel at the blunt edge, and the blunt edge with the melting of the weld, the requirements of the bevel gap is larger than the diameter of the wire, is a plate, then you can bend the wire into an arc. Its advantages because the wire on the reverse side of the bevel, you can clearly see the blunt edge and the melting of the wire, the afterglow of the eyes can also see the reverse side of the residual height of the situation, so the weld fusion is good, the reverse side of the residual height and not fused can be well controlled. The disadvantage is that it is difficult to operate, requiring the welder to have more skillful operating skills, because the gap is large, so the amount of welding has to be increased accordingly, the gap is large, so the current is low, and the efficiency is slower than the outer filler wire.
(2) transport welding handle, divided into shaking handle and mop.
Shake the welding nozzle is slightly pressed on the welding seam, arm greatly shaking for welding. Its advantages because the welding nozzle pressed on the weld, the welding handle in the running process is very stable, so the weld protection is good, good quality, the appearance of the formation is very beautiful, the product qualification rate is high, especially the weld is very easy to weld the back weld, weld stainless steel can be obtained when the color of the appearance is very beautiful. The disadvantage is that it is difficult to learn, because the arm shaking amplitude, so can not be in an obstacle to the welding.
Mop is the welding nozzle gently leaning or not leaning on the top of the weld, the right hand little finger or ring finger is also leaning or not leaning on the workpiece, the arm swing is small, dragging the welding handle for welding.
The advantage is that it is easy to learn, good adaptability, the disadvantage is that the shape and quality is not shaken good, especially the back welding is not shaken convenient welding, welding stainless steel is difficult to get the ideal color and shape.
(3) arc: arc generally use arc inducer (high-frequency oscillator or high-frequency pulse generator), tungsten electrode and the weldment does not touch the ignition of the arc, there is no arc inducer when the use of contact arc (mostly used in construction site installations, especially high altitude installations), can be used in copper or graphite placed on the weldment bevel to induce the arc, but this method is more troublesome, use less, generally use the wire gently a row to make the weldment and the tungsten electrode direct short-circuit and rapid disconnect and Ignite the arc.
(4) Welding: After the arc is ignited in the beginning of the weldment should be preheated for 3-5 seconds, the formation of a molten pool after the start of wire feeding. When welding, the angle of the welding torch should be appropriate, wire feeding should be uniform. Welding gun forward movement should be smooth, left and right swing is a little slower on both sides, slightly faster in the middle. To pay close attention to the changes in the melt pool, pool melt pool becomes larger, wider weld or concave, to speed up the welding speed or re-adjust the welding current.
When the melt pool fusion is not good and send wire to send the feeling of immobility, to reduce the welding speed or increase the welding current, if it is the bottoming of the welding gaze attention should be focused on the bevel of the two sides of the blunt edge of the eye of the eye in the opposite side of the seam, pay attention to the rest of the changes in the high.
(5) close the arc: if the direct arc is easy to produce shrinkage holes, if there is an arc inducer torch to intermittent arc or adjust the arc current to the appropriate arc slow arc, such as no arc inducer welding machine will slow the arc to the side of the bevel, do not produce shrinkage holes, such as shrinkage holes to be polished clean before welding.
Close the arc if it is in the joints, should be the first to be joints polished into a beveled mouth, to be fully melted joints and then welded forward 10-20mm and then slowly close the arc, do not produce shrinkage holes.
Often seen in the production of joints do not grind into a beveled mouth, directly lengthen the joint welding time for joints, which is a very bad habit, so that the joints are prone to concave, joints are not fused and the opposite side of the disjointed impact on the molding of the aesthetic, such as high alloy materials are also prone to cracks.
After welding to check the appearance of qualified, people to go off the power supply and gas.