18 Nov 2021
Tungsten arc welding can be used for welding almost all metals and alloys. It is usually used for welding non-ferrous metals such as aluminum, magnesium, titanium, and copper, as well as stainless steel and heat-resistant steel. For metals with low melting point and easy to evaporate (such as lead, tin, zinc), soldering is more difficult. For certain thick-walled important components (such as pressure vessels and pipelines), argon arc welding is often used for bottoming in order to ensure the quality of the bottom welding when the bottom layer is welded by penetration bead welding, all-position welding and narrow gap welding. To obtain high-quality argon tungsten arc welding seams, you need to master these basic operating skills when operating the welding machine, such as: arc ignition, arc stabilization, arc closing, welding, joints, wire filling technology, Arc operation technology.
The first one talks about the ignition of argon tungsten arc welding. High-frequency oscillator and high-voltage pulse non-contact arc ignition are usually used for arc ignition. When there is no arc starter, you can touch the arc starter, that is, use pure copper or graphite plate as the arc starter plate and place the arc on the groove. Before starting the arc, air should be supplied 1.5~4s in advance, and the arc should be started on the positioning weld at the end of the workpiece. When starting the arc, use a longer arc (arc length 4~7mm) to preheat 3~5s outside the groove. There are three arc ignition methods: contact short circuit ignition, high frequency and high voltage ignition and high voltage pulse ignition. The first type is contact short-circuit ignition. The tungsten electrode is used to directly ignite the arc by contacting and short-circuiting the arc plate or copper plate or carbon rod. The second type is arc ignition with high frequency and high voltage. The high-frequency and high-voltage generated by the high-frequency oscillator is used to break down the gap (2~5mm) between the tungsten electrode and the weldment to ignite the arc. The third type,High-voltage pulse arc ignition: A high-voltage pulse (pulse amplitude=800V) is added between the tungsten electrode and the weldment to ignite the arc due to the ionization of the body medium between the two electrodes. Using high-voltage pulses to start arc is a better way to start arc.
The second one talks about the stable arc method of argon tungsten arc welding. Arc stabilization mainly adopts methods such as high-frequency stabilization, high-voltage pulse stabilization, and AC rectangular wave stabilization. High-frequency arc stabilization adopts high-frequency and high-voltage arc stabilization, which can appropriately reduce the intensity of high frequency during arc stabilization. High voltage pulse arc stabilization is to add a high voltage pulse at the moment of current zero crossing (current zero crossing is the moment when the current passes through the zero position in the process of the current changing from the positive direction to the reverse direction.). Manifold wave arc stabilization: The use of AC rectangular wave has a very high current rate of change at the moment of zero crossing, so as to help the welding arc to quickly reverse ignite when the polarity is switched.
The third talk about the arc operation technology of argon tungsten arc welding. Tungsten argon arc welding is realized by moving arc welding torch, which is divided into crank and mop (also called floating handle). Among them, the crank handles the nozzle lightly leaning against the groove of the weld, using the flexibility of the wrist to perform left and right zigzag or reverse crescent-shaped swings to complete the bottom and cover welding, as shown in Figure 4. Try to use a lighter or changeable xenon arc welding gun. The nozzle size can be selected according to your preference and the width of the weld. There are no special requirements for bottom welding, but it is easier to master and more flexible to use a slightly larger nozzle for cover welding.
The fourth talk about the arc extinguishing method of argon tungsten arc welding. Extinguish the arc when changing the welding wire or suspending welding. The methods of extinguishing arc include current attenuation method and molten pool attenuation method. Regardless of which arc extinguishing method is used as shown in Figure 5, after the arc is extinguished, the welding torch should still be aimed at the molten pool for 5 to 10 seconds, and the welding torch should be removed after the molten pool has solidified. When making joints, the joints should be polished out of the slope, and there should be no dead corners. If the joint is not polished into a bevel, the joint is made by directly lengthening the welding time at the joint, and the joint is prone to defects such as concave, unfused, and disjointed reverse surface, which affects the appearance of the shape. The re-ignition position is behind the original arc pit, so that the welds overlap by 15-20mm, and no or less welding wire is added at the overlap. Bottom welding makes the molten pool penetrate to the root of the joint to ensure that the joint is penetrated.
The fifth talk about the arc closing method of argon tungsten arc welding. The arc closing method of argon tungsten arc welding is the same as the arc extinguishing method. When closing the arc, the angle between the welding torch and the workpiece should be reduced, so that the heat is concentrated on the welding wire, and the arc crater should be filled by sending 2 to 3 drops of filler metal to the molten pool. Welding guns with arc starters need to close the arc intermittently or slowly close the arc to an appropriate arc closing current, the current decays, the temperature of the molten pool gradually decreases, and the molten pool changes from large to small; welding torches without an arc starter need to lead the arc to Cut off the control switch on the side of the bevel. At this time, do not leave the welding torch immediately to prevent the molten pool metal from being oxidized at high temperatures. The air supply should be stopped after 5~10s to avoid shrinking holes and crater cracks. If the arc is closed at the joint, first grind the joint into a bevel, and after the joint is fully melted, weld forward 10-20mm and then slowly close the arc until the arc crater is filled. The welding machine with high frequency device can fill the arc crater by repeatedly extinguishing the arc; if the arc is closed directly, it is easy to produce shrinkage holes.
The sixth talk about filler wire technology of argon tungsten arc welding. At present, in the actual operation of argon tungsten arc welding, the filler wire technology mainly includes two methods: continuous filler wire and intermittent filler wire. The operation method and scope of use are shown in Table 1.There are two ways to fill wire: inner wire and outer wire, as shown in the figure 7.
Finally, let's talk about the welding of argon tungsten arc welding. After the welding arc is ignited, it should be preheated for 3~5s at the beginning of welding to form a molten pool (melt holes should also appear during bottom welding) and then start wire feeding. The angle of welding wire and welding torch should be appropriate, and the welding wire should be given evenly. The operation of wire feeding must be stable and accurate, and the continuity of wire feeding should be maintained to prevent the occurrence of untimely wire feeding or wire threading. If the bottom welding gap is too large, the arc must first be lowered for bypass welding when starting the arc. The so-called bridge welding means that the arc is first aligned with one side of the blunt edge to weld. When the root edge of the one-side groove starts to melt, a small amount of welding wire is added, and then the arc is aimed at the other side of the blunt edge to melt and add welding wire. Then swing the welding torch to connect the blunt edges of the grooves on both sides, and at the same time form a certain size and clear molten hole before entering the formal welding.
The argon tungsten arc welding machine produced by our Kingsiri has powerful functions and better improves the operation technology of argon tungsten arc welding. It is a digital intelligent welding machine that can avoid more welding defects and achieve a more perfect welding effect.
Keywords: welding machine
Originally published 18 Nov 2021, updated 18 Nov 2021.