15 Nov 2021
The welding parameters of argon tungsten arc welding mainly include welding current, welding polarity, welding speed, arc length, tungsten electrode diameter and shape, gas flow and nozzle diameter. These parameters often affect the use of argon tungsten arc welding machine and the quality of welding results. How to control the speed and size of these parameters is very important, let's talk about it in detail below.
The first one talks about welding current and speed. Welding current is the main welding parameter of argon tungsten arc welding. As the welding current increases (or decreases), the depression depth, weld metal thickness, penetration depth, and weld width increase (or decrease) accordingly. When the welding current is too large, the weld is prone to defects such as weld penetration and undercut; on the contrary, the weld is prone to defects such as incomplete penetration. The size of the welding current when welding is selected according to the material, thickness of the workpiece and the spatial position of the joint. Under normal circumstances, the welding speed is adjusted at any time according to the size of the molten pool, the shape of the molten pool and the fusion of both sides. As the welding speed increases (or decreases) during argon tungsten arc welding, the penetration depth and weld width decrease (or increase) accordingly, as shown in Figure 1. When the welding speed is too fast, the gas protection is damaged, and the weld is prone to defects such as incomplete penetration, lack of fusion, and porosity; on the contrary, the weld is prone to defects such as weld penetration and undercut.
The second one is the arc voltage. The arc voltage of argon tungsten arc welding is mainly determined by the arc length. Normally, the arc length is approximately equal to the diameter of the tungsten electrode. As the arc length increases (or decreases), the weld width slightly increases (or decreases), and the penetration depth decreases (or slightly increases). When the arc length is too long, the gas protection effect is not good, and the weld is prone to defects such as undercut, incomplete penetration and oxidation. Therefore, in the case of ensuring that the arc is not short-circuited, short arc welding is used as much as possible. In this way, the gas protection effect is good, the heat concentration is stable, the arc is stable, the penetration is uniform, and the deformation of the weldment is small. But the arc cannot be too short. When the arc is too short and the arc voltage is too low, the wire feeder will easily touch the tungsten electrode, causing a short circuit and burning the tungsten electrode, causing tungsten to be clamped.
The third one is the diameter of the tungsten electrode. In argon arc welding, the tungsten electrode acts as an electrode to conduct current, ignite the arc and maintain the normal combustion of the arc. Commonly used tungsten electrodes include thorium tungsten (red head), cerium tungsten (gray head) and lanthanum tungsten (blue head). The diameters of tungsten electrodes commonly used in manual argon arc welding are 1.6mm, 2.0mm, 2.4mm, 3.2mm, etc. The tungsten electrode is a high melting point material with a melting point of 3410℃±20℃ (pure tungsten rod). It has a strong electron emission ability at high temperature, and the tungsten electrode has a large current carrying capacity. During the bottoming of argon arc welding, the surface of the tungsten electrode must be smooth, the end must be sharpened, and the concentricity must be well polished, which is conducive to high-frequency arc ignition and arc stability. The diameter of the tungsten electrode should be selected according to the weldment material, thickness, groove form, welding position, welding current and power source polarity. When the diameter of the tungsten electrode is selected, there is a certain allowable welding current. During welding, if the allowable current value is exceeded, the tungsten electrode will produce intense heat, melting and volatilization, causing problems such as unstable arc and tungsten in the weld. When choosing different power polarity, the allowable current of the tungsten electrode is also different. The allowable currents of different power supply polarities and different diameter tungsten electrodes are shown in Table 1.
The fourth is the shape and extension length of the tungsten tip. The choice of the shape of the tungsten extreme tip should be determined according to the degree of penetration of the weldment, the requirements of weld formation and the type of welding base metal, as shown in Figure 2. The smaller the diameter of the tungsten tip, the greater the arc umbrella tendency and the more serious the tip burn. As the diameter of the tungsten tip increases, the arc columnar tends to become larger, and the arc is concentrated and stable. However, when the diameter of the tungsten electrode tip increases to a certain value, it will cause the arc to drift and become unstable. When using DC tungsten argon arc welding to weld low-carbon steel and its alloy steel, the tungsten terminal must be ground into a flat-bottomed cone. The relationship between the cone diameter and the diameter of the tungsten electrode: L≈3D; d≈0.3D. In the formula, L---cone length (mm); d---cone minimum diameter (mm); D---tungsten pole diameter (mm). The extension length of the tungsten electrode refers to the length of the tungsten electrode between the tip of the tungsten electrode and the tungsten electrode clip. It not only affects the protection effect, but also affects the maximum allowable current of the tungsten electrode, as shown in Figure 3. The longer the protruding length of the tungsten electrode of the same diameter, the smaller the allowable current; the shorter the protruding length, the better the protection of the tungsten electrode and the molten pool, but it hinders the observation of the molten pool and easily burns the nozzle. Under normal circumstances, when welding butt welds, the recommended tungsten electrode extension length is 5~6mm; when welding fillet welds, the recommended tungsten electrode extension length is 7~8mm.
The fifth talk about gas purity and flow. The performance of argon protection depends not only on the purity and flow rate of argon, but also on welding speed, arc length, nozzle diameter, tungsten electrode extension length and joint shape. The higher the argon purity, the better the protection effect, and the stronger the protective layer's ability to resist flowing air. However, when the gas flow is too large, gas turbulence will be generated, which will reduce the protection performance, resulting in unstable arc, and pores and oxidation defects in the weld. On the contrary, the air is easy to invade the molten pool, causing pores and oxidation defects in the weld. As the welding speed and arc length increase (or decrease), the gas flow rate should also increase (or decrease) accordingly, otherwise it is easy to cause poor gas protection. As the nozzle diameter and the elongation of the tungsten electrode increase (or decrease), the gas flow rate also increases (or decreases). Welders can judge the effect of argon protection by observing the color of the weld surface, as shown in Table 2.
The sixth talk about nozzle diameter selection and the distance from the nozzle to the workpiece. Under certain conditions, there is an optimal range of gas flow and nozzle diameter matching. At this time, the gas protection effect is the best and the effective protection zone is the largest. See Table 3. When the nozzle diameter and gas flow increase at the same time, the protection zone also increases, but the nozzle diameter is too large, the air velocity is small, the stiffness is small, and the protection effect is not good. This will not only increase the argon consumption, but also affect the welder’s sight. Therefore, the appropriate nozzle diameter should be selected according to the welding position and the groove form. The greater the distance from the nozzle to the workpiece, the worse the gas protection effect. On the contrary, the protection effect is better. However, too close a distance will affect the welder’s line of sight, and it is easy for the tungsten electrode to contact the molten pool, resulting in tungsten clamping. Therefore, under the premise of not affecting the operation, the smaller the distance between the nozzle and the workpiece, the better. It is generally recommended that the distance between the nozzle end and the workpiece be 7~12mm, as shown in Figure 3.
Tungsten argon arc welding can weld both thick parts and thin parts; it can weld the welds in the flat welding position, and it is also suitable for welding various space welds. Due to the protection of argon, the harmful effects of air on molten metals are isolated, and it can weld easily oxidized non-ferrous metals and their alloys (aluminum, magnesium, etc.), stainless steel, high-temperature alloys, titanium and titanium alloys, and refractory active metals ( Such as molybdenum, berkelium) and so on. Tungsten argon arc welding is widely used in various industrial structure metal welding, used in aircraft manufacturing, atomic energy, chemical industry, textile, power station boiler engineering and other industries.
Keywords: welding machine
Originally published 15 Nov 2021, updated 15 Nov 2021.