Horizontal welding of aluminium alloys by soft plasma arc

Abstract

Horizontal welding plays an important role in manufacture of large and heavy aluminium alloy structures. But there are many problems such as bad weld formation, porosity and low efficiency. Variable polarity plasma arc welding is a low-defect and high-efficiency welding technology, but it has difficulty in horizontal position. The maximum weldable thickness is less than 6.4 mm in single-pass weld. The soft plasma arc was proposed in this article. Horizontal welding of aluminium alloy plates with 8 mm thickness was realized successfully. The joint was free of defects and had excellent mechanical properties. This is a breakthrough in single-pass horizontal welding. Moreover, the characteristic of the soft plasma arc was studied in detail and the fluid flow in weld backside was observed. Finally, the forming mechanism of a stale weld pool was discussed. Results indicated that the arc pressure with the soft plasma arc was lower than that with the ordinary plasma arc. The fluid flow was asymmetric in horizontal position. The forming of a keyhole was realized by the bridging of the molten metals in the upper and lower sides. The weld pool was stable with the soft plasma arc because the maximum diameter of keyhole was bigger than that with the ordinary plasma arc.

Fluid Flow Characteristics and Weld Formation Quality in Gas Tungsten Arc Welding of a Thick-Sheet Aluminum Alloy Structure by Varying Welding Position

“…In addition, as the workpieces and heat source (welding arc) are symmetrical about the central plane of a butt joint, only one half of the weld joint was included in the numerical model. The dimensions of the computation domain are 50  25  9.5 mm 3 , and the minimum cell in the model is 1.0  1.0  0.95 mm 3 . A mesh-independency study was performed, in which a one-half smaller mesh (0.5  0.5  0.475 mm 3 ) was also used.…”

“…The dimensions of the computation domain are 50  25  9.5 mm 3 , and the minimum cell in the model is 1.0  1.0  0.95 mm 3 . A mesh-independency study was performed, in which a one-half smaller mesh (0.5  0.5  0.475 mm 3 ) was also used. The differences in the results from two meshes were within 1.5%, indicating the mesh used in the study was fine enough.…”

“…are more apt to occur for welding positions (e.g., vertical welding) other than the flat position. This becomes even more serious when the aluminum alloy sheets are thick (with thickness greater than 5.0 mm) [3]. The welds with poor formation quality need be repaired, or even scraped when the defects are too serious, which then lead to increase in cost and waste of materials.…”

On the effect of heat input in plasma microwelding of maraging steel

“…PAW is one of the low-cost welding processes that has been used extensively for the joining of aluminum alloy using mainly keyhole mode process. [16][17][18] An increase in the plasma gas flow rate as well as increase in the welding current generates a smooth transition during start-up of welding. The variable polarity PAW actually reduces the formation of defects.…”

“…Pulsed current PAW is beneficially used to produce a keyhole in peak current and close the keyhole in base current. The horizontal welding with soft plasma arc for high thickness aluminum alloy was developed by Zhang et al 18 In soft arc, the plasma arc pressure is more distributed than stiff distribution of conventional PAW process with retention of keyhole formation, which is significant for horizontal welding. The PAW is also developed for microscale application with reduction and control of low-amperage current.…”