Main operating points of ordinary aluminium welding
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MIG argon arc welding is mainly used for welding aluminum alloys, stainless steel and some low alloy steels. In order to obtain good welding quality and high productivity, the following three aspects are mainly considered:
One is the preparation before welding and good gas protection effect. The second is to select reasonable droplet transfer forms and process parameters. The third is to choose reasonable welding equipment and welding process procedures.
Aluminum can be oxidized at any temperature, forming an oxide film Al2O3 on its surface. The oxide film has a high melting point and is insoluble in liquid metal, hindering the normal fusion of the weld, worsening the weld shape and joint quality. Since hydrogen can dissolve in large amounts in molten aluminum, it can easily cause pores, especially Al-Mg alloys, which are more likely to generate pores during welding. When the thickness of aluminum and its alloy workpieces exceeds 4mm, melting arc welding (MIG) is a more economical and efficient welding method. Pure aluminum and aluminum alloy welding wires are less rigid than steel welding wires, so the diameter of the welding wire used for aluminum alloy MIG welding should be no less than 1.5mm, and the welding current should be greater than 130~140A to ensure the current density required for jet transition.
When welding aluminum and its alloys with melted arc welding (MIG), the gas protection must be reliable. The purity of the argon gas is required to be high (>99.8%), and the welding wire and groove welding wire must be carefully cleaned. After cleaning, in order to prevent the re-formation of oxide film and hydrogen adsorption on the surface of the welding wire, the cleaned welding wire must be used within 8 to 12 hours. The cleaned welding wire can also be stored in an argon-filled sealed package for later use. The base metal to be welded is generally cleaned mechanically, and cleaning should generally not exceed 3 to 4 days and nights.
When welding aluminum and its alloys, AC or DC reverse polarity is usually used. When welding medium and thin plates, use pure argon for protection; when welding thick and large parts, use Ar+(50~60)%He mixed gas protection. Metal arc welding (MAW) welding of aluminum and its alloys can use short-circuit transfer, jet transfer, pulse current and high current MG welding. The following is a brief description of each (pulse current has been discussed before, so it is omitted here):
(1) Short circuit transition welding
Short-circuit transition welding of aluminum and its alloys requires the use of thin wires (diameter Φ0.8mm and Φ1.0mm) and low current welding. Process parameters of short-circuit transition melting arc welding of aluminum and its alloy sheets.
Because the welding wire is soft and difficult to feed, a small wire spool for storing the welding wire is often placed on the wire drawing welding gun. At this time, all-position welding of butt, lap, corner and end face welds of aluminum alloy sheets with a thickness of 1 to 2 mm can be welded. Process parameters of fusion arc welding of aluminum and its alloy butt joints.
(2) Jet transfer MG welding
The most commonly used method for MG welding of aluminum and its alloys is jet transfer. Therefore, the welding current must always be greater than the critical current to achieve stable welding. For welding wires with diameters of 1.2mm, 1.6mm and 2.4mm, the critical currents are 130A, 170A and 220A respectively. During jet transfer welding, a constant voltage power supply is used in conjunction with constant speed wire feeding, and the arc self-regulating effect of the welding power supply is used to maintain Stable jet transition. Aluminum alloy jet transfer MIG welding process.
(3) High current MG welding is a process developed to improve the welding productivity of thick aluminum plates. When welding with aluminum wires with a diameter of less than 2.4mm, when the welding current reaches more than 500A, the surface of the weld bead is very rough and many pores appear. This phenomenon is called “wrinkling.” The phenomenon of “wrinkling” on the weld surface limits the improvement of productivity. There are two ways to solve the “wrinkling” of the weld seam: one is to use a double-layer nozzle to improve the protective effect of the gas; the other is to increase the diameter of the welding wire to reduce the arc pressure and use high-current submersible arc welding. The use of narrow gap submersible arc welding can avoid such defects. When the workpiece thickness is less than 200mm, no beveling is required, leaving only a gap of 6 to 12mm. The diameter of the welding wire
1.5～2.0mm, the welding current can reach 300～500A.
When using aluminum alloy thick wire with a welding wire diameter of 3.2 to 5.6 mm, a larger current (500 to 1000A) can be used for welding, which will prevent the weld seam from
The welding current of “wrinkling” can be increased to 1000A, so for a thick aluminum plate with a thickness of 75mm, only one layer of welding is needed on the front and back to meet the welding requirements.