(1) Preparation before welding
Use chemical or mechanical methods to strictly clean the surface oxide film on both sides of the weld groove.
Chemical cleaning is to use alkali or acid to clean the surface of the workpiece. This method can remove both the oxide film and the oil stain. The specific process is as follows: sodium hydroxide solution with a volume fraction of 6% to 10%, soak at about 70 ℃. 5min → water washing → nitric acid with a volume fraction of 15% is soaked at room temperature for 1 minute for neutralization → water washing → warm water washing → drying. The surface of the aluminum alloy after washing is matte silver white.
Mechanical cleaning can use air-driven or electric milling cutters, scrapers, files and other tools. For thin oxide films, use a 0.25mm copper wire brush to remove the oxide film.
Solder immediately after cleaning, if it is left for more than 4h, it should be cleaned again.
(2) Determine assembly gap and tack welding pitch
During the welding process, the aluminum plate is thermally expanded, resulting in a decrease in the weld bevel gap. If the assembly gap before welding is too small, the grooves of the two plates will overlap during the welding process, increasing the unevenness and deformation of the plate surface after welding. ; On the contrary, if the assembly gap is too large, welding is difficult and there is a possibility of burning through. Appropriate tack welding pitch can ensure the required tack welding gap. Therefore, choosing an appropriate assembly gap and tack welding pitch is an effective measure to reduce deformation. According to experience, the reasonable assembly process parameters of different thicknesses for the joints are shown in Table 2.
(3) Select welding equipment
Currently there are many types of welding products on the market, generally speaking, AC tungsten arc welding (ie TIG welding) should be used. It is a welding method that uses the arc heat generated between the tungsten electrode and the workpiece to melt the base metal and fill the welding wire under the protection of argon gas. When the welding machine is working, since the polarity of the alternating current is periodically changed, in each cycle, the half-wave is direct-current DC connection, and the half-wave is direct-current DC reverse connection. The tungsten electrode can emit enough electrons during the half-wave of direct connection without overheating, which is conducive to the stability of the arc. The oxide film generated on the surface of the workpiece during the half-wave of reverse connection is easily cleaned away to obtain a bright and beautiful surface and a well-formed weld.
(4) Select welding wire
Generally choose 301 pure aluminum welding wire and 311 aluminum silicon welding wire.
(5) Select welding method and parameters
Is generally carried out by the left welding method, the welding torch and the workpiece are at an angle of 60 °. When the welding thickness is more than 15mm, the right welding method is used, and the welding torch and the workpiece are at an angle of 90 °.
When the welding wall thickness is more than 3mm, open the V-shaped groove, the angle is 60 ° ~ 70 °, the gap should not be greater than 1mm, and it is completed by multi-layer welding. When the wall thickness is less than 1.5mm, there will be no bevel, no gap, no filler wire. When welding the butt joint of the pipe, when the pipe diameter is 200mm and the wall thickness is 6mm, a tungsten electrode with a diameter of 3 to 4mm should be used, with a welding current of 220 to 240A, and a filler wire with a diameter of 4mm, with 1 to 2 layers Welded.