Preparation before welding: the thickness less than 4mm need not be broken, and it can be directly welded, penetrating one side at a time. Butt welds with a thickness of 4 to 6 mm can be welded on both sides of the joint without breaking. More than 6 mm, generally open V-shaped or U, X-shaped groove.
Secondly, degreasing and derusting are carried out on the welding wire filled in the welding position. So as to ensure the welding quality.
Welding parameters: including welding current, tungsten electrode diameter, arc length, arc voltage, welding speed, shielding gas flow, nozzle diameter, etc. (1) welding current is the key factor to determine weld formation. It is usually determined by the material, thickness and groove shape of the weldment.
(2) The electrode diameter is determined according to the welding current, and the larger the current, the larger the diameter.
(3) For welding arc and arc film, the arc length is about 0.5 ~ 3mm, and the corresponding arc voltage is 8~ 10V.
(4) Welding speed: Current, sensitivity of weldment material, welding position and operation mode should be considered when selecting.
1 hand welding (MMA):
Manual welding is a very common and easy-to-use welding method. The length of the arc is adjusted by hand, depending on the gap between the electrode and the workpiece. Meanwhile, when used as an arc carrier, covered electrode is also a welding filler.
This welding method is simple and can be used to weld almost all materials. Outdoor use, good adaptability, even underwater use. In electrode welding, the arc length depends on the human hand: when you change the gap between the electrode and the workpiece, you also change the arc length. In most cases, direct current is used for welding, and the electrode is used as both arc carrier and weld filler. Covered electrode is composed of alloy or non-alloy metal core wire and coated covered electrode coating, which protects the weld from air, stabilizes the arc, and also causes the formation of slag layer, protecting the weld and shaping it. The electrode can be a titanium-coated electrode or an alkaline electrode, depending on the thickness and composition of the coating. Titanium covered electrode is easy to weld, the weld is smooth and beautiful, and the welding slag is easy to remove. If covered electrode is stored for a long time, it must be baked again, because the moisture in the air will quickly accumulate in covered electrode.
2 MIG/MAG welding:
This is an automatic gas shielded arc welding method. In this method, the arc generates heat between the current-carrying wire and the workpiece under the protection of protective gas, and the wire fed by the machine is used as the covering electrode and melted under its own arc. Because of the universality and particularity of MIG/MAG welding method, it is still the most widely used welding method in the world, which is suitable for steel, non-alloy steel, low alloy steel and high alloy-based materials. This makes it an ideal welding method for production and maintenance. When welding steel, MAG can meet the requirements of thin steel plate with a thickness of only 0.6 mm. The protective gas used here is active gas, such as carbon dioxide or mixed gas.
3 TIG welding:
An arc is generated between the refractory tungsten welding wire and the workpiece. The shielding gas is generally pure argon, and the welding wire is not charged, so it can be sent manually or mechanically, and there are some special uses that do not need to be sent. The material to be welded determines whether DC or AC is used: when DC is used, tungsten welding wire is designated as the negative electrode, because it has strong penetration ability and is suitable for different kinds of steel, but it has no "cleaning effect" on the molten pool.
The main advantage of TIG welding method is that it can weld a wide range of large materials, including workpieces with a thickness of more than 0.6 mm. Materials include alloy steel, aluminum, magnesium, copper and its alloys, gray cast iron, common valve stem, various bronzes, nickel, silver, titanium and lead. The main application field is welding thin and medium-thick workpieces, which is used as the root pass of thicker parts.