Welding process parameters:
Standard welding process parameters:
Standard welding process parameters may vary depending on the welding process, the material to be welded and the desired weld quality. However, some general guidelines for defining welding process parameters.
5. Common gas tungsten arc welding (GTAW) processes:
1. Gas tungsten arc welding (GTAW) for low carbon steel and low alloy steel:
MAG welding can be used for low carbon steel and low alloy steel, with Ar+ (5-20)% CO2 mixture gas used as shielding gas and sometimes a small amount of O2 added.
The droplet transfer mode can be short-circuit transition, spray transition or pulsed transition in MAG welding.
(1) Short-circuit transition MAG welding:
Compared to CO2 welding, short-circuit transition MAG welding has a more stable arc and less spatter. It can use thinner welding wire and lower welding current, resulting in shallower weld penetration and slower welding speed. This makes it suitable for welding thin sheets.
(2) Spray transition MAG welding:
Spray transition is the most common droplet transfer mode in MAG welding. Generally, the welding current is set 30-50A above the critical spray transition current. When the plate thickness is greater than or equal to 3.2 mm, the welding arc is very stable, resulting in a flat surface and good weld formation with minimal spatter.
2. Argon arc welding with melting electrode for stainless steel.
Short circuit transition, jet transition and pulse transition can be used.
(1) Transition from short circuit to stainless steel MIG welding.
The diameter of the welding wire is 0.8-1.2 mm and the shielding gas used is Ar+(1~5%)O2 or Ar+(5~20%)CO2. The welding current is lower than the critical jet transition current and is mainly used for single-layer welding of thin plates with a thickness of less than 3.0 mm.
(2) Jet transition to MIG welding of stainless steel.
The welding wire used has a diameter of 0.8, 1.0, 1.2, 1.6 mm, and the shielding gas used is Ar+(1~2%)O2 or Ar+(5~10%)CO2. The welding current is greater than the critical jet transition current and is mainly used for welding steel plates with a thickness of more than 3.2 mm.
3. Argon arc welding with melting electrode for copper alloys.
Copper and copper alloys have very strong thermal conductivity, which can easily cause poor melting, so preheating is required before welding. Due to the need for a large welding current, the molten droplets exhibit jet transition.
The characteristic of welding parameters for purple copper welding is high preheating temperature and large welding current (up to 600A). When using pure argon gas protection, the arc power is small. Using Ar+(50-75%)He protection can increase the arc power and reduce the preheating temperature.
4. Argon arc welding with melting electrode for aluminum alloys.
When MIG welding aluminum alloys, it is necessary to use the cathodic cleaning effect to remove the oxide film. Aluminum alloys have fast thermal conductivity and require sufficient arc power to melt the base material and form the weld. Pure argon gas is generally used as a shielding gas for thin plate welding. When welding large and thick materials, Ar+He gas mixture protection is used, and the proportion of He is generally around 25%. Short circuit transition or spray transition can be used.
Observation:
By reversing the polarity of the direct current, i.e. using the welding wire as the positive electrode and the workpiece as the negative electrode, droplets of molten welding wire generally enter the weld pool in a very fine granular “spatter transition” with a relatively large current used, resulting in high productivity. For aluminum plates with a thickness of more than 8 mm, to stabilize the arc, argon arc welding with melting electrode usually adopts DC reverse polarity, which has a “cathodic fragmentation” effect when welding aluminum parts.
(1) MIG welding in short circuit
This method uses pure argon gas as the shielding gas and typically uses a wire diameter of 0.8-1.0 mm, with a small spool of 0.5 kg wire and a special feed gun, for welding thicknesses of 1-2mm. Thinner aluminum alloy wires can be difficult to feed.
(2) Spray transition and subsonic MIG welding
This method also uses pure argon gas as the shielding gas and typically uses a wire diameter of 1.2 to 2.4 mm.
(3) High current MIG welding
Thick aluminum alloy plates can be welded using thick wires (3.2-5.6mm diameter) and high-current MIG welding, with welding currents reaching 500-1000A and resulting in high productivity. A shielding gas mixture of 50% Ar + 50% He is used in the inner nozzle to increase the arc power, while the outer nozzle is filled with Ar gas to further strengthen the shielding effect.
