MIG/MAG Welding: Principles, Parameters, and Equipment
MIG/MAG Welding Principles
MIG/MAG welding is a process where an arc is established between a continuous wire electrode and the workpiece. It is protected by an inert gas (MIG) or an active gas (MAG).
Process Types:
- Semiautomatic: Voltage, speed, intensity, and flow are pre-regulated. The torch is moved manually.
- Automatic: All parameters are pre-regulated, and the application is automatic.
- Automated: All parameters are programmed by a specific unit.
This welding type is used for low and medium carbon content steels.
Influence of Parameters
Polarity: Usually reverse polarity is used, with the workpiece negative and the wire positive. The positive pole heats up 65% more than the negative pole.
Arc Voltage: Decisive in the metal transfer method to the workpiece.
Wire Feed Speed: Adjusting the wire feed speed causes intensity variation through self-regulation.
Gas Type: Significantly influences the metal transfer form, penetration aspect of the weld, and spatter.
Operating Method
The gun must be held in a proper position for the gas to protect the molten pool effectively. Welding can be done from right to left or left to right. Right-to-left welding results in high-speed, thin welds, while left-to-right welding produces bulkier welds. Right to left is generally preferred. Tilt the gun by 10°. The wire length should be between 8 and 20mm. If the length is too short, it increases spatter.
Movements
- Linear: Preferred for stringer beads.
- Circular: Suitable for preventing large penetrations.
- Impulses: Forward and backward movement, thin threads for great penetration.
- Pendulum: Suitable for wide ranges.
MIG/MAG Equipment
Most important elements:
Transformer
Reduces the AC voltage from the network to a level suitable for welding. It consists of a core made of laminated sheets. The primary and secondary circuits operate when magnetic flux circulates.
Rectifier
Converts alternating voltage to continuous voltage, required for MIG/MAG welding. It consists of power semiconductors.
Inductance
Aims at isolating the welding current, which reduces spatter.
Wire Feeder Unit
Provides wire at a constant speed using a motor, usually DC. The operator can regulate the speed. The drive system is formed by one or two rollers; their maintenance is important for thread uniformity.
Protective Gas Circuit
Flows from the cylinder to the welding zone through a gas hose and the welding torch. A pressure regulator-flowmeter must be incorporated to allow for regulation. The greater the distance from the base metal, the higher the flow rate needed to ensure protection.
Welding Torch
Carries the wire, current, and gas. The tip of the gun is coupled outside the dips that channels gas to the weld zone and an inner nozzle, which provides the necessary electrical contact to the tip of the wire for the welding arc.
Electronic Control
Guarantees practically unlimited equipment life.
Optional Cooling Circuit
Cools the welding torch.
Voltage and Feed Rate Variations
A voltage variation triggers a change in intensity. For welding changes, adjust the wire speed control.
The feed rate of the wire will be reset for automatic balance between increased energy and the amount of material to be merged. A decrease in the thread rate causes a new state of welding characteristics, a considerable decrease in current, and a slight increase in tension.