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MIG MAG - Arc welding through the MAG process
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1. Process description
Electric arc welding with gas protection is a welding process wherein the necessary heat is generated by an arc that is established between a consumable electrode and the metal to be welded.
A solid wire, peeled, that is fed automatically in a continuous manner and is converted into the deposited metal as it is consumed, carries out the function of the electrode.
The electrode, arc, founded metal and adjacent zones of the metal base, are protected from contamination by atmospheric gas through a gas current that is proportioned by the gun’s nozzle, concentrically, to the wire / electrode.
2. Applications
The MIG / MAG process can be used for the welding of all materials (carbon steel, stainless steel, aluminium.....)
The electrode is continuous, which increases productivity due to not having to change the electrode and the deposition rate is elevated. Much more elevated welding velocities can be obtained than with coated electrodes.
It is a matter of an easily applied process that allows welding in any position. Long weldings can be carried out without splices between cords. It is not necessary to eliminate any slag, since it does not exist.
On the other hand, it is a matter of costlier equipment, of bigger dimensions and that requires gas installation, which makes its use restricted to spacious industrial interiors.
3. MIG / MAG welding equipment:
El equipo básico para el soldeo TIG consiste en una fuente de energía o de alimentación, una antorcha TIG equipada con un electrodo de Tungsteno no consumible, una pinza de masa y una botella de gas inerte (mayoritariamente ARGON 100%).
3.1. Power source
The power supply must be able tooperate at high currents and provide constant direct current in orderto melt the filler material so that it can flow in a regular manner.
This power source will require a single-phase power supply (1ph) or three-phase (3ph) according to its power or, therefore, its consumption.
3.2. System for feeding in solder wire
The feeding in solder wire unit is the device that makes the wire pass through the contact tube of the gun for melting in the arc. The equipment MIG / MAG has a system for varying the advance velocity of the wire, as well as a magnetic valve for the passing of the gas.
A motor transmits the power to the shifting rollers so that these move the wire from the spool to the contact point of the torch. Usually one of the contact rollers is flat and the other one with bevel. The bevel is in the shape of a V for hard materials like steel and stainless steel, and in the shape of a U for soft materials, like aluminium. It is absolutely necessary to select the rolls in accordance with the diameter of the wire.
3.3. Torch
The continuous wire welding guns have to allow the wire to pass through them at a predetermined velocity and, in the second place, transmit the welding current to the wire and direct the protection gas.
The torch is principally connected to the equipment through the EURO CONNECTOR, which makes the change of it easy in case this is necessary. The maximum longitude recommended for the welding of carbon steel and stainless steel is 4m. In these cases, the haulage (the duct through which the wire passes along the entire torch) is of steel. During aluminium welding through the MIG process, the recommended longitude is about 3 m, whereby the haulage is, in this case, of a softer material, such as Teflon.
3.4. Ground clip
The correct connection of the ground clip is of extreme importance. The location of the corresponding cable is especially relevant in the welding process. A poorly fastened cable cannot provide a constant good electrical connection and could easily heat up, leading to a break in the circuit and consequent loss of arc. The ground clip contact area must be thoroughly clean and free from any substances that could prevent good contact, such as paint, varnish, oils...
4. Welding parameters
4.1. Filler materials
The cord or the wire carry out the function of the electrode during the welding process and proportions the necessary material to make the joining.
The employed wires usually have diameters of 0.6; 0.8; 1.0; 1.2;... and are delivered on a spool that is placed directly over the feeding systems. In order to achieve a uniform and smooth feeding of the wire, this should be wound up in perfectly straight layers and it is necessary that it is not taut during its use.
Often the wire cables have a coating of copper that improves the electric contact, the resistance to corrosion and diminishes the rubbing with the different supply systems and with the torch.
The filler material has to be similar in its chemical composition as the base metal.
When the diameter of the used wire is varied, the guiding tube should be changed. The contact tube and adjusting the rollers to the new wire size.
4.1.1. GASLESS welding
Existe un tipo de alambre denominado "hilo animado" o "hilo tubular" que permite el soldeo sin la necesidad de aportar gas de protección. Esto lo hace ideal para soldar en exteriores o en ambientes con grandes corrientes de aire. Para poder soldar con este tipo de alambre es necesario disponer de equipos que nos permitan invertir la polaridad.; antorcha al polo negativo (-) y pinza de masa al polo positivo (+).
4.2. Velocidad del hilo
There is a type of wire called “shielded wire” or “tubular wire”, which permits welding without the necessity of proportioning gas protection. This makes it ideal for welding outdoors or in surroundings with important air currents. In order to be able to weld with this type of wire, it is necessary to have equipment that lets us invert polarity; torch to the negative pole (-) and ground clip to the positive pole (+).
+ intensity = + velocity
- intensity = - velocity
4.3. Welding intensity
This parameter is selected in function of the material to be welded, the thickness of it and the wire diameter. The selected intensity will condition the wire velocity.
4.4. Protection gases
The fundamental objective of the protection gas is to protect the founded metal from contamination by the surrounding atmosphere. Many other factors affect the choosing of the gas protection. Some of these are: material to be welded, transference mode of the desired filler material, penetration and form of the cord, welding velocity and, of course, the price of the gas.
Generally speaking, the most commonly used gases are:
Material
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Protection gas
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Steel
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Argón 85% + CO2 15%5% + CO2 15%
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Stainless steel
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Aluminium
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Argón 100%
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The gas flow to be used will depend on the conditions under which we are working, but generally speaking, we can calculate it on the base of 10 times the diameter of the wire. Ex. Wire of 0.8mm x 10 = 8 l/min.
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