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CONTINUOUS WIRE WELDING WITH OR WITHOUT GAS
First of all, continuous wire welding is possible without a protective gas cylinder, with a flux-cored wire (NO GAS or FLUX). The "gas" protection is replaced by the core inside the wire. This welding process is mainly used outdoors in windy conditions, or for do-it-yourself use, to avoid having to purchase gas cylinders and associated pressure reducers. However, flux-cored wire welding does not provide a very high aesthetic value and, above all, can't be used to weld very thin parts (0.6 or 0.8 mm). It is not used, for example, to repair metal plates in body shops, when the material is very thin and often with paint or other oxidizing agents. The bead must be tapped with a hammer and brushed to remove the slag that remains above. We can say that the aesthetic aspect is very similar to MMA electrode welding, with the important advantage that the continuous wire process is much faster.
WIRE WELDING: THE GENERATOR
The welding generator is a device used to supply the welding area with filler material, using a special torch, and to keep the electric arc between the welded piece and the fusible wire-electrode going. Unlike MMA and TIG welding generators, which have only one adjustment parameter (welding current), in the wire welding machine there are two devices, one that regulates the intensity of the electric arc (welding voltage) and the other that regulates the welding wire feed rate (welding current).
MIG WELDING: GAS
The shielding gases used in MIG MAG welding processes essentially fall into two categories: inert and active. The first category includes argon, helium, and argon-helium mixtures, while active gases are carbon dioxide and mixtures of argon with oxygen or carbon dioxide.
Argon (Ar) is an inert gas that is, however, suitable for almost all welding applications. The use of this gas in MIG wire welding provides good arc stability and easy ignition.
Helium (He) is a rare inert gas that is much more expensive than argon. Compared to argon, it has lower arc stability but greater penetration. It is mainly used to weld thick parts and materials with high thermal conductivity, such as copper and aluminum. Since helium, unlike argon, is lighter than air and therefore more volatile, you must use more of it to ensure the proper protection of the area that you are welding.
Carbon Dioxide (CO2) is an active gas that gives its name to MAG wire welding. The most common problem caused by this type of protection is causing excessive spatter and the formation of an unstable arc. However, maintaining a fairly short constant arc makes it possible to have good arc control. With CO2 protection, it is generally possible to obtain good penetration.
Active mixtures. It is often possible to use the qualities of the single gases, using a mixture of them as gas protection, such as Argon-Oxygen, Argon-Oxygen-CO2, Argon-CO2.
TYPES OF MIG MAG WELDING ARC
In the MIG wire welding machine, to transfer the metal filler from the wire-electrode (solid or flux cored) to the weld pool, you have to use a method that depends not only on the electrical welding parameters, but also on the diameter of the wire, the type of generator used, and the gas used. Depending on these parameters, droplet transfer can occur with:
Immersion transfer (short-arc)
Spray transfer (spray-arc)
Pulse or pulsed-arc transfer (pulsed-arc)
1. Immersion transfer (short-arc or short-circuit): The filler metal is transferred into the weld pool as droplets, creating continuous short circuits. This short-arc transfer is characterized by current intensities up to 200 A and the use of thin solid wires, from 0.6 mm to 1.2 mm, making it possible to weld thin parts in all positions. This is achieved with DC generators.
2. Spray transfer (spray-arc): With this method the droplets of filler material aren't transferred by contact with the weld pool but. By using high current, they are sprayed into the pool itself, creating a continuous flow of material. This can be obtained with DC generators with a high current, greater than 200 A, and when the wires are over 1 mm in diameter. It creates a very fluid weld pool with considerable penetration, suitable for flat welding especially on medium and large thickness parts.
3. Pulse or pulsed arc transfer: This process can be obtained only with pulsed current generators. The pulsations cause small droplets to detach, making it possible to obtain the characteristic of the spray arc even at low currents. The heat input, pool size and penetration are very similar to the spray arc mode. This procedure is widely used in materials such as aluminum or stainless steel, where the short arc procedure does not guarantee adequate results. This is a very special arc dedicated to a professional welding machine.
MIG MAG WELDING OF MATERIALS
1. Mild carbon steels: Applications range from the use of CO2 alone, to Ar-CO2 mixtures in various percentages (the most common is 80% Argon, 20% CO2). The higher the percentage of Argon present in the mixture, the better the characteristics and arc stability.
The welding characteristics are very good, especially with the short arc process, where you have weld pools that can be used in all positions.
2. Stainless steels: The shielding gas used must be composed of Ar + CO2 or Ar + O mixtures. The percentage of Argon must not, however, be less than 98% of the mixture to avoid strong oxidation of the chromium present in the base material. The filler material must be chosen based on the quality of the stainless steel that you want to weld.
3. Aluminum and its alloys: The shielding gas used is generally pure Argon. For flat welding, regardless of the thickness, the spray-arc and/or pulsed-arc technique are commonly used. The short-arc technique is used to weld thin parts in vertical and angled positions.
4. Other materials: The MIG MAG wire welding process is also used on materials such as nickel and its alloys, copper and its alloys. For copper welding on parts thicker than 5 mm, it is recommended to use the MIG process, while keeping in mind that the current intensity must be adjusted according to the welding position and the thickness of the joints.
Professional MIG MAG Welding Machine
At Tuttosaldatura.it we recommend particular MIG welding machine models with an integrated PFC device. These new generation machines allow very high current welding at full power, even in a domestic environment where only 3.5 kw are available. They also allow the use of long extension cords, even longer than 100 meters, and are fully protected for use with motor generators, which often do not guarantee a constant, stable power supply.
HOW THE GAS MIG WELDING MACHINE WORKS
The MIG welding machine, used mainly in the industrial sector, is increasingly in demand for home and DIY use. Compared to coated-electrode welding, the wire welding machine uses a wire coil that is pushed by a motor inside a torch until it reaches the part where it will be weld. When the wire closes the electrical circuit with the ground clamp, it bursts and releases its material in the form of countless drops of molten material, creating what is called the welding bead.
There are two main types of wire welding:
- no-gas flux-cored wire welding, which uses a special wire containing a material that, during fusion, protects the weld pool from oxygen and external oxidizing agents. In this case, it will not be possible to weld parts thinner than one and a half millimeters, and the bead must be brushed and cleaned to eliminate deposited slag.
- welding with solid wire and gaseous protection, which uses a wire that varies according to the material that you are going to weld, and a protective gas that allows the welded bead to be "finished" without having to brush or clean it. This type of welding is the same used in industrial applications and for bodywork repairs, and it allows you to weld very thin parts with a high efficiency. The aesthetics of the bead are far better than those of the no-gas flux-cored wire.
The operator will then have to figure out which procedure is best suited to his needs: use flux-cored wire, which is much more expensive than solid wire, but without having to purchase a gas cylinder, or equip the welding machine with gas to obtain an excellent bead finish and be able to weld even the thinnest parts down to 6 - 8 tenths of a millimeter.
HOW NO GAS WIRE WELDING MACHINE WORKS
No-gas wire welding is used to weld iron (mild steel) with a special flux-cored wire that does not require gas protection. Therefore, you don't need to use a gas cylinder to protect the weld bead.
The flux-cored wire is very similar to an MMA coated electrode and contains the material that, when melting, will protect the weld bead from the oxygen in the air and external agents. However, since it works like an MMA coated electrode, the operator must clean and brush the bead to remove the slag.
Besides the advantage of not needing to connect to a cylinder, the no-gas flux-cored wire is used for outdoor welding jobs, when the wind is blowing, which could cause issues to the gas protection in MIG MAG welding.
When purchasing a wire welding machine, it is important to check whether it is set up for welding with or without gas, because it is important to reverse the polarity when switching from one procedure to the other. When welding with flux cored wire, the torch is connected to the negative pole, and when welding with gas, on the other hand, you can usually invert the + and - terminals inside the coil holder or on the front of the welding machine.
However, there are also some negative aspects associated with the use of a no-gas flux cored wire welding machine: even if you don't have to clean the bead at the end of the process, keep in mind that with this wire you can't weld parts that are less than one and a half millimeters thick. The aesthetics of the bead is not the best, and there can often be spatter and pellets deposited near the weld bead. For faster and more aesthetically pleasing welding operations, it is generally recommended to use gaseous protection and therefore the Argon CO2 mixture when welding iron.
