Advantages with MIG-MAG-welding
There are advantages and disadvantages to the different welding processes. The advantages of MIG-MAG welding are the following:

The method is economically good due to a high welding speed and because a long arc time can be maintained, while electrode replacement is avoided
The method makes it possible to rationally weld so-called difficult-to-weld materials
Welding can be performed in all positions
The arc and the welding site are fully visible
As a rule, there is little finishing of the weld

Disatvantages with MIG-MAG-welding
Some of the disadvantages of MIG-MAG welding are the following:

The method is very vulnerable to drafts from the ventilation system in the workshop, open doors and windows as well as fans on air-cooled welding systems
Risk of gross welding defects such as bonding defects and the like, if the welder is not trained, so that he / she has an in-depth knowledge of the process and its welding parameters
Larger costs for covering the welding site for outdoor work
Larger investment in welding equipment
Larger costs for maintenance of welding equipment

MIG-welding
By MIG-welding (Metal Inert Gas) the electrode is melted and an inert gas is used, eg. argon or helium that does not react with the molten bath.
MIG welding is welding in a noble gas atmosphere, ie. welding under a shielding gas that cannot react with other substances. It is i.a. argon and helium, of which argon is the most widely used in our latitudes. The process is usually called MIG welding, even when the noble gas is mixed with small amounts of O2, CO2, H2 or similar.

MAG-welding
By MAG-welding (Metal Active Gas) is used in addition to a melting electrode an active gas (most often CO2) this process is also known as CO2 welding. The MIG / MAG process originates from the USA, where it was introduced in 1950 for aluminum welding. Today it is mostly used for aluminum, stainless steel and copper.
MAG welding is welding in an atmosphere of reacting gases, or as it is also called, under the cover of an active gas. This means that the gas is split in the arc, and to a greater or lesser degree reacts with the molten bath. CO2 is mainly used as the active shielding gas, which is why the process is also known as CO2 welding.

TIG-welding
The term TIG is an abbreviation for Tungsten Inert Gas.
T - Tungsten is a metal that has a melting point above 3,300 ° C, ie. more than twice as high as the melting point of the metals normally welded.
IG - Inert Gas is the term for inert gas, ie. a gas which has the property of not being involved in chemical compounds with other substances.
This methods is often referred to in Germany WIG-welding, where W stands for tungsten (Wolfram). TIG-welding is the international and Danish standardized term for the welding method. According to DS / EN 24063, the welding method is indicated by no. 141.
The principle of TIG-welding
TIG welding is an electric arc welding method where the melt energy comes from an electric arc that burns between the workpiece and the tungsten electrode. The electrode, the arc and the molten bath are protected during welding against the harmful effects of atmospheric air by an inert shielding gas. The shielding gas is led by means of a gas cup down around the welding zone, where it displaces the atmospheric air. TIG welding differs from the other arc welding methods in that the electrode does not melt and is thus not consumed as an additive material. It is often necessary to use additive material.

The TIG arc
As mentioned, the melt energy of TIG welding comes from an arc that burns between the tungsten electrode and the welding workpiece. The feed can be done manually or mechanically. In direct current TIG welding, the tungsten electrode is usually connected to the negative pole and the welding workpiece to the positive pole. When the arc is turned on, according to the electron theory, a migration of negatively charged electrons and positively charged ions takes place. The electrons move from the negative pole to the positive pole, while the ions move in the opposite direction. In the arc, there is a collision between the electrons and the ions, and thereby heat energy is formed.

The electron current from the tip of the electrode takes place at a very high speed, and when they hit the weld, a lot of heat energy is generated. On the other hand, when the ion current hits the tip of the electrode, the same amount of heat energy is not generated. The electrode tip, which is connected to the negative pole, is affected by approx. 30% of the total heat generation, while the remaining 70% affects the welding workpiece that was connected to the positive pole.

Alternating current
Alternating current is characterised by the voltage changing polarity a certain number of times, usually 100 times per second. The electrode is positive for half a period and during the same half period the weld is negative. In the next half period, it is the other way around. Which causes the heat energy to be distributed with 50% on the electrode and 50% on the welding workpiece.
Application
TIG welding has a very wide range of applications due to its many advantages, the following can be mentioned:

• It provides a concentrated heating of the weld blank
• It keeps the molten bath effectively protected with inert shielding gas
• It can be independent of filler material
• The additive material does not have to be finely processed, as long as the alloy is in order
• There is no need for post-processing of the weld, as no slag or splashes are formed
• One can weld hard-to-reach weld seams

Areas of application
TIG welding is often used where there are high demands on the quality of the welding, such as in:

• Offshore industry
• Pharma industry
• The food industry
• The chemical industry

Aluminum welding
Aluminum differs from other metals in that the alumina formed on its surface has a melting point of approx. three times higher than the melting point of aluminum, which makes it very difficult to weld, as the oxide film must be broken before the aluminum. Therefore, AC welding is used when welding in aluminum.
When welding in aluminum, enormously high demands are placed on the cleanliness of the material. If the material is not completely clean, welding defects will occur.

Welding with alternating current is used for welding of:

• Aluminum and aluminum alloys
• Magnesium and magnesium alloys

TIG welding in aluminum
The tungsten electrode is here positive for one half period and negative in the next half period, which means that the heat energy is distributed with 50% on the tungsten electrode and 50% on the workpiece.

MIG welding in aluminum
MIG-welding in aluminum takes place in the same way as welding in stainless steel. The main difference is that, as in TIG welding, aluminum is welded with alternating current in order to be able to break through the oxide film.

Pipe wire welding
Pipe wire welding is a process in which the welding electrode is formed as a tube in which powder is filled. The purpose of this powder is to have an oxidation-protective effect and is of the same nature as the coating on the coated electrodes. The process can be performed with and without the use of shielding gas, and it has a high productivity.

Laser welding
In laser welding, the heating takes place using laser light; a shielding gas or vacuum is also used here. Laser welding has the great advantage that the heat source is very concentrated, which makes it possible to achieve a large penetration depth in relation to the amount of energy used and thereby e.g. achieve less throwing of the items. Depending on the laser used, the process is more or less suitable for position welding.

Welding parameters
The different welding processes can be optimised with regard to the process-related welding parameters. In the case of a shielding gas welding, the most important parameters are current, voltage and wire feed speed, while in a resistance welding it is current, voltage and compressive force. In a laser welding, the most important welding parameters are the applied power as well as the focus of the beam.

The different processes have different areas of application depending on e.g. the material to be welded, design of the weld, part numbers, dimensions, strength requirements, corrosion requirements, etc.

In particular, the heat exposure of the workpiece material is different; it has a great influence on the quality of the welding, as the surrounding material is affected by the heating. The heat affected zone is called HAZ (Heat Affected Zone). In this zone, the material has altered properties especially in terms of strength and corrosion. The impact is greatest close to the weld and decreases away from it.

The temperature differences in the workpiece can also give rise to thermal stresses that can result in distortions and deformations. This can be counteracted by preheating the items, heat treating them after welding or using slow cooling.

Classification and testing
Welds can be classified according to the amount and size of the defects that occur, eg crater cracks, long pores, inclusions or inadequate penetration. To check whether a weld meets the requirements of the specified class, it can be tested by non-destructive testing, eg X-ray examination, eddy current testing, ultrasound or by the penetration method.

Furthermore, destructive tests can be applied to test pieces that are subjected to the same welding procedure as the construction itself, after which they are cut through, prepared and inspected under a microscope. Destructive strength tests can also be performed by breaking welded samples by, for example, tensile testing or impact strength tests.

Physical simulations of welds can be performed with machines, where it is especially welding parameters and HAZ that are simulated and inspected. Numerical simulation of welds is used especially for optimising welding processes.