Welding technology is an important metal processing technology, and its degree of automation is increasing with the development of the era. MIG welding is a product of welding automation.
MIG welding, short for Metal Inert Gas Welding, is one of the commonly used arc welding methods at present. This welding method uses the burning arc between the continuously fed welding wire and the workpiece as a heat source, and the gas sprayed from the welding torch nozzle to protect the arc for welding.
It is suitable for welding low carbon steel, low alloy steel, stainless steel, non-ferrous metals and their alloys. MIG welding is divided into automatic and semi-automatic types.
Automatic MIG welding is suitable for welding regular longitudinal seams, circumferential seams and horizontal positions; semi-automatic MIG welding is mostly used for spot welding, short seam intermittent welding, and welding of heads, pipe joints, and reinforcement rings in aluminum containers.
I. Development and Practical Application of MIG Welding
1. Appearance and Application of MIG Welding
In recent years, the development of aerospace, transportation, marine engineering, and other industries has greatly promoted the development of welding technology.
Accompanied by a variety of products, structures, materials, and usage conditions, the demand for welding quality is getting higher and higher, and the amount of welding work is gradually increasing.
According to statistics, the amount of welding work in our country has reached the level of world welding powers.
Therefore, efficient welding methods that can improve welding production efficiency and welding quality and reduce the existence of welding defects have become an urgent requirement in actual production.
Currently, a large number of efficient welding methods and combinations of different welding processes have been applied to various production occasions, thereby improving welding production efficiency and reducing production costs.
Since the advent of the inverter arc welding machine in the 1980s, through continuous development and improvement, it has become the mainstream product of welding power sources. Before the 1990s, most boiler factories at home and abroad adopted multi-head (6-8 heads) submerged arc automatic welding.
In many years of actual production, it has been found that this submerged arc welding method has a fatal flaw, that is, submerged arc welding can only be welded from one side, and pipe welding will inevitably cause severe warping deformation.
The longer the length of the screen pipe, the greater the deformation, and it must be corrected through a laborious process. This not only increases production costs but also extends the production cycle.
Therefore, a more reasonable welding method must be sought. In the late 1980s, Mitsubishi Heavy Industries of Japan took the lead in developing a new welding method and welding equipment for double-sided pulse MAG automatic welding of membrane water-cooled wall screen pipes and successfully applied it to welding production.
This welding method is commonly known as the MPM method in Japan, characterized by multiple MAG welding heads welding from both sides of the screen pipe at the same time.
During the welding process, the welding deformation of the welds on the front and back sides cancels each other out. There is basically no bending deformation after the screen tube is welded. This is a significant technological breakthrough with significant economic benefits.
A few years later, Harbin Boiler Factory was the first to introduce this advanced technology and equipment from Mitsubishi, Japan, and successfully applied it to the welding production of boiler membrane wall screen pipes.
Since then, it has been gradually promoted and applied in major boiler factories in our country, and to date, more than ten MPM welding production lines are in normal operation.
MIG welding can be semi-automatic or fully automatic and has a wide range of applications. MIG welding can weld various materials, but in recent years, due to the more widespread use of gas-shielded welding with rich argon mixed gas for welding carbon steel and low-alloy steel, pure inert gas shielded welding is seldom used.
Therefore, Metal Inert Gas Welding is commonly used for welding aluminum, magnesium, copper, titanium and their alloys, and stainless steel.
Metal Inert Gas Welding can weld workpieces of various thicknesses, but in actual production, thinner plates are generally welded, such as thin plates with a thickness of less than 2mm, which have better welding effects with Metal Inert Gas Welding. Metal Inert Gas Welding can achieve intelligent control of all-position welding.
MAG welding, due to its oxidizing arc atmosphere, cannot be used for the welding of active metals (such as Al, Mg, Cu and their alloys). Metal Active Gas welding is widely used for welding carbon steel and some low-alloy steels, which can improve arc stability and welding efficiency.
Metal Active Gas welding has been widely used in industries such as automobile manufacturing, chemical machinery, construction machinery, mining machinery, and power station boilers.
2. Development Trends of MIG Welding
MIG welding is divided into semi-automatic and automatic. Automatic MIG welding is suitable for more regular longitudinal seams, circumferential seams, and horizontal position welding; semi-automatic MIG welding is mostly used for spot welding, short seam intermittent welding, and welding of weldments such as end caps, pipe joints, and reinforcement rings in aluminum containers.
With the expansion of MIG welding applications, it is difficult to meet the requirements with only Ar or He as the shielding gas. Therefore, a method of using a mixture composed of a small amount of active gas such as oxygen, carbon dioxide, etc., added to the inert gas as the shielding gas has been developed.
It is usually referred to as Metal Active Gas welding, abbreviated as MAG. In the production of welding structures, especially in the welding production of high alloy materials and non-ferrous metal and alloy materials, MIG welding occupies a very important position.
II. Basic Principles of MIG Welding
MIG welding is an arc welding method that uses inert gas as the shielding gas and welding wire as the molten pole electrode. This method usually uses argon or ammonia or their mixed gas as the protective gas.
The continuously fed welding wire serves both as the electrode and the filler metal. During the welding process, the welding wire is constantly melting and transitioning to the weld pool to form a weld seam.
III. Advantages and Disadvantages of MIG Welding
1. Advantages of MIG Welding
(1) Good welding quality:
Due to the use of inert gas as the shielding gas, the protective effect is good, the welding process is stable, deformation is small, and there is no spatter. When welding aluminum and aluminum alloys, direct current reverse polarity can be used, which has a good cathode breaking effect.
(2) High welding productivity:
Since the welding wire is used as the electrode, a large current density welding can be adopted, the parent metal melts deeply, the welding wire melts quickly, and when welding thick aluminum, copper, and their alloys, it has a higher productivity than tungsten inert gas welding.
Compared with manual arc welding, it can continuously feed the wire, save material processing time, the weld does not need to be deslagged, thus the production efficiency is higher.
(3) Wide application range:
Because inert gas is used as the shielding gas, it does not react with the molten pool metal, the protection effect is good, almost all metal materials can be welded, so the application range is wide.
However, due to the high cost and price of inert gas production, metal inert gas welding is mainly used for welding of non-ferrous metals and their alloys, stainless steel, and some alloy steels.
2. Disadvantages of MIG Welding
MIG welding has no deoxygenation and dehydrogenation function, so it is sensitive to oil and oxide on the parent material and welding wire, and it is easy to form defects, so the requirements for cleaning the surface of the welding material are particularly strict.
In addition, Metal Inert Gas Welding has poor wind resistance and is not suitable for outdoor welding. The welding equipment is also relatively complex, consisting of welding power supply, wire feeding mechanism, welding gun, control system, water and gas supply system, etc.
With the development of China’s economy, there are more and more mechanized and automated equipment. In terms of metal structures, the requirements for welding technology are also getting higher and higher, and the application of welding automation is also increasing.
MIG welding will also become more and more perfect, and its functions will be suitable for field operations. By perfecting the welding equipment, it can adapt to various working conditions.
Of course, no matter how it develops, it will ultimately not avoid the constraints of its shortcomings on construction.