Briefly about welding and its main types

 

Briefly about welding and its main types

Welding is a technological process of obtaining an integral connection of materials due to the formation of an atomic bond between the parts being welded when they are heated, or plastic deformation, or the combined action of both

 All types of portable welding machine can be divided into three categories: fusion welding, pressure welding and therm mechanical welding.

Melting welding refers to the types of welding performed by melting without applied pressure. Its essence consists in the fact that the metal along the edges of the welded parts is melted under the influence of the heat of the heating source. The source of heating can be an electric arc, a gas flame, plasma, etc. In all types of fusion welding, the resulting liquid metal of one edge is combined and mixed with the liquid metal of the other edge, creating a total volume of liquid metal, which is called a welding bath. After solidification of the metal of the welding bath, a welding seam is obtained.

Thermo mechanical welding uses thermal energy and pressure. The combination of the connected parts into a monolithic whole is carried out by applying mechanical loads, and the heating of the work pieces provides the necessary plasticity of the material.

Pressure welding refers to operations carried out when mechanical energy is applied in the form of pressure. As a result, the metal is deformed and begins to flow, like a liquid. Only plastic metals are well welded by pressure welding: copper, aluminum, lead and others. Also, such welding is called cold welding.

 Next, we will consider the most common types of welding – this is welding with a coated electrode, welding with wire and welding with tungsten electrodes in argon.

 Manual arc welding with piece electrodes with a coating. MMA.

 The electrode has the form of a rod with a diameter of 1.5-10 mm, fixed in a manual electrode holder. When the electrode touches the metal part to be welded, the current circuit is closed, and the end of the electrode is heated. If then the electrode is removed 3-5 mm from the part, then an arc discharge is established, due to which the current is further maintained. Intense local heating causes the base metal (the metal of the part) to melt near the discharge arc. The end of the electrode is also melted, and the metal of the electrode is poured into the molten "welding bath" of the base metal. The welder, making sure that the arc gap does not change, leads the electrode along the joined edges of the welded parts. During the passage of the electrode, a molten welding bath is formed from the base metal and the metal of the electrode, which then immediately solidifies. As a result of a single passage of the arc along the welding contour, a welding roller is formed.

The described welding method is quite versatile and is used for welding soft and alloy steels, cast iron, stainless steels and in some cases non-ferrous metals. MMA is characterized by simplicity, reliability, high efficiency, quality, lack of gas cylinders, Among the disadvantages it is worth noting a rather rough result and low productivity.

MMA welding can be a choice for both a professional worker and a beginner. It is widely used in the construction and installation of metal structures, in various areas of heavy industry. This can be the choice of a locksmith's workshop for the manufacture of metal doors, a machine-building plant or an ordinary summer resident who decided to make grilles for basement window openings with his own hands.

 Semi-automatic welding with an electrode wire in a protective gas environment. MIG/MAG.

 Welding is separated in an atmosphere of an inert gas, for example argon, (MIG) and in an atmosphere of an active gas, for example carbon dioxide, (MAG). A metal wire is used as an electrode, to which a current is supplied through a special device (a conductive tip). The electric arc melts the wire, and to ensure a constant arc length, the wire is fed automatically by the wire feeder. Protective gases (argon, helium, carbon dioxide and their mixtures) supplied from the welding head together with the electrode wire are used to protect against the atmosphere. It should be noted that carbon dioxide is an active gas — at high temperatures, it dissociates with the release of oxygen. The released oxygen oxidizes the metal. In this regard, it is necessary to introduce de oxidizers (such as manganese and silicon) into the welding wire. Another consequence of the influence of oxygen, also associated with oxidation, is a sharp decrease in surface tension, which leads, among other things, to a more intense splashing of metal than when welding in argon or helium.

This method of welding is characterized by high productivity and a small amount of smoke, the disadvantages include the inaccuracy of the seam, the presence of a cylinder and limited use in the open air.

This method has become widely used in European and North American countries. It allows you to work with low-alloy and high-alloy steels, with many types of cast iron, aluminum, copper, nickel, manganese and their alloys, to combine different types of metals.

 Manual welding with non-melting tungsten electrodes in a protective gas environment. TIG.

 This method differs from the previous ones in that it uses a short non-melting tungsten electrode. In this process, the weld is formed only from the metal of the connected parts, or with the addition of an additive, which uses metal rods and strips. The presence of inert gases or their mixtures in the welding zone protects the weld metal from the harmful effects of air components and maintains the stability of the electric arc. Such welding can take place using alternating and direct current. This type of welding is characterized by a neat weld, the absence of splashes, welding of parts of small thickness. Among the disadvantages of the method: high requirements for the operator's experience, low productivity, the presence of a gas cylinder

TIG welding is used when it is necessary to obtain critical seams that can withstand high loads and have an acceptable aesthetic appearance.

This can be welding of gas and oil pipelines, high-pressure vessels, items for the food industry, microchips in the electrical industry.

It is indispensable when working with thin-walled metal structures and sheet metal (up to 6 mm), with stainless, alloy, carbon steel, copper, titanium, magnesium.

 For welding by any of the above methods, the welder must have a special shield with glass light filters on his head to protect the face, head and neck from welding splashes, and the eyes from blinding light. In addition, special gloves made of heat-insulating and non-flammable material with leggings, as well as an apron are required.