In the welding process, the mechanical effect arising from the pressing of the parts against each other plays the main role. Its main types are:


    1. Furnace welding: Parts heated up to the welding temperature are put on top of each other and beaten. Thus, their unification is achieved.


    2. Gas pressure source: Acetylene, propane, hydrogen or a similar flammable gas is burned with the help of oxygen, and the desired welding temperature is obtained. Both gases are taken from the tubes. Necessary adjustments are made on the torch according to the shape of the weld and the type and thickness of the surfaces to be welded. The temperature obtained in this way reaches 3000 degrees. The pressure required for the connection is inversely proportional to the welding temperature.


    3. Electric resistance welding: In this method, the effect of heating the conductor through which the electric current passes is utilized. This heating section depends on the specific resistance and current strength of the material.


    There are the following types according to the source type:


       a. Butt welding: The parts to be welded are taken between two jaws joined by the ends of the secondary winding of a transformer. As the current passes, the parts become hot. Connection is provided by applying pressure on the heated parts. This type of welding is mostly used for welding the ends of steel profiles to each other.


       b. Spot welding: Used for welding thin sheet metal sheets to each other. It is widely used in mass production in vehicle, aircraft and light structure constructions. Between the two copper rod electrodes connected between the ends of the transformer, the parts are welded to each other in the form of points under force and with the heat effect provided by the electric current. Electrodes are pressed mechanically, hydraulically and pneumatically to ensure good contact between the sheets.


       c. Seam welding: It is used if sealing is required in the welding connection in sheet constructions. For example, in the construction of tanks and fuel tanks, the metal parts are passed between the electrodes in the form of round spools that are cooled with water and continuous welding seam is achieved.


       D. Resistance welding of pipes: It is used in pipe production. After the material passes through the profile rolls and takes the form of a slit pipe, the joint is heated by direct current. The pipe passed between the pressure rollers is welded along the joint under pressure.


    4. induction welding: In this method, which is especially used in modern pipe manufacturing, the pipe is passed through a coil. With the induction currents generated by the coil, the pipe heats up and is welded from the joint while it passes between the pressure rollers.


    5. Termite welding: The welding ends of the parts are embedded in iron oxide aluminum powder and pressed together. When the mixture is ignited, a very strong exothermic chemical reaction begins. Once the reaction is initiated, it continues itself under the protective barium super oxide powder. The temperature of the resulting melt reaches 3000 degrees. After the welding ends are sufficiently heated, the welding connection is provided by pressing them together. It has been used for joining rails since time immemorial.


    6. Impulse welding: It is widely used for the welding of rotationally symmetrical ends of parts such as profiles, shafts, pipes. One of the pieces is kept fixed. The other is rotated and pressed to the fixed part in the axial direction. When the welding temperature arises from the heat arising from friction, the welding connection is provided by increasing the pressure.


    7. Supersonic welding: In this type of welding, a regional warming is provided in the welding area by making use of the very high energies of supersonic vibrations. The surfaces pressed together are obtained with a special device and welded with the help of the heat generated by the supersonic waves passed between the electrodes.

8. Blast welding: It is used for the welding of overlapping sheets. Hair surfaces are slammed against each other due to the explosion effect of an explosive substance. Welding is made with the help of the resulting heat and pressure.


    9. Cold pressure welding: It is mostly used in welding plastic materials. Although no heat is supplied, the required pressure is greater. By pressing the connection surfaces with force to each other, the material crystals in the pressure zone dissolve and regenerate the connection. It can be performed as a forehead, point or stitch.

B. Melting Sources

In these welds, no pressure is applied to the parts to be welded. The connection surfaces are melted and mixed with the heat effect applied, or the gap between the parts is filled with a filler material that is melted in its own way. Its main types are:

    1. Gas melting source: Also called oxy-acetylene source. Acetylene, which is used as a flammable gas, combines with oxygen in the torch and is burned. With the heat obtained, the welding surfaces of the pieces brought together and an electrode made of the same material are melted as a filler metal and a welding connection is provided. There is no force applied to the parts during welding. The welding temperature reached with the acetylene flame is 3200 degrees and it is sufficient for welding all metals except some special cases.


    2. Electric arc welding: By utilizing the heat effect of the generated electric arc, it is ensured that the welded area of ​​the material is melted. The electric arc is created between the electrode and the part or between the electrodes when double electrodes are used. The rod used as a filler in welding can serve as an electrode, and an independent rod can also be melted for this purpose. Since the temperature is very high in this type of welding, the welding must be protected from the atmospheric effect in order to prevent the metal from burning. It is divided into two groups as open or closed arc sources according to the form of protection and preventing the contact of the source with the atmosphere:


       a. Open arc welding:


         1) Arc welding with carbon electrode: In this type of welding, the arc is formed between the carbon electrode and the part (arc welding with one carbon electrode) or between two carbon electrodes (arc welding with two carbon electrodes). Direct current is used for the formation of the arc. In this type of welding, the welding material is usually melted in the form of a wire to fill the weld seam. Although the CO and CO2 gases prevent oxidation in the welding area due to the burning of the carbon electrode, the effect of the atmosphere cannot be completely prevented, so the welding quality is low.


         2) Arc welding with metal electrode: The arc is formed between the rod-shaped metal electrode and the part. The electrode melts due to the heat generated by the arc and fills the weld seam. The electrode is chosen in the properties of the material being welded. Electrodes are usually covered with a special mantle material to protect the source from atmospheric effects. During welding, this mantle melts and forms a layer on the molten source material, preventing the atmospheric effect. This type of welding is the most widely used welding method.


       b. Closed arc welding: Even if jacket metal electrodes are used with open arc welding, quality welding is not performed due to the effects of oxygen and nitrogen in the air on the weld seam. For this purpose, closed arc welding methods have been developed to cut off the contact of the weld seam with the atmosphere.


         1) Shielding gas welding: In this method, one of the hydrogen, argon, helium, carbon dioxide gases is continuously sent to the weld seam and the air is completely removed from the welding place. Although wire electrodes that melt with carbon dioxide are used in shielding gas welding, non-melting wolfram electrodes are used in other methods. Gas is sprayed from inside the electrode housing to the weld seam. If desired, a welding wire that melts in the welding process can be used as filler metal.


         2) Submerged arc welding: In this type of welding, welding is performed with a bare electrode under a special welding dust. Dust laid on the welding seam prevents contact with the atmosphere. The method can also be applied with automatic welding equipment. It is widely used in the manufacture of ships, pressure vessels and pipes in the all steel processing industry.


         3) Electron current source: Electron welding is made by making use of the high energy density of the electron beam obtained from electrons emitted from a cathode with a very low potential relative to the anode. Electrons emitted from the tungsten cathode pass through the circular anode and are focused with the help of an electromagnetic coil and sent to the part. It is possible to weld any metal (such as molybdenum, wolfram, titanium, alloy steels, etc.) up to 20 cm thickness with a very high temperature between 3,000-10,000 ° C at the focal point adjustable between 2 mm and 20 cm.  The method is used in cutting and drilling. However, the biggest drawback of this kind of welding is that the welding process has to be done in a vacuum chamber.