Welding is a process of joining two similar or dissimilar materials with the application of heat and also with or without the application of pressure and filter material. In the other cases the joining are also done with the help of nuts and bolts. Heat must be supplied in the form of electricity or gas torch. In this process gaps are formed, to fill these gaps filler materials are used.
Types of welding process:
Welding process are divided into two types they are
- Solid state welding
- Liquid state welding
Solid state welding
In the solid state welding the mechanical forces are applied on the materials. Later, the materials are deforms to the plastic condition. Due to the molecular interaction in the welding process bonds are formed.
Solid state welding process consists of
- Cold welding
- Diffusion welding
- Hot forge welding
Cold welding is a solid state of welding process. This process is done without the help of heating or fusion, where one can join the two work piece materials. Coming to the fusion welding there is no molten or liquid state presence to join the materials. Under vacuum condition the clean, flat and similar metal surfaces are strongly joined.
Diffusion welding is also solid state of welding process. In which two dissimilar materials are bonded together. Due to the diffusion the relocation of the atoms takes place in the joints because of the absorption gradients. The materials are to be put under pressure together at the high temperatures of nearly 50% to 70 % of the melting point.
Hot forge welding
Hot forge welding is also known as solid state welding process. The two work pieces are joined by applying high amount of temperatures and then beating them together. By using this process we can join the similar and dissimilar metals. Similar materials are welded by using the diffusion process and the dissimilar materials are welded by using the low melting temperatures. The temperature required for the hot forge welding is 50% to 90%.
Liquid state welding
In the liquid state welding process heat is supply to the base material, till the base material is converted to soft state. In this process filler materials are also supplied to the material. After completion of the welding process the cooling process starts then later the strong joint is formed. Liquid state welding is divided into four types they are
- Electrical welding
- Chemical welding
- Radiant welding
The electrical welding is divided in to three types they are
- Arc welding
- Resistance welding
- Induction welding
Arc welding is a fusion type of welding process. During the process arc is obtained between the work piece material and the electrode. The temperature that is produced by the electrode nearly ranges from 6000c to 7000c. The direct current and alternative current must be used in the welding process. In most of the cases direct current is preferable for welding. Arc welding is further divided into 5 types they are
Arc welding types:
- MIG welding
- TIG welding
- Plasma arc welding
- Shield metal arc welding
Resistance welding processes are also known as pressure welding process. In this process heavy current is passed between the metal and the electrode to join the work pieces. The pressure is applied through electrodes for the process. The current varies from 2 to 12 volts and the time varies from minutes to seconds.
Heat generate during the process is:
I = current in amperes
R = resistance
T = time during the flow of current
Induction welding is similar to the resistance welding. Electromagnetic induction is used in the welding process to heat the wok piece. Induction coil is placed in between the work pieces. As an alternative of induction current be passes in between the wok pieces. With the help of radio frequency the electric current is used to energize the induction coil to heat the work piece.
Chemical welding consists of two types they are Gas welding and thermochemical welding
Gas welding is defined as the process of joining metals at the ends, in which strong gas combustions are used to generate the high temperature and heat. The heat is applied along with the pressure, where the joints are to be made on the work pieces. The molten metal should be passes toward the edges to form joints. In some case filler materials are also used to fill the cavities that are present at edges. To get the strong joint, molten metal should be solidifying. Gas welding is also divided into three types they are
- Air acetylene welding
- Oxy acetylene welding
- Oxy hydrogen welding
Air acetylene welding
It is the combination of air and acetylene to produce heat for the process of welding process
Oxy-acetylene welding is used for welding the extensive range of alloys and metals. When the acetylene is mixed with the oxygen, at that instance high amount of heat and high temperature is produced. During the burning process carbon dioxide is produced, that helps in welding process to prevent oxidation of metals. At the time of processing it produces the high amount of temperature is 3200 C. The chemical reaction formed is
It is a mixture of oxygen and hydrogen gases to form oxy hydrogen for the welding process.
- Thermit welding
- Atomic welding
- Laser welding
- Electron beam welding
Welding defects take place because of wrong welding process, incorrect welding constraints, wrong combination of filler materials etc. Mainly the defects take place on the surface of the material or inside of the welding material. Cracks are the main defects that are not acceptable, whereas few defects are considered with certain limitations.
Welding defects are classified into 6 types they are
- Imperfect shapes
- Solid inclusion
- Lack of fusion
- Miscellaneous defects
The size of the crack must be macro or micro in size. We find the cracks on the boundary of the base or weld material. Cracks are further divided into three types they are Transversal or start cracks, longitudinal cracks and Cracks in the weld basin. When the local stresses exceed the tensile strength then cracking is occurred in the material. In the solidification process, the welding material shrink, in the process stresses is developed. Cracks are developed because of poor ductility present in the base material, arc travelling with high speed, carbon content and high sulphur.
In the welding process if the obtained shape is different from the actual shape, at that time one can observe the defect in the shape. The occurred shape is not acceptable for the process, as the welded joint shows poor strength.
Imperfect shapes are formed because of underfilling, excessive sag, undercut, undercutting, excessive reinforcement, overlap and linear misalignment.
Solid Inclusion is in the form of slag or non-metallic material captured with the weld material. It shows that the welding material is not able to drift on the external surface of the solidifying weld material. During the arc welding process flux must be in the form of granules. Granules react with the molten material to remove the impurities and oxides in the form of slag. Due to the low density of the removed impurities they float on the surface of the weld material. If the molten metals have the low temperature or high viscosity or rapidly cooling nature, at that case the slag must not release from the weld group, it leads to inclusion. Inclusion is stopped with the help of selecting proper grooves. During the process the slag is removed, that was present on the bead. Try to avoid too high and low currents at the case of welding process.
Lack of fusion
During welding process, incomplete fused sports are occurred so it is known as lack of fusion. In this process the base metal and weld metal does not forms a cohesive bond. The main reason for this defect is because of lack of preheat, unclean base metal, arc off seam, fast travel speed, step electrode angle and short arc gap.
During solidification small voids are present on the weld metals when the gases are captured. Voids are in the form of elongated holes or spherical holes. At the time of the welding process gases are generated from the coating substances or flux of the shielding gases or electrodes used. To avoid the porosity you need to clean the work piece to free of rust, oil, dust and grease. Different types of porosity are present they are
- Linear porosity
- Clustered porosity
- Uniformly Distributed porosity
- Worm porosity
Miscellaneous defects take place due to several arc strikes, chipping and grinding marks, spatter, tack weld defects, unremoved slag, misalignment of beads, oxidized surface these are some of the miscellaneous defects that was found during the welding process.
Advantages of welding:
- The welding equipment is not very high in range
- Portable welding tools are also available
- With the help welding we can join similar and dissimilar materials.
- Welding can be computerized
Disadvantages of welding:
- During the welding process it can produce harmful radiations, smokes and splatter.
- Skilled persons are required for the welding process
- The welded joint is not same as the parent metal.
- Stresses and bending of work pieces are takes place in the welding process.
- Before starting the process edge grinding is performed on the work piece
Application of Welding
- We can observe the welding process in industries and in constructions areas like pressure vessels, water pipelines, tankers, submarines, bridges, press frames, storages, water turbines, ships etc.
- Fabrication of fixtures, jigs, clamps, oil machinery, boilers, railway coaches and kitchen cabin etc.
- In the household equipment’s also the welding process is used.
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