Table of Contents
Introduction
Take a look around you, it looks like most of the things that are surrounding you are welded in some way. Look at the burglar bars, the door screens, the chairs you sit on, the vehicles and airplanes you board, bridges, railways, and many other things around you have a component of welding in them. How versatile welding is! Welding is a materials manufacturing branch that is used in almost every department of the manufacturing industry. One of the branches of materials technology that is mainly used in production industries is the joining and assembling of different parts to obtain sizes, make shapes, and shape complexity.
The process of joining can be categorized into four fundamental components which are: mechanical fastening, friction welding, adhesive bonding, and fusion welding. In this article, the process of welding will be explored with its different sub-processes and advantages and disadvantages. For someone who likes travelling a lot, welding would be a good career to explore, because welders travel a lot since welding is done everywhere, from machines that are used in the sea to those that are used in the outer space and anywhere on the land. We cannot discuss the great advantages of welding, without mentioning the good salaries earned by welders.
A highly skilled welder can earn a salary anywhere between $100000 and $200000 depending on where you are working (GoWelding). Furthermore, welding does not require a factory environment for it to be undertaken, it can be done anywhere, which means you can weld something at your backyard according to your specifications. It is also the cheapest method of joining materials in terms of fabrication costs and material usage (Groover, 2012).
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However, like any other skill, it needs to be acquired and a welding certificate is simple to get and it can be acquired within nine months (GoWelding). Therefore, as a materials science major, you can learn to be a highly skilled welder. Welding is mainly used when joining metallic materials. It is generally defined as a joining process where two or more parts are joined at their point of contact by the application of heat or pressure. Welding can be categorized as either fusion welding or friction welding. Fusion welding involves the joining of two materials in order to achieve the material properties of the parent material. Manufacturers make the decision to take one type of welding over the other after careful consideration of the costs, advantages, and disadvantages of different types of welding processes involved.
After all, making profits is what every career path is concerned about. The diagram below shows how a finished weld looks like. The parent metal may be referred to as the base metal, and the fusion line is a boundary that marks the fusion zone. The fusion zone and the heat-affected zone (HAZ) make up the completed weld mainly. The fusion zone is the section of the material that remains when the material has been welded. The heat- affected zone is the area of the material that has not melted during the welding but has changed its properties due to the exposure to great heat during the welding process and this zone is adjacent to the fusion zone. According to welding specialists, the intensity of heat sources of different welding processes can affect the HAZ in different ways.
This calls for a better knowledge, from the welder, of the effects of different heat intensities on the weld surface. According to the fabricator (2016), high heat intensity leads to a small HAZ because it applies heat on a small area and a low heat intensity causes a high HAZ because heat is applied on a large area. HAZ is the weakest point on a weld; therefore, a skilled materials manufacturer would try to minimize its area. Additionally, knowing other factors like the temperature at which the joined metals can be worked at, the speed at which the weld can be carried out, the depth of the metal to be welded, and the degree of thermal conductivity of the material may also improve the weld surface.
Fusion Welding
In the fusion welding processes, heat is used to melt the base metal and usually, the process is facilitated by the use of a filler metal. The fusion welding process can be classified into three classes which are gas welding, arc welding, and high energy beam welding. Each class has its own advantages and drawbacks in its application. The sources of heat for gas welding is a gas flame, that for arc welding is an electric arc, and that for a high energy beam welding is a high energy beam. Power density, which is a measure of how intense a heat source is, plays a vital role when these welding processes are used. The power density from a high energy beam is higher than that from that of an electric arc which in turn is higher than that from a gas flame.
Gas Welding
Oxyacetylene welding process falls under this class. Oxygen and a fuel gas are reacted to produce a flame that is used to melt the materials to be welded. The flame used can be classified as neutral, reducing, or oxidizing depending on the proportions of reactants used to produce the flame (Weld, 1998). The neutral flame is produced when equal proportions of oxygen and the fuel gas are mixed.
The reducing flame is produced when excess the fuel gas is used and the oxidizing flame is produced when excess oxygen is used. Some of the advantages of this process are the simplicity, portability, and inexpensiveness of the equipment used hence it can be used for general maintenance. However, its drawback is the process’s low power density which yields a large heat-affected zone, and this causes the material to be distorted.
Arc Welding
Arc welding is usually performed by a skilled welder who would be helped by a fitter whose job is to arrange the components prior to the welding. Therefore, using this welding process, the fitter does all the hard labour and the welder just comes in to apply his expertise. How exciting! This process can be further classified into shielded metal, metal, gas-tungsten, plasma, gas-metal, flux-cored, submerged arc welding, and electroslag welding.
Shielded metal arc Welding
This process melts and joins the metals by heating them with an arc produced between an electrode and a metal. It is sometimes called stick weldi…
Gas-Tungsten Arc Welding
In this process, a tungsten electrode is used in the same way as the electrode is used in the shielded metal. The electrode used is non-consumable. The process has different polarities (American Welding Society, 1978). One of the polarities is the direct-current electrode negative which is when the electrode is connected to the negative terminal of the power supply.
Another polarity is the direct-current electrode positive which is when the electrode is connected to the positive terminal of the power supply. One of the advantages of the process is its ability to weld thin sections due to the little heat input of the process. However, the electrode may be melted by excessive current and this can lead to the brittle tungsten being deposited on the material.
Plasma Arc Welding
In this process, a constricted arc is used to heat the metals so that they melt and join. The arc is established between a tungsten electrode and the metals. A high-frequency generator helps in the arc initiation. One of the advantages of the process is its full penetration which in turn accounts for high welding speeds. However, the disadvantage is the expensiveness of the equipment for polarity variation.
Gas-Metal Arc Welding
In this process, a filler wire is used as the electrode. Shielding gases are often used in this process. These shielding gases help in the transfer of stable metal droplets, one example is argon. The advantage of the process is its ability to allow for the fast welding of thick sections because of the high deposited rate associated with the process. However, the guns used may not access the corners due to their bulkiness.
Sub Merged Arc Welding
A consumable wire is used as an electrode in this process. The arc used will be shielded by a molten slag and a granular flux. The arc is submerged and hence invisible. The advantage is that the submergence of the arc minimizes heat losses to the surroundings. However, distortions can form on the material due to high heat input.
Electroslag Welding
This is a process where metals are melted and joined by heat from molten slag held between the metals. A filler wire electrode is continuously fed into the slag. The molten slag covers the weld pool and it moves up the metal as the welding progresses. The advantage of this welding process is its high deposition rates. However, the high heat input may reduce the quality of the weld.
High energy beam Welding
This is classified into electron beam welding and laser beam welding.
Electron beam Welding
Metals are melt and joined by heating them with an electron beam. The cathode used is an electronic filament which emits electrons upon heated to its temperature of thermionic emission. An electromagnetic coil is used to focus the electrons to the point to be welded. An advantage of this process is the full penetration even on thick joints which is effected by high power density. Furthermore, a very small heat-affected zone is produced from this process. However, the equipment used is very costly.
Laser beam Welding
The process melts and joins metals by heating them with a laser beam. A diode laser, a solid- state laser or a gas laser can produce the beam. Gas lasers may use gases like argon, helium, or carbon dioxide. Optical fibres may be used to guide the beam to the focusing optic which in turn focuses the beam to the workpiece surface. During the process, the metal will evaporate when heated to a certain intensity of the beam. The beam absorption is increased by the stabilization of the keyhole formed by the pressure from the vapour produced. The keyhole reflects the beam through an internal reflection process before the beam leaves the keyhole. The beam power and intensity influence the weld depth.
Due to various distortions of manual welding and attempts to increase productivity, various forms of automation have been developed (World Guru, 2019). For example, the interaction time of the laser beam is very small as compared to the human reaction time. Therefore the process must be automated because the human reaction time cannot keep up with the interaction time of the beam. Automatic welding can be effected when the equipment is able to perform the welding procedure without the intervention of a human operator (World Guru, 2019). A human operator may at times be needed to oversee the process. Industrial robots or other manipulators may be used to move the welding head in this automation process (World Guru, 2019).
The advantages of this process are that it can allow for narrow and deep welds at high welding speeds which produces small heat-affected zones with very little distortion of the material. The process can also be used in joining two metals of dissimilar sizes and properties. High- quality welds and low total thermal input can be added to the advantages. However, some of its drawbacks are the high reflectivity of the beam by the metal surface. Also, the equipment used is very costly and precise fitting and joint alignment is required for the weld to be undertaken properly.
Laser beam welding is still developing and hence there is a chance of having cheaper equipment and improvements on the process in the future (World Guru, 2019). Recent use of fibre optics in focusing the beam to the weld area has aided in the expansion of the use of the process in metallic elements. When the weld is complete, it possesses different parts as a result of the welding procedure.
Friction Stir Welding
In this process, a rotating tool is inserted into the metals to be joined and then traversed along the joint line. The tool serves to heat the workpiece, produce the joint and to contain the hot metal beneath the tool shoulder. The heat used is created by friction. The welded zone is divided into parent metal, heat affected zone, thermomechanically affected zone, and weld nugget. The parent metal refers to the not deformed part of the workpiece. The weld nugget is the zone previously occupied by the tool pin (Mishra & Mahoney, 2007).
Conclusion
In conclusion, welding is one of the fundamental components of material manufacturing and engineering in this day and age. It can be seen that almost every part of production has a component of welding within it. The make-up of all those fancy car bodies is effected by welding. Taking a materials science and engineering major would be an exciting thing for someone who wants to develop and produce some fancy shapes and structures within the industries.
References
- American Welding Society. (1978). Welding Handbook, Vol. 2, 7th edn. Miami, FL.
- Groover, M.P. (2013). Fundamentals of Modern Manufacturing. Materials, Processes, and Systems. 5th edn. Published by John Wiley & Sons.
- Kallee, S.W., Kell, J.M., Thomas, W.M., & Wiesner, C.S. (2005). Development and Implementation of Innovative Joining Processes in the Automotive-Industry. TWI Ltd. UK.
- Mishra, R.S., & Ma, Z.Y. (2005). Material Science Engineering. R, Vol 50
- Mishra, R.S., & Mahoney M.W. (2007). Centre for Friction Stir Processing. University of Missouri-Rolla, Rockwell Scientific Company.
- Shrijit G. (2017). Adhesive Bonding: Introduction, Joint Design, and Methods. Retrieved from http://www.yourarticlelibrary.com/welding/adhesive-bonding/adhesive-bonding-introduction-joint-design-and-methods/97604
- The fabricator. (2016). All you need to know about the heat-affected zone. Retrieved from https://www.thefabricator.com/thefabricator/article/shopmanagement/all-you-need-to-know-about-the-heat-affected-zone
- The GoWelding network. Facts about career in welding. Retrieved from http://gowelding.org/articles/facts-about-career-welding/
- TWI. What is Welding? – Definition, Processes, and Types of Welds. Retrieved from https://www.twi-global.com/technical-knowledge/faqs/what-is-welding
- Weld, J. (1998). Welding Workbook, Data Sheet 212a.
- Weld Guru (2019). Laser Welding (LBW): The Principles & Advantages.
- https://www.thefabricator.com/thefabricator/article/shopmanagement/all-you-need-to-know-about-the-heat-affected-zone
- http://gowelding.org/articles/facts-about-career-welding/
- https://www.twi-global.com/technical-knowledge/faqs/what-is-welding
