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Welding - Introduction
Welding is the process by which two pieces of metal can be joined together. The process of welding doesn't merely bond the two pieces together as in brazing and soldering, but, through the use of extreme heat and sometimes the addition of other metals or gases, causes the metalic structures of the two pieces to join together and become one. There are a number of different welding methods, including spot welding, metal inert gas (MIG), and tungsten inert gas, which are forms of gas metal arc welding, arc welding, and gas welding, to name a few. Welding can even be done underwater.
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A weld joint must be designed to withstand the forces to which it is expected to be subjected to during its service life. This means that the design of the joint is determined by the type and magnitude of the load that is expected to act on the weld. Certain types of welding joints are designed to withstand extreme shear loads, while others are designed to withstand extreme torsional loads. Types of joints used for welding are butt, lap, corner, T, and edge.
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The type of joint to be created and the type of material to be used, among other considerations, will determine the type of welding process that will be used to complete the project. All welding processes can be broken down into the two following categories:
Pressure welding is a process in which external pressure is applied to produce welded joints either at temperatures below the melting point, which is solid state welding, or at a temperature above the melting point, which is fusion state welding. The atoms are moved together to a distance that is equal to or less than the equilibrium inter atomic separation distance. This type of welding process requires the two pieces being joined to be extremely clean and especially free of oxides and non metallic films which must be removed from the surfaces of the metals by wire brush, so as to ensure the strongest welded joint possible. Pressure welding techniques are used primarily on metals that are highly ductile or whose ductility increases with increasing temperatures. Types of commonly used pressure welding processes in industrial applications are:
- Cold pressure welding is used for joining sheets, wires and electric components.
- Explosive welding is used when joints of dissimilar metals are to be welded.
- Ultrasonic welding, when thin sheets are to be joined.
- Percussion welding is utilized for joining dissimilar metals.
- Friction welding is used when similar or dissimilar metals are to be joined.
- Induction welding is used for welding pipes
- Inertial welding is for welding of high strength alloys.
Fusion welding produces welded joints by localized heating of the edges of the base metals, above their melting temperature. A filler metal may or may not be used, and no external pressure is required. Inert gases may or may not be used to enhance the quality of the weld created. The welded joint is achieved after solidification of the fused weld pool. Metals to be joined must possess some degree of mutual solubility in solid state. Metals that are completely soluble in the solid state, exhibit the highest degree of weld ability, and metals with no solubility in the solid state, are not weld able, for which an intermediate soluble metal is used.
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The Welding Techniques Most Commonly Used
Most forms of pressure welding are highly specialized and aren’t used outside of a few industries. However, fusion welding processes, such as gas welding, arc welding, and gas metal arc welding are used in a large number of industries. Gas welding is a process by which the two pieces of metal are locally heated to beyond their melting point, at which time they effectively become one piece of metal. This can be done with or without an alloy rod. Metal inert gas and tungsten inert gas welding are examples of gas metal arc welding processes. Arc welding uses a metal welding rod that is melted to help form the welded joint. The arc types of welding all require electricity at relatively high voltage and current. The gas metal arc types also use an inert or active gas to create a barrier between the weld and the atmosphere, enhancing the quality and strength of the joint.
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All welders need to respect the job and the equipment being used. The following is a list of safety equipment and precautions
- Wear welding gloves
- Wear eye protection-For arc-type welding, a much darker lens is required than for gas welding.
- Keep a suitable Class ABC fire extinguisher nearby while welding.
- Keep the work area clean and free of flammables and obstructions.
- Welding helmet and gloves pictures provided by author. All rights reserved.
- Image: Wikimedia Commons, Underwater Welding, Spangineer
- Image: Wikimedia Commons, Miller Spot Welder-Triddle, Saperaud
- The author has over 30 years of experience using welding in a variety of trades from auto repair and restoration to residential and commercial construction.
- Image: Wikimedia Commons, Arc Welding, Jorgebarrios
- Image: Wikimedia Commons, SMAW Welding, Spangineer