What Is Welding?

Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature metal-joining techniques such as brazing and soldering, which do not melt the base metal. It is a fabrication process that involves the usage of heat, pressure, or both to fuse two parts.

In addition to melting the base metal, a filler material may also be added to the joint to form a pool of molten material called the weld pool, which cools to form a joint that can be stronger than the base material. Pressure may also be used in conjunction with heat or by itself to produce a weld. Welding also requires a form of shield to protect the filler metals or melted metals from being contaminated or oxidized. Many different energy sources can be used for welding, including a gas flame (chemical), an electric arc (electrical), a laser, an electron beam, friction, and ultrasound. While often an industrial process, welding may be performed in many different environments, including in open air, under water, and in outer space. Welding is a hazardous undertaking and precautions are required to avoid burns, electric shock, vision damage, inhalation of poisonous gases and fumes, and exposure to intense ultraviolet radiation.

Fundamentals of Welding

• Welding involves a high skill level and practical knowledge of subjects like physics, chemistry, and metallurgy.
• Welding is generally done on metals but is also used for fusing wood or thermoplastic parts.
• A completed joint is a weld joint or weldment.
• The parts fused are the parent material, while the material used to help form this weld joint is the filler material.
• Welding involves bonding the same type of material (metal and metal, or wood and wood) using heat welding, pressure welding, or both.
• Welders add metal to the welded joint to strengthen the weldment, while a shielding gas like carbon dioxide protects the joint from contamination through natural elements.
• Different metals react in different ways, depending on their physical, mechanical, and chemical properties.
• Heat can alter the strength, ductility, and malleability of metal. Welding can straighten out a warped piece of metal by applying adequate heat.
• Welding involves the heating and cooling of the metal – there is no other chemical reaction involved. However, the weld becomes weak if oxygen reacts with the molten metal. Using protective gases around the weld pool prevents oxygen and other contaminants from damaging the joint.
• Extreme heat can alter the crystalline structure and weaken any metal.

Benifits of Welding:

• The technique creates a permanent weld and is excellent for the fusion of two materials.
• Using the right filler metal ensures strength and durability, producing long-lasting weld joints.
• In terms of costs, this method is quite economical in terms of materials, fabrication, and equipment.
• The process is versatile and flexible – used indoors as well as outdoors.
• Welded joints look good, smooth, and polished in terms of appearance.
• One of the fastest methods in terms of the speed of fabrication.

Welding Types and Processes

The most popular types of welding processes include:

• Stick Welding (SMAW) - Shielded metal arc welding, more commonly referred to as stick welding, involves using welding rods or sticks. The stick electrodes consists of the filler material and flux which enable the welding process and protect the weld. Used across construction, shipbuilding, field repair, mining, manufacturing, and aerospace, this type of welding is affordable.
• Gas Metal Arc Welding (GMAW) - Also called metal inert gas (MIG) welding, the gas metal arc welding process uses a welding gun through which an electrode wire passes. The result is an electric arc that produces the heat required for welding. It also creates a shielding gas that protects the weld.
• Flux-Cored Arc Welding (FCAW) - Just like MIG welding, flux-cored arc welding is great for outdoor welding work and general repairs. This technique finds its application in industrial welding, manufacturing, pipeline repairs, shipbuilding, and manufacturing. The difference between MIG and FCAW is that the latter uses a tubular filler wire that contains the flux.
• Tungsten Inert Gas Welding (TIG Welding) - This particular type of welding uses a non-consumable electrode of tungsten to produce the arc. Tungsten inert gas (TIG) welding is among the most popular types of welding, TIG welding creates a clean, smooth, and superior quality weld. Industries like art, automotive, and aerospace use gas tungsten arc welding.
• Submerged Arc Welding (SAW) - Submerged arc welding is a welding method that uses flux but is different from FCAW because the process happens under a blanket of granular flux. This is one of the safest types of welding because it creates lesser welding fumes and ultraviolet light. SAW is the preferred welding technique in vessel construction, industrial manufacturing, and structural construction.
• Oxy-fuel welding - Oxy-fuel welding (oxy welding or gas welding) uses fuel gases like acetylene or liquid fuels like gasoline and oxygen to weld metals. In oxy-fuel welding, a welding torch is used to weld metals. Welding metal results when two pieces are heated to a temperature that produces a shared pool of molten metal. The molten pool is generally supplied with additional metal called filler. Filler material selection depends upon the metals to be welded.
• Plasma Arc Welding (PAW) - Plasma arc welding is an arc welding process in which the electric arc is formed between an electrode and the workpiece. The electrode, usually made of sintered tungsten, is positioned within the body of the torch, hence, the plasma arc is separated from the shielding gas envelope. The plasma is then forced through a fine-bore copper nozzle which constricts the arc and the plasma exits the orifice at high velocities approaching the speed of sound and a temperature approaching 28,000 °C or higher.
• Electroslag Welding (ESW) - Electroslag welding is a highly productive, single pass welding process for thick materials in a vertical or close to vertical position. An electric arc is initially struck by wire which is fed into the desired weld location and then flux is added. Additional flux is added until the molten slag, reaching the tip of the electrode, extinguishes the arc. The wire is then continuously fed through a consumable guide tube into the surfaces of the metal workpieces and the filler metal are then melted using the electrical resistance of the molten slag to cause coalescence. The wire and tube then move up along the workpiece while a copper retaining shoe is used to keep the weld between the plates that are being welded. Electroslag welding is used mainly to join low carbon steel plates and/or sections that are very thick.
• Electrogas Welding (EGW) - Electrogas welding is a continuous vertical position arc welding process in which an arc is struck between a consumable electrode and the workpiece. A shielding gas is sometimes used, but pressure is not applied, and additionally, the arc remains struck throughout the welding process. It is used to make square-groove welds for butt and t-joints, especially in the shipbuilding industry and in the construction of storage tanks.
• Atomic Hydrogen Welding (AHW) - Atomic hydrogen welding is an arc welding process that uses an arc between two tungsten electrodes in a shielding atmosphere of hydrogen. The electric arc efficiently breaks up the hydrogen molecules, which later recombine with tremendous release of heat, reaching temperatures from 3400 to 4000 °C. The heat produced by this torch is sufficient to weld tungsten, the most refractory metal. The presence of hydrogen also acts as a shielding gas, preventing oxidation and contamination by carbon, nitrogen or oxygen.
• Carbon Arc Welding (CAW) - Carbon arc welding is a process which produces coalescence of metals by heating them with an arc between a non-consumable carbon (graphite) electrode and the work-piece. The purpose of arc welding is to form a bond between separate metals. In carbon-arc welding a carbon electrode is used to produce an electric arc between the electrode and the materials being bonded. It is not used for many applications today, having been replaced by twin-carbon-arc welding and other variations.
• Electron Beam Welding (EBW) - Electron beam welding is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined. The workpieces melt and flow together as the kinetic energy of the electrons is transformed into heat upon impact. This process is mostly performed under vacuum conditions to prevent dissipation of the electron beam.
• Resistance Spot Welding - Spot welding is a type of electric resistance welding used to weld various sheet metal products, through a process in which contacting metal surface points are joined by the heat obtained from resistance to electric current. The process uses two shaped copper alloy electrodes to concentrate welding current into a small "spot" and to simultaneously clamp the sheets together. Work-pieces are held together under pressure exerted by electrodes. Forcing a large current through the spot will melt the metal and form the weld. That permits the welding to occur without excessive heating of the remainder of the sheet.
• Laser Beam Welding (LBW) - Laser beam welding is a welding technique used to join pieces of metal or thermoplastics through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume applications using automation, as in the automotive industry. It is based on keyhole or penetration mode welding. It is a versatile process, capable of welding carbon steels, HSLA steels, stainless steel, aluminum, and titanium.
• Hyperbaric Welding - This is a process called hyperbaric welding is one that welders use underwater. The wet welding technique utilizes stick welding, where the flux produces bubbles that act as a shield to prevent the welder from being electrocuted.

Some alternative resistance welding methods include seam welding, butt welding, flash welding, projection welding, and upset welding.

Some other niche solid-state welding processes which do not involve the melting of the materials being joined include friction welding (including friction stir welding and friction stir spot welding), magnetic pulse welding, co-extrusion welding, ultrasonic welding, cold welding, diffusion bonding, exothermic welding, high frequency welding, hot pressure welding, induction welding, and roll bonding.

Apart from these, various plastic welding processes, braze welding or brazing, solvent welding, Forge welding, X-ray welding, explosion welding, and vibrations are some of the other rather extreme welding processes used for fusing metals and other materials.

Welding Electrodes

A welding electrode is a metal wire utilised in the welding process through which current is passed. Welding electrodes may made out of materials with a similar composition to the metal being welded along with additional materials to help the welding process or of an entirely different material when it is not being consumed. Welding electrodes are essential, and it is important that a welder knows which type to use for different jobs.

In arc welding, an electrode is used to conduct current through a workpiece to fuse two pieces together. Depending upon the process, the electrode is either consumable, in the case of gas metal arc welding or shielded metal arc welding, or non-consumable, such as in gas tungsten arc welding. The consumable electrodes used for stick welding are called stick electrodes which include heavy-coated electrodes, shielded arc electrodes, and light coated electrodes. Non-consumable electrodes do not melt during the welding process. For a direct current system, the weld rod or stick may be a cathode for a filling type weld or an anode for other welding processes. For an alternating current arc welder, the welding electrode would not be considered an anode or cathode.

A variety of factors that go into choosing the right electrode for each project, generally:

• SMAW or stick electrodes are consumable, meaning they become part of the weld and are also referred to as a filler electrode or welding rod.
• TIG tungsten electrodes are non-consumable as they do not melt and become part of the weld, requiring the use of a welding rod.
• TIG filler rods are an optional filler material used to fuse two pieces of stock together as a composite.
• The MIG welding electrode is a continuously fed wire referred to as MIG wire.

Welding Joints

A welding joint is a point or edge where two or more pieces of metal or plastic are joined together. They are formed by welding two or more workpieces, metal or plastic, according to a particular geometry. These various joint configurations may have various configurations at the joint where actual welding can occur.

There are five types of joints referred to by the American Welding Society, and depending on what kind of joint configuration welders are aiming for, there are various types of welding joints:

• Butt joint - A versatile and common welding joint, where you place two metal pieces together in the same plane, welding the side of each piece.
• Tee joint - This joint features two pieces intersecting at a 90-degree angle, which forms a T shape. You can also create the joint by welding a tube or pipe onto the base metal.
• Corner joint - As the name suggests, a corner joint meets in the corner, forming an L shape.
• Lap joint - Used for sheet metal, this joint features two pieces of the metal placed on top of each other to create the lap joint.
• Edge joint - Known to withstand force and pressure better than any other joint, the edge joint involves placing metal surfaces together to ensure even edges.

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