What is the use of welding?
Welding is a fabrication or sculptural 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.
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Welding is an operation whereby two or more parts are united by means of heat or pressure or both. It is usually used on metals and thermoplastics but can also be used on wood.
Some materials require the use of specific processes and techniques. A number is considered 'unweldable,' a term not usually found in dictionaries but useful and descriptive in engineering.
The parts that are joined are known as the parent material. The material added to help form the join is called filler or consumable. The form of these materials may see them referred to as parent plate or pipe, filler wire, consumable electrode (for arc welding), etc.
Consumables are usually chosen to be similar in composition to the parent material, thus forming a homogenous weld. Still, there are occasions, such as when welding brittle cast irons, when a filler with a very different composition and, therefore, properties are used. These welds are called heterogeneous.
What are the different types of welding, and what are they used for in the industry?
MIG welding is one of the more natural types of welding for beginners to learn. MIG welding is actually two different types of welding. The first use bare wire and the second flux core. Bare wire MIG welding can be used to join thin pieces of metal together. Flux core MIG welding can be used outdoors because it does not require a flow meter or gas supply. MIG welding is usually the welding of choice for DIY enthusiasts and hobby welders who don't have the money to spend on expensive equipment.
Stick welding, also known as Arc welding, is doing it the old fashioned way. Stick welding is a bit harder to master than MIG welding, but you can pick up a stick welding equipment for very little if you want to have a go at home. Stick welding uses a stick electrode welding rod.
TIG welding is extremely versatile, but it is also one of the more difficult welding techniques to learn and Lincoln Electric TIG welders are skilled individuals. Two hands are needed for TIG welding. One hand feeds the rod while the other holds a TIG torch. This torch creates the heat and arc, which are used for welding most conventional metals, including aluminium, steel, nickel alloys, copper alloys, cobalt and titanium.
Plasma Arc Welding
Plasma arc welding is a precision technique and is commonly used in aerospace applications where the metal thickness is 0.015 of an inch. One example of such an application would be on an engine blade or an air seal. Plasma arc welding is very similar in technique to TIG welding, but the electrode is recessed, and the ionizing gases inside the arc are used to create heat.
Electron Beam and Laser Welding
Electron beam and laser welding are extremely precise, high energy welding techniques.
In electron-beam welding, the workpiece is bombarded with a dense stream of high-velocity electrons. The energy of these electrons is converted to heat upon impact. A beam-focusing device is included, and the workpiece is usually placed in an evacuated chamber to allow uninterrupted electron travel. Heating is so intense that the beam almost instantaneously vaporizes a hole through the joint. Extremely narrow deep-penetration welds can be produced using very high voltages—up to 150 kilovolts. Workpieces are positioned accurately by an automatic traverse device; for example, a weld in material 13 mm (0.5 inches) thick would only be 1 mm (0.04 inch) wide. Typical welding speeds are 125 to 250 cm (50 to 100 inches) per minute.
Gas welding is rarely used anymore and has been largely superseded by TIG welding. Gas welding kits require oxygen and acetylene and are very portable. They are still sometimes used to weld bits of car exhaust back together.
There is currently a huge shortage of skilled welders in the US and the rest of the world, so for young people who do decide to take up a career as a welding technician, the job prospects are good.
How Does Welding Work?
As opposed to brazing and soldering, which do not melt the base metal, welding is a high heat process which melts the base material. Typically with the addition of a filler material.
The high heat causes a weld pool of molten material which cools to form the join, which can be stronger than the parent metal. Pressure can also be used to produce a weld, either alongside the heat or by itself.
It can also use a shielding gas to protect the melted and filler metals from becoming contaminated or oxidized.
Plastics welding also uses heat to join the materials (although not in the case of solvent welding) and is achieved in three stages.
Firstly, the surfaces are prepared before heat and pressure are applied and, finally, the materials are allowed to cool to create fusion. Joining methods for plastics can be separated into external or internal heating methods, depending on the exact process used.
Wood welding uses heat generated from friction to join the materials. The materials to be joined are subjected to a great deal of pressure before a linear friction movement creates heat to bond the workpieces together.
This is a fast process which allows the wood to be joined without adhesives or nails in a matter of seconds.
What is a weld joint?
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.
What are the common joint configurations?
A connection between the ends or edges of two parts making an angle to one another of 135-180° inclusive in the region of the joint.
A connection between the end or edge of one part and the face of the other part, the parts are making an angle to one another of more than five up to and including 90° in the region of the joint.
A connection between the ends or edges of two parts making an angle to one another of more than 30 but less than 135° in the region of the joint.
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A connection between the edges of two parts making an angle to one another of 0 to 30° inclusive in the region of the joint.
A connection in which two flat plates or two bars are welded to another flat plate at right angles and on the same axis.
A connection between two overlapping parts making an angle to one another of 0-5° inclusive in the region of the weld or welds.
What are the types of welding joints?
Welds Based on Configuration
The joint between two overlapping components made by depositing a fillet weld around the periphery of a hole in one component so as to join it to the surface of the other component exposed through the hole.
Weld is made by filling a hole in one component of a workpiece with filler metal so as to join it to the surface of an overlapping component exposed through the hole (the hole can be circular or oval).
Based on Penetration
Full penetration weld
A welded joint where the weld metal fully penetrates the joint with complete root fusion. In the US, the preferred term is complete joint penetration weld (CJP, see AWS D1.1).
Partial penetration weld
Weld in which the fusion penetration is intentionally less than full penetration. In the US, the preferred term is partial joint penetration weld (PJP).
Welds Based on Accessibility
Metal to be joined or surfaced by welding, braze welding or brazing.
Metal added during welding, braze welding, brazing or surfacing.
All metal melted during the making of a weld and retained in the weld.
Heat Affected Zone (HAZ)
The part of the parent metal metallurgically affected by the weld or thermal cutting heat, but not melted.
The boundary between the weld metal and the HAZ in a fusion weld. This is a non-standard term for weld junction.
A zone containing the weld metal and the HAZ.
The surface of a fusion weld exposed on the side from which the weld has been made.
Zone on the side of the first run furthest from the welder.
The boundary between a weld face and the parent metal or between runs. This is a very important feature of a weld since toes are points of high-stress concentration, and often they are initiation points for different types of cracks (e.g. fatigue cracks, cold cracks).
In order to reduce the stress concentration, toes must blend smoothly into the parent metal surface.
What is excess weld metal?
Weld metal lying outside the plane joining the toes. Other non-standard terms for this feature: reinforcement, overfill.
Note: the term reinforcement, although commonly used, is inappropriate because any excess weld metal over and above the surface of the parent metal does not make the joint stronger.
In fact, the thickness considered when designing a welded component is the design throat thickness, which does not include the excess weld metal.
What are the welding processes?
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 interatomic 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 elasticity 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.
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Fusion welding produces welded joints by localized heating of the edges of the base metals, above their melting temperature. 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 a solid-state. Metals that are completely soluble in the solid-state exhibit the highest degree of weldability, and metals with no solubility in the solid-state, are not weldable, for which an intermediate soluble metal is used.
What are the different types of welding methods, and what are they used for?
There are a variety of different processes with their own techniques and applications for industry; these include:
This category includes a number of common manuals, semi-automatic and automatic processes. These include inert metal gas (MIG) welding, stick welding, inert tungsten gas (TIG) welding, gas welding, active metal gas (MAG) welding, flux-cored arc welding (FCAW), gas metal arc welding (GMAW), submerged arc welding (SAW), shielded metal arc welding (SMAW) and plasma arc welding.
These techniques usually use filler material and are primarily used for joining metals including stainless steel, aluminium, nickel and copper alloys, cobalt and titanium. Arc welding processes are widely used across industries such as oil and gas, power, aerospace, automotive, and more.
Shielded metal-arc welding accounts for the largest total volume of welding today. In this process, an electric arc is struck between the metallic electrode and the workpiece. Tiny globules of molten metal are transferred from the metal electrode to the weld joint. Since arc welding can be done with either alternating or direct current, some welding units accommodate both for wider application. A holder or clamping device with an insulated handle is used to conduct the welding current to the electrode. A return circuit to the power source is made by means of a clamp to the workpiece.
Gas-shielded arc welding, in which the arc is shielded from the air by an inert gas such as argon or helium, has become increasingly important because it can deposit more material at higher efficiency and can be readily automated. The tungsten electrode version finds its major applications in highly alloyed sheet materials. Either direct or alternating current is used, and filler metal is added either hot or cold into the arc. Consumable electrode gas-metal arc welding with a carbon dioxide shielding gas is widely used for steel welding. Two processes are known as spray arc, and a short-circuiting arc is utilized. The metal transfer is rapid, and the gas protection ensures a tough weld deposit.
Submerged arc welding is similar to the above except that the gas shield is replaced with a granulated mineral material as a flux, which is mounded around the electrode so that no arc is visible.
Plasma welding is an arc process in which a hot plasma is the source of heat. It has some similarity to gas-shielded tungsten-arc welding, the main advantages being greater energy concentration, improved arc stability, and easier operator control. Better arc stability means less sensitivity to joint alignment and arc length variation. In most plasma welding equipment, a secondary arc must first be struck to create an ionized gas stream and permit the main arc to be started. This secondary arc may utilize either a high-frequency or a direct contact start. Water cooling is used because of the high energies forced through a small orifice. The process is amenable to mechanization, and rapid production rates are possible.
This original fusion technique dates from the earliest uses of iron. The process was first employed to make small pieces of iron into larger useful pieces by joining them. The parts to be joined were first shaped, then heated to welding temperature in a forge and finally hammered or pressed together. The Damascus sword, for example, consisted of wrought-iron bars hammered until thin, doubled back on themselves, and then rehammered to produce a forged weld. The larger the number of times this process was repeated, the tougher the sword that was obtained. In the Middle Ages cannons were made by welding together several iron bands, and bolts tipped with steel fired from crossbows were fabricated by forge welding. Forge welding has mainly survived as a blacksmith's craft and is still used to some extent in chain making.
Friction welding techniques join materials using mechanical friction. This can be performed in a variety of ways on different welding materials, including steel, aluminium or even wood.
The mechanical friction generates heat which softens the materials which mix to create a bond as they cool. The manner in which the joining occurs is dependant on the exact process used, for example, friction stir welding (FSW), friction stir spot welding (FSSW), linear friction welding (LFW) and rotary friction welding (RFW).
Friction welding doesn't require the use of filler metals, flux or shielding gas.
Friction is frequently used in aerospace applications as it is ideal for joining otherwise 'non-weldable' light-weight aluminium alloys.
Friction processes are used across industry and are also being explored as a method to bond wood without the use of adhesives or nails.
This fusion joining process uses a beam of high-velocity electrons to join materials. The kinetic energy of the electrons transforms into heat upon impact with the workpieces causing the materials to melt together.
Electron beam welding (EBW) is performed in a vacuum (with the use of a vacuum chamber) to prevent the beam from dissipating.
There are many common applications for EBW, as can be used to join thick sections. This means it can be applied across a number of industries from aerospace to nuclear power and automotive to rail.
Used to join thermoplastics or pieces of metal, this process uses a laser to provide a concentrated heat ideal for barrow, deep welds and high joining rates. Being easily automated, the high welding speed at which this process can be performed makes it perfect for high volume applications, such as within the automotive industry.
Laser beam welding can be performed in the air rather than in a vacuum such as with electron beam joining.
Laser welding is accomplished when the light energy emitted from a laser source is focused upon a workpiece to fuse materials. The limited availability of lasers of sufficient power for most welding purposes has so far restricted its use in this area. Another difficulty is that the speed and the thickness that can be welded are controlled not so much by power but by the thermal conductivity of the metals and by the avoidance of metal vaporization at the surface. Particular applications of the process with very thin materials up to 0.5 mm (0.02 inch) have, however, been very successful. The process is useful in the joining of miniaturized electrical circuitry.
This is a fast process which is commonly used in the automotive industry. This process can be split into two types, resistance spot welding and resistance seam welding.
Spot welding uses heat delivered between two electrodes which are applied to a small area as the workpieces are clamped together.
Seam welding is similar to spot welding, except it replaces the electrodes with rotating wheels to deliver a continuous leak-free weld.
Spot, seam, and projection welding are resistance welding processes in which the required heat for joining is generated at the interface by the electrical resistance of the joint. Welds are made in a relatively short time (typically 0.2 seconds) using a low-voltage, high-current power source with force applied to the joint through two electrodes, one on each side. Spot welds are made at regular intervals on sheet metal that has an overlap. Joint strength depends on the number and size of the welds. Seam welding is a continuous process wherein the electric current is successively pulsed into the joint to form a series of overlapping spots or a continuous seam. This process is used to weld containers or structures where spot welding is insufficient. A projection weld is formed when one of the parts to be welded in the resistance machine has been dimpled or pressed to form a bump that is melted down during the weld cycle. The process allows a number of predetermined spots to be welded at one time. All of these processes are capable of very high rates of production with continuous quality control. The most modern equipment in resistance welding includes complete feedback control systems to self-correct any weld that does not meet the desired specifications.
Flash welding is a resistance welding process where parts to be joined are clamped, the ends brought together slowly and then drawn apart to cause an arc or flash. Flashing or arcing is continued until the entire area of the joint is heated; the parts are then forced together, and pressure maintained until the joint is formed and cooled.
Low- and high-frequency resistance welding is used for the manufacture of tubing. The longitudinal joint in a tube is formed from metal squeezed into shape with edges abutted. The current passing governs welding heat through the work and the speed at which the tube goes through the rolls. Welding speeds of 60 metres (200 feet) per minute are possible in this process.
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 metallic structures of the two pieces to join together and become one. There are a number of different welding methods, including spot welding, inert metal gas (MIG), and inert tungsten gas, which are forms of gas metal arc welding, arc welding, and gas welding, to name a few.