What is welding and its types pdf
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- What is Welding? - Types of Welding Processes
- What is Welding? - Definition, Processes and Types of Welds
- What is Welding? - Definition, Processes and Types of Welds
Welding is an exciting and rewarding technique for enthusiasts and professionals alike. Using a couple of tools and various types of metals, welders can transform any piece into any shape and design they desire, all with sparks flying around in the process. However, in order to be able to master the art of welding, you need to start with the basics and be aware of the different types of welding processes. More than 30 different types of welding exist, and they range from simple oxy-fuel to high-tech processes such as laser beam welding. Each of them comes with its own advantages and disadvantages and you need to have proper training to practice them.
What is Welding? - Types of Welding Processes
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. In addition to melting the base metal, a filler material is typically added to the joint to form a pool of molten material the weld pool that cools to form a joint that, based on weld configuration butt, full penetration, fillet, etc.
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.
Until the end of the 19th century, the only welding process was forge welding , which blacksmiths had used for millennia to join iron and steel by heating and hammering. Arc welding and oxy-fuel welding were among the first processes to develop late in the century, and electric resistance welding followed soon after.
Welding technology advanced quickly during the early 20th century as world wars drove the demand for reliable and inexpensive joining methods. Following the wars, several modern welding techniques were developed, including manual methods like shielded metal arc welding , now one of the most popular welding methods, as well as semi-automatic and automatic processes such as gas metal arc welding , submerged arc welding , flux-cored arc welding and electroslag welding.
Developments continued with the invention of laser beam welding , electron beam welding , magnetic pulse welding , and friction stir welding in the latter half of the century. Today, as the science continues to advance, robot welding is commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality.
The term "weld" is of English origin, with roots from Scandinavia. It is often confused with the Old English word, weald , meaning "a forested area", but this word eventually morphed into the modern version, "wild". It was first recorded in English in , from a version of the Christian Bible that was originally translated into English by John Wycliffe in the fourteenth century.
The original version, from Isaiah , reads, " The word is derived from the Old Swedish word valla , meaning "to boil". Sweden was a large exporter of iron during the Middle Ages , and many other European languages used different words but with the same meaning to refer to welding iron, such as the Illyrian Greek variti to boil , Turkish kaynamak to boil , Grison Swiss bulgir to boil , or the Lettish Latvian sawdrit to weld or solder, derived from wdrit , to boil. The word possibly entered English from the Swedish iron trade, or possibly was imported with the thousands of Viking settlements that arrived in England before and during the Viking Age , as more than half of the most common English words in everyday use are Scandinavian in origin.
The history of joining metals goes back several millennia. The ancient Greek historian Herodotus states in The Histories of the 5th century BC that Glaucus of Chios "was the man who single-handedly invented iron welding". The Middle Ages brought advances in forge welding , in which blacksmiths pounded heated metal repeatedly until bonding occurred.
In , Vannoccio Biringuccio published De la pirotechnia , which includes descriptions of the forging operation. In , Sir Humphry Davy discovered the short-pulse electrical arc and presented his results in Of great importance in this work was the description of a stable arc discharge and the indication of its possible use for many applications, one being melting metals.
The advances in arc welding continued with the invention of metal electrodes in the late s by a Russian, Nikolai Slavyanov , and an American, C. Coffin Around , A. Strohmenger released a coated metal electrode in Britain , which gave a more stable arc.
In , Russian scientist Vladimir Mitkevich proposed using a three-phase electric arc for welding. Alternating current welding was invented by C.
Holslag in , but did not become popular for another decade. Resistance welding was also developed during the final decades of the 19th century, with the first patents going to Elihu Thomson in , who produced further advances over the next 15 years. Thermite welding was invented in , and around that time another process, oxyfuel welding, became well established.
Acetylene was discovered in by Edmund Davy , but its use was not practical in welding until about , when a suitable torch was developed. As the 20th century progressed, however, it fell out of favor for industrial applications. It was largely replaced with arc welding, as advances in metal coverings known as flux were made.
World War I caused a major surge in the use of welding, with the various military powers attempting to determine which of the several new welding processes would be best.
The British primarily used arc welding, even constructing a ship, the "Fullagar" with an entirely welded hull. During the s, major advances were made in welding technology, including the introduction of automatic welding in , in which electrode wire was fed continuously.
Shielding gas became a subject receiving much attention, as scientists attempted to protect welds from the effects of oxygen and nitrogen in the atmosphere. Porosity and brittleness were the primary problems, and the solutions that developed included the use of hydrogen , argon , and helium as welding atmospheres.
This in conjunction with developments in automatic welding, alternating current, and fluxes fed a major expansion of arc welding during the s and then during World War II. During the middle of the century, many new welding methods were invented. In , Kyle Taylor was responsible for the release of stud welding , which soon became popular in shipbuilding and construction. Submerged arc welding was invented the same year and continues to be popular today.
In a Russian, Konstantin Khrenov eventually implemented the first underwater electric arc welding. Gas tungsten arc welding , after decades of development, was finally perfected in , and gas metal arc welding followed in , allowing for fast welding of non- ferrous materials but requiring expensive shielding gases. Shielded metal arc welding was developed during the s, using a flux-coated consumable electrode, and it quickly became the most popular metal arc welding process.
In , the flux-cored arc welding process debuted, in which the self-shielded wire electrode could be used with automatic equipment, resulting in greatly increased welding speeds, and that same year, plasma arc welding was invented by Robert Gage.
Electroslag welding was introduced in , and it was followed by its cousin, electrogas welding , in Kazakov proposed the diffusion bonding method. Other recent developments in welding include the breakthrough of electron beam welding, making deep and narrow welding possible through the concentrated heat source. Following the invention of the laser in , laser beam welding debuted several decades later, and has proved to be especially useful in high-speed, automated welding.
Magnetic pulse welding MPW has been industrially used since These processes use a welding power supply to create and maintain an electric arc between an electrode and the base material to melt metals at the welding point. They can use either direct current DC or alternating current AC , and consumable or non-consumable electrodes.
The welding region is sometimes protected by some type of inert or semi- inert gas , known as a shielding gas, and filler material is sometimes used as well. To supply the electrical power necessary for arc welding processes, a variety of different power supplies can be used.
The most common welding power supplies are constant current power supplies and constant voltage power supplies. In arc welding, the length of the arc is directly related to the voltage, and the amount of heat input is related to the current. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a relatively constant current even as the voltage varies.
This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as gas metal arc welding, flux cored arc welding, and submerged arc welding. In these processes, arc length is kept constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current.
For example, if the wire and the base material get too close, the current will rapidly increase, which in turn causes the heat to increase and the tip of the wire to melt, returning it to its original separation distance.
The type of current used plays an important role in arc welding. Consumable electrode processes such as shielded metal arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively.
In welding, the positively charged anode will have a greater heat concentration, and as a result, changing the polarity of the electrode affects weld properties. If the electrode is positively charged, the base metal will be hotter, increasing weld penetration and welding speed.
Alternatively, a negatively charged electrode results in more shallow welds. However, with direct current, because the electrode only creates the arc and does not provide filler material, a positively charged electrode causes shallow welds, while a negatively charged electrode makes deeper welds.
One disadvantage of AC, the fact that the arc must be re-ignited after every zero crossing, has been addressed with the invention of special power units that produce a square wave pattern instead of the normal sine wave , making rapid zero crossings possible and minimizing the effects of the problem. One of the most common types of arc welding is shielded metal arc welding SMAW ;  it is also known as manual metal arc welding MMAW or stick welding.
Electric current is used to strike an arc between the base material and consumable electrode rod, which is made of filler material typically steel and is covered with a flux that protects the weld area from oxidation and contamination by producing carbon dioxide CO 2 gas during the welding process.
The electrode core itself acts as filler material, making a separate filler unnecessary. The process is versatile and can be performed with relatively inexpensive equipment, making it well suited to shop jobs and field work. Weld times are rather slow, since the consumable electrodes must be frequently replaced and because slag, the residue from the flux, must be chipped away after welding. Gas metal arc welding GMAW , also known as metal inert gas or MIG welding, is a semi-automatic or automatic process that uses a continuous wire feed as an electrode and an inert or semi-inert gas mixture to protect the weld from contamination.
A related process, flux-cored arc welding FCAW , uses similar equipment but uses wire consisting of a steel electrode surrounding a powder fill material. Gas tungsten arc welding GTAW , or tungsten inert gas TIG welding, is a manual welding process that uses a non-consumable tungsten electrode, an inert or semi-inert gas mixture, and a separate filler material. GTAW can be used on nearly all weldable metals, though it is most often applied to stainless steel and light metals.
It is often used when quality welds are extremely important, such as in bicycle , aircraft and naval applications. The arc is more concentrated than the GTAW arc, making transverse control more critical and thus generally restricting the technique to a mechanized process.
Because of its stable current, the method can be used on a wider range of material thicknesses than can the GTAW process and it is much faster. It can be applied to all of the same materials as GTAW except magnesium, and automated welding of stainless steel is one important application of the process.
A variation of the process is plasma cutting , an efficient steel cutting process. Submerged arc welding SAW is a high-productivity welding method in which the arc is struck beneath a covering layer of flux. This increases arc quality, since contaminants in the atmosphere are blocked by the flux. The slag that forms on the weld generally comes off by itself, and combined with the use of a continuous wire feed, the weld deposition rate is high.
Working conditions are much improved over other arc welding processes, since the flux hides the arc and almost no smoke is produced. The process is commonly used in industry, especially for large products and in the manufacture of welded pressure vessels. The most common gas welding process is oxyfuel welding,  also known as oxyacetylene welding. It is one of the oldest and most versatile welding processes, but in recent years it has become less popular in industrial applications.
It is still widely used for welding pipes and tubes, as well as repair work. A similar process, generally called oxyfuel cutting, is used to cut metals.
Resistance welding involves the generation of heat by passing current through the resistance caused by the contact between two or more metal surfaces.
What is Welding? - Definition, Processes and Types of Welds
Welding is the process by which two pieces of metal can be joined together. 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. 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.
Welding is a permanent joining process in which two pieces of metal together to form one piece by heating the metals to their melting points. Additional metal also called filler metal is added during the heating process to help bond the two pieces together. A welding machine is used to create the heat and apply the filler metal. The following are types of welding processes according to the method of heat generated:. MIG welding holds for metal inert gas welding. In this types of welding, a thin wire works as the electrode which is fed from a spool attached on a gun through a flexible tube and comes out of the nozzle on the welding gun or torch.
Welding: Welding is a process of joining two metal pieces by the application of heat. Welding is the least expensive process and widely used now a days in fabrication. Welding joints different metals with the help of a number of processes in which heat is supplied either electrically or by mean of a gas torch. Different welding processes are used in the manufacturing of Auto mobiles bodies, structural work, tanks, and general machine repair work. In the industries , welding is used in refineries and pipe line fabrication.
What is Welding? - Definition, Processes and Types of Welds
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. In addition to melting the base metal, a filler material is typically added to the joint to form a pool of molten material the weld pool that cools to form a joint that, based on weld configuration butt, full penetration, fillet, etc. 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.
Welding is a fabrication process whereby two or more parts are fused together by means of heat, pressure or both forming a join as the parts cool. Welding is usually used on metals and thermoplastics but can also be used on wood.