What is the Source |
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Welding is a manufacturing method used to combine materials with each other, often used on metal or thermoplastic materials. In this method, the part of the work pieces to be welded is usually melted and filling material is added to this part, then the joint is cooled and hardened, in some cases, heat joining is done under pressure. This method differs with soldering and brazing, joining in brazing and brazing methods consists of low melting points and melting of workpieces. Many different energy sources such as gas flame, electric arc, laser, electron beam, friction, ultra sound waves can be used for welding. In industrial processes, welding can be performed in many different environments such as open air, underwater, space. However, regardless of where it is made, the source poses several dangers. It is necessary to take measures against flame, electric shock, toxic fumes and ultraviolet rays. Until the end of the 19th century, the welding method, in which only the blacksmith used heating and forging, and the metals were combined, was known. Electric arc welding and oxy-gas welding are the first methods that developed at the end of the century, followed by a resistance source. Welding technology developed rapidly and became one of the reliable and inexpensive methods to meet the increasing demand during the early 20th century (after World War I and World War II). After the wars, various modern welding techniques have been developed, including manual methods (manual metal arc welding), semi-automatic and automatic methods (gas metal arc welding, etc.). The developments continued with the discovery of laser beam source and electron beam source in the second half of the century. Science is still continuing development. Robot welding has gained a widespread place in the industry, research and development efforts are underway to develop new welding methods and resource quality and features, and to reduce costs |
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Stick Electrode Arc Welding |
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Covered electrode arc welding is a manual arc welding method in which the heat required for welding occurs due to the arc formed between a covered coated electrode and the workpiece. In this method, both direct (DC) or alternate (AC) current types can be used. In some cases, the welding area is protected by a gas known as shielding gas and covered electrode arc welding is performed. The tip of the electrode, the welding bath, the arc and the parts of the workpiece close to the welding are protected from the harmful effects of the atmosphere by the gases formed by the burning and decomposition of the covering material. The slag formed by the molten cover provides additional protection for the molten weld metal in the welding bath. Additional metal (filler metal) is provided by the core wire of the depleted electrode, and in some electrodes by metal powders in the electrode cover. Covered electrode arc welding is the most widely used welding method for joining metals due to its advantages. | | 
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Advantages: |
Covered electrode arc welding can be applied in open and closed areas. Welding is possible at any point and position that can be reached with the electrode. It is possible to weld in narrow and limited areas that cannot be reached with other welding methods. Since the power supply ends of the welding machine can be extended, it can be welded in the connections at long distances. Welding equipment is light and portable There are covered electrode types to meet the chemical and mechanical properties of many materials. Therefore, welded joints can also have the properties of the main material.
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Disadvantages:
The metal deposition rate and efficiency of the covered electrode arc welding is lower than many arc welding methods. Electrodes are in the form of cut bars of certain sizes, so it is necessary to stop welding each time the electrode runs out. After each welding pass, it is necessary to clean the slag formed on the weld metal. |
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Electric Resistance Source |
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Resistance welding is the method of welding between two or more metal surfaces on the basis of producing heat with the resistance against the current passing over the metals. Due to the high current through metal (1000 - 100,000 A.), a small molten metal pool is formed in the welding zone. In general, resistance welding methods are efficient and less polluting, but their applications are limited and equipment is very expensive.
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Core Wire Arc Welding |
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Flux cored arc welding is an arc welding method in which the heat required for welding occurs due to the arc formed between an exhausted cored wire electrode and the workpiece. The function of protecting the arc and the welding zone is performed by the gases formed as a result of the combustion and decomposition of the substance in the core wire or by an externally fed shielding gas as in the gas source. Welding process, which is self-protected (open-arc core welding wires), is more like gas protection in the covered electrode welding method. The covering material on the covered electrodes causes the electrodes to be produced as straight rods and length restriction. As for flux cored wires, this covering material is produced in the form of wire wrapped on spools as it is inside the tubular wire electrode and can be fed to the welding zone continuously. This welding method can be applied in both semi-automatic and automatic welding systems. The disadvantage of the cored wire arc welding is that a slightly thin layer of slag is formed, as in the electrode arc welding covered, on the weld seam. However, many types of core electrodes are currently produced that do not require slag cleaning or produce slag. |
Oxy-Acetylene Source |
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The most common use of this method is the oxy-gas source (also known as the oxy-acetylene source). It is one of the oldest and most versatile welding methods, but its popularity in industrial applications has declined in recent years. It is still widely used in pipe and duct welding and repair work. Its equipment is cheap and simple, usually the welding flame (about 3100 ° C) is produced by the burning of acetylene with oxygen. Since the flame is less powerful than the electric arc, welding cooling will be slower and may allow less stress and weld distortion, so welding of high alloy steels is easier with this method. This method is also used for cutting metals. Other gas welding methods are very similar, such as air-acetylene welding, oxygen-hydrogen welding and compressed gas welding, only the type of gas used varies. Gas welding is also used in plastic welding |
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Gas Supply |
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Gas welding is an arc welding method in which the heat required for welding is generated by the arc formed between a depleted electrode and the workpiece. Continuously fed (driven) to the welding zone, the massive wire electrode melts and forms the weld metal as it runs out. The electrode, welding bath, arc and the parts of the workpiece close to the welding are protected from the harmful effects of the atmosphere by gas or mixed gases from the welding torch. The gas must be able to fully protect the weld zone, otherwise even a very small intake of air will cause an error in the weld metal. The main types are MIG-MAG and WIG (TIG) gas welding techniques. In this type of welding, MIG (Metal Inert Gas) welding technique, which uses noble gases such as Argon and Helium, and MAG (Metal Active Gas) techniques that use carbon dioxide, which is an active gas as a protective gas, are used most intensively. The difference of WIG technique, which is used relatively less than others, is the use of Wolfram (Tungsten) electrode which does not melt. | | 
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1. Source direction
2. Torch 3. Welding wire 4. Shielding gas 5. Source bath 6. Weld seam 7. Workpiece |
Its advantages:
Under gas welding is a faster welding method than covered electrode arc welding. Because; Since the wire-shaped welding electrode is continuously fed into the welding zone, the welder does not have to stop welding to replace the depleted electrode, as in the covered electrode arc welding method. Since there is no slag formation, there is no slag removal process after every pass as in covered electrodes and higher quality welds are obtained since there is no risk of slag residue forming in the weld metal. Since the electrodes with a lower diameter are used compared to the covered electrode arc welding, they have high current density and high metal deposition rate in the same current range. The weld metal obtained by the gas welding has low hydrogen content, which is especially important for steels with hardening properties. Since deep penetration can be achieved in the under gas welding, it sometimes allows small corner welding and provides a smoother root penetration than the covered electrode arc welding. Although thin materials are mostly combined with or without additional metal by the TIG welding method, the gas welding gives better welding to thin materials than the covered electrode arc welding. It is very suitable for use in both semi-automatic and fully automatic welding systems Disadvantages: Under gas welding equipment is more complex, more expensive and more difficult to transport than covered electrode arc welding equipment. It is not easy to weld in hard-to-reach areas such as covered electrode arc welding, as the under gas welding torch must be close to the workpiece. Weld joints made with gas welding in hardening steels are more prone to cracking. Because, as in the covered electrode arc welding, there is no slag layer that reduces the cooling rate of the welding metal. Under gas welding requires additional protection against air currents that can move the gas shield away from the welding zone. Therefore, the covered electrode is not suitable for welding in open areas than arc welding. |
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TIG Welding |
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TIG welding is an arc welding method in which the heat required for welding occurs thanks to the arc formed between an inexhaust electrode (tungsten electrode) and the workpiece. The electrode, the welding bath, the arc and the parts of the workpiece close to the welding are protected from the harmful effects of the atmosphere by gas or mixed gases from the welding torch. The gas must be able to fully protect the weld zone, otherwise even a very small air intake will cause an error in the weld metal | | 
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Advantages: TIG welding can be applied both manually and with automatic welding systems to weld continuously, weld and weld at intervals. Since the electrode does not run out, welding is done by melting the base metal or using an additional weld metal. It can be welded in any position and is particularly suitable for welding thin materials. It gives high penetration and nonporous welds in root pass welding. Since the heat input is concentrated in the welding zone, deformation in the workpiece is low. Gives smooth weld seam and no need to clean the weld seam. Disadvantages: The metal deposition rate of TIG welding is lower than other arc welding methods. It is not an economical method in the welding of thick section materials. |
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Submerged Arc Source |
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Submerged arc welding is an arc welding method in which the required heat for welding occurs due to the arc (or arcs) formed between the depleted electrode (or electrodes) and the workpiece. The arc zone is protected by a layer of welding dust and the weld metal and the base metal close to the weld by melting weld dust (slag) and the weld seam. In submerged arc, the electricity passes through the arc bath and the welding bath, which consists of molten metal and molten slag. The arc heat electrode forms the welding bath, which fills the welding powder and base metal and fills the welding nozzle. The welding powder, which acts as a protector, also reacts with the welding bath and deoxides the weld metal. The welding powders used when welding alloy steels may contain alloying elements that balance the chemical composition of the welding metal. Submerged arc welding is an automatic welding method. In some submerged welding applications, two or more electrodes can be applied to the welding nozzle at the same time. Electrodes can be applied to the weld bath side by side (twin arc), or high welding speed and high metal deposition rate can be achieved by driving one after the other, far enough to allow the welding baths to solidify independently.
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Advantages: It is a method with high welding speed and high metal deposition rate that can be used for welding of flat and cylindrical parts, for welding pipes of any thickness and size, and for hard filler welding. Gives accurate and high mechanical strength weld seams. During welding, there is no splash and arc rays are not visible, therefore the protection required for the welding operator is less. It is possible to weld bevel angles according to other methods. Submerged arc welding can be applied indoors and outdoors. Disadvantages: Submerged welding dusts tend to absorb moisture from the air, causing pores in the welding. In order to obtain high quality welds, the base metal should be flat, smooth and free from oil, rust and other impurities on the base metal surface. The slag must be cleaned over the weld seam, which can be difficult in some applications. In multi pass welds, the slag should be cleaned after every pass in order to prevent any slag residue on the weld seam. It is generally not suitable as the submerged arc can burn in materials thinner than 5 mm. The method is suitable for butt welding and corner welding in flat, horizontal position, except for some special applications. |
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Factors Affecting Welding Seam Form For Under Gas And Submerged Arc Welding |
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SUBMERGED SOURCE | GAS SOURCE SOURCE | Dust Consumption | 
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penetration
t(mm)
| Stitch Width
b(mm) |
Stitch Height
h(mm)
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current intensityI (A) - increases
| increases | increases | increases | constant | Wire Feed Speed v (m/dak) - increases | increases | increases | increases | constant | Arc Voltage U(V) - increases | decreases | increases | decreases | increases | Electrode Diameter (mm) increases | decreases | increases | increases | increases | Welding Speed (m/dak) - increases | decreases | decreases | decreases | decreases | Current Type / Polarization | D.C. (+) | increases | decreases | decreases | decreases | D.C. (-) | decreases | increases | increases | increases | Free wire length (mm) increases | decreases | increases | increases | increases | Powder grain size increases | decreases | increases | decreases | increases |
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Solid state welding methods |
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Like the forging method, the first known welding method, some modern welding methods take place before the welding material melts. One of the most common methods, ultrasonic welding, is used to connect vibration under high pressure and high frequency with cables or thin layers made of thermoplastic or metal material. Equipment and methods are similar to the resistance source. Here, electric current is replaced by energy supplied by vibration. In this method, the welding metals do not melt, instead there is mechanical vibration applied horizontally under pressure. In the welding of plastics, the materials should be brought to a temperature close to the melting temperature and vibration should be applied vertically. Ultrasonic welding is used in aluminum or copper material and polymers, which are generally used for electrical connections.
Geometry
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Common resource addition types
Adding forehead V-opening by opening the welding mouth Add an overlay Add in T shape Add a corner The parts to be welded can be prepared geometrically for welding in various ways. There are also different variations depending on the shape of the part; such as adding double-V. Single-U and double-U shaped bevelings are also frequently used, and are similar to V-type welds. Overlapping joints are generally used depending on the part thickness, for some thin pieces, overlapping joints may become mandatory. In order to fully realize the welding process, special splicing methods are also frequently used. For example, resistive welding, laser beam welding, and electron beam welding give the best performance overlay insertion. However, some welding methods, like shielded (under gas or submerged) metal arc welding, are versatile and can be applied with all types of piecing. In addition, some processes can use multi-pass welding methods (allowing the previous one to cool when doing the next welding). This method allows the use of single-V welding splicing in the welding of thick sections. | | 
Cross section of the joint at the butt welding Dark area: Source area Gray zone: Heat-effect area Light gray zone: Main material |
After welding, different regions are formed in the welding zone. The weld itself is called the melting zone, where there is filled filler metal during the welding process. The characteristics of this region depend primarily on the filling material used and its compatibility with the base material.
Immediately around this region, there is the region that is affected by heat, microstructure and properties in this region have been changed by welding process. These properties change depending on the behavior of the main material under heat. It is seen that the metal in this region is generally weaker than both the base metal and the weld zone, where permanent material stresses occur. |
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Quality |
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In general, the biggest criterion used to measure the quality of the weld is the strength of the weld and the surrounding material (strength). There are many factors that affect this; such as welding method, addition method, amount of heat, base material and filling material and interactions between them. Examinations to measure the quality of the resource are generally grouped into two groups, destructive and non-destructive inspection methods. In the measurements made with these examinations, there should be no visible defects in the source, permanent stress and distortions should be at an acceptable level, and heat-affected zone properties should be at an acceptable level. |
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Heat affected area |
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The blue colored area in the picture was formed due to oxidation at 316 ° C. This color indicates the temperature, but is not a sufficiently sensitive indicator for the HAZ (Heat Affected Zone). HAZ is the narrow zone surrounding the welded mine section. The effects of welding on the material around the welding place can be harmful (the size and strength of the affected area may vary depending on the material used and the heat input used in the welding process). The thermal diffusion of the actual material (thermal diffusivity, ie thermal conductivity / volumetric heat capacity) also plays a major role here. If the diffusion is large, the cooling rate of the material will be high and the heat affected zone will be relatively smaller. Otherwise, low emission will bring slow cooling and larger heat-affected zone. The amount of heat injected by the welding process plays an important role in methods such as the oxy-acetylene welding method, the intense heat input causes the heat-affected zone to expand. Processes such as laser beam welding give condensed heat to the welding zone, the amount of heat is limited and as a result, a small area affected by heat appears. The electric arc welding remains between these two conditions due to variations in the source-specific heat input. The heat input for the arc welding procedure is calculated by the formula:
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Q = Heat input (kJ / mm)
V = Voltage (V) I = Current (A) S = Welding speed (mm / min) is given. The efficiency depends on the welding method used in the welding process; For example, it is 0.75 in normal metal arc welding, 0.9 in sub-gas metal arc welding and 0.8 in sub-gas tungsten welding. |
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