✏️Spot welding is the simplest type of welding where the work portions are held jointly below the force of anvil face. The copper (Cu) electrodes will make contact with the work portion & the flow of current through it. The work portion material applies a few resistances within current flow which will cause limited heat production. The resistance is high at the edge surfaces because of the air gap. The current begins to supply through it, then it will reduce the edge surface.
✏️The current supply & the time must be enough for the correct dissolving of edge faces. Now the flow of current will be stopped however the force applied with electrode continued for a second, whereas the weld quickly cooled. Later, the electrodes eliminate as well as get in touch with new spot to create a circular piece. The piece size mainly depends on electrode size (4-7 mm).
✏️This type of welding is also known as continuous spot welding where a roller form electrode can be utilized to supply current throughout work parts. Initially, the roller electrodes are getting in touch with the work part. High current can be supplied through these electrode rollers to melt the edge surfaces & shape a weld joint.
✏️At present, the electrode rollers will begin rolling on work plates to make a permanent weld joint. The weld timing & electrode movement can be controlled to guarantee that the weld overlap & work part doesn’t acquire too warm. The speed of the welding can be about 60 in per min within seam welding, which is used to make airtight joints.
✏️Projection welding is similar to spot welding apart from a dimple can be generated on work parts at the place wherever weld is preferred. At present the work parts held among electrode as well as a huge quantity of current flow through it. A little quantity of pressure can be applied throughout the electrode on welding shields. The flow of current throughout dimple which dissolve it & the force reasons the dimple level & shape a weld.
✏️Thus, this is all about the resistance welding process , which is used for welding two metals. It includes a welding head used to hold the metal among its electrodes & applies a welding power supply & force to welding the metal. When the force is applied, the resistance produces heat, then resistance welding utilizes the heat. Likewise, whenever the flow of current attempts to move ahead throughout two metals, then heat can be generated because of the resistance of the metal. So finally this welding can be used to weld the metals using the pressure as well as heat.
✏️Butt welding is best performed with MIG or TIG welding applications due to their natural ability to connect two pieces of metal together.Using different types of welding electrodes for the welder will determine the properties of the weld such as its resistance against corrosion and strength.Electrodes conduct current through the metal being welded in order join the two pieces.The metal determines the type of welding that is required.The electrodes are either heavily or lightly coated. For the heavily coated electrodes are commonly used in structural welding because they are much stronger and corrosion resistant.The lightly coated electrodes are not as structurally sound.Butt welding is performed with the arc, TIG, or MIG welder held at a slight angle the weld if the weld is laying flat in order to achieve the least amount of porosity in the weld and also to increase the weld's strength.Fillet welding make up about 80 percent of the connection despite being weaker that butt welds.The reason it is used more often is because fillet welds offer more room for error with much larger tolerances. Fillet welding is not a type of butt weld despite its similarities.
The flash butt welding is a form of resistance welding, used for welding tubes as well as rods within steel industries. In this method, two work parts are welded which will be held tightly during the electrode holders as well as a high pulsed flow of current within the 1,00,000 ampere range can be supplied toward the work part material.
In the two electrode holders, one is permanent & other is changeable. At first, the flow of current can be supplied & changeable clamp will be forced against the permanent clamp because of the get in touch with the two work parts at high-current, the spark will be generated. Whenever the edge surface approaches into plastic shape, the flow of current will be stopped as well as axial force can be improved to create joint. In this method, the weld can be formed because of plastic deformation.
✏️Pressure is applied before heating is started and is maintained throughout the heating period. The equipment used for upset welding is very similar to that used for flash welding. It can be used only if the parts to be welded are equal in cross-sectional area. The abutting surfaces must be very carefully prepared to provide for proper heating. The difference from flash welding is that the parts are clamped in the welding machine and force is applied bringing them tightly together. High-amperage current is then passed through the joint, which heats the abutting surfaces. When they have been heated to a suitable forging temperature an upsetting force is applied and the current is stopped. The high temperature of the work at the abutting surfaces plus the high pressure causes coalescence to take place. After cooling, the force is released and the weld is completed.
📝Stud Welding
✏️Stud welding is a complete one-step fastening system, using fasteners called weld studs. Weld studs come in a variety of designs, threaded, unthreaded, tapped, etc., sizes and shapes for a wide range of applications.
✏️A weld stud can be end-joined to a metal work piece instantaneously for a high quality, high strength permanent bond.
✏️The base metal and the welded stud fastener do not need to be the same material. For example these combinations can be welded together - brass to copper, brass to steel, copper to steel and similar combinations.
✏️Stud welding is less expensive than other fastening methods and can used in locations which do not allow the use of other fasteners. Weld studs can be installed by one man, working on one side of the work piece, in less than a second.
✏️There are many reasons why the stud welding process is superior over other fastening systems.
📝Stud Welding Equipment
✏️The equipment required for stud welding is composed of the following:
- A direct current Power Supply
- A Controller
- A Weld Gun
- Cables to tie the system components and base metal together
✏️In most systems, the power supply and controller are combined as one component called the "Welder".
📝Arc Stud Welding Process
✏️Arc Stud Welding is generally used to weld large diameter fasteners to rougher and thicker base metals.
✏️Arc weld studs may be almost any shape and there are literally hundreds of designs, however they must have one end of the fastener designed for Arc welding equipment.
✏️Mild steel, stainless steel and aluminum are applicable materials for Arc welding.
📝Capacitor Discharge (CD) Stud Welding Process
✏️Capacitor Discharge Stud Welding is generally used to weld smaller diameter fasteners to thin base metals.
✏️Since the entire weld cycle is completed in milliseconds, welds can be made without pronounced distortion, burn-through or reverse side discoloration. As long as one end of the fastener is designed for CD welding equipment, CD Studs can be manufactured in almost any shape.
2)ARC WELDING
✏️Arc welding is a welding process that is used to join metal to metal by using electricity, to create enough heat to melt metal, and the melted metals when cool result in a binding of the metals. It is a type of welding that uses a welding power supply. to create an electric arc between a metal stick electrode and the base material to melt the metals at the point of contact. Arc welders can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes.
✏️The welding area is usually protected by some type of shielding gas vapor, or slag. Arc welding processes may be manual, semi-automatic, or fully automated. First developed in the late part of the 19th century, arc welding became commercially important in shipbuilding during the Second World War. Today it remains an important process for the fabrication of steel structures and vehicles.
📝POWER SUPPLIES
✏️To supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used. The most common classification is constant current power supplies and constant voltage power supplies. In arc welding, the voltage is directly related to the length of the arc, and the current is related to the amount of heat input. 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 direction of current used in arc welding also plays an important role in 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 general, the positively charged anode will have a greater heat concentration (around 60%).Note that for stick welding in general, DC+ polarity is most commonly used. It produces a good bead profile with a higher level of penetration. DC- polarity results in less penetration and a higher electrode melt-off rate. It is sometimes used, for example, on thin sheet metal in an attempt to prevent burn-through.With few exceptions, electrode-positive (reversed polarity) results in deeper penetration. Electrode-negative (straight polarity) results in faster melt-off of the electrode and, therefore, faster deposition rate.Non-consumable electrode processes, such as gas tungsten arc welding, can use either type of direct current (DC), as well as alternating current (AC). With direct current however, 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.Alternating current rapidly moves between these two, resulting in medium-penetration 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 sin wave, eliminating low-voltage time after the zero crossings and minimizing the effects of the problem.
✏️Duty cycle is a welding equipment specification which defines the number of minutes, within a 10-minute period, during which a given arc welder can safely be used. For example, an 80 A welder with a 60% duty cycle must be "rested" for at least 4 minutes after 6 minutes of continuous welding.Failure to observe duty cycle limitations could damage the welder. Commercial- or professional-grade welders typically have a 100% duty cycle.
📝CORROSION ISSUES
✏️Some materials, notably high-strength steels, aluminium, and titanium alloys, are susceptible to hydrogen embrittlement. If the electrodes used for welding contain traces of moisture, the water decomposes in the heat of the arc and the liberated hydrogen enters the lattice of the material, causing its brittleness. Stick electrodes for such materials, with special low-hydrogen coating, are delivered in sealed moisture-proof packaging. New electrodes can be used straight from the can, but when moisture absorption may be suspected, they have to be dried by baking (usually at 450 to 550 °C or 840 to 1,020 °F) in a drying oven. Flux used has to be kept dry as well.
✏️Some austenitic stainless steels and nickel alloys are prone to intergranular corrosion . When subjected to temperatures around 700 °C (1,300 °F) for too long a time, chromium reacts with carbon in the material, forming chromium carbide and depleting the crystal edges of chromium, impairing their corrosion resistance in a process called sensitization . Such sensitized steel undergoes corrosion in the areas near the welds where the temperature-time was favorable for forming the carbide. This kind of corrosion is often termed weld decay.
✏️Knife line attack (KLA) is another kind of corrosion affecting welds, impacting steels stabilized by niobium. Niobium and niobium carbide dissolves in steel at very high temperatures. At some cooling regimes, niobium carbide does not precipitate, and the steel then behaves like unstabilized steel, forming chromium carbide instead. This affects only a thin zone several millimeters wide in the very vicinity of the weld, making it difficult to spot and increasing the corrosion speed. Structures made of such steels have to be heated in a whole to about 1,000 °C (1,830 °F), when the chromium carbide dissolves and niobium carbide forms. The cooling rate after this treatment is not important.
✏️Filler metal (electrode material) improperly chosen for the environmental conditions can make them corrosion-sensitive as well. There are also issues of galvanic corrosion if the electrode composition is sufficiently dissimilar to the materials welded, or the materials are dissimilar themselves. Even between different grades of nickel-based stainless steels, corrosion of welded joints can be severe, despite that they rarely undergo galvanic corrosion when mechanically joined.
✏️Welding can be a dangerous and unhealthy practice without the proper precautions; however, with the use of new technology and proper protection the risks of injury or death associated with welding can be greatly reduced.
📝Heat, fire, and explosion hazard
✏️Because many common welding procedures involve an open electric arc or flame, the risk of burns from heat and sparks is significant. To prevent them, welders wear protective clothing in the form of heavy leather gloves and protective long sleeve jackets to avoid exposure to extreme heat, flames, and sparks. The use of compressed gases and flames in many welding processes also pose an explosion and fire risk; some common precautions include limiting the amount of oxygen in the air and keeping combustible materials away from the workplace.
📝EYE DAMAGE
✏️Exposure to the brightness of the weld area leads to a condition called arc eye in which ultraviolet light causes inflammation of the cornea and can burn the retinas of the eyes. Welding goggles and helmets with dark face plates—much darker than those in sunglasses or oxyfuel goggles—are worn to prevent this exposure. In recent years, new helmet models have been produced featuring a face plate which automatically self-darkens electronically
To protect bystanders, transparent welding curtains often surround the welding area. These curtains, made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc.
📝Inhaled matter
✏️Welders are also often exposed to dangerous gases and particulate matter. Processes like flux-cored arc welding and shielded metal arc welding produce smoke containing particles of various types of oxides. The size of the particles in question tends to influence the toxicity of the fumes, with smaller particles presenting a greater danger. Additionally, many processes produce various gases (most commonly carbon dioxide and ozone, but others as well) that can prove dangerous if ventilation is inadequate.
📝Interference with pacemakers
✏️Certain welding machines which use a high frequency alternating current component have been found to affect pacemaker operation when within 2 meters of the power unit and 1 meter of the weld site.
