Arc Welding: Definition, Process, Types, Applications, Materials, and Advantages
Arc welding is a widespread, versatile, and reasonably accessible method for joining metals. Different types of arc welding are suited to joining different metals and different geometries. Arc welding is typically recognized by the bright flash of light generated by the arc.
Arc welding is the use of an electrical arc to heat and melt metal so that it can be joined together. The principle of arc welding is that an electrode is held close to the metal to be joined, with an electrical voltage applied to create the arc. The intense heat generated by the electrical arc in the gap between the electrode and the workpiece melts the metals so that they can be fused together. There are a number of variations in the arc welding process: consumable or non-consumable electrodes, the direction of current flow, choice of shielding gas, and how new material is supplied to fill the gap between the metal pieces being joined. These different approaches are tailored towards specific combinations of metals and joint geometry to create strength and longevity in the weld.
Many variations of arc welding exist, each with its own name. One commonly used technique is called "stick welding." The "stick" is a consumable electrode in the form of a short, stiff rod. The arc is struck between the tip of the welding rod and the workpiece. It is manually fed into the weld zone, where it melts. A coating of flux on the outside of the welding rod generates the gas shield around the weld pool as it is consumed.
Stick welding is the most accessible type of arc welding (requiring the least specialized equipment), which is why it is sometimes used as another term for arc welding. However, it is only one type of arc welding — four other types of arc welding include: tungsten/inert gas (TIG) welding, metal/inert gas (MIG) welding, flux cored arc welding (FCAW), and submerged arc welding (SAW).
Arc welding started in 1887 with the patent of a carbon electrode for arc welding by Russians Nikolai Bernardos and Stanislaw Olszewski. The process developed from there, with a metal electrode being patented in the USA in 1890, and then coated electrodes in 1900. Equipment using alternating current was introduced in 1911 but only became popular later.
Arc welding is used to join and repair metal components, which finds its application in multiple industries. Some examples of sectors that rely heavily on joining metal parts include automotive manufacturing, industrial piping, shipbuilding, and structural steel erection. Due to the versatility of metallic materials, they are used widely throughout modern manufacturing, and arc welding (as a common fabrication tool for metal) is therefore applied widely too.
The arc welding process works by using an electrical arc to melt metal. An arc is created by applying a voltage across two separated conductive electrodes (one of which is the workpiece) until an electrical path is created through the air gap between them. One conductive electrode is the base metal workpiece; the other electrode is movable, either manually or automatically. The electric arc passing through the air between the two electrodes has a high temperature of over 3000 °C. This arc, therefore, heats the metal to be welded past its melting point, making a pool of molten metal at the termination of the arc. The edges of the two metals are melted, usually together with filler material from a consumable electrode, and they combine to form a single molten mixture. As the arc moves on, the melt pool cools and the metal hardens into a strong weld.
The temperature of the electric arc in an arc welding process can be in the range of 3500 °C up to more than 20,000 °C! Although the temperature is very high, it is focused on a very small area of the metal surface. The high temperature of the arc means that the melting point of the metal to be welded is reached very quickly. The temperature of the weld pool itself reaches a range of 2000 to 2500 °C.
The type of electrode used for an arc welding process is selected to match the details of the specific method. Arc welding electrodes can be grouped into two broad categories: non-consumable and consumable, as described below:
- Non-consumable: Non-consumable electrodes help to start and channel the welding arc, but they contribute no filler metal to the weld and are not used up during the welding process. in TIG (tungsten inert gas) welding, for example, a tungsten-based electrode is guided along the weld joint to complete the arc that melts the metal, but if filler metal is needed to complete the weld, it must be fed into the joint as a separate wire with an appropriate chemical composition.
- Consumable: Many arc welding electrodes are consumable, which means that they melt into the weld as the arc is created between the electrode and the workpiece. Some electrodes are bare, with no coating. An example is a continuously fed wire electrode for MIG (metal inert gas) welding. Electrodes can also be lightly coated with a thin layer of deoxidizing agent (often copper, but various chemical compounds are available). This coating helps stabilize the arc that is created between the melting electrode and the workpiece. A heavier electrode coating can be used to provide a protective sheath of inert gas around the arc. This not only helps improve arc stability but also helps to prevent the formation of oxides or nitrides within the weld.
The most important parameter in choosing the correct electrode for your welding job is the material that you are welding. For instance, there are electrodes for welding 308 stainless steel, and different electrodes for welding 316 stainless steel. Electrodes can be classified according to a system set up by the American Welders Society. These codes begin with the letter “E” for “electrode”, and then have four or five trailing numerical digits to provide information on the tensile strength of the deposited material, the flux composition and the power supply to be used with the electrode.
Another factor that may influence which electrode you choose may be the geometry of the weld that you want to create. Some electrodes are suitable for any geometry, including vertical, but some electrodes are only suitable for horizontal welds. This is designated in the code of the electrode.
Some of the different types of arc welding include:
- Shielded Metal Arc (SMAW) Welding: SMAW (sometimes called "stick welding") is the most common and accessible type of arc welding. It makes use of a consumable, hand-held electrode (the "stick"). This electrode is coated with flux, which melts at the tip of the electrode and produces the shielding gas, as well as a slag product that protects the weld from oxidation during welding.
- Flux Cored Arc Welding (FCAW): This is similar to SMAW welding, but it is semi-automatic. The consumable electrode used contains flux and it is continuously fed.
- Metal Inert Gas (MIG) Welding: This welding technique uses shielding gas to protect the molten metals from the atmosphere. The metal consumable electrode is machine-fed.
- Tungsten Inert Gas (TIG) Welding: This welding method uses a non-consumable electrode made of tungsten, and therefore requires a filler wire to be fed to make the weld. Shielding gas is necessary.
- Submerged Arc Welding (SAW): This strategy is used with automated welding processes, where the joint to be welded is completely submerged in flux. The flux is conductive when molten, and the weld is completed below this blanket of flux.
TIG (tungsten inert gas welding) is generally accepted as producing the strongest arc welds because it generates very high temperatures and has a slow cooling rate. This causes excellent fusion between two pieces of metal, providing the strongest bond. However, it is not quite that simple, as the strength of any weld depends on a number of external factors such as the skill of the welder, preparation of workpieces, correct filler or electrode being used, and the length and depth of the weld. No single type of arc welding will therefore be consistently stronger than all other types of arc welding.
Arc welding is applied in many different industries. Some examples are given below.
- Maintenance and Repair: Arc welding is a versatile method of performing repairs to metallic components. Not only can it be used for repairing cracks or attaching patches, but it can also be used for building up new material where there has been excessive wear.
- Ship Building: Arc welding is the fundamental construction method used to join plate metal together with a watertight seal.
- Industrial Piping: Arc welding is used in workshops and in the field to fabricate industrial piping runs of various materials.
- Vehicle Assembly: Large automated automobile assembly plants use arc welding (typically MIG welding) to join the various parts of the vehicle frame and other components together.
Arc welding is versatile and can be applied to a variety of metals. Some common metal applications of arc welding are discussed below, each with some of their considerations and the preferred arc welding approach:
Magnesium can be arc welded but requires some specialized equipment. Typically, magnesium welding is used to repair castings by depositing new material on the worn or broken surface. The electrode to be used must be free of sodium chloride to avoid corrosion. The incredible bright light from magnesium must also be protected against.
Aluminum is commonly arc welded, usually with MIG or TIG welding. Aluminum can be difficult to weld due to its high thermal conductivity and its surface oxide layer, which has a higher melting point than pure aluminum. However, arc welding is able to overcome these difficulties. For more information, see our guide on Aluminum Material.
Stainless steel can be easily welded by more than one type of arc welding. Stick welding stainless steel is possible, but does not give an aesthetically pleasing weld. MIG welding provides more speed and strength than a stainless steel weld, but the aesthetics are not always very good. If the weld needs to be visually pleasing, then TIG welding is necessary. TIG is the best welding for stainless steel due to the strength of the weld and its beautiful finish, but it is not always applied as it is complex and requires a very high skill level from the welder. For more information, see our guide on Stainless Steel Metal.
Steel is the most common material that is arc welded and was the foundation of much of the early development of the process. Stick welding (SMAW) is easily applied to steel to give good-quality welds. However, each of the other types of arc welding can also be applied depending on the specific need.
Titanium is usually welded using the TIG process, but can also be welded by MIG. It is readily welded, but special attention must be paid to the cleanliness of the metal pieces, as well as ensuring complete shielding from the environment with shielding gas — this inert atmosphere is critical when arc welding titanium.
Cast iron can be arc welded, but it is a challenging material to weld because of its high carbon content. When welding cast iron, it is critical to managing the heating of the material. Since it is not ductile, it has a high risk of experiencing stress cracking due to thermal stresses from localized heating. Generally cast iron will need to be preheated before welding, and the cooling after welding should be controlled.
Copper and brass (as well as bronze) are easily arc welded. Copper alloys can be welded by stick welding, but a higher quality finish is possible by MIG or TIG welding. Weldability may be low for some specific alloys, but the vast majority are easily welded. For more information, see our guide on What Are the Properties of Copper.
Nickel alloys can be arc welded with a similar approach to welding other high-performance metals such as stainless steel and titanium. TIG is the preferred method, but MIG and stick (SMAW) are also possible.
There are numerous advantages to arc welding compared to other common types of fusion welding. These are:
- Arc welding can use relatively simple and portable equipment, making it suitable for use in the field.
- Arc welding is more versatile than approaches such as laser welding. It can be applied to many different metals with different properties, including those that are highly reflective.
- Arc welding can accommodate imprecise fitment of the components to be welded and is generally tolerant of non-ideal conditions. This is an advantage over techniques such as laser welding.
- Considering stick welding specifically as an entry point, arc welding is accessible. The equipment is relatively cheap (affordable even to a hobbyist), and it is possible for most people to learn. This is in contrast to some welding techniques like laser welding that require highly specialized equipment.
There are some limitations and disadvantages of arc welding. Some of these are outlined below:
- Arc welding requires a skilled welder, particularly if the weld is to withstand significant load or meet aesthetic criteria.
- Due to arc welding’s high heat input to the base metal, there are risks of warping. Within the heat-affected zone, changes in the metal’s microstructure can reduce the strength and corrosion resistance of the weld.
- Arc welding is not capable of welding thin sheets of metal — generally anything thinner than 2 mm is very difficult. The arc tends to melt the edges of thin sheets away.
- Arc welding, unlike laser welding, is limited to welding metals, and cannot be used to weld plastics.
- From variations of arc welding that require flux, there is usually some generation of fumes, which requires safe ventilation.
Depending on the type of arc welding, different equipment is necessary. All arc welding processes require similar personal protective equipment to be worn, such as a welding helmet/visor, a fire-retardant cap, welding gloves, leather overalls or coverings, and steel-toed safety boots. The most common type of arc welding, stick or shielded metal arc welding (SMAW), requires an electric welding machine, the electrode clamp, the workpiece clamp, and the consumable electrodes.
For MIG and TIG welding, additional equipment includes the cylinders of shielding gas such as argon or carbon dioxide. For TIG welding, the electrodes are non-consumable, so filler wire is also required.
To make sure that you are safe while arc welding, there are steps that should be followed. First, it is important to be sure that you have a tidy workplace. This means that there is no debris on the floor and no tripping hazards; no spills or wet patches that could either cause a slip or conduct electricity; and the area is well-ventilated. Second, be sure that you are wearing the correct personal protective equipment, and that it is all in good condition. This includes a welding visor and welding gloves, as well as a cap, overalls, and boots. Third, inspect your equipment to be sure that there are no electrical faults or damage to gas lines or clamps. Fourth, it is always important to have the correct firefighting measures in place when arc welding, in the case of sparks, spatter, or molten metal being dropped. This may include having a dedicated fire extinguisher or hose reel nearby, a second person present to assist and to spot any risk of fire, or damp blankets on the ground below if welding at heights on scaffolding or a pipe bridge.
Manual arc welding that produces strong, aesthetically pleasing welds requires skill. However, it is fairly easy to learn basic arc welding. Certain materials, such as stainless steel, are more challenging to weld than arc welding. Also, the weld joint geometry can add to the difficulty. A circular butt weld which requires a portion to be welded underneath a pipe, for example, requires a high level of skill.
No, arc welding is generally not for beginners. Arc welding typically requires a skilled operator. However, stick welding (shielded metal arc welding (SMAW)) is more forgiving, and so is often used for initial training of new welders. Beginners must practice non-critical repairs or projects while building their dexterity and control of the electrode and arc. After gaining experience, the welder would then progress to more challenging types of arc welding as necessary.
The two key aspects of improving a welder’s skills are training and experience. During formal training, the welder gains an understanding of the process of arc welding, so that they have insight into how their actions and adjustments affect the welding process. Formal training is still necessary for experienced welders if they are to be qualified in a new welding procedure. The welder is to be trained on that specific procedure with the specific materials and types of welds.
However, experience is perhaps the most influential factor in improving a welder’s skills. Practicing welding in a variety of conditions and on a variety of joint geometries will improve a welder’s capabilities. Learning welders should seek out feedback from more experienced welders, as well as from the results of quality control tests such as metallographic sections of weld joints, or nondestructive techniques such as radiography or ultrasonic testing. If a welder is to be certified for a specific weld procedure, they will need to pass tests witnessed by a third party. The welder will need to have gained experience in that welding procedure to be able to satisfy the criteria and be qualified.
Arc welding will cost a different amount depending on the materials to be welded and the specific type of arc welding to be used. The cheapest is stick welding (SMAW), with other types of arc welding, such as TIG welding, being more expensive. Further, the cost of labor and materials will be affected by the location of the work (which country and state) and current market dynamics.
For stick welding, the costs will include the price of the welding machine, the supply of the electrical energy to power the machine, the consumable electrodes, and of course the labor cost for the welder. For TIG welding, the costs will include the machine and power supply, the tungsten electrode, the shielding gas, the filler wire (if used), and the welder’s labor. An approximate cost for arc welding, including all of the above, is in the range of $20-40 per hour.
Arc welding differs from other welding processes in the mechanism for heating and melting the metal to be welded. In arc welding, an electric arc is used to generate a high temperature. Other fusion welding processes include gas (oxyacetylene) and laser welding. With gas welding, the combustion of an oxyacetylene mixture provides the heat to melt the metal, and in laser welding, focused optical energy is used to form the melt pool.
The method of providing heat to the metal is the fundamental difference between these types of welding, but that works out into other practical differences, such as the equipment needed, the metals and material thicknesses that it can be applied to, and the filler material used.
Yes, arc welding is still used widely in multiple industries. In fact, it is probably the most widely used welding method, globally. It is used extensively for a number of reasons: it can be applied to a range of different metals, it is a fairly robust process, and compared to other types of welding, it can be done with fairly simple equipment and limited operator skill.
Yes, essentially arc welding can be the same as stick welding, but that is an oversimplification. Stick welding, or more accurately, shielded metal arc welding (SMAW), is one form of arc welding. It is the most common type. However, arc welding also incorporates other welding approaches, such as metal inert gas (MIG) welding and tungsten inert gas (TIG) welding. In TIG welding, the tungsten electrode is not consumed, and the filler material is not encased in flux, which is fundamentally different than stick welding. Therefore, although stick welding is a type of arc welding, it is not correct to say that all arc welding is the same as stick welding.
Yes, arc welding generally produces stronger welds than gas welding. The primary reason for this is that an electric arc generates a temperature in the region of 6000 °C, whereas an oxyacetylene torch used for gas welding reaches a temperature of about 3600 °C. The higher temperature generated by the electric arc means that it takes less time to melt the parent material and therefore to complete the weld. This reduced heating time to melting results in a smaller heat-affected zone (HAZ) and less distortion of the parent metal. The heat-affected zone around a weld impacts its durability and limits its longevity, so generally a smaller HAZ will result in a stronger weld.
Whether or not arc welding is better than laser welding depends on the application. Laser welding is better than arc welding when the pieces of metal to be joined are relatively thin, as the energy from the focused laser beam will be sufficient to achieve the desired weld penetration. However, laser welding does not work on all combinations of materials. Arc welding is better suited than laser welding when the pieces of metal to be joined are relatively thick, when the materials require a filler material to create a strong weld when onsite repairs or welds are required, and when working with reflective materials.
The main difference between arc welding and laser welding is that arc welding uses an electrical arc to provide the heat to melt the metal for joining, whereas laser welding uses optical energy in a focused laser beam to heat up and melt metal. A further difference is that a filler material must be used with arc welding, whereas laser welding is a direct melting of two adjacent pieces of metal.
This article presented arc welding, explained it, and discussed its process, types, and various applications. To learn more about arc welding, contact a Xometry representative.
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