A Comprehensive Guide to Welding
Welding is a fabrication method that fuses materials, typically metals or thermoplastics. The process uses intense heat to melt the components together and then allows them to cool, resulting in fusion. Welding differs from lower-temperature techniques such as brazing and soldering because it does not melt the parent metal.
Filler material is introduced regularly into the joint along with the base metal to form the weld pool after cooling. The weld may be stronger than the underlying parent metal, depending on how it is configured.
Pressure or heat may be used individually or together to create a weld. A shield is also required during welding to prevent contamination or oxidation of filler or molten metals.
Welding has been used extensively in fabricating a wide range of products, including:
- Storage facilities
- Construction materials
- Machinery (industrial and agricultural)
- Pipelines (land and underwater)
Welding technology has evolved from its primitive forms to modern, sophisticated fabrication. Currently, there are several methods of welding, which include MIG, Arc, and TIG welding, among others. Programmable robots have also been introduced for industrial applications and are slowly taking over large-scale welding processes.
History of Welding
Modern blacksmiths continue to forge swords and blades using forge welding procedures developed in the medieval centuries. De la Pirotechnia, the first printed book on metallurgy, was published in 1540 by Italian metallurgist Vannoccio Biringuccio and included descriptions of iron smelting and forging.
In 1802, Russian scientist Vasily Petrov invented the steady electric arc, which enabled metalworkers to melt metals. Edmund Davy discovered acetylene in 1836, which has proved to be instrumental in providing an inert environment for welding. These discoveries paved the way for the development of the electric generator, gas welding and cutting, and more reliable stick welding in the mid-nineteenth century.
Along with advancements in weapon manufacturing and global transportation, World War I saw a significant increase in the use of welding. Stick welding was widely used to construct ships and aircraft in England and Germany. Automatic welding, which feeds an electrode wire continuously through the welding machine, was invented in 1920.
Many novel techniques, such as underwater and stud welding, were invented in the mid-twentieth century. After decades of development, gas tungsten welding became safer and more widespread in 1941, allowing welders to fuse a wide range of non-ferrous metals.
Because of a focus on sustainability and safety, the performance of modern welding procedures has improved. Modern inspection techniques have reduced flaws and irregularities, raising quality and safety standards.
Types of Welding
Tungsten Inert Gas Welding (TIG)
In the TIG welding, an arc is formed in an inert argon or helium atmosphere between the workpiece and a non-consumable tungsten electrode. Because the electrode is not consumed during welding, the TIG welder does not need to balance the heat input from the arc as the metal is deposited from the melting electrode.
If filler metal is required, it must be added to the weld pool separately. TIG welding must be performed with a low, constant current power source to avoid drawing substantial current when the electrode short-circuits on the workpiece surface. The welding arc can be initiated by establishing a short circuit on the surface.
Until the short-circuit is closed, the primary welding current will not flow. The most common method of igniting the TIG arc is high frequency (HF), which consists of high voltage sparks with several thousand volts that lasts for a few microseconds. Because of the HF sparks, the electrode-workpiece gap will collapse or ionize, and current will flow from the power source.
In AC, the polarity of the electrodes is reversed roughly 50 times per second, extinguishing the arc with each polarity change. HF sparks are created across the electrode/workpiece gap at the start of each half-cycle to ensure that the arc is reignited at each polarity change.
DC welding electrodes are commonly constructed of pure tungsten with 1 to 4% thoria to improve arc ignition. Lanthanum oxide and cerium oxide are replacement additives that promise improved performance. The tungsten electrode is advantageous because it melts all metals below its melting point of 3380℃.
The appropriate electrode diameter and tip angle must be selected based on the amount of welding current. Electrodes with smaller diameters and tip angles utilize lower current. Zirconia-added tungsten reduces electrode erosion because the electrode in AC welding operates at a much higher temperature.
The shielding gas used is determined by the material being welded and includes:
- Argon – it’s used to weld materials such as titanium, steel, and stainless steel.
- Helium/Argon mixture – adding helium to argon raises the temperature of the arc, allowing for faster welding and deeper weld penetration.
TIG produces exceptionally high-quality welds on a wide range of materials with thicknesses ranging from 8 to 10mm and works exceptionally well with sheet material. This welding process's success is determined by several factors, including welding technique, welding wire, and shielding gas selection.
Metal Inert Gas Welding
MIG welding is a technique in which filler metal is continually fed into the welding gun while a welding current fuses the base materials. Electric current is generated by a wire continuously passing through the welding torch that melts the base metal. This process utilizes a constant voltage power supply.
An inert gas is pulled from a supply tank and directed to the nozzle simultaneously. This allows the shielding gas to shield the weld pool from impurities uniformly. Metal wire can be delivered to the weld pool using a variety of MIG welding processes, including:
- Globule transfer
- Pulsed method
- Short circuit welding.
- Spray welding
The same wire feed machine supplies different types of wire electrodes. Most MIG users prefer hard wire since it is convenient and inexpensive. Flux-cored wire does not require a shielding gas during welding because the flux is already incorporated into the wire. Due to the lack of additional shielding gas, flux-core is better suited to working outdoors and in windy conditions.
MIG welding gas is supplied through the welding torch as the metals melt in the welding zone to prevent contamination of the weld pool. The inert gasses, which have no impact or reaction with the weld, preserve the metal's properties at the operating temperatures of 1650℃.
Argon and helium are the two most commonly used gasses in MIG welding. Semi-inert gasses containing trace levels of carbon dioxide are another alternative. Carbon dioxide is inexpensive and produces more spatter in the weld pool while allowing deeper penetration.
Liners are essential because they ensure that the wire feeds smoothly during the welding process. A welding torch is a necessary tool for melting and fusing metals. MIG torches are classified into two categories and can be used for a variety of metal thicknesses and metal types:
Gas-cooled welding torches work well for little jobs but overheat when used for larger projects.
Water-cooled welding torches are more powerful, consume more amperage, and provide smoother control over the nozzle's contact tip.
Because DC provides continuous voltage, the power supply in a MIG welder is commonly set to DC. Modern MIG welding equipment automatically adjusts the current when the arc length and wire feed speed vary, allowing the MIG welder to generate a consistent weld puddle.
AC electricity is almost always used in metal inert gas welding. It is used while working on a tight budget and is preferable for welding non-ferrous metals. Other welding procedures are recommended instead of AC power because the difficulties of losing arc control and spatter in the weld pool are already severe.
Arc welding is a process of connecting two metals that involves utilizing electricity to generate enough heat to melt metal and then allowing the melted metal to cool. It is a type of welding in which an electric arc is generated between a metal electrode and the base material, melting the metals there. Arc welders can also use direct or alternating current and consumable or non-consumable electrodes.
The arc is started and maintained by the power supply, and the electrode is either mechanically or manually pushed along the joint to complete the weld. The welding arc needs a temperature of 3590°C to melt and fuse the metal. As a result, the metal parts melt and fuse, but this causes another issue; molten metal may react with gasses in the air at extremely high temperatures.
The resulting welded component has flaws, such as weak and porous welds. Therefore, it’s common practice to offer molten pool shielding to eliminate these welding problems during arc welding. There usually are two ways to accomplish this:
Flood the hot weld with a specialized shielding gas – this protects the molten metal from atmospheric air; the shielding gas type and flow rate must be appropriate.
Flux – this generates its shielding gas and slag when subjected to high welding temperatures. The flux's inert gas and slag cover the weld, keeping atmospheric gases at bay.
Stick welding is the most common and straightforward method of welding. As a result, it is used in virtually every industry, including:
- Manufacturing – pressure vessels
- Oil and gas pipelines
- Construction – bridges
- Machines – ships, trains, and farm machinery
- Automotive – cars and trailers
Because of how rapidly and economically it can be done, stick welding is effectively used whenever two pieces of metal need to be connected. However, the extreme heat created can be a problem for some operations. Therefore, stick welding is only suitable for some projects.
Differences between TIG, Arc, and MIG Welding
TIG welding uses a long rod to fuse metals, as opposed to MIG welding, which uses a feed wire to generate a lot of sparks that melt to produce a welded finish.
Because of MIG's wire feed, which serves as a filler and an electrode, thicker metals can be fused without being heated to their cores. Because MIG welding employs filler, you won't have to change the wire as frequently.
Stick welding produces a near-perfect quality pass while also being efficient and fast. The arc is undoubtedly one of the strongest metal-to-metal bonds formed during welding.
MIG can weld a variety of metals, including steel and aluminum. MIG is beneficial for heavy-duty applications and heavier metals. TIG welding can join a wide range of metals, although it is unreliable when working with thicker metals.
Arc is undeniably one of the fastest techniques, but mastering it takes a lot of practice. Operators must be highly knowledgeable and capable of performing at a high level of professionalism. However, the technique could be more beginner-friendly because it entails high temperatures, which can be uncomfortable.
Welding Safety and Precautions
Welders need protective breathing equipment, goggles, helmets, and gloves to protect themselves from physical harm and burns. Equipment must be regularly inspected and maintained to ensure it is safe.
Standard processes should be in place, providing immediate direction for those who find themselves in dangerous situations. The welding area must be close to fire extinguishers and a fire alarm. A first aid kit that is adequately supplied should be simple to get to so that any injuries can be treated right away.
Clean workplaces free from clutter and the threat of fire should be used for welding, preferably in a dry location. Regulators shouldn't be exchanged between gas cylinders, and the cylinders should always be kept upright. Gasses and liquids that can catch fire should be kept out of the welding area.
Equipment needs to be adequately insulated and kept in good working order to protect welders against electrical shock. To prevent electrodes from touching wet clothing or flesh, welders should wear the appropriate gloves. Continuous training helps welders adhere to safety precautions and stay current with industry standards.
Welding is an essential skill for a beginner based on the numerous applications in the industry. Most engineering projects greatly depend on welding for joining metal pieces of all shapes and sizes. However, the complexity of a welding technique determines a beginner’s progression. Regardless of the several challenges one may face when learning how to weld, it's a worthwhile endeavor.