What is the daily life of a welder?
Welding refers to a process of joining materials, often metals and thermoplastics. It involves using high heat to melt parts together and then cooling them to cause fusion. Welding differs from other lower-temperature techniques like brazing or soldering that do not melt the parent metal. A filler material is usually added to the joint to melt the base metal. This pool of molten materials (the weldpool) cools to form the joint. It can be based on the weld configuration (butt or full penetration, fillet etc. The base metal can be stronger than the filler material. To create a weld, pressure can be combined with heat or used by itself. To prevent filler metals and melted metals being oxidized or contaminated, welding requires some form of shield.
The heat affected zone (HAZ), is an area surrounding the weld that alters the heat treatment properties of the alloy due to the combination of uneven heating and cooling. The effects of welding on the material surrounding the weld can be detrimental--depending on the materials used and the heat input of the welding process used, the HAZ can be of varying size and strength. The thermal diffusivity, or heat exchange rate, of the base materials plays an important part in the HAZ. High diffusivity material will cool faster and have a lower HAZ. A lower diffusivity means slower cooling and an increased HAZ. Heat injected by welding processes plays an important part. Processes such as oxyacetylene-welding have unconcentrated heat inputs and increase the HAZ. Laser beam welding, for example, produces a very concentrated and limited amount heat. This results is a low HAZ. Arc welding falls somewhere between these extremes. The heat input for each individual process can vary slightly. Here is a formula that can be used to calculate the heat input needed for arc welding.
Arc welding is influenced by the type of current used. Direct current is used for consumable electrode processes like shielded metal and gas metal welding. However, the electrode can be charged positively or negatively. The heat concentration of the positively charged anode in welding will be higher, so changing the polarity can affect weld properties. Positively charged electrodes will have higher weld penetration and faster welding speeds. A negatively charged electrode will result in shallower welds. For non-consumable processes like gas tungsten or arc welding, you can use both alternating and direct current. Direct current is not able to create an arc, and therefore a negatively charged electrode will cause deeper welds. The medium-penetration welds are created by alternating current, which rapidly moves between them. AC's disadvantage, that the arc must be re-ignited after each zero crossing, was addressed by the invention of special power units. These produce a square wave pattern, instead of the usual sine wave. This makes it possible to quickly zero cross and minimizes the problems.
The embrittlement effect of impurities or, in the case of body-centred cubical metals, a decrease in temperature can also cause a decrease in fracture toughness. Metals, and especially steels, have a range of transitional temperatures where the metal's notch-ductility is acceptable above which the material becomes brittle below. The materials' behavior within this range is unpredictable. A decrease in fracture toughness can be accompanied by a change of fracture appearance. The fracture appearance is fibrous when it rises above the transition. The fracture will display cleavage features when temperatures drop. These appearances can be seen by the naked eye. Under a microscope, chevron marks may be visible from steel plates with brittle fracture. These arrow-shaped ridges at the crack surface indicate the source of the fracture.
Gas metal arc welding, also known as MIG welding or metal inert gaz welding (GMAW), is a semiautomatic or automated process that uses a continuous wire-feed as an electrode. To protect the weld against contamination, an inert- or semi-inert mixture of gases is used. GMAW is faster than SMAW due to the continuous electrode. The flux-cored process of arc welding (FCAW) is similar but uses wire that has a steel electrode around a powdered fill material. While cored wire costs more than regular solid wire and can produce fumes and/or lead, it is also easier to weld and allows for greater metal penetration. Gas tungsten-arc welding (GTAW), also known as tungsten-inert-gas (TIG) welding is a manual process that uses a nonrecyclable tungsten-electrod, inert, semi-inert, or gas mixture, and a filler material. This method is particularly useful for welding thin material. It produces a stable arc, high-quality welds and requires significant operator skill.
GTAW is able to be used on almost any weldable metal. But it is most commonly used on stainless steel and other light metals. This method is most commonly used for high-quality welding, such in aircraft, naval, and bicycle applications. Plasma arc welding, which uses a tungsten arc electrode and plasma gas to create it, is another similar process. The arc's concentration is higher than that of the GTAW arc. This makes transverse control more crucial and restricts the ability to use this technique for a more automated process. Because the method uses a stable current it can be used to work with a greater range of material thicknesses then the GTAW process. Additionally, it is faster. This process can be applied to almost all materials, with the exception of magnesium. Another important application is automated welding stainless steel. Another variant is plasma cutting, which is a highly efficient steel cutting process.
Many welding processes require specific joint designs. Other welding techniques, such as shielded-metal arc welding are very versatile and can be used to weld any type joint. Multipass welding, where one weld cools and another weld follows, can also be done. This allows for welding thick sections in a single-V joint. You can identify a number distinct areas in the weld zone after welding. The fusion zone, or the location where the metal filler was laid during welding, is what is known as the weld itself. The properties of a fusion zone are largely determined by the filler material used and their compatibility with base materials. It is surrounded with the heat affected zone, an area whose microstructure was altered and whose properties were changed by welding. These properties are determined by how heat affects the base metal. This area often contains more metal than the base material and fusion zone. Additionally, residual stresses are common.
Welding can be dangerous and unhealthy if the proper precautions are not taken. However, using new technology and proper protection greatly reduces risks of injury and death associated with welding. Since many common welding procedures involve an open electric arc or flame, the risk of burns and fire is significant; this is why it is classified as a hot work process. To prevent injury, welders wear personal protective equipment in the form of heavy leather gloves and protective long-sleeve jackets to avoid exposure to extreme heat and flames. Synthetic clothing such as polyester should not be worn since it may burn, causing injury. Additionally, the brightness of the weld area leads to a condition called arc eye or flash burns in which ultraviolet light causes inflammation of the cornea and can burn the retinas of the eyes. Goggles and welding helmets with dark UV-filtering face plates are worn to prevent this exposure. Since the 2000s, some helmets have included a face plate which instantly darkens upon exposure to the intense UV light. To protect bystanders, the welding area is often surrounded with translucent welding curtains. These curtains, made of a polyvinyl chloride plastic film, shield people outside the welding area from the UV light of the electric arc, but cannot replace the filter glass used in helmets.
