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Welding is the process of permanently joining two or more metals through the application of high heat, which is typically achieved by either flame or electricity. Essentially, the fused metals become one, with the welded joint area assuming the same properties as the base metal, and in some cases, the welded portion has the same strength as the parent metal. Welding is vital to any industry involving metal fabrication, including construction, aerospace, aviation, and shipbuilding, to name a few.
Of the various welding methods that are utilized today, one of the most commonly used and heavily relied upon is known as TIG welding.
How strong is TIG welding? TIG (“Tungsten Inert Gas”) welding is an extremely strong and versatile process of fusing metals. Not only does this welding method produce incredibly strong bonds, but because the resulting weld assumes the same anti-corrosion characteristics as the parent metal, it is commonly used in the fabrication of critical spacecraft, aircraft, naval craft, and automobile components.
To fully appreciate the crucial role that TIG welding plays in today’s industrialized society and the highly specific characteristics of TIG welds, it is essential to understand the basic concepts of welding in general, and what sets TIG welding apart from other welding processes.
Although there are over 50 different welding methods to join metals together, they all share a common goal: to fuse two or more metals, essentially creating one single piece. To accomplish this objective, metal welding can be broken down into three phases, (1) melting the metal, (2) creating the weld joint, and (3) preventing contamination of the weld.
Welding is not the same as soldering. Whereas metals are heated and bound together through the process of soldering, when metals are welded, they are melted to a molten state and fused to become structurally homogeneous.
Melting the Metal
Welders employ a variety of technologies to achieve the high temperatures needed to melt certain metals to their molten state. The most common methods of heating and melting metal are:
- Electrical – electric arc
- Chemical – gas flame
- Electron beam
Of these, the electric arc heating method is the most widely used in both automated and manual welding operations. Power is supplied to an electrode, which in turn creates and maintains an electric arc between the tip of the electrode and the weld point on the base metal material. The electric arc focuses such high temperature at the weld point that the metal melts and reaches a molten (semi-liquid) state. This molten material is known as a weld pool.
Creating the Joint
The main objective of welding is to fuse two or more pieces of metal into a single piece. The specific point or points where the metal pieces come into contact with each other and where the welding will join the pieces together are called welding joints.
Depending on how the metal pieces are oriented in relation to each other, a different type or style of welding joint will be utilized. For example, if two pieces of metal are perpendicular to each other edge to edge (thereby creating a 90° angle), then a corner joint will be welded. If one piece of metal is oriented perpendicular to another piece creating a T shape, then a tee joint will be welded. Other common weld joints include:
|Used to join two pieces of metal that are parallel to each other, either end to end or side by side (commonly used in automated welding operations).
|When one piece of metal is placed on top of another in an overlapping fashion, a lap joint is used to fuse the pieces in this orientation.
|This type of joint is typically used to join adjacent pieces of metal along a common edge (this type of joint is seldom used).
Here’s a good visual breakdown of the different types of welding joints with corresponding weld types.
There are specific types of welds that are utilized with specific welding joints. The weld type refers to the particular style or shape of the weld itself. It is beneficial when trying to visualize a particular weld type to imagine a cross-section of the weld as it is used in relation to the weld joint.
The types of welds most commonly used are bead, fillet, and groove welds. A bead weld has a uniform, domelike shape, while a fillet weld has the appearance of a right triangle when viewed in cross-section. A groove weld can be best visualized as filling an angular void or gap between two pieces of metal.
Some other common types of welds include:
Illustrations of these weld types, along with weld joints that are commonly used, can be found here.
As the weld joint is created and heated to a molten state, a small pool of the molten material is formed. Typically a filler material consisting of a softer metal like aluminum is added to this weld pool (the particular filler material used will depend on the specific metals being welded). The filler serves as a binding agent. Once the weld cools, the previously molten material hardens into a cohesive bond that is as strong and structurally sound as the original material itself. Filler rods come in various thicknesses and lengths but often have the appearance of a wire coat hanger.
Preventing Oxidation and Contamination of the Weld
During the welding process, extreme temperatures cause various chemical and physical changes to occur that fuse metal surfaces to each other. It is during this period of controlled volatility that appropriate steps must be taken to protect the newly formed metal entity from contamination or oxidization.
Oxidization of metal occurs on a molecular level and compromises the metal’s strength and integrity. An example of oxidization that we can see every day is rust. In the case of a weld, however, oxidization has far more profound ramifications beyond appearance. If a weld oxidizes, the structural strength of the metal will be weakened, dramatically increasing the possibility that the weld will fail. If such welds are used in the fabrication of vital aircraft or automobile parts, or the construction of spacecraft components, the results of a weld failure could be catastrophic.
Fortunately, the utilization of shielding gases during welding virtually eliminates the possibility of oxidization. Inert gases (also known as noble gases) are used to shield the metal and filler from oxygen, and water vapor as the weld pool forms and the weld joint is created. The specific shielding gas used during a welding operation will depend on the particular metals being welded along with the filler material being used. There are specific protocols for the selection of shielding gases, and in many cases, multiple gases are combined for use in a particular welding operation.
Here is a chart of shielding gas mixtures for welding various metal types – it is essentially a recipe chart of gases.
What is TIG Welding?
The method of TIG welding was developed in the 1930s for welding magnesium in the aircraft industry, and perfected in 1941 by Northrop Aircraft. TIG welding is also known as gas tungsten arc welding or GTAW.
The tungsten, in its name, refers to the material used for the electrode in the welding torch. The electrode used in TIG welding is made of tungsten or a tungsten alloy. Tungsten has the highest melting point among all pure metals at 6,192° F. At this temperature, the tungsten electrode does not melt or deteriorate during the welding process – this is also known as a non-consuming electrode – and remains largely intact, which promotes purity of the weld. (Electrodes which melt during the welding process are known as consuming electrodes.)
TIG welding can be performed on more types of metal than any other welding method, and as a result, is widely used across a broad range of industries and applications. The only metals on which TIG welding cannot be used are zinc and zinc alloys. Furthermore, because of the non-consuming tungsten electrode it uses, a greater number of filler materials can be used, allowing for better compatibility matching between welded metal and filler material, thereby producing higher quality welds. In other words, specific filler materials can be utilized with particular types of metal, even exotic ones.
TIG welding is even popular with artists specializing in metal sculpting because of the incredibly diverse palette of materials it can work with, and the detailed, intricate welds it can produce in the hands of an experienced welder.
The Unique Characteristics and Benefits of TIG Welding
TIG welding is a two-handed, manual welding process, meaning that the welder holds the welding torch in one hand while feeding the filler material with the other. Often, the intensity of the electric arc and the resulting heat that is produced can be adjusted with foot pedals or a thumb switch on the torch. Because it is performed manually versus via automation, TIG welding is usually reserved for those applications which require the greatest weld strength and highest weld quality.
A TIG welder must have excellent manual dexterity to manage the multiple processes occurring simultaneously during TIG welding such as (1) adjusting the electrical amperage or current going to the welding torch to increase or decrease the intensity of the arc, and thereby the amount of heat applied to the base metal, (2) the flow of shielding gas to protect the welding zone from any impurities, and (3) assessing proper penetration and depth levels of the material and welds as the welding is proceeding.
As a result, TIG welding is a far slower, more deliberate process than automated welding methods. It is more difficult for welders to master due to its complex nature, but it does produce higher quality welds. TIG welding can also produce more intricate welds, such as curved or complex joints.
Because of the stable arc and consistently high-quality welds it produces, this welding method is the preferred choice for welding thin pieces of metal, including stainless steel and non-ferrous (containing no appreciable amounts of iron) metals such as aluminum, magnesium, copper alloys. It is also extremely versatile. It is capable of working with the broadest range of both metals and fillers, including exotic materials used in highly specialized applications such as space vehicles and military assets.
Applications for TIG Welding
Because of its highly specialized nature, TIG welding is typically reserved for applications that require highly precise, structurally sound welds with zero failure rates. These parameters certainly speak not only to the strength of TIG welds but also their overall quality and reliability.
Here are some examples of industries that utilize TIG welding with specific applications and uses. This is by no means an exhaustive list, but rather a small sampling of the vast implementation of TIG welding across a broad and diverse range of industries.
|APPLICATIONS AND USES OF TIG WELDING
|Highly specialized need for durable but lightweight materials and precision welding of components subject to extreme temperature differentials Examples: Lunar vehicles and space vehiclesFabrication of spacecraft componentsSpacecraft delivery equipment (rockets, boosters)
|Similar requirements as aerospace – lightweight materials and precision welding, extreme conditions Examples: Crossbeams and strutsStructural componentsLanding gear assembliesFuel delivery systems (pipes and tubing)
|Need for corrosion-resistant components subject to extreme environmental conditions (below freezing to above boiling) Examples: ManifoldsStruts and suspensionFront and rear fender
|Bicycle frames consist of lightweight metals formed into small-diameter tubes with thin walls Examples: Welding of bike frame tubing (top bar, bottom bar, forks, seat post)Handlebar assembly, cranks
|Similar requirements as aerospace and aviation industries, extreme temperature differentials, zero tolerance for weld failure Examples: Military hardware and assets (cross beams, supports, struts)Fuel delivery systems (pipes and tubing)Specialized vehicles (frames and structural aspects)
|Structurally sound welds with zero failure rate Examples: Fuel delivery systems (pipes and tubing)ManifoldsBarrels used to dispose of spent nuclear waste
|A broad range of applications ranging from specialized equipment needs to product/material conveyance and industrial processes Examples: Manifolds, piping, and tubingStructural elementsMaterial handling and conveyanceIndustrial processes (thermal, hydraulic, etc.)
|Precision welding of components of intricate medical devices and apparatus Examples: Intricate piping and tubingEquipment support frames
|Lightweight materials with greatest structural strength possible for load-bearing, high-stress components Examples: Motorbike frames and supportsRacecar struts, crossbars and supportsRacecar fabrication
|Piping and Plumbing
|Welding of a wide variety of materials in shapes and sizes of all kinds into a broad range of designs and configurations (many of which are customized) Examples: Odd sized pipingCustom plumbing fittingsManifolds
|Repair or refurbishment of industrial tools, molds, dies and other apparatus, particularly those composed of specialized materials Examples: Custom dies, molds and jigs (using highly specialized materials)Repair of aluminum toolsRetrofitting older equipment with newer componentry or features
It is particularly telling that in today’s industrial world where automation is increasingly replacing skilled labor, the critical welding jobs requiring absolute accuracy and reliability are still left to the two capable hands of a TIG welder.
Other Common Welding Methods
Because of its slow and deliberate nature, TIG welding is not suited for applications requiring high-volume production or faster turnaround times. It is also an expensive process because of the high-end nature of the equipment and materials used. There are numerous applications where precision welding or the specialized nature of TIG welding are not needed or applicable.
Other common welding techniques and processes include:
|Shielded Metal Arc Welding (SMAW)
|Also known as manual metal arc welding (MMAW) or stick welding, this may be the most versatile form of welding with the least expensive equipment and materials needed. It is commonly found in repair shops and utilized for fieldwork. Unlike TIG welding, the electrode is consumable and doubles as the filler. A flux (a substance that inhibits oxidation) is incorporated into the core around the electrode.
|Gas Metal Arc Welding (GMAW)
|Also known as metal inert gas (MIG) welding. This is a semi-automated or fully automated welding process that achieves greater welding speed through the utilization of a continuous feed electrode. Inert or semi-inert gases are used to shield the metal from contamination or oxidization.
|Flux Cored Arc Welding (FCAW)
|Uses equipment similar to MIG welding but utilizes a steel core wire integrated with powder fill material that achieves greater welding speed and deeper penetration than MIG welding. The drawbacks are more fumes and slag (residual material consisting of oxidized metal and contaminants).
|Submerged Arc Welding (SAW)
|This welding method is popular in industrial applications for its high arc quality and low contamination rate, and because of its high deposition rate and low smoke emissions. In this method, the arc is created and maintained beneath a layer of flux. It is particularly well suited for large welding jobs.
|Electroslag Welding (ESW)
|This is a specialized form of welding that is usually reserved for thicker materials (from 1” to 12” thicknesses). This is a single pass method that is performed in a vertical orientation.