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Fusion welding
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Fusion welding is a generic term for welding processes that rely on melting to join materials of similar compositions and melting points.[1] Due to the high-temperature phase transitions inherent to these processes, a heat-affected zone is created in the material[1]: 755 (although some techniques, like beam welding, often minimize this effect by introducing comparatively little heat into the workpiece[2]).
In contrast to fusion welding, solid-state welding does not involve the melting of materials.
Applications
[edit]Fusion welding has been a critical factor in the creation of modern civilization due to its vital role in construction practices. Besides bolts and rivets, there are no other practical methods for joining pieces of metal securely. Fusion welding is used in the manufacture of many everyday items, including airplanes, cars, and structures. Beyond construction, a large community uses both arc and flame contact welding to create artwork.
Types
[edit]Electrical
[edit]Arc
[edit]Arc welding is one of the many types of fusion welding. Arc welding joins two pieces of metal together by using an intermediate filler metal. The way this works is by completing an electrical circuit to create an electrical arc. This electrical arc is 6500 °F (3593 °C) in its center.[3] This electrical arc is created at the tip of the filler metal. As the arc melts the metal, it is moved either by a person or a machine along the gap in the metals, creating a bond. This method is very common as it is typically done with a hand held machine. Arc welding machines are portable and can be brought onto job sites and hard to reach areas. It is also the most common method of underwater welding. Electrical arcs form between points separated by a gas. In the process of underwater welding a bubble of gas is blown around the area being welded so that an electrical arc may form. Underwater welding has many applications. Ship hulls are repaired and oil rigs are maintained with underwater arc welding.
Resistance welding is done using two electrodes. Each comes into contact with one of the pieces being welded. The two pieces of metal are then pressed together between the electrodes and an electric current is run through them.[4] The pieces of metal begin to heat up at the point where they come into contact. The current is passed through the metal until it is hot enough that the two pieces melt and conjoin. As the metal cools the bond is solidified. This process requires large amounts of electricity. In most cases transformers are needed to provide enough amps. Resistance welding is a very prevalent form of fusion welding. It is used in the manufacturing of automobiles and construction equipment.
Laser beam
[edit]Conduction welding, also known as laser beam welding or radiation welding, is a highly precise form of fusion welding. "Laser" is an acronym for Light Amplification by Stimulated Emission of Radiation. The laser emits light in bursts called pumps.[5] These bursts are aimed at the seam of the metals desired to be conjoined. As the laser bursts it is guided along the seam. These intense bursts melt the metal. The two metals when melted mix with each other. Once it has cooled the seam created is a strong bond. Lasers are efficient because they can be configured to make multiple welds at once. The laser beam can be split and sent to multiple locations greatly reducing the cost and amount of energy required. Laser beam welding finds applications in the automotive industry.
Induction
[edit]Induction welding is a form of resistance welding. However, there are no points of contact between the metal being welding and the electrical source or the welder. In induction welding a coil is wrapped around a cylinder. This coil causes a magnetic field across the surface of the metal inside. This magnetic field flows in the opposite direction of the magnetic field on the inside of the cylinder. These magnetic flows impede each other.[6] This heats the metal and causes the edges to melt together.
Chemical
[edit]Oxyfuel
[edit]Flame contact is a very common form of welding. The most popular kind of flame contact welding is oxyfuel gas welding. Flame contact welding uses a flame exposed to the surface of the metals being welded to melt and then join them together. Oxyfuel uses oxygen as a primary ignition source in tandem with another gas such as acetylene to produce a flame which is 2500 °C at the tip and 2800-3500 °C at the tip of the inner cone.[7] Other gasses such as propane and methanol can be used for oxyfuel welding. Acetylene is the most common gas used in oxyfuel welding.
Solid reactant
[edit]Solid reactant welding uses reactions between elements and compounds. Certain compounds when mixed create an exothermic chemical reaction, meaning they give off heat. A very common reaction uses thermite, a combination of a metal oxide (rust) and aluminum. This reaction produces heat over 4000 °F.[7] Solid reactant compounds are channeled to the two pieces of metal being joined. Once in place, a catalyst is used to start the reaction. This catalyst can be a chemical or another heat source. The heat created melts the metals being joined. Once it cools, a bond is formed. From welding together train tracks to entering bank vaults, solid reactant welding has many niche uses.
See also
[edit]- Autogenous welding – Form of welding where no additional filler material is added
References
[edit]- ^ a b Schey, John A. (2000) [1977], Introduction to Manufacturing Processes, McGraw-Hill series in mechanical engineering and materials science (3rd ed.), McGraw-Hill Higher Education, ISBN 978-0-07-031136-7, retrieved May 15, 2010,
In the great majority of applications, the interatomic bond is established by melting. When the workpiece materials (base or parent materials) and the filler (if used at all) have similar but not necessarily identical compositions and melting points, the process is referred to as fusion welding or simply welding.
- ^ Bull, Steve (March 16, 2000), "Fusion Welding Processes", MMM373 Joining Technology course website, Newcastle upon Tyne, England, United Kingdom: Newcastle University School of Chemical Engineering and Advanced Materials, archived from the original on September 11, 2007, retrieved May 16, 2010
- ^ L. (n.d.). Arc Welding Fundamentals. Retrieved March 17, 2016, from http://www.lincolnelectric.com/en-us/support/process-and-theory/Pages/arc-welding-detail.aspx
- ^ E. (n.d.). RESISTANCE WELDING BASICS. Retrieved March 17, 2016, from https://www.entroncontrols.com/images/downloads/700081C.pdf
- ^ U. (n.d.). YAG Laser Welding Guide. Retrieved March 17, 2016, from http://www.amadamiyachieurope.com/cmdata/documents/Laser-Welding-fundamentals.PDF Archived 2016-04-17 at the Wayback Machine
- ^ WRIGHT, J. (n.d.). PRINCIPLES OF HIGH FREQUENCY INDUCTION TUBE WELDING. Retrieved March 17, 2016, from http://www.eheimpeders.com/uploads/TB1000.pdf
- ^ a b H. (n.d.). FUSION WELDING PROCESSES. Retrieved March 17, 2016, from http://www4.hcmut.edu.vn/~dantn/lesson/POW/POW-p1c3.pdf[permanent dead link]
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Fusion welding
View on Grokipediafrom Grokipedia
Overview
Definition and Principles
Fusion welding is a joining process that permanently bonds two or more materials, typically metals, by melting the base metals at the joint interface and often incorporating a filler material of compatible composition, forming a molten pool that solidifies to create a metallurgical bond upon cooling.[1][6] This method relies on localized heating to exceed the melting point of the materials, enabling atomic diffusion and fusion without the need for external pressure in most cases, distinguishing it from solid-state welding techniques.[7][8] The fundamental principles of fusion welding center on controlled heat input to achieve melting while managing thermal effects on the surrounding material. Heat is supplied via concentrated sources, raising the temperature at the joint to 1000–2500°C depending on the metal's melting point, such as approximately 1500°C for steels or lower for aluminum alloys.[8][6] The energy required accounts for the materials' thermal conductivity, which governs heat dissipation; specific heat, which determines the energy to raise temperature; and latent heat of fusion, the energy absorbed during phase change from solid to liquid.[8] These properties influence the size of the molten pool and the overall efficiency of the process, as excessive heat can lead to unwanted distortion from differential thermal expansion.[7][6] In a typical fusion weld, the joint anatomy comprises distinct zones: the fusion zone, where base and filler metals fully melt and mix to form a solidified weld metal with a cast-like microstructure; the heat-affected zone (HAZ), an adjacent region that experiences elevated temperatures sufficient for microstructural alterations like grain growth or phase transformations (e.g., austenite formation in steels) without melting, potentially altering mechanical properties; and the unaffected base metal beyond the HAZ.[6][8] The HAZ width depends on heat input and material thermal diffusivity, typically following , where is the diffusion depth, is thermal diffusivity, and is exposure time.[8] Heat input in fusion welding, particularly for electrical arc-based methods, is often approximated as the power delivered to the weld, given by , where is heat energy rate, is voltage, is current, and is process efficiency (typically 0.6–0.9); this can be generalized for other heat sources like lasers by considering total energy per unit length to account for travel speed and beam power.[8][9] Several factors influence the quality and feasibility of fusion: material properties such as melting point and coefficient of thermal expansion, which affect compatibility and residual stresses; joint design, including configurations like butt, lap, or fillet joints that determine accessibility and load distribution; and shielding techniques, such as inert gas atmospheres, to prevent oxidation or contamination of the molten pool by atmospheric gases.[6][8]Comparison with Other Welding Methods
Fusion welding differs fundamentally from solid-state welding processes, such as friction stir welding or diffusion bonding, in that it requires heating the base metals to their melting point to form a molten pool that coalesces upon solidification, whereas solid-state methods join materials below the melting temperature using pressure and deformation without melting.[10] This melting in fusion welding can introduce solidification defects like porosity or cracking but enables the use of filler metals to bridge gaps and alloy dissimilar materials more readily.[11] In contrast, solid-state welding minimizes heat-affected zones (HAZ) and preserves original material properties, making it preferable for heat-sensitive alloys, though it often demands precise surface preparation and is less versatile for thick sections.[12] Unlike brazing and soldering, which are filler-metal-based joining techniques, fusion welding melts the base metals themselves to achieve metallurgical bonding, resulting in joints that are integral to the parent material rather than relying solely on capillary action of a lower-melting filler.[13] Brazing occurs at temperatures above 450°C but below the base metal's melting point, while soldering uses even lower temperatures (typically under 450°C), both avoiding base metal fusion to prevent distortion in delicate assemblies.[13] Consequently, fusion welds offer superior shear and tensile strength for load-bearing applications, though they require higher energy input and skilled operators to control the melt pool.[10] Fusion welding provides distinct advantages over mechanical fastening methods like riveting or bolting, producing permanent, airtight joints that distribute loads continuously across the interface without stress concentrations from holes or fasteners, thereby enhancing overall structural integrity in metal components.[14] These joints can achieve strengths exceeding the base material when properly executed, and they reduce assembly weight by eliminating additional hardware, which is particularly beneficial in aerospace and automotive structures.[14] However, mechanical fastening allows for disassembly and is less prone to residual stresses from heating. Relative to adhesive bonding, fusion welding excels in creating high-strength, fatigue-resistant connections for metallic structures under dynamic loads, as the fused joint forms a homogeneous bond without relying on chemical adhesion that can degrade over time due to environmental exposure.[15] Adhesives, while offering uniform stress distribution and suitability for dissimilar or thin materials, often introduce heat distortion challenges in fusion processes, though adhesives avoid such thermal effects entirely and enable bonding of non-metals like plastics.[15] Fusion welding's thermal input can cause warping in thin sections, limiting its use where dimensional precision is critical without fixturing.| Method Type | Heat Involvement | Material Suitability | Joint Strength | Equipment Cost |
|---|---|---|---|---|
| Fusion Welding | Melting of base metals required | Primarily metals; some alloys | High (often > base metal) | Medium to high (e.g., arc/laser setups) |
| Solid-State | Below melting point; pressure-based | Metals, including heat-sensitive | High, preserves properties | High (specialized tools) |
| Adhesive Bonding | None; chemical curing | Metals, plastics, dissimilar | Medium to high | Low (applicators) |
| Mechanical Fastening | None; physical interlocking | Metals, composites | Medium | Low (tools/hand) |