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Since the mid-20th century, electron-beam technology has provided the basis for a variety of novel and specialized applications in semiconductor manufacturing, microelectromechanical systems, nanoelectromechanical systems, and microscopy.
Free electrons in a vacuum can be manipulated by electric and magnetic fields to form a fine beam. Where the beam collides with solid-state matter, electrons are converted into heat or kinetic energy. This concentration of energy in a small volume of matter can be precisely controlled electronically, which brings many advantages.
The rapid increase of temperature at the location of impact can quickly melt a target material. In extreme working conditions, the rapid temperature increase can even lead to evaporation, making an electron beam an excellent tool in heating applications, such as welding. Electron beam technology is used in cable-isolation treatment, in electron lithography of sub-micrometer and nano-dimensional images, in microelectronics for electron-beam curing of color printing [1] and for the fabrication and modification of polymers, including liquid-crystal films, among many other applications.
In a vacuum, the electron beam provides a source of heat that can melt or modify any material. [2] This source of heat or phase transformation is absolutely sterile due to the vacuum and scull of solidified metal around the cold copper crucible walls. This ensures that the purest materials can be produced and refined in electron-beam vacuum furnaces. Rare and refractory metals can be produced or refined in small-volume vacuum furnaces. For mass production of steels, large furnaces with capacity measured in metric tons and electron-beam power in megawatts exist in industrialized countries.
Since the beginning of electron-beam welding on an industrial scale at the end of the 1950s, countless electron-beam welders have been designed and are being used worldwide. These welders feature working vacuum chambers ranging from a few liters up to hundreds of cubic meters, with electron guns carrying power of up to 100 kW.
Modern electron-beam welders are usually designed with a computer-controlled deflection system that can traverse the beam rapidly and accurately over a selected area of the work piece. Thanks to the rapid heating, only a thin surface layer of the material is heated. Applications include hardening, annealing, tempering, texturing, and polishing (with argon gas present). If the electron beam is used to cut a shallow trough in the surface, repeatedly moving it horizontally along the trough at high speeds creates a small pile of ejected melted metal. With repetition, spike structures of up to a millimeter in height can be created. These structures can aid bonding between different materials and modify the surface roughness of the metal.
Additive manufacturing is the process of joining materials to make objects from 3D model data, usually by melting powder material layer upon layer. Melting in a vacuum by using a computer-controlled scanning electron beam is highly precise. Electron-beam direct manufacturing (DM) is the first commercially available, large-scale, fully programmable means of achieving near net shape parts.
The source billet metal is melted by an electron beam while being spun vigorously. Powder is produced as the metal cools when flying off the metal bar.
Electron-beam machining is a process in which high-velocity electrons are concentrated into a narrow beam with a very high planar power density. The beam cross-section is then focused and directed toward the work piece, creating heat and vaporizing the material. Electron-beam machining can be used to accurately cut or bore a wide variety of metals. The resulting surface finish is better and kerf width is narrower than what can be produced by other thermal cutting processes. However, due to high equipment costs, the use of this technology is limited to high-value products.
An electron lithograph is produced by a very finely focused electron beam, which creates micro-structures in the resist that can subsequently be transferred to the substrate material, often by etching. It was originally developed for manufacturing integrated circuits and is also used for creating nanotechnology architectures. Electron lithographs uses electron beams with diameters ranging from two nanometers up to hundreds of nanometers. The electron lithograph is also used to produce computer-generated holograms (CGH). Maskless electron lithography has found wide usage in photomask making for photolithography, low-volume production of semiconductor components, and research and development activities.
Physical vapor deposition takes place in a vacuum and produces a thin film of solar cells by depositing thin layers of metals onto a backing structure. Electron-beam evaporation uses thermionics emission to create a stream of electrons that are accelerated by a high-voltage cathode and anode arrangement. Electrostatic and magnetic fields focus and direct the electrons to strike a target. The kinetic energy is transformed into thermal energy at or near the surface of the material. The resulting heating causes the material to melt and then evaporate. Temperatures in excess of 3500 degrees Celsius can be reached. The vapor from the source condenses onto a substrate, creating a thin film of high-purity material. Film thicknesses from a single atomic layer to many micrometers can be achieved. This technique is used in microelectronics, optics, and material research, and to produce solar cells and many other products.
Electron-beam curing is a method of curing paints and inks without the need for traditional solvent. Electron-beam curing produces a finish similar to that of traditional solvent-evaporation processes, but achieves that finish through a polymerization process. E-beam processing is also used to cross-link polymers to make them more resistant to thermal, mechanical or chemical stresses.
E-beam processing has been used for the sterilization of medical products and aseptic packaging materials for foods, as well as disinfestation, the elimination of live insects from grain, tobacco, and other unprocessed bulk crops.
An electron microscope uses a controlled beam of electrons to illuminate a specimen and produce a magnified image. Two common types are the scanning electron microscope (SEM) and the transmission electron microscope (TEM).
Electron beams impinging on metal produce X-rays. The X-rays may be diagnostic, e.g., dental or limb images. Often in these X-ray tubes the metal is a spinning disk so that it doesn't melt; the disk is spun in vacuum via a magnetic motor. The X-rays may also be used to kill cancerous tissue. The Therac-25 machine is an infamous example of this.
MEMS is the technology of microscopic devices incorporating both electronic and moving parts. MEMS are made up of components between 1 and 100 micrometres in size, and MEMS devices generally range in size from 20 micrometres to a millimetre, although components arranged in arrays can be more than 1000 mm2. They usually consist of a central unit that processes data and several components that interact with the surroundings.
Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as brazing and soldering, which do not melt the base metal.
Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.
Lamination is the technique/process of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance, or other properties from the use of the differing materials, such as plastic. A laminate is a permanently assembled object created using heat, pressure, welding, or adhesives. Various coating machines, machine presses and calendering equipment are used.
Induction heating is the process of heating electrically conductive materials, namely metals or semi-conductors, by electromagnetic induction, through heat transfer passing through an inductor that creates an electromagnetic field within the coil to heat up and possibly melt steel, copper, brass, graphite, gold, silver, aluminum, or carbide.
Electron-beam welding (EBW) is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined. The workpieces melt and flow together as the kinetic energy of the electrons is transformed into heat upon impact. EBW is often performed under vacuum conditions to prevent dissipation of the electron beam.
Plastic welding is welding for semi-finished plastic materials, and is described in ISO 472 as a process of uniting softened surfaces of materials, generally with the aid of heat. Welding of thermoplastics is accomplished in three sequential stages, namely surface preparation, application of heat and pressure, and cooling. Numerous welding methods have been developed for the joining of semi-finished plastic materials. Based on the mechanism of heat generation at the welding interface, welding methods for thermoplastics can be classified as external and internal heating methods, as shown in Fig 1.
A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films is a fundamental step in many applications. A familiar example is the household mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as sputtering. Advances in thin film deposition techniques during the 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media, electronic semiconductor devices, integrated passive devices, LEDs, optical coatings, hard coatings on cutting tools, and for both energy generation and storage. It is also being applied to pharmaceuticals, via thin-film drug delivery. A stack of thin films is called a multilayer.
Ultra-high vacuum (UHV) is the vacuum regime characterised by pressures lower than about 1×10−6 pascals. UHV conditions are created by pumping the gas out of a UHV chamber. At these low pressures the mean free path of a gas molecule is greater than approximately 40 km, so the gas is in free molecular flow, and gas molecules will collide with the chamber walls many times before colliding with each other. Almost all molecular interactions therefore take place on various surfaces in the chamber.
Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode are protected from oxidation or other atmospheric contamination by an inert shielding gas. A filler metal is normally used, though some welds, known as autogenous welds, or fusion welds do not require it. When helium is used, this is known as heliarc welding. A constant-current welding power supply produces electrical energy, which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma. TIG welding is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminum, magnesium, and copper alloys. The process grants the operator greater control over the weld than competing processes such as shielded metal arc welding and gas metal arc welding, allowing stronger, higher-quality welds. However, TIG welding is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques. A related process, plasma arc welding, uses a slightly different welding torch to create a more focused welding arc and as a result is often automated.
Powder coating is a type of coating that is applied as a free-flowing, dry powder. Unlike conventional liquid paint which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as household appliances, aluminium extrusions, drum hardware, automobiles, and bicycle frames. Advancements in powder coating technology like UV-curable powder coatings allow for other materials such as plastics, composites, carbon fiber, and MDF to be powder coated due to the minimum heat and oven dwell time required to process these components.
In vacuum tubes and gas-filled tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. This is in contrast to a cold cathode, which does not have a heating element. The heating element is usually an electrical filament heated by a separate electric current passing through it. Hot cathodes typically achieve much higher power density than cold cathodes, emitting significantly more electrons from the same surface area. Cold cathodes rely on field electron emission or secondary electron emission from positive ion bombardment, and do not require heating. There are two types of hot cathode. In a directly heated cathode, the filament is the cathode and emits the electrons. In an indirectly heated cathode, the filament or heater heats a separate metal cathode electrode which emits the electrons.
Electron-beam physical vapor deposition, or EBPVD, is a form of physical vapor deposition in which a target anode is bombarded with an electron beam given off by a charged tungsten filament under high vacuum. The electron beam causes atoms from the target to transform into the gaseous phase. These atoms then precipitate into solid form, coating everything in the vacuum chamber with a thin layer of the anode material.
Physical vapor deposition (PVD), sometimes called physical vapor transport (PVT), describes a variety of vacuum deposition methods which can be used to produce thin films and coatings on substrates including metals, ceramics, glass, and polymers. PVD is characterized by a process in which the material transitions from a condensed phase to a vapor phase and then back to a thin film condensed phase. The most common PVD processes are sputtering and evaporation. PVD is used in the manufacturing of items which require thin films for optical, mechanical, electrical, acoustic or chemical functions. Examples include semiconductor devices such as thin-film solar cells, microelectromechanical devices such as thin film bulk acoustic resonator, aluminized PET film for food packaging and balloons, and titanium nitride coated cutting tools for metalworking. Besides PVD tools for fabrication, special smaller tools used mainly for scientific purposes have been developed.
Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface. The "feedstock" is heated by electrical or chemical means.
Evaporation is a common method of thin-film deposition. The source material is evaporated in a vacuum. The vacuum allows vapor particles to travel directly to the target object (substrate), where they condense back to a solid state. Evaporation is used in microfabrication, and to make macro-scale products such as metallized plastic film.
Electron-beam additive manufacturing, or electron-beam melting (EBM) is a type of additive manufacturing, or 3D printing, for metal parts. The raw material is placed under a vacuum and fused together from heating by an electron beam. This technique is distinct from selective laser sintering as the raw material fuses having completely melted.
A variety of processes, equipment, and materials are used in the production of a three-dimensional object via additive manufacturing. 3D printing is also known as additive manufacturing, because the numerous available 3D printing process tend to be additive in nature, with a few key differences in the technologies and the materials used in this process.
Laser welding of polymers is a set of methods used to join polymeric components through the use of a laser. It can be performed using CO2 lasers, Nd:YAG lasers, Diode lasers and Fiber lasers.
Advanced thermoplastic composites (ACM) have a high strength fibres held together by a thermoplastic matrix. Advanced thermoplastic composites are becoming more widely used in the aerospace, marine, automotive and energy industry. This is due to the decreasing cost and superior strength to weight ratios, over metallic parts. Advance thermoplastic composite have excellent damage tolerance, corrosion resistant, high fracture toughness, high impact resistance, good fatigue resistance, low storage cost, and infinite shelf life. Thermoplastic composites also have the ability to be formed and reformed, repaired and fusion welded.
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