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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.
In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure, or mixing with a catalyst. Heat is not necessarily applied externally, but is often generated by the reaction of the resin with a curing agent. Curing results in chemical reactions that create extensive cross-linking between polymer chains to produce an infusible and insoluble polymer network.
A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite to the head is called the tail. On installation, the rivet is placed in a punched or drilled hole, and the tail is upset, or bucked, so that it expands to about 1.5 times the original shaft diameter, holding the rivet in place. In other words, the pounding or pulling creates a new "head" on the tail end by smashing the "tail" material flatter, resulting in a rivet that is roughly a dumbbell shape. To distinguish between the two ends of the rivet, the original head is called the factory head and the deformed end is called the shop head or buck-tail.
Ultrasonic welding is an industrial process whereby high-frequency ultrasonic acoustic vibrations are locally applied to work pieces being held together under pressure to create a solid-state weld. It is commonly used for plastics and metals, and especially for joining dissimilar materials. In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together. When used to join metals, the temperature stays well below the melting point of the involved materials, preventing any unwanted properties which may arise from high temperature exposure of the metal.
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 fastener or fastening is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or dismantled without damaging the joining components. Welding is an example of creating permanent joints. Steel fasteners are usually made of stainless steel, carbon steel, or alloy steel.
Polyoxymethylene (POM), also known as acetal, polyacetal, and polyformaldehyde, is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability. As with many other synthetic polymers, it is produced by different chemical firms with slightly different formulas and sold variously by such names as Delrin, Kocetal, Ultraform, Celcon, Ramtal, Duracon, Kepital, Polypenco, Tenac and Hostaform.
Stud welding is a technique similar to flash welding where a fastener or specially formed nut is welded onto another metal part, typically a base metal or substrate. The fastener can take different forms, but typically fall under threaded, unthreaded, or tapped. The bolts may be automatically fed into the stud welder. Weld nuts generally have a flange with small nubs that melt to form the weld. Weld studs are used in stud welding systems. Manufacturers create weld studs for the two main forms of stud welding: capacitor discharge stud welding and drawn arc stud welding
Galling is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together. Galling is caused by a combination of friction and adhesion between the surfaces, followed by slipping and tearing of crystal structure beneath the surface. This will generally leave some material stuck or even friction welded to the adjacent surface, whereas the galled material may appear gouged with balled-up or torn lumps of material stuck to its surface.
A heat sealer is a machine used to seal products, packaging, and other thermoplastic materials using heat. This can be with uniform thermoplastic monolayers or with materials having several layers, at least one being thermoplastic. Heat sealing can join two similar materials together or can join dissimilar materials, one of which has a thermoplastic layer.
A wall plug, also known as an anchor (US) or "Rawlplug" (UK), is a fibre or plastic insert used to enable the attachment of a screw in material that is porous or brittle or that would otherwise not support the weight of the object attached with the screw. It is a type of anchor that, for example, allows screws to be fitted into masonry walls. In US English, mentions of drywall anchors are sometimes meant to refer specifically to the type of plastic wall plugs with expandable wings for hollow walls, in contradistinction with mollies and toggle bolts.
Anchor bolts are used to connect structural and non-structural elements to concrete. The connection can be made by a variety of different components: anchor bolts, steel plates, or stiffeners. Anchor bolts transfer different types of load: tension forces and shear forces.
Filler materials are particles added to resin or binders that can improve specific properties, make the product cheaper, or a mixture of both. The two largest segments for filler material use is elastomers and plastics. Worldwide, more than 53 million tons of fillers are used every year in application areas such as paper, plastics, rubber, paints, coatings, adhesives, and sealants. As such, fillers, produced by more than 700 companies, rank among the world's major raw materials and are contained in a variety of goods for daily consumer needs. The top filler materials used are ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), kaolin, talc, and carbon black. Filler materials can affect the tensile strength, toughness, heat resistance, color, clarity etc. A good example of this is the addition of talc to polypropylene. Most of the filler materials used in plastics are mineral or glass based filler materials. Particulates and fibers are the main subgroups of filler materials. Particulates are small particles of filler which are mixed in the matrix where size and aspect ratio are important. Fibers are small circular strands that can be very long and have very high aspect ratios.
Acrylonitrile styrene acrylate (ASA), also called acrylic styrene acrylonitrile, is an amorphous thermoplastic developed as an alternative to acrylonitrile butadiene styrene (ABS), but with improved weather resistance, and is widely used in the automotive industry. It is an acrylate rubber-modified styrene acrylonitrile copolymer. It is used for general prototyping in 3D printing, where its UV resistance and mechanical properties make it an excellent material for use in fused deposition modelling printers.
Welding of advanced thermoplastic composites is a beneficial method of joining these materials compared to mechanical fastening and adhesive bonding. Mechanical fastening requires intense labor, and creates stress concentrations, while adhesive bonding requires extensive surface preparation, and long curing cycles. Welding these materials is a cost-effective method of joining concerning preparation and execution, and these materials retain their properties upon cooling, so no post processing is necessary. These materials are widely used in the aerospace industry to reduce weight of a part while keeping strength.
Aluminium alloys are often chosen due to their high strength-to-weight ratio, corrosion resistance, low cost, high thermal and electrical conductivity. There are a variety of techniques to join aluminium including mechanical fasteners, welding, adhesive bonding, brazing, soldering and friction stir welding (FSW), etc. Various techniques are used based on the cost and strength required for the joint. In addition, process combinations can performed to provide means for difficult to join assemblies and to reduce certain process limitations.
Adhesive bonding is a process by which two members of equal or dissimilar composition are joined. It is used in place of, or to complement other joining methods such mechanical fasting by the use nails, rivets, screws or bolts and many welding processes. The use of adhesives provides many advantages over welding and mechanical fastening in steel construction; however, many challenges still exist that have made the use of adhesives in structural steel components very limited.
IR welding is a welding technique that uses a non-contact heating method to melt and fuse thermoplastic parts together using the energy from infrared radiation. The process was first developed in the late 1900s, but due to the high capital cost of IR equipment the process was not commonly applied in industry until prices dropped in the 1990s. IR welding typically uses a range of wavelengths from 800 to 11,000 nm on the electromagnetic spectrum to heat, melt, and fuse the interface between two plastic parts through the absorption and conversion of the IR energy into heat. Laser welding is a similar joining process that applies IR radiation at a single wavelength.
Solvent bonding is one of several methods of adhesive bonding for joining plastics. Application of a solvent to a thermoplastic material softens the polymer, and with applied pressure this results in polymer chain interdiffusion at the bonding junction. When the solvent evaporates this leaves a fully consolidated bond-line. An advantage to solvent bonding versus other polymer joining methods is that bonding generally occurs below the glass transition temperature of the polymer.
Adhesive bonding is a joining technique used in the manufacture and repair of a wide range of products. Along with welding and soldering, adhesive bonding is one of the basic joining processes. In this technique, components are bonded together using adhesives. The broad range of types of adhesives available allows numerous materials to be bonded together in products as diverse as vehicles, mobile phones, personal care products, buildings, computers and medical devices.
References
- ↑ R.Crawford (1985). Plastics and Rubber-Engineering Design and Application. MEP Ltd=Location=London. p. 148. ISBN 0-85298-571-1.
- ↑ O.Balkan, H.Demirer, A.Ezdesir, H.Yildirim (2008). "Polym.Engin.Sci". Polymer Engineering and Science 1961-1995. 48: 732. doi:10.1002/pen.21014. ISSN 1548-2634.
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