Welding is the act of seamlessly uniting metals, thermoplastics, or wood with heat or pressure, to form a longer, more stable piece. During the process, high heat is used to melt the parts together before allowing them to cool, causing fusion. Aside from the original pieces, also known as 'parent materials', welding also uses an additional material called a filler or consumable that's responsible for binding the separate pieces together. This usually comes in the form or a plate, pipe, wire or electrode, and varies depending on the type of materials being welded.
Unlike other metal-joining techniques like brazing and soldering, welding is a high heat process which melts pieces of the base material, and then joins them together with the addition of a filler material. The high heat causes a weld pool of molten material which cools to form the join, which can be stronger than the parent metal. Pressure can also be used to produce a weld, either alongside the heat or by itself. Welders also often use shielding gas to protect the melted and filler metals from becoming contaminated or oxidised. If not controlled, these natural processes can result in a weaker bond and significantly affect the strength of the material.
When it comes to plastics, the process is similar, and takes part in three stages. Firstly, the surfaces are prepared before heat and pressure is applied and, finally, the materials are allowed to cool to create fusion. Joining methods for plastics can be separated into external or internal heating methods, depending on the exact process used. There's also another, more inexpensive way of welding plastics together known as solvent welding. This refers to a process in which a solvent or solvent blend with no dissolved polymer is used to create a joint between two thermoplastic parts. This no-heat process uses pressure to form a chemical bond between pieces of plastic, though the welded joint is often weaker than the individual parent materials.
In wood welding, the process differs quite significantly. Unlike metal and plastic welding which uses a heated filler to create a joint, wood welding uses heat generated from friction to join the materials. The materials to be joined are subjected to a great deal of pressure before a linear friction movement creates heat to bond the workpieces together. This is a fast process which allows wood to be joined without adhesives or nails in a matter of seconds.
Welded joints come in a number of different flavours, depending on their final use and application. In a butt joint, the connection between the ends or edges of two parts makes an angle of 135-180° inclusive in the region of the joint. T-joints, as their name suggest, form an almost perpendicular joint. Corner joints occur at 90 degrees to each other, mimicking the corner of a box. In a lap joint, the connection between two overlapping parts makes an angle to one another of 0-5, while cruciform joints form a kind of cross-like shape with two flat plates being welded to another flat plate at right angles to each other. Welds can also be divided according to the placement of the filler material, the area filled, and the technique used. These cover the full gamut of welding types including full penetration welds, partial penetration welds, single side welds, double side welds, single run welds, and multi-run welds.
The process uses a variety energy sources to create the requisite heat, including gas flames (chemical), electric arcs (electrical), lasers, electron beam,s friction, and ultrasound. While it's usually an industrial process conducted on plants, factories or machine shops, welding can be performed in open air, under water, and in outer space. It is considered a hazardous procedure, and the risk of burns, electric shock, vision damage, inhalation of poisonous gases and fumes, and exposure to intense ultraviolet radiation is quite high. To mitigate any injuries, welders are required to wear complete PPE, which can include helmets with filter plates, handshields, goggles and safety glasses with filter lenses, flame-resistant gloves, gauntlet cuffs, flame-resistant aprons, respirators, ear muffs and plugs, rubber-soled safety shoes and specialised clothing made of suitable materials to minimize skin burns caused by sparks, spatter or radiation
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