Post 144 ⇒ by Gautam Shah
Fusion joining without using an intermediate material, are used to join mainly metals and thermoplastics. Fusion joining is a common term used for many different types of welding processes. The welding processes rely on high temperatures that change the phase of materials to be joined aided by pressure (or impact). For phase change, the materials to be joined should have same softening-melting temperature and nearly similar composition.
|Raincoat with fused joints > Flickr image by Mantelmann|
Fusion joining as a category may include many other nearly similar processes, but which involve an intermediate to form the joint. There are three categories of such fusion joining systems, Soldering and Brazing, where the work pieces are not melted, yet joined using a meltable filler material, Welding the work pieces, and in some instances, the filler material, both are melted, and Chemical fusing or solvent welding (which are actually forms of adhesion fixing), where plastics are joined by solvents to dissolve (soften) the surface areas of the work pieces. The joint is created with or without application of pressure.
|Brass vessel making 4 by Forging joining > Flickr image by McKay Savage (HiH - Enterprises - MSE )|
The first fusion joining process was the forge welding. Blacksmiths used to beat the heated metals like brass, copper etc. for joining. For heating the work pieces, wood, charcoal and later mineral coals were used. Forging: Forging was an ancient process of hammering to shape materials like iron and other malleable metals, or by pressing (or rolling)in their plastic state (by application of heat).
|Forged joints of Brass vessel at Madhurawada Visakhapatnam India > Wikipedia image by Asityamadhav83|
Forging has many modern versions. In these variants, the heat is created by electrical resistance, friction, laser beams, etc. Continuous pressure or intermittent impaction is done to fuse the heated components. Forge welding components are in sheet, or small section forms.
Forging created desired form, but also refined the grain size and arrangement, and thereby improve the structure of the metal. Forged metal is stronger and more ductile than cast metal, and exhibits greater resistance to fatigue and impact. Forging is also used to compact materials by removing gases and by packing the cavities.
Butt or spot welding is a widely employed technique for assembling sheet components of metals and plastics like car bodies, cabinets, furniture. It is a type of spot resistance welding. A high electric resistance-heat softens the material close to the melting level, and under pressure (of impact) the thin walls fuse and join. The joint developed has no apparent deformity, except a charred spot.
Seam or strip welding: Seam or strip welding is also a type of resistance welding method. It is used to join overlapping metal sheets of up to 3 mm thick. Instead of pointed (butt end) electrodes, and wheel-shaped electrodes roll along the work-piece, making a long continuous weld. Weld strength though is lower than other welding methods. The method is suitable for specific uses like formation of seamed pipes, and in terms integrity it is a fairly reliable process.
Seam or strip welding is also used for joining plastic sheet materials, like raincoats, wind-cheaters, shopping bags, containers, etc. In one process the sheet materials to be joined are pressed by a preheated straight wire, knife or a roller.
Induction welding is a form of resistance welding. Here the materials to be joined are heated by induction (non-touching or a distanced heat source). For this purpose a coil wrapped around a cylinder, causes opposite direction magnetic field in the materials, to melt-join together.
Butt fusion welding creates a joint between pipes gas and water pipe or other sections of doors, windows etc. The ends are pressed against a heated plate, and brought together to form a ‘beaded joint’.
Fusion joining requires a heat source, such as a gas flame, an electric arc, a laser, an electron beam, friction, or ultrasound. Fusion joining sometimes requires a slight to very heavy pressure. Forging is a very noisy process. Fusion joining is done under many different environmental conditions like open air, rain, frost, underwater in vacuum or space and sometimes under the shield of inert gases like Nitrogen, Argon, Helium, Carbon dioxide, etc. Fusion joining in spite of all care is essentially a hazardous procedure. It involves risks of high electric currents, high temperatures, sparks, fumes, and radiation.
|Felt Cloth non woven assembly of fibres > Wikipedia image by en:User:Sannse from english WP|
There are several other joining systems that use pressure, but not the heat (high enough for softening or melting). Here the (often purposely disarrayed fibres) two surfaces are pressed or rolled together to form a joint. These techniques are used for joining fibrous surfaces like papers, leathers, woven and non-woven fabrics, etc.