Post 144 ⇒ by Gautam Shah
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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.
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| 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.
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| 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).
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| 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.
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| Wrought iron joints > Pixabay free images by avantrend |
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.
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| Blister packing -fusion joining > Wikipedia image by Alex Khimich |
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.
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| 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.
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