A weld occurs when pieces of metal are joined by causing the interface to melt
and blend prior to solidifying as a uniform metal joint. This process
may be caused by heat, pressure or a combination of both. When heat alone is used
the process is called fusion welding.
Pressure welding usually involves heating the surfaces to a plastic state and then
forcing the metal together. The heating can be by electric current of by friction resulting
from moving one surface relative to the other.
The methods and equipment used for welding metal are also associated with cutting metal.
There are a large number of welding and allied processes including the following.
| Gas Welding | Arc Welding | Brazing | Soldering | Resistance Welding | Solid State Welding | Other Welding |
| Adhesive Bonding | Thermal Spraying | Oxygen Cutting | Thermal Cutting | Arc Cutting | Electron Beam Cutting | Laser Cutting |
Calculation relating to welded joints can be found on webpage... Weld Stress Calculations
Notes on drawing representations of welds can be found on webpage .. Drawing of Weld Symbols.
Manual Metal Arc Welding Process
Electric Arc welding is based on providing an electric circuit comprising the Electric current source the feed and return path, the electrode and the workpiece. The arc welding process involves the creation of a suitable small gap between the electrode and the workpiece. When the circuit is made a large current flows and an arc is formed between the electrode and the workpiece. The resulting high temperatures causing the workpiece and the electrode to melt The electrode is consumable. It includes metal for the weld, a coating which burns off to form gases which shield the weld from the air and flux which combines with the nitrides and oxide generated at the weld. When the weld solidifies a crust is formed from the impurities created in the weld process (Slag). This is easily chipped away.
MIG & TIG WeldingThe Metal Inert Gas Process uses a consumable electrode of wire form and an inert gas shield of
carbon dioxide when welding carbon steel.. The wire electrode provides a continuous feed
of filler metal allowing welds of any length without stopping. The inert gas shield eliminates
slag and allows cleaner and stronger weld.. This process is used widely for automated welding
using robots.
The Tungsten Inert gas (TIG) system uses a non-consumable electrode of tungsten
and also provides an inert gas shield of argon or helium.
This process was orginally developed for welding
magnesium and it is now used for welding aluminium, copper, stainless steel, and a wide range of
other metals that are difficult to weld. Consumable rods may be used depending on the
type of weld and the thickness of weld.
The welding process designations provided below are based on BS EN ISO 4063 and are used when identifying welds to BS EN 22553
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1 Arc welding
11 Metal-arc welding without gas protection.
141 TIG welding: tungsten inert gas arc welding 149 Atomic-hydrogen welding 15 Plasma arc welding 18 Other arc welding processes 181 Carbon-arc welding 185 Rotating arc welding 2 Resistance Welding 21 Spot welding 22 Seam welding 221 Lap seam welding 225 Seam welding with strip. 23 Projection welding 24 Flash welding 25 Resistance butt welding 29 Other resistance welding processes 291 HF (High-Frequency) resistance welding 3 Gas welding 31 Oxy-fuel gas welding 311 Oxy-acetylene welding 312 Oxy-propane welding 313 Oxy-hydrogen welding 32 Air-fuel gas welding 321 Air-acetylene welding 322 Air-propane welding 4 Pressure welding 41 Ultrasonic welding 42 Friction welding 43 Forge welding 44 Welding by high mechanical energy 441 Explosive welding 45 Diffusion welding 47 Gas pressure welding 48 Cold pressure welding. Other welding processes 71 Thermit welding 72 Electro-slag welding 73 Electro-gas welding 74 Induction welding 75 Light radiation welding 751 Laser beam welding 752 Arc image welding 753 Infrared welding 76 Electron beam welding 77 Percussion welding 78 Stud welding 781 Arc stud welding 782 Resistance stud welding |