Understanding Welding

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To effectively design metal components and assemblies, it is critical to understand the metal fabrication processes.
How welding works  
Welding is a common way to join metals. It is faster and often more structurally reliable than other kinds of joining techniques.
Essentially; welding is a process whereby metal is heated and made molten using an electrode. The electrode creates and ‘arc’ targeting a specific area of the metal to create a pool. When we weld two pieces of metal together, we are essentially melting their respective edges into a pool and inserting extra material, or 'fillers' to create a new join between the two parts.  
Welding Types
MIG Welding 
Metal Inert Gas (MIG) Welding. Also known as gas metal arc welding (GMAW), MIG welding uses a continuously fed electrode wire that melts into the weld. This melted wire acts as a filler material in the weld—allowing two pieces of metal to be joined without having to heat them to the melting point. 
Good for thicker materials where a strong weld is required.
Typically a little messier than TIG welds, more commonly used when a weld will be ground down or not seen.
Used for structural applications
Easy to learn, hard to master.
TIG Welding
Tungsten Inert Gas (TIG) Welding. Also known as gas tungsten arc welding (GTAW), TIG welding has a non-consumable electrode that heats metal to the melting point so it can be fused directly. Requires strict control to prevent over-heating of metal. Filler material is fed by hand, but is not always required for smaller ‘tack’ welds.
Ideal for more delicate welding jobs where a higher quality finish is desired
Not used for heavy or structural applications.
Arc welding, also known as ‘stick welding,’ or shielded metal arc welding (SMAW) is similar to MIG welding, in that it uses the filler material, (in this case a rod or ‘stick’) to operate as an electrode in creating the welding arc. Rather than using inert gas to shield the welding puddle from oxygen, the rod contains a special material called ‘flux’ which provides this function. Arc welding is good for very heavy duty applications and outdoor applications where gas shielding is an issue due to wind interference.
Best for heavy duty applications.
Not ideal for light fabrication or thin metal.
Preferable for outdoor applications where environment cannot be controlled.
Easy to learn, hard to master.
Welding Process
There are two key phases in the welding process.
1.Tack welding – This is where small welds are made in strategic positions to hold all parts together into the finished object. While tack welding does not provide a great deal of strength, it allows for the job to be checked for mistakes or inaccuracies. The nature of the tack weld allows easier rectification before proceeding. Sometimes, in order to reduce heat deformation in thinner materials, a tack weld is all that is required. This is subject to material dimensions and application.
2.Bead welding – Once checked for accuracy, the joins can be made permanent using full slug welding.
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Metals
Assisting the Welder
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