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Metal fabrication is the building of metal structures by cutting, bending, and assembling processes:
Fabrication comprises or overlaps with various metalworking specialties:
Metal fabrication is a value added process that involves the construction of machines and structures from various raw materials. A fab shop will bid on a job, usually based on the engineering drawings, and if awarded the contract will build the product. Large fab shops will employ a multitude of value added processes in one plant or facility. These large fab shops offer additional value to their customers by limiting the need for purchasing personnel to locate multiple vendors for different services.
Standard raw materials used by metal fabricators are;
The raw material has to be cut to size. This is done with a variety of tools.
The most common way to cut material is by Shearing (metalworking);
Special band saws designed for cutting metal have hardened blades and a feed mechanism for even cutting. Abrasive cut-off saws, also known as chop saws, are similar to miter saws but with a steel cutting abrasive disk. Cutting torches can cut very large sections of steel with little effort.
Burn tables are CNC cutting torches, usually natural gas powered. Plasma and laser cutting tables, and Water jet cutters, are also common. Plate steel is loaded on a table and the parts are cut out as programmed. The support table is made of a grid of bars that can be replaced. Some very expensive burn tables also include CNC punch capability, with a carousel of different punches and taps. Fabrication of structural steel by plasma and laser cutting introduces robots to move the cutting head in three dimensions around the material to be cut.
Machining is a trade, in and of itself, although Fab shops will generally entail a limited machining capability including; metal lathes, mills, magnetic based drills along with other portable metal working tools.
Welding is the main focus of steel fabrication. The formed and machined parts will be assembled and tack welded into place then re-checked for accuracy. A fixture may be used to locate parts for welding if multiple weldments have been ordered.
The welder then completes welding per the engineering drawings, if welding is detailed, or per his own judgment if no welding details are provided.
Special precautions may be needed to prevent warping of the weldment due to heat. These may include re-designing the weldment to use less weld, welding in a staggered fashion, using a stout fixture, covering the weldment in sand during cooling, and straightening operations after welding.
Straightening of warped steel weldments is done with an Oxy-acetylene torch and is somewhat of an art. Heat is selectively applied to the steel in a slow, linear sweep. The steel will have a net contraction, upon cooling, in the direction of the sweep. A highly skilled welder can remove significant warpage using this technique.
Steel weldments are occasionally annealed in a low temperature oven to relieve residual stresses. Such weldments, particularly those employed for engine blocks, may be line-bored after heat treatment.
After the weldment has cooled it is generally sand blasted, primed and painted. Any additional manufacturing specified by the customer is then completed. The finished product is then inspected and shipped.
Many fabrication shops have speciality processes which they develop or invest in, based on their customers needs and their expertise:
And higher-level specializations such as:
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