Fabrication is an industrial term generally applied to the building of metal machines and structures. The term is also used for Semiconductor device fabrication and non-metal manufacturing . Small business that specialize in metal fabrication are called Fab shops.
Fabrication shops and machine shops have overlapping capabilities, with fabrication shops concentrating on metal forming and welding.
Metal fabrication
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.
Fabrication shops are employed by contractors, OEM's and VAR's. Typical projects include; loose parts, structural frames for buildings and heavy equipment, and hand railings and stairs for buildings.
Planning
Once awarded the bid, the shop will begin planning the job. Purchasing agents will order materials and sub-contract out work to other shops if specialized fabrication equipment is needed. A manufacturing engineer will program CNC machines for the order as needed.
Raw materials
Standard raw materials used by metal fabricators are;
- plate metal
- formed and expanded metal
- tube stock, CDSM
- square stock
- sectional metals (I beams, W beams, C-channel...)
- welding wire
-
hardware
-
castings
- fittings
Cutting and burning
The raw material has to be cut to size. This is done with a variety of tools;
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 burn tables 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.
Forming
Hydraulic breaks with v-dies are the most common method of forming metal. The cut plate is placed in the press and a v-shaped die is pressed a predetermined distance to bend the plate to the desired angle. Wing breaks and hand powered breaks are sometimes used.
Tube bending machines have specially shaped dies and mandrels to bend tubular sections without kinking them.
Rolling machines are used to form plate steel into a round section.
Fab shops will generally have a limited machining capability including; metal lathes, mills, mag drills and 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; welding in a staggered fashion, using a stout fixture, covering the weldment in sand during cooling, and straightening operations.
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 contract, 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.
Final assembly
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.
Specialties
Many fab shops have specialty processes which they develop or invest in, based on their customers needs and their expertise;
See also
Last updated: 05-22-2005 06:44:14
