Metal
fabrication is the building of metal structures by cutting, bending, and
assembling processes.
It is a value-added process that involves the creation of machines, parts, and
structures from various raw materials. A fabrication shop will bid on a job,
usually based on the engineering drawings, and if awarded the contract will
build the product. Large fab shops employ a multitude of value-added processes
in one plant or facility including welding, cutting, forming, and machining.
These large fab shops offer additional value to their customers by limiting the
need for purchasing personnel to locate multiple vendors for different
services. Metal fabrication jobs usually start with shop drawings including
precise measurements, then move to the fabrication stage and finally to the
installation of the final project. Fabrication shops are employed by contractors,
OEMs and VARs. Typical projects include loose parts, structural frames for
buildings and heavy equipment, and stairs and hand railings for buildings.
Processes
- Cutting is done by sawing, shearing, or chiseling
(all with manual and powered variants); torching with hand-held torches
(such as oxy-fuel torches or plasma torches); and via numerical control
(CNC) cutters (using a laser, mill bits, torch, or water jet).
- Bending is done by hammering (manual or powered) or via press brakes and similar tools. Modern metal fabricators use press brakes to either coin or air-bend metal sheets into form.
CNC-controlled back gauges use hard stops to position cut parts in order to place bend lines in the correct position. Off-line programming software now makes programming the CNC-controlled press brakes seamless and very efficient.
- Assembling (joining of the pieces) is done by welding, binding with adhesives, riveting, threaded fasteners, or even yet more bending in the form of a crimped seam. Structural steel and sheet metal are the usual starting materials for fabrication,
along with the welding wire, flux, and fasteners that will join the cut pieces. As with other manufacturing processes, both human labor and automation are commonly used. The product resulting from fabrication may be called a
fabrication. Shops that specialize in this type of metalwork are called fab shops. The end products of other common types of metalworking, such as machining, metal stamping, forging, and casting, may be similar in shape and function, but those processes are not classified as fabrication.
Fabrication comprises or overlaps with various metalworking
specialties:
- Fabrication shops and machine shops have overlapping capabilities, but fabrication shops generally concentrate on metal preparation and assembly as described above. By comparison, machine shops also cut metal, but they are more concerned with the machining of parts on machine tools. Firms that encompass both fab work and machining are also common.
- Blacksmithing has always involved fabrication, although it
was not always called by that name.
- The products produced by welders, which are often referred to
as weldments, are an example of fabrication.
- Boilermakers originally specialized in boilers, leading to
their trade's name, but the term as used today has a broader meaning.
- Similarly, millwrights originally specialized in setting up
grain mills and sawmills, but today they may be called upon for a broad
range of fabrication work.
- Ironworkers, also known as steel erectors, also engage in fabrication. Often the fabrications for structural work begin as prefabricated segments in a fab shop, then are moved to the site by truck,
rail, or barge, and finally are installed by erectors.
Raw materials
Standard raw
materials used by metal fabricators are:
- Plate metal
- Formed and expanded metal
- Welding wire/welding rod
- Casting
Cutting and
burning
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.
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 have 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 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.
