Related Articles and Information About
Metal Works
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.
Engineering
The fabricator may employ or contract out steel
detailers to prepare shop drawings, if not provided by
the customer, which the fabricating shop will use for
manufacturing. Manufacturing engineers will program CNC
machines 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 brakes 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 brakes and
hand powered brakes 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.
Machining
Main article: machining
Fab shops will generally have a limited machining
capability including; metal lathes, mills, magnetic
based drills along with other portable metal working
tools.
Welding
Main article: welding
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 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.
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;
brazing
casting
drawing
extrusion
forging
heat treatment
hydroforming
oven soldering
plastic fabrication
powder coating
powder metallurgy
punching
shearing
spinning
welding
And higher-level specializations such as:
electrical
hydraulics
prototyping/machine design/technical drawing
sub-contract manufacturing
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