Metal fabrication :- Metal fabrication is the fabrication of metal by cutting, bending, and assembling (by welding, binding with adhesives,riveting, threaded fasteners,etc.) processes.
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.
1.FABRICATION PROCEDURES
1. Workshop
Layout
Fabricators
range from small general firms to large specialized producers with different
facilities at their disposal. In either case the fabrication must always be
organized in such a way that the material will pass through a one-way system
from receipt to final dispatch. A flow cart, as indicated in the main areas of
activity in a modern fabrication shop; the specific activities for a simple
steel beam can also be organized as a production line.
Most fabrication shops are
equipped with overhead travelling cranes, sometimes remotely controlled from
the shop floor. Mechanized conveyor systems are common in the larger shops.
They can greatly reduce handling costs.
.
2. Material
Handling and Preparation
Material is
taken into temporary stock in such a way that it can be easily identified and
moved. Some companies stack the material for easy access and move it by using
cranes equipped with chains and hooks. Other companies use a high degree of
automation in their material handling, using cranes on conveyors with magnetic
lifting devices; Slide 4, for example, shows a travelling Goliath Magnet Crane
with the capacity to lift both plates and sections. Computerised records hold
details of member sizes, lengths, weights and steel quality, all related to an
identification mark.
3. Templates and Marking
Steel may be
marked directly by hand with scribe lines and hole centres; nowadays, however,
in most shops pre-programmed automatic plant is in use. Traditionally,
full-sized templates, made of timber or heavy cardboard, were used to mark the
steel for cutting and for centre popping where holes were to be drilled.
4. Sawing
Line and Rolled Sections
The
rolled sections are in most cases sawn to length, the other options being
mechanical cutting or flame burning. Three types of saws are available to the
fabricator:
- Circular
saw;
- Band
saw;
- Motor operated hacksaw.
5.Drilling and the Beam Line System
The
traditional method of drilling involves three operations:
- Marking
the position of the holes to be drilled;
- Moving
the member to the drill by crane, by conveyor, or by other means;
- The
actual drilling of the hole, using for instance, a radial drilling machine
(radius about 1,5 metre).
Like
the sawing line, this system is controlled by computer programs; some machines
are equipped with multiple drilling heads enabling them to drill several holes
simultaneously in each axis.
New twist
drills are currently available which are capable of higher speeds and greater
efficiency as follows:
- Coolant
fed drills, giving a threefold increase in drilling speed.
- Titanium
nitride coated drills, enabling a six-fold speed increase.
- Carbide
tipped drills with exceptionally high cutting speeds.
6.Punching
Punching
holes in steelwork is much faster, and therefore less costly, than drilling;
its use, however, is generally limited to predominantly statically loaded
structures with limited thickness, or to secondary members, unless HSFG bolted
connections are used or the holes are reamed out to a larger size. The maximum
thickness where punching is applicable depends on the material grade and
quality.
7.Pressing and Forming
For the
modern fabricator the most important application of plate forming and pressing
is to add to the available range of rolled sections. The trapezoidal shaped
trough used to stiffen bridge decks, is a very good example. Other examples are
the circular sections of larger than standard dimensions.
8.Methods of Welding
Three
welding processes are most commonly used in modern fabrication shops:
- Manual
Metal-Arc Welding for fittings and for some profile and positional welding.
- Metal
Active Gas Welding (MAG) and Cored Wire Welding with and without gas.
- Submerged Arc Welding for fully automatic processes; particularly useful for heavy welding in the flat or horizontal-vertical position and for the long-run welds in plate and box girders.
- uses laser welding, etc..
9.Machine Operations
Most
fabrication shops are equipped with facilities for edge planing, for end
milling and for surface machining of plate.
Unacceptable
levels of hardness at the edge of the plate, often caused by burning, can be
removed by planing.
End planing
of members is used to get a higher standard of squareness than can be achieved
by sawing. Optical laserbeam methods are used to align the axis of the member
to the cutting head.
Surface
machining is only necessary for special bearing surfaces and sometimes for the
slab base plates of columns.
10. Fabrication Tolerances
Modern
fabrication shops have accurate dimensional control over fabricated sections
and have no problems in cutting the rolled material to length. The main problem
is coping with the deviations in the sections and plates received from the
steelmills. Euronorm (CEN) and ISO standards give dimensional tolerances for
rolled sections, plates and flats, hollow sections and angles respectively. The
fabricator will use bending rolls to straighten the material and to
"square" flanges of beam sections at critical connection points. As
already mentioned, the control of distortion due to The details and the
connections must be designed in such a way that the tolerances will be met
within the limits of good workmanship.
11.Inspection and Quality Control
Quality
Control should commence with the designer and continue through the preparation
of drawings and material procurement; maintaining the quality during the entire
production process will depend heavily on the fabrication details and on the
material obtained.
The larger
fabricators have their own Quality Control Department, which will create and
maintain a QC-manual, describing the method of operation throughout the
fabrication process. The Quality Control Department will liaise with the shop
management to make sure that all workers have the skill required for the job on
hand and that welders are qualified to undertake the prescribed welding
procedures.
Regular
checks are necessary to ensure that:
- All
materials can be checked against specifications.
- Material
is checked for laminations.
- Welding
electrodes are identifiable.
- Welding
electrodes are stored in the required conditions.
- Welding
procedures are being followed.
- Welding
is being inspected during the process.
- Correct
procedures are in operation for tightening HSFG bolts.
- Identification
marks are clear and visible.
- All
equipment is maintained correctly.
Hmmm...basically these are the process of stainless steel fabrication. Thanks for sharing!
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