Design Considerations:
Do's and Don'ts of Roll Forming Design
Only the imagination limits the potential applications for
roll formed shapes.
When designing a product, do not limit thinking to shapes
already seen, to straight shapes or to shapes which appear
easy to make. Think in terms of bending metal into the shapes
really wanted. Two shapes can even be joined to make one.
The roll forming process produces a high quality product. By
its very nature, it permits close tolerances for either heavy-
or light-gauge material and provides uniform shapes and
dimensions. Finished shapes have an excellent appearance (with
no die marks even on precoated material), and the roll forming
process also lends itself to fine detail.
As these attributes have become more widely known, designs and
applications using roll formed shapes have increased steadily,
so that nearly every industry in the country utilizes these
shapes in its products. As the benefits of using a custom roll
former to help design and produce desired shapes become
apparent, more and more companies are turning to Samson Roll
Formed Products Company. They have found that Samson has the
skill and experience to create many shapes in the most
economical manner possible.
Here in a nutshell is what designers should and should not do
when designing roll formed shapes.
CURVING
Because roll formed shapes have uniform cross sections, they
are easily bent. When rings or segments of rings are required,
shapes can be curved to uniform radii at the rolling machine
without wrinkles and without disturbing a prefinished surface.
Helices are also possible. Consider material elongation in
designing parts for rings to help eliminate wrinkles and
fractures. Usually, the more elongation a material has, the
easier it is to bend. Where curves are not a constant radius,
the uniformity of roll formed shapes makes them ideal for
stretching or tangent bending.
PREPIERCING
Prepiercing is the fabrication of a series or pattern of holes
in the flat strip before forming. It is done in one continuous
operation together with roll forming and, therefore, can be a
cost saver. Repetitive piercing, as in a wallboard plaster
bead or shelf posts, will minimize the piercing tool cost,
because a small die can be used.
POSTPIERCING
Postpiercing is piercing in the line with forming, but after
the part is formed. It is part of a sequence of operations,
all of which are performed without handling, and is therefore
very efficient. If piercing, notching or tabbing is required
at either or both ends of the part, keep the pattern of holes
and' notches close to the end of the part, so that these
operations need not repeat throughout the full length of the
part. Often, this is less expensive and more desirable than
prepiercing, because better dimensional accuracy from the end
of the part is attainable.
FORMING IN LINE
Welding dimples or projections can be formed while the parts
are being rolled to improve accuracy in the finished part and
save money. Tabs, stops or raised areas can also be formed.
MATERIAL
Almost any material obtainable in coils can be roll formed.
The material should be as ductile as design strength will
allow;
this allows crisp design, sharp corners and easy bending. When
high-strength alloy steels, heat-resistant steels, titanium
and other alloys are used, bend radii specified by the mill
should be followed.
In many circumstances, bend radii can be reduced.
GUIDES FOR ECONOMY
- The shape should not be too
deep.
- Since the raw stock is sheet
metal, the part should have uniform thickness throughout.
However, thickness may be increased by folding the material
to double thickness.
- If wide, flat areas are
required at the edge of a part, consider using small
stiffening ribs. The part will stay flatter and be much
stronger.
- When planning a leg, as with
an angle or a channel, the length of the leg should not be
less than three times the thickness of the material. This
also applies when hemming or bending the material back on
itself.
- When planning prepiercing
where location is not critical, design the pattern to be
repetitive without specifying the location of the beginning
of the pattern from the end of the part.
- When the prepiercing pattern
is critical and not repetitive within the part, try to
design it to be less than 6 feet long.
- If a piercing pattern is
used which requires holes in a specific area relative to the
end of the part, try to keep it more than 1/2 inch (but
within 4 inches) from the end of the part.
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