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 pre-coated 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.
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.
Pre-piercing 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.
Post-piercing 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 pre-piercing 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.
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 pre-piercing 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 pre-piercing 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.