Corrugated Metals: Metal Tips
Roll Forming Tutorial - Part 2
Roll Forming Design Issues and Advantages

To help our site visitors understand the roll forming process, Corrugated Metals has included this roll forming tutorial. Part 2 addresses Roll forming design issues and Roll forming advantages and limitations.

The most successful and problem-free roll forming operations involve shapes that are previously designed under the assumption they will be shaped through roll forming. Metal sections that have been routinely produced in the past by press braking, stamping, or extruding, can be effectively and profitably switched to the roll forming process. The end-user or roll former must be aware of eight key roll forming considerations:

	Cross section depth
	Blind corners
	Symmetry of roll forming design
	Length of the leg
	Radius of the bend
	Notches/punched holes
	Width of the section
	Length of the part

Cross section depth

End-users of the roll forming process should avoid forming pieces with extreme (??) depth in a cross section. The movement of the metal around the arc of the bend is much greater in a deep piece, so the stress produced on that piece during roll forming is much greater and that produces stress on the formed piece’s edges.

Blind corners

A blind corner can be defined as a bend that can’t be handled by direct roll contact. Blind corners eliminate the precise control of sectional dimensions unless the corner is reachable by slides or other forming rolls. Blind corners should be designed out before roll forming a part.

Symmetry of roll forming design

Nonsymmetrical sections are often roll formed without problems, but the section that is symmetrical to its vertical centerline [could use an illustration here!] when formed creates equal forming pressure being applied to each edge of the metal as it is roll formed. Symmetrical pieces reduce metal stress since the roll forming pressure is equal.

Length of the leg

A good rule of thumb is the leg length should be three times the thickness of the material. Shorter legs do not allow the rolls to properly form the leg resulting in nipping the edge of the material that will produce an undesirable wave along the finished part’s edges. Follow the 3x thickness guideline! [could use an illustration here!]

Radius of the bend

Sharper radius creation can be produced by roll forming than by any other conventional metal forming methods. Generally, the bend radius should be equal to, or greater than, the material thickness. Smaller radius creation can often result in fracturing at the bends due to the thinning of the metal that does occur at the bend radius (only).

Notches/punched holes

Design roll formed parts to keep pre-punched holes or notches away from bend lines or material edges. Place part holes at least three to five times the material thickness past the bend radius. Slight distortions in the size and shape of the notches/holes during forming are very possible and should considered a normal probability of the process. If the number of passes your material makes through the roll former is increased, the occurrence of hole distortion will be reduced.

Width of the section

Wide sections with wide flat areas are difficult to form and hide imperfections like curvy edges or lack of center flatness. Roll forming can’t remove flaws inherent in the coil or surface imperfections in wide flat areas. However, roll forming can try to conceal them or disguise them in the roll formed cross-section.

Length of the part

Design or roll form your shape to facilitate cutoff that will minimize part distortion. Design for cutoff so the shortest length for precut parts is no less than twice the horizontal center distance between roll forming stations.

Advantages

Roll forming offers a number of distinct advantages over other metal fabricating methods. Advantages include:

• The initial cost of a roll forming line is no more, and often less, than the cost of a standard stamping line or progressive die operation.

• Production speeds of 50-600 feet per minute can be attained but 100-180 feet per minute is a reasonable average for most current equipment.

• Roll forming is a high volume process that makes uniform and accurately dimensioned parts.

• Parts are produced with little handling, minimizing labor costs, needing only the coils to be loaded at the starting end of the machine and removal of finished parts at the other end. This process can usually be handled with a minimal number of operators.

• Roll forming can also be used for low-volume production because setup or changeover time for new parts is not lengthy.

• Maintenance costs are generally low. The form rolls can produce several million feet of product before problems occur when properly maintained.

• The roll forming process is easily combined with other operations and processes to automatically form a considerable range of metal parts.

Limitations

A few limitations also exist. Roll forming limitations include:

• Experienced roll design engineers must design those rolls designed for complex shape forming.

• Complicated tubular shapes, and some closed shapes, may need mandrels to form the shape accurately.

• Delicate, breakable, machine parts may need recurrent replacement during high volume production runs.

Next: Part 3 of the Roll Forming Tutorial discussing materials that can be roll formed, the kinds of tolerances that can be expected from the roll forming process, especially as they regard material straightness.  

Roll Forming Tutorial Sections

	What is roll forming?			Tolerance expectations
	Roll forming techniques			Quality and accuracy
	Roll forming design issues			Common roll forming applications
	Roll forming advantages and limitations			Roll forming tooling
	Materials that can be roll formed			Operating parameters

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