Until you’ve actually sent a piece of material through a roll former it can be difficult to grasp how the process works. Even a single 90° bend has calculations and considerations that must be taken into account for the end result to be to spec, and those issues are compounded as you add subsequent formations to the part. Even today’s modern CAD programs sometimes struggle in creating blank sizes for roll forming compared to press brakes and similar machinery.
Of course, not many design firms or procurement departments will find it feasible to install a roll former on their premises, as such prints are commonly outsourced to companies like ours here at Cargowall. Many times there are adjustments that need to be made to flat blank size, tolerances, and similar print callouts, but the more information designers have before sending out those specifications, the less time will be required to obtain the desired shape.
1 – Roll Form Shape
Roll forming is a desirable manufacturing process because the production runs can be very quick, the method is relatively inexpensive, and the labor involved in the operation is minimal. That being said, more complex designs will completely negate these benefits and roll forming callouts should be done so with manufacturing efficiency in mind.
Something else to take into consideration when designing a roll formed part is the location and type of corresponding cutouts. Slots, holes, embosses, and other features will be distorted if they are too close to the bend. These features also may not be machinable once the part has been rolled so it’s important to consider the feasibility/alternate production methods of every cutout near a bend.
2 – Number of Bends
Single bends, whether they are in the middle or end of a part can be held to the tightest tolerances. The more subsequent bends that are added, the more difficult the manufacturing process becomes. Parts with 5-6 bends or more will inevitably create blind bends that may be accomplished but are going to be harder to control. In some cases welding two parts together is more feasible than multiple bends within a small area.
3 – Type / Thickness of Material
Any material that can withstand the specified bend to the radius can be roll formed. These materials include hot-rolled, cold-rolled, mill finished, mirror finished, or other coated metals. Material type, yield strength, and bend radius will all contribute to the bend allowance (K-factor) that determines flat blank size before rolling. One design tip to remember is that the maximum thickness within the specified gauge range should be used during the design process. This will eliminate potential roll interference.
4 – Tolerances
Part of designing for manufacturing involves exploring tolerances in depth. If a measurement is non-critical, it should be denoted and opened up so that the operator can focus on the key dimensions while using the secondary ones for runout. Typically on a roll former, cross-sectional flanges can be held to .015 (1/64) and angles to within 2° or less.
5 – Springback
When a part is removed from the roll former, a certain amount of springback and end flare occurs as the pressure is relaxed. Thinner gauge materials will have more of this elasticity and thus the part may need to be overformed to reach the desired print angle. Therefore, designers should place a tolerance callout on all dimensional angles if they are critical. Superior designs will include spring back compensation enabling the operator to control the whole range of material thickness and yields strengths that impact springback.
The best tips for creating the perfect designs for the roll former are to ask the manufacturers themselves. Cargowall is available to assist in the design process or to answer any other specific roll forming inquiries you may encounter. Please contact us at your convenience.