Roll forming design can go off the tracks quickly if your concept involves one or more of these features:
As with all manufacturing processes, careful design of your component impacts your overall costs, lead times, and quality performance.
Some components require complicated or non-standard manufacturing work, so you may not be able to follow all of these rules. But by removing as many hurdles as possible in the roll forming design phase, you can reduce up-front costs, maintain part functionality, and improve manufacturing consistency.
Roll Forming Design: 7 Flaws to Avoid
Roll forming design can go off the tracks quickly and lead to many costly mistakes. The most common design flaws to be on the lookout for include:
- Small bend radii
- Extremely short flanges
- Wide, curved shapes
- Blind corners
- Narrow openings
- Deep, vertical sections
- Shapes with high anti-symmetry or a long, flat un-formed side.
1. Small Bend Radii
The Problem: Tight corners can cause cracking in heavy-gauge, galvanized, or pre-painted materials due to stresses generated on the outer fibers of the bend. They also increase tool wear and breakage and require a mill with greater horsepower (all of which affect your costs).
The Fix: Allow for a minimum radius of 1.5 to 2x the material thickness for best results. Or, consider whether a more ductile material can be used to produce your component.
Watch Dahlstrom Roll Form president Robert White explain roll forming metal using a roll form mill to shape material.
2. Extremely Short Flanges
The Problem: If your flanges, or legs, are too short, they will not form properly and the roll forming process will be more difficult.
The Fix: Allow for at least 3x the material gauge as a minimum flange length. Longer legs provide more leverage to bend heavier materials.
3. Wide, Curved Features
The Fix: Design for flat sections with discrete bends to reduce roll forming tool design costs and initial setup scrap. Or, consider a material with lower yield strength to ensure that curve holds.
4. Blind Corners
The Problem: Also called “air bends,” blind corners occur when the roll forming dies cannot contact both the inside and the outside of a formed corner. These bends are less accurate and more difficult to control throughout the forming process.
The Fix: Design your component to avoid this situation completely -- make sure the part will be in contact with inside and outside rollers at all times.
5. Narrow Openings
The Problem: Narrow openings (in relation to the overall size of shape) make designing cutoff tooling extremely difficult. They can also result in frequent roll die maintenance and cutoff die breakage.
The Fix: When designing your roll formed part, allow for more than half of the section width for your opening.
6. Deep, Vertical Sections
The Problem: These designs require large-diameter forming dies, which increases the cost of tooling. These components might also be "partially" formed via roll forming, then finished in a brake-press as a secondary operation.
The Fix: Make the flat section wider, or open the sidewalls at an angle. If you absolutely require a deep, narrow channel, ask about MeshTrim.
7. Wide Shapes with an Un-formed Edge
The Problem: Parts with high anti-symmetry or a long, flat un-formed side are unbalanced and incredibly difficult to keep from twisting or rippling.
The Fix: Add a small leg on the un-formed edge or introduce a stiffening rib for greater overall strength and consistent formability.
What else WILL make your design better for roll forming?
A great part design also includes tolerances that are tight enough to meet the expected quality range and part function, but broad enough to allow the manufacturer to succeed. As with all part designs, tighter tolerances usually lead to higher costs associated with the tools needed to control them.
While we've provided guidelines on what to avoid, all of these features CAN be overcome through:
- Smart roll forming tool design
- Collaboration with your roll form partner
- Appropriate metal specification control
- The proper roll forming equipment
Need Help Designing a Great Roll Formed Part?
To learn more about designing great roll formed parts, check out our free e-book below:
(Editor's note: This article was originally published in January 2016 and was recently updated.)
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