Roll Forming Defects FAQ: Camber, Sweep, Bow, Twist, Oil Canning & End Flare
Most roll forming issues are rooted in incoming strip condition, alignment, and forming pressure distribution. This FAQ explains common defect terms and the practical levers used to reduce them.
What is camber in roll forming?
Camber is a lateral departure of a strip edge from a straight line, commonly introduced during slitting. Excess camber can contribute to sweep/curve, bow, and twist in the finished profile if it forces the strip to track inconsistently through the passes.
- Often originates upstream (slitting/coil condition)
- Drives tracking challenges through stations
- Can magnify sweep and twist
What is sweep (curve) in roll formed parts?
Sweep (curve) is deviation from a straight line in the horizontal plane after forming. It’s commonly caused by incorrect horizontal roll alignment, uneven forming pressure, or incoming camber that forces the strip to “walk” as it forms.
- Check alignment and strip tracking
- Review forming pressure balance
- Validate incoming coil quality
What is bow in roll formed parts?
Bow is deviation from straightness in the vertical plane. It can appear as cross bow or longitudinal bow and may be influenced by strip shape variation, uneven forming, residual stress, or leveling effectiveness.
- Confirm leveler settings and strip flatness
- Check station-to-station alignment
- Evaluate residual stress and forming progression
What is twist in roll forming?
Twist is a corkscrew-like rotation along the part length, often seen in asymmetrical profiles or when the final passes apply uneven forming pressure. A common guideline is keeping twist below ~5° in 10 feet, depending on application requirements.
- Watch final-pass pressure and symmetry
- Use straightening fixtures if needed
- Review flower/passes for balanced forming
What is oil canning in roll formed parts?
Oil canning is a waviness in flat areas between bends, often tied to cross bow or shape variation. It may be influenced by material properties, residual stresses, and how strain is distributed during the forming sequence.
- Reduce uneven strain in wide flats
- Confirm leveling and strip shape
- Review pass design for flatness control
What is end flare, and why does it happen?
End flare is deformation at the ends of a roll formed part after cutoff. It occurs when residual forming stresses release, causing one end to open and the other to close. Proper tooling design and process control can reduce it.
- Commonly most visible after cutoff
- Linked to stress release at ends
- Reduced through tool design and process tuning
What are coil breaks (crossbreak) and why do they matter?
Coil breaks (crossbreak) are ridges or creases across strip width caused by improper coiling/leveling and are often seen as transverse lines. They can affect appearance and may influence forming consistency if severe.
- Often more common in uncoiled hot rolled strip
- Can be reduced with leveling and handling control
- Impacts cosmetic and sometimes functional quality
What is coil set?
Coil set is a lengthwise curve retained from coiling, causing longitudinal flatness departure. It can often be reduced with roller or stretcher leveling—especially in softer temper ranges—improving feeding stability and forming consistency.
- Affects flatness and feeding
- Reduced with proper leveling
- Important for punching accuracy and forming stability
What are reel kinks and reel breaks?
Reel kinks are strip damage near the coil core often caused by the uncoiler. Reel breaks are fractures typically associated with poor leveling, seen as light kinks across the width. Both can affect quality and create downstream instability.
- Inspect payoff equipment and setup
- Improve leveling practices
- Reject severely damaged coil sections