Other Causes for Distortion
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| Figure 3 Prenotched material doesn't go through the rolls as smoothly as material that has continuous channel flanges. The back edges of the notches can hit the roll tooling. |
Figure 4 Both ends are flared by the cutoff process—in this case, a slug-type cutoff die with a pushing-out design that cuts in the vertical direction. |
Prenotched material also provides a challenge for producing good parts with no distortion.
In prenotched material, the notches separate the channel flanges into segments. The back edges of the notches can hit the rolls (see Figure 3). The higher the forming speed, the harder the back edges hit. This impact bends up the back edge of the notch and can cause it to toe in.
During the coil threading process, the two corners at the leading end of the coil act similarly to the back edge of a notch: The front two corners of the coil hit the rolls, the two corners bend up, and the leading end of the channel toes in.
Another potential cause of distortion is the cutoff process. A cutoff die can cause distortion at both the leading and trailing ends of a roll formed profile (see Figure 4).
