Line Configurations
Panel roll forming lines can be configured in a couple of different ways.
One is a start-stop line. The material starts moving by ramping up to speed and then decelerates and stops when it is time to cut. This type of line typically is inexpensive overall, because you do not have to fly the cutoff die. However, since the line has to stop, total throughput is limited. The line might run at a top speed of 100 feet per minute, but the average line speed for the day might be only 60 FPM.
A continuous roll forming line runs constantly. However, the overall cost usually is higher than on a start-stop line, because you must add a flying cutoff configuration.
With either of these configurations, you can add a precut/shear die or a postcut die (see Figure 4). Most new panel lines have a precut die. Precut dies use a common stationary or flying cutoff set for the maximum width, which provides versatility. Even a common stacker can be applied. You can change part widths (such as from 36-in. to 24-in. coverage) with a simple stock guide adjustment and coil change and no die changeout.
Figure 4
Most new panel lines have a precut shear die (top), which use a common stationary or flying cutoff set for the maximum width. Typically, you will get a better overall profile with a postcut die (bottom) because you eliminate some of the additional flare that can occur during precutting. Depending on the panel type, a postcut die might require a die insert changeout or complete die changeover.
Depending on the panel type, a postcut die might require a die insert changeout or complete die changeover. When running precut products, you need to be careful not to add flare on the ingoing and outgoing ends of the material—a common occurrence on precut lines.
With a postcut die, you will typically get a better overall profile because you eliminate some of the additional flare that can occur during precutting. Also, depending on the panel profile and the roll tooling design, you might be able to use a common cutoff die by simply changing the material strip width. For uncommon shapes, a cutting blade or entire die changeover might be required.
Roll tooling change is an issue because the sets have a lot of rolls. Rafting, double-wide roll formers, two-part roll formers, and machines with combination tool sets can help minimize the machine downtime. However, making the roll forming system more complex to decrease downtime usually increases the overall machine cost.
