Understanding bending, moving material in roll forming-3

Linear Forces

A primary consideration is the workpiece's form and how that form will resist force. To put the least stress on the tooling and the material, the process should move the material in a direction that has a low moment of inertia, whether linear or rotational.

Figure 2
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When a force (F) is vertical, a vertical beam provides greater resistance (I) than a horizontal beam does.

Figure 2 illustrates one piece of beam in two settings. A force F is directed downward. The moment inertia of the vertical beam is:¹

The moment inertia of the horizontal beam is:

Because d is greater than b, the moment inertia of the vertical beam is bigger than the moment inertia of the horizontal beam. This means that the vertical beam is stronger than the horizontal beam is under the vertical force F. In construction applications, a vertical beam is useful because it is lightweight and strong. In roll forming applications, roll design engineers can take advantage of a horizontal beam feature to move a formed or unformed section to a different location easily without changing it or destroying its shape. A rule of thumb: Do not move a horizontal section horizontally, and do not move a vertical section vertically. If you do, compression will likely wrinkle the inner edge of the bend, and tension likely will stretch the outer edge to a thinner gauge. Eventually waves may develop along the stretched edge.