These features enable better control of the rolling and forming of doubly curved aluminium and steel plates.
When a plate is developed in Workshop, you can display rolling lines on the developed plate that provide information about the directions of the principal curvatures (or radii) and the magnitude of these curvatures (or radii).
Note:
If these are not displayed after loading a Workshop file, you should re-calculate the plates.
You turn on these rolling lines using the Structure dialog from the Display menu. Each one of these markers has two numbers associated with it, the major and minor principal curvatures. The magnitude of the number associated with the small arm of the cross will always be greatest - this is the major principal curvature. The magnitude of the curvature associated with the long arm of the cross is the minor principal curvature. This is the direction along which plates are generally rolled or stretched to introduce double curvature.
If both curvatures are zero, then the plate is locally flat. If the minor curvature is zero or close to zero, the plate can be considered to be developable, and the long axis of the cross will correspond with the direction of the developable ruling line.
If the sign of the major and minor principal curvatures is the same, then the plate has spherical (or positive Gaussian) surface curvature. If these curvatures are different, as in the example above, this indicates that the plate has saddle shaped , or negative Gaussian curvature.
Curvatures are measured on the plate using a jig similar to the following.
A dial gauge is placed centrally on a beam that has two pins 300 mm apart and the dial gauge is calibrated to read zero when the jig is placed on a flat surface. Sufficient travel should be allowed for so that the dial gauge can read both positive and negative deflections.
To check the minor curvature on a plate being rolled the jig is placed with the tip of the dial gauge on the centre of the marker and the pin tips at the end of the long axis of the cross. To measure the major curvature the jig is rotated 90° while keeping the dial gauge centred on the cross.
This method has the advantage of being lightweight, portable and accurate. As a result it is a more flexible approach than using templates and pin jigs, but as it only measures curvature locally should be used in conjunction with these methods on large or complex plates.