GENERAL CONCEPTS of cold roll former line processing:
Roll-forming is a process in which the shape of a metal panel is developed by gradually bending the metal through a series of roll stands, or passes. Each stand must generate the appropriate amount of deformation for which it was designed. In general, the level o deformation at each stand is not constant due to adjustments for springback and the preservation of dimension. Since the tooling is designed to control the outside dimensions o a panel, roll formers are usually designed to overwork the metal in specific stands. Problems in the forming system or tooling design may exist if materials have to be overworked in the stands/tooling other than those designed for overwork. Therefore, when roll-forming problems occur, it is important to examine each stage of the process and not merely the stand at which the problem initially appears.
The goal of a smooth ‘roll-forming’ operation is achieved when there is uniform meta deformation throughout the line. Roll formers are designed to be reasonably quiet during the operation. They are not designed to run with material “popping” and wrinkling throughout the operation. If this occurs, the operation needs to be investigated.
Two basic types of roll-forming systems are utilized: a precut line and a postcut line. A precut line shears the incoming material to a specific length prior to roll-forming. During post cut line operation, the roll formed panel runs continuously and is sheared to the required length after roll-forming. Figure 1 on page 15 illustrates an example of both types of systems.
One of the principal parameters that define the success of a roll-forming operation is the nature of the material. In order to design the optimal process, the tooling designer should be provided material information to be used prior to the tooling designing. This includes material mechanical property ranges, gauge tolerances and shape tolerances. In addition, different metallic coatings (hot-dip galvanized or GALVALUME®1 Coated Sheet Steel), organic coatings or paint will result in differences in performance even with the same set of tooling due to their different frictional characteristics.
The designer requires a clear understanding of the gauge tolerance to be supplied. Ideally, a more robust operating window can be achieved if the full range of tolerance is provided to the tooling designer. The tooling designer will generally design the tooling to the thickest gauge. Ordering the tooling to a full ASTM tolerance while receiving materials with a half or one-quarter standard tolerance will produce a roll former with a less robust operating window than either the designer or the panel manufacturer intended.