The Effect of Concave Base Shape Elements on the Three Dimensional Forming Process of Advanced Paperboard Structures

The underlying paper examines the material behaviour of paperboard during three-dimensional forming, especially deep drawing with concave shape elements in the base geometry of the bottom. Therefore, a parametric geometrical description of the concave section is established. Experimental investigations to the material displacement and to appearing wrinkles and fractures at the wall of the samples related to stepwise increasing levels of the concave geometry prove a proposed material displacement theory as well as the hypothesis that material overflow from convex sections is delivered into concave sections. Secant length and concave radius turn out to be of significant influence for the load that is applied to the material. Paperboard early reaches its maximum strain at break in concave sections and thereby should reveal close limits for concave shapes. However, a considerable concave level can be formed without structural damage of the material. Furthermore, the investigations show that there are possibilities to support the strain conditions in the concave section. Copyright © 2014 John Wiley & Sons, Ltd.