Advances on Geometrical Limits in the Deep Drawing Process of Paperboard

Abstract

The geometrical limits of the deep drawing process of paper to advanced shapes are not known. This report examines the technological limits of convex elements of the base shape in relation to the drawing height and shows the material behavior in the bottom radius of 3D shapes with regard to special material properties. In the bottom radius, non-compressed wrinkles occurred due to the in-plane compression, but wrinkles were reduced by an increased blank holder force or tool temperatures and improved extensibility or in-plane compressive strain. The forming ratio during deep drawing (drawing height related to base diameter) was increased to a value of more than 1 by a blank holder force, which increased with the drawing height such that the initial blank holder force was reduced concurrently. Straight sections in the base shape reduced the risk for ruptures in the edge radii of rectangular shapes, producing a forming ratio in these radii of 2.5. The forming ratio was further supported by a pattern of creasing lines at the blanks with a radial orientation and a number near the expected maximum number of wrinkles. The spring-back at rectangular shapes mainly depended on the drawing height and edge radius.