LAUSR

Abstract Press forming is a three-dimensional forming process used for industrial converting of large quantities of fibre-based composite materials such as barrier coated paperboard. The technology enables the production of plate and tray packages of such high quality that it is possible to lid seal them to create a gas-tight package. The method is primarily based on the controlled folding and compression of materials using high forming forces and elevated tool temperatures. The corner of the container is folded utilizing creases and a certain amount of force is needed to achieve the desired result. Sliding of the package blank is restrained with blank holding force which defines the overall forming force. The magnitude of blank holding force is determined by the shape and dimensions of the package and the properties of the material to be moulded. In some cases, the force optimized to produce high-quality packages will cause fractures, which are only on the surface layer of the paperboard, at corners of the tray. The packaging is still fully functional, but the visual disadvantage makes it look defective. The phenomenon is accentuated in converting of printed paperboard, where the potentially brittle surface layer breaks more easily and the colour difference makes the fractures eye-catching. This study investigated how by adjusting the blank holding force, paperboard surface layer breakage can be prevented during processing. Various ramps were programmed to control the forming cycle, which changed the magnitude of the force during the pressing stroke. The results show that there is no need to compromise the quality of the package as long as the average magnitude of the blank holding force is maintained. If the strength properties of the material to be formed are not sufficient to apply a constant blank holding force, by reducing the force slightly at certain points in the process cycle, material damage can be reduced or prevented completely.