Role of positional assembly accuracy in press forming of paperboard

Abstract The press forming method is used to produce sustainable packages out of paperboard. The press forming equipment consists of a press unit that creates the forming force and a changeable mould set that forms the substrate to the desired shape. Successful production requires accurate positioning of each part of the mould set. The positioning of the mould set is demanding, because variable clearances in the forming equipment cause a need for fine-tuning of the assembly after the first trial runs. This study investigates the effect of mould part positioning and symptoms of misalignment in the end product, i.e. paperboard trays. The interpretation of these signs and defects has a vital role in determining the direction of misalignment and the selection of the correct adjustment method. The study also evaluates the effect of the play on the forming device and how the mould seeks to self-align due the influence of the shape of the mould parts. Clearances and temperatures between the parts of the mould set were measured in practical tests in three different positioning setups. It was concluded that temperature had a significant influence in the clearances of corners, depending on the mould alignment. Primarily, an elevation of mould temperature increased the clearance between the mould parts due to thermal expansion, but misalignment intensified this phenomenon. The final positioning of the mould set can be achieved in an acceptable way in room temperature with proper clearance measurements.