Fundamentals of paperboard formability
Paperboard is a very attractive material for commercial and ecological products because of its low density and mechanical strength as well as its ecological compatibility. Processing of paperboard into complex three-dimensional structures is today mainly based on energy-intensive molding processes and simple folding operations. Only few scientific publications exist, which particularly focus on specific parameters and processes.
The aim of this research project is to examine the material and process fundamentals that are necessary to form three-dimensional structures of paper (board) based materials. In addition to the optimization of the material and the identification of important parameter for the forming process, the optimization process itself is a substantial part of this project.
The experimentally identified material parameters are used to describe the formability and damage behavior of paper-based materials. The aim was to model the processes with FEA and with the help of the possibilities of continuum mechanics. This results in a deeper understanding of the procedures occuring while forming paperboard and thus helping to optimize the forming process and the possibilities of generating complex three-dimensional structures.
Based on chosen parameters, different kinds of paperboard with various material properties are produced. In the next step, the materials will be tested with different testing methods to identify their suitability for the project (i.e. forming operations). Afterwards, material parameters of the selected materials will be determined experimentally. Based on these parameters, FEA and continuum mechanical models will be developed. In following experiments, the FEA-models will be optimized and validated. Parallel to these operations optimized forming processes will be developed and example products are generated.
Within the completed research project, fundamental knowledge regarding the formability of paper had been collected. For this purpose, testing devices especially for paperboard testing had been developed. In particular here mentioned, a pneumatic test press to realize a pneumatic bulge test (adapted from hydraulic bulge test in metal forming technology). This machine can also be used to shape paper in typical load environments. Special test specimen geometries were developed to fit in with the fracture behavior of paper and paperboard. Based on the made material characterization, following parameters had been carried out to be mostly responsible for the mechanical forming behavior of paper:
- Moisture content of paper
- Fiber orientation in the paper
- Pretreatment of fibers (e.g. cutting or curling)
- Proceeding while specimen manufacturing (e.g. kind of drying)
With the help of the generated material data, numerical models could be built up. On the basis of a rotationally symmetric, double curved, geometry the simulation model as well as the improvement of the forming characteristics had been checked.
This research project was a cooperation between the chair of “Paper Technology and Mechanical Process Engineering” (PMV, head of institute: Prof. Dr.-Ing. Samuel Schabel) and the “Institute for Production Engineering and Forming Machines” (PtU, head of institute: Prof. Dr.-Ing. Dipl.-Wirtsch.-Ing. Peter Groche).