An increased demand for sustainable materials has led to intensive research in the field of three-dimensional paperboard forming. To date, this work has focused on forming processes with shape-giving tools. However, individual shapes are often required, especially for large-format products. Incremental forming can be used in metal processing for small batches. In this article, the technology of incremental forming is transferred to paperboard. The results showed that elevated moisture content and a superimposed counter pressure significantly increased the forming limits. In addition, the use of polymer layers increased the shape accuracy. An extended understanding of the underlying mechanisms was achieved by analyzing the forming behavior. In uniaxial and biaxial characterization tests the influence of the moisture content on the forming behavior was investigated with conditions relevant for incremental forming. It was found that the bulge test is suitable to determine the most suitable moisture content regarding the forming limits and the spring back behavior in incremental forming. In addition, it was observed that the bearable elongations during the incremental forming of paperboard are significantly higher than in the established characterization tests. The reason for this is a compression of the fiber network during forming.

The use of paperboard can significantly improve the environmental compatibility of everyday products such as packages. Nevertheless, most packages are currently made of plastics, since the three-dimensional shaping of paperboard is possible only to a limited extent. In order to increase the forming possibilities, deep drawing of cardboard has been intensively investigated for more than a decade. An improvement with regard to increased forming limits has been achieved by heating of the tool parts, which leads to a softening of paperboard constituents such as lignin. A further approach is the moistening of the samples, whereby the hydrogen bonds between the fibers are weakened and as a result an increase of the formability. It is expected that a combination of both parameter approaches will result in a significant increase in the forming capacity and in the shape accuracy. For this reason, a new tool concept is introduced within the scope of this work which makes it possible to moisten samples during the deep drawing process by means of steam supply. The conducted investigations show that spring-back in the preferred fiber direction can be reduced by 38%. Orthogonal to the preferred fiber direction a reduction of spring back of up to 79% is determined, which corresponds to a perfect shape. Moreover, it was determined that the steam duration and the initial moisture content have an influence on the final shape. In addition to the increased dimensional accuracy, an optimized wrinkle compression compared to conventional deep drawing is found. According to the results, it can be summarized that a steam application in the deep drawing of paperboard significantly improves the part quality.

The increasing demand for lightweight design requires the use of multi materials such as metal-polymer-metal composites. These so-called sandwich panels offer a good stiffness-to-weight ratio. Production technologies like shear cutting have to be adapted for these materials. For a targeted adaption, a comprehensive knowledge about the cutting phases of the shear cutting process of sandwich panels is essential. Therefore, within this paper, the shear cutting process of sandwich panels is studied in detail. The conducted experimental studies indicate that the shear cutting process can be divided into five stages. Based on these findings, a new analytic model is introduced to predict the force displacement curves of sandwich panels. The quality of the new model is proven by comparison with existing analytic models for monolithic materials as well as with the experimental data.

The increasing social demand for sustainable material use leads to new process strategies as well as to the use of new materials in nearly all industries. In light of this demand, paperboard shows potential to substitute polymer-based components while also exhibiting improved ecological properties. However, in contrast to polymer-based products, the forming limits of paperboard are relatively low. Therefore, three dimensional forming of paperboard is subject of current research. One area of research focuses on the control of the fiber orientation dependent anisotropic material behavior of industrial paperboard in forming processes. For an examined industrial paperboard, an average elongation at break of 1.2 % in the so called machine direction (fiber preferential direction, MD) has been determined at standard climate conditions. In contrast, in cross-direction (orthogonal to the machine direction, CD) a value of 2.6 % was observed. With increased moisture content of the specimens the difference between the mechanical properties in MD and CD even increases. As a result of the various fiber-orientation dependent mechanical properties, forming with symmetric tools leads to asymmetrically shaped final parts. Within this article, an approach to reduce the asymmetric shape of threedimensional formed paperboard by using single point incremental forming technology is presented. For a free spatial processing strategy the 3D Servo Press Technology, which enables circular as well as free processing strategies, is used. Based on reference tests with a circular processing strategy, it is shown that by using an adapted, elliptical tool path, an almost symmetric shaped part can be formed.

Although the tribological advantages of textured surfaces in sheet metal forming are well known, the texturing of drawing tools is not yet established due to the intensive processing efforts. With the surface treatment technology of machine hammer peening (MHP), deterministic macro- and micro-textures can be machined on free-form surfaces, while simultaneously the time need for tool production is reduced significantly compared to the conventional process chain. Therefore, this paper investigates the influence of hammer-peened surface textures on the friction behavior. First, the general texturing process is optimized and suitable process parameters are identified. Using a strip drawing test, the friction behavior of different geometrical textures, varying ratio of surface textures (area) to the total surface and different lubrication systems are determined. It is shown that MHP with surface textures can reduce friction in sheet metal forming compared to conventionally polished tools.

Continually increasing exhaust emission standards for automobiles and an increasing environmental awareness push design engineers to develop new constructive and material concepts. So-called sandwich panels, consisting of stiff facings and light-weight cores, offer the possibility to combine properties of different materials synergistically. When processing large quantities, as is the case in the automotive industry commonly used manufacturing processes for cutting sandwich panels, like sawing or milling, are not applicable. A common manufacturing process to cut metal sheets in high quantities is shear cutting. However, pre-trials of shear cutting of sandwich panels have shown that it is not possible to achieve flawless cutting surfaces with current process layouts. Characteristic types of failure like high bending of the facings, delamination effects, burr formation and an undefined cracking of the core material were ascertained. Thus, in this study, the influence of cutting parameters, such as the clearance and the punch diameter, on these types of failure is examined. Five different clearances between 0.025 mm and 0.4 mm with two punch diameters, 8 mm and 32 mm, were investigated. In order to compare the influence of different materials, three commercially available sandwich panels were studied. The chosen sandwich panels differ both in the face sheet thickness and the core material. Finally, the shear cutting force is measured to identify a possible correlation between the cutting force and the face bending. As a result, optimal clearances to minimize the face bending are derived. Additionally, the influence of the core stiffness on the cutting force is determined.

Bei der Entsorgung von polymerbasierten Schichtverbunden (Aluminium – Polymer – Aluminium) wird eine grose Menge klimaschadliches CO2 freigesetzt. Um die Freisetzung von CO2 zu reduzieren, sind nachhaltige Kernwerkstoffe notig. Eine Alternative hierfur ist Papier. Neben der Nachhaltigkeit weist Papier gegenuber herkommlichen Polymeren wie Polyethylen eine vergleichbare Dichte sowie Zugfestigkeit auf. Ziel der Untersuchungen war es daher, Schichtverbunde mit Deckblechen aus Aluminium und Kernen aus Papier (Recycling- und Frischfaserkarton) zu fertigen und anschliesend hinsichtlich ihrer mechanischen Kennwerte zu untersuchen. Daruber hinaus wurden wirkmedienbasierte Umformversuche an mit Aluminiumfolie beschichteten Schichtverbunden durchgefuhrt. Hierbei zielten die Untersuchungen auf die Entwicklung geeigneter Prozessstrategien fur eine fehlerfreie Bauteilumformung ab. Fur die Ermittlung der Verbundfestigkeit wurden Scherzugversuche mit drei verschiedenen Klebstoffen durchgefuhrt. Mit 800 kN/m² wies der verwendete Ein-Komponentenklebstoff im ausgeharteten Zustand (nach 48 h) die hochste Scherfestigkeit auf. Im nicht-ausgeharteten Zustand (nach 10 min.) wies der verwendete Dispersionsklebstoff die hochste Scherfestigkeit auf. Die erreichbaren Werte lagen jedoch um den Faktor 8 niedriger als im ausgeharteten Zustand. Das Papier und die Schichtverbunde in unterschiedlichen Aushartezustanden und Feuchtegehalten wurden zudem in Tiefungsversuchen charakterisiert. Hierbei zeigte sich, dass der Klebstoff und die Aluminiumfolie das anisotrope Werkstoffverhalten im ausgeharteten Zustand nicht beeinflussen. Im Fall der Charakterisierung mit auf 15 befeuchteten Papier und einer 100 µm Aluminiumfolie hingegen konnte der Unterschied in der Dehnungsverteilung zwischen MD und CD von einem Verhaltnis von 1 : 5,14 (Frischfaserpapier bei Raumfeuchte) auf ein Verhaltnis von 1 : 1,07 reduziert werden. Entsprechend kann festgehalten werden, dass eine Umformung mit befeuchtetem Papier und Aluminiumfolie vorteilhaft hinsichtlich der Formhaltigkeit ist. Fur die Untersuchung des Biegeverhaltens wurden Schichtverbunde gefertigt, deren Papierkerndicken in guter Naherung der Polymerkerndicke eines handelsublichen Schichtverbundes entsprach. Mit einer durchschnittlichen, maximalen Biegesteifigkeit von 275,31 kNmm² fur den Verbund mit recyceltem Papier und 149,50 kNmm² fur den Frischfaserverbund weisen beide Verbunde eine deutlich geringere Biegesteifigkeit als die untersuchten, industriell gefertigten polymerbasierten Verbunde (442,15 kNmm²) auf. Im Vergleich zu monolithischen Materialien wie Stahl ist die Biegesteifigkeit bezogen auf das Gewicht dennoch um den Faktor 3 hoher. Es kann daher festgehalten werden, dass papierbasierte Schichtverbunde hinsichtlich biegesteifer Strukturen, wie sie im Fassadenbau verlangt werden, deutliche Vorteile gegenuber monolithischen Blechen aufweisen und gleichzeitig eine nachhaltige Alternative zu polymerbasierten Verbunden darstellen. Durch ihren mehrlagigen Aufbau und die eingeschlossenen Luftkammern, weisen papierbasierte Verbunde gegenuber monolithischen Blechen eine bessere thermische Isolationswirkung auf.