Extrusion International USA 5-2019

43 Extrusion International 5/2019 Institut for Plastics Processing at RWTH Aachen University Seffenter Weg 201, 52074 Aachen, Germany E-Mail: dennis.balcerowiak@ikv.rwth-aachen.de Particularly homogeneous wall thickness distributions, i.e. those with a small wall thickness difference, can with- stand higher top-loads. Thin spots are thickened and thus lead to more stability. Particularly inhomogeneous wall thickness distributions, such as those produced by a pointed plug with a large wall angle, have poor top-load properties because they have thinner wall thicknesses in the wall and transition area. With the selected cup geom- etry, the assumption that more homogeneous wall thick- ness distributions lead to better mechanical properties of the cups in top-load tests can be confirmed. The ten- dency that better top-load stability can be achieved with more homogeneous wall thickness distributions can also be confirmed with other filmmaterials and film tempera- tures. Conclusion & outlook It can be shown that the plug edge radius has compara- tively little influence on the resulting wall thickness dis- tribution. The plug wall angle, on the other hand, en- ables the adjustment and homogenisation of the wall thickness distribution. Nevertheless, it is not possible to select a plug in advance in order to predict the most ho- mogeneous wall thickness distribution directly. The wall thickness distribution differs enormously depending on the film material and the temperature of the film due to the greatly changed stretching resistances. Only pointed plugs lead to a poor wall thickness distribution for all ma- terials and are therefore not suitable for homogenisation, as they lead to a particularly large amount of material in the bottom of the investigated cup geometry. The top-load properties can be increased for all cups manufactured with pre-stretching plugs, with the excep- tion of the pointed plugs. Particularly homogeneous wall thickness distributions also exhibit the best mechanical properties and top-load stability. In retrospect, the film thickness can be reduced if the material is specifically stretched through the use of pre-stretching plugs com- pared to compressed air forming. Thin or weak areas can be prevented. In further trials it has to be investigated to what extent the results can be transferred to larger or deeper cup geometries. Acknowledgements The research project (19342 N) of the Forschungsvereini- gung Kunststoffverarbeitung has been sponsored as part of the „industrielle Gemeinschaftsforschung und -ent- wicklung (IGF)“ by the German Bundesministerium für Wirtschaft und Energie (BMWi) due to an enactment of the German Bundestag through the AiF. We would like to extend our thanks to all organisations mentioned. Fur- thermore we would like to thank Kiefel GmbH, Freilass- ing, Marbach Werkzeugbau GmbH, Heilbronn, Kiefer Werkzeugbau GmbH, Schwaigern, and W.u.H. Fernholz GmbH & Co.KG, Meinerzhagen for the provision of equip- ment, mould technology and test materials. The Authors Univ.-Prof. Dr.-Ing. Christian Hopmann; Dennis Balcerowiak, M.Sc. Institut for Plastics Processing at RWTH Aachen University Literature [CHM02] COLLINS, P.; HARKIN-JONES, E. M. A.; MARTIN, P. J.: The Role of Tool/Sheet Contact in Plug-assisted Thermoforming. International Polymer Processing 17 (2002) 4, pp. 361 – 369 [Ede14] EDERLEH, L.: Simulative and Experimental Re- search on the Forming Behaviour of Thermoplastics during Thermoforming. RWTH Aachen, Ph.D. Thesis, 2014, ISBN: 978-3-95886-026-1 [HB18] HOPMANN, CH.; BALCEROWIAK, D.: Der Schreck- marke den Kampf angesagt. Kunststoffe 118 (2018) 11, pp. 81-85 [HM15] HOPMANN, CH.; MICHAELI, W.: Einführung in die Kunststoffverarbeitung. München: Carl Hanser Verlag, 2015 [HW03] HABERSTROH, E.; WIRTZ, J.: Helfer für die Becher- formung. 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