To cite this version:P. Molnár, A. Ogale, R. Lahr, P. Mitschang. Influence of drapability by using stitching technology to reduce fabric deformation and shear during thermoforming. Composites Science and Technology, Elsevier, 2009, 67 (15-16), pp.3386. <10.1016/j.compscitech.2007.03.022>. I n f l u e n c e o f d r a p a b i l i t y b y u s i n g s t i t c h i n g t e c h n o l o g y t o r e d u c e f a b r i c d e f o r -m a t i o n a n d s h e a r d u r i n g t h e r m o f o r m i Accepted Manuscript ACCEPTED MANUSCRIPTInfluence of drapability by using stitching technology to reduce fabric deformation and shear during thermoforming Molnár, P., Ogale, A., Lahr, R., and Mitschang, P.Institut für Verbundwerkstoffe GmbH, Erwin-Schrödinger-Straße 58, 67663 Kaiserslautern, Germany AbstractForming of woven fabric into a complex shape involves shear deformation of the fabric elements (warp and weft). Various researchers investigated the shear deformation during the manufacturing of thermoplastic composites (TPC) based on the hemispherical geometry, where the highly deformed edges and corners are considered as a waste. In many applications the complete formed geometry including areas around the curvature has to be used. A new idea to influence the deformation behavior of woven fabric by incorporated seams at localized sections is presented in this paper. The study is based on the photographic analysis of dry sewn preforms and thermoplastic matrix (PA12) impregnated laminates, before and after the deformation. The seams applied at the highly deformable and predefined zones help to reduce fabric shearing or to transfer the shear forces into the unsheared areas during the thermoforming process. The intensity of reduction in the fabric shear depends on the type of the sewn geometry. The results obtained can be applied in the part design, the preform engineering, and the positioning of stitches.

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A considerable number of process versions of Liquid Composite Moulding (LCM) technologies have been commercialised during the last few years. Only recently there have been attempts to reduce costs and to implement more complex components by the application of preform technology. This article indicates the most appropriate application fields for LCM techniques for the manufacture of fibre reinforced polymers. Different LCM methods are described and summarised. The preforming techniques and particularly the sew -and -cut philosophy for developing a tailored reinforcement is explained. Investigations designed to elucidate the influence of sewing parameters and thread properties have led to an understanding of the requirements and preform characteristics needed to operate the quality controlled LCM process. Some concepts related to the control of the resin injection are described, and a realization of a decision-tree-concept is shown. Finally, a comparison of cost effects for different preforming methods shows a need to define a “critical preforming effort” to manufacture quality components as well as economically optimised parts.

The manufacturing of textile preforms is a well-established process for developing three-dimensional (3D) composite structures. The process of liquid composite molding (LCM) is an efficient method for the production of fibrereinforced polymer composite (FRPC) products. For the production of highperformance FRPCs, the sewn, the net shape, and ready-to-impregnate preforms are economically well suited in the LCM process [Mitschang, P., Ogale, A., Schlimbach, J., Weyrauch, F. and Weimer, C. (2003). Preform Technology: A Necessary Requirement for Quality Controlled LCM-processes, Polymers & Polymer Composites, 11(8): S. 605-622.]. Though the process of sewing has a long history, its usefulness in the area of composite manufacturing has not yet been fully exploited. The sewing technology, its associated parameters, required thread construction, and finally the stitch geometry are required to be considered thoroughly. Understanding the process of stitch formation and analysis of the available stitch geometries for preform stitching are the aims of this study. Various kinds of seams can be used in the preform development and structural assembling. The micrographic observations at the stitched zones help us to know the actual stitch geometry inside the FRPC structure, the amount of threads involved in each stitch type, the fibre displacement, and the structural properties. Furthermore, in order to widen the preform and the composite manufacturing practices, new technologies like single-sided-stitch, blind stitch, chain stitch, etc. are compared with the modified lock stitch. For structural reinforcements, the process-compatible carbon fibre thread, developed at the Institut fu¨r Verbundwerkstoffe GmbH (IVW) has been explained in detail. In this paper, the usefulness of tailored preforming technology and process optimisation steps are described briefly.

Applying sewing technologies for manufacturing preforms, which later used for Liquid Composite Moulding processes (LCM), requires an adoption of different sewing resources. As the number of applications of stitched preforms are growing [1 ,2 ], the issue of improving thread quality and its compatibility with the Fibre Reinforced Plastic (FRP) is getting into the interest of both industry and science. Within this study the relationship between the thread design and the FRP quality with respect to the LCM technique was evaluated.