JEC COMPOSITES MAGAZINE - Issue #73 - June 2012 - 63

with a lifting table is necessary to keep the top layer in the same position. Therefore, the best system has to be selected based on the boundary conditions, such as the number of pieces, available space, flexibility, shape of the tailored NCF, etc. As mentioned before, multi-step preforming corresponds to the assembly line in steel processing. Semi-finished parts such as multiaxial non-crimp fabrics or woven fabrics, but also tailored NCF, are being assembled to complex shaped, highly integrated preforms in a sequence of automated process steps. The main steps within this textile assembly process are cutting, handling, draping and joining of the textiles. ITA developed the ITA-Preformcenter to enhance the individual technologies and to perform fully automated preforming processes at the laboratory scale. The ITAPreformcenter is described schematically in Fig. 13. The individual preforming technologies are briefly introduced below [13].

thus incomplete impregnation. Edge trimming by means of robotically operated ultrasonic knives is a suitable way to fulfil RTM tolerance requirements. Due to the geometrical flexibility of standard robots, even complex shaped preforms can be trimmed. Handling Other than cutting, the handling of limp semi-finished parts such as reinforcement textiles is an enormous automation challenge. Still it is a very important process step, as handling operations are the interface between all the other steps. Various handling devices have been invented in order to automate the preforming process. These devices typically use needle, vacuum, Bernoulli, electrostatic or cryogenic grippers. More sophisticated devices are capable of positioning pre-cut textiles into uniaxial or even slightly multiaxial curved moulds. However, so far none of these devices are able to fulfil all of the requirements associated with textile reinforcement structures preforming, namely low damage, absence of contamination, low fibre disorientation and sufficient holding forces along with high accuracy. Thus, most handling and draping operations are still accomplished manually while automated technologies for this part of the preforming process are currently under investigation. In particular, the difficulties in automating draping processes are even stronger if locally adjusted NCF are used instead of standardized ones. Therefore, the development of textile machine technology for tailored preforms has to go hand in hand with the characterization and simulation of textile fabrics. This way, it can be best guaranteed that tailored preforms keep their good mechanical performance and allow lowering the amount of manual work during both handling and draping. ITA is performing research in the field of draping characterization. A draping tester was developed to measure the deformation behaviour of textiles more closely to real-world draping processes [ 14]. Based on the ARGUS optical 3D measuring system, the strain fields of draped textiles are recorded and can be used for experimental characterization and for the calibration and validation of numerical simulations [15]. Joining Joining technologies can be used in preform production for several purposes. First, joining semi-finished textile parts can improve the handling properties of the preforms and avoid frazzling. While this affects the production process, joining can also influence properties of the cured composite, such as fracture toughness or interlaminar shear strength and energy release rate. Multiple textile layers can be joined by means of both onesided stitching and binder technologies. Several one-sided stitching devices are available for robotically-operated stitching of large and complex preforms. Binders can either be applied extensively during the proNo73 June 2012

Fig. 13:The ITA-Preformcenter

Cutting Manual cutting operations are usually performed with wheel cutters, standard or electrical scissors. Productivity, accuracy and reproducibility can be significantly increased using state-of-the-art automated cutting technologies. CNC cutting tables can be used to cut textiles prior to subsequent preforming processes. Rotating cutting discs or oscillating knives are typically used. In both cases, the textiles are usually held in place by a vacuum. Preforms for RTM processing have to fulfil certain contour tolerances as size variations can lead to race tracking and

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JEC COMPOSITES MAGAZINE - Issue #73 - June 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #73 - June 2012