Contour scanning of textile preforms using a light-section sensor for the automated manufacturing of fibre-reinforced plastics

Abstract

Fibre-reinforced plastics (FRP) are particularly suitable for components where light-weight structures with advanced mechanical properties are required, e.g. for aerospace parts. Nevertheless, many manufacturing processes for FRP include manual production steps without an integrated quality control. A vital step in the process chain is the lay-up of the textile preform, as it greatly affects the geometry and the mechanical performance of the final part. In order to automate the FRP production, an inline machine vision system is needed for a closed-loop control of the preform lay-up.This work describes the development of a novel laser light-section sensor for optical inspection of textile preforms and its integration and validation in a machine vision prototype. The proposed method aims at the determination of the contour position of each textile layer through edge scanning. The scanning route is automatically derived by using texture analysis algorithms in a preliminary step. As sensor output a distinct stage profile is computed from the acquired greyscale image. The contour position is determined with sub-pixel accuracy using a novel algorithm based on a nonlinear least-square fitting to a sigmoid function. The whole contour position is generated through data fusion of the measured edge points.The proposed method provides robust process automation for the FRP production improving the process quality and reducing the scrap quota. Hence, the range of economically feasible FRP products can be increased and new market segments with cost sensitive products can be addressed. MANUFACTURING OF COMPOSITE PARTS Manufacturing of composite partsFibre-reinforced plastics (FRP) have become an important material group for light-weight structures with advanced mechanical properties. FRP can be described as composite materials consisting of a textile reinforcement structure, e.g. fabrics, meshwork or unidirectional layers and the polymer matrix [1].Because of their excellent weight specific mechanical properties, FRP parts replace aluminium parts for aerospace applications. This trend is driven by a significant weight reduction, which leads to a lower fuel consumption thus cutting of operating costs. Different to metal parts, FRP usually do not have isotropic properties even for symmetric preform layups [1]. This means that only along the fibre orientation the maximum stiffness and strength in the composite part can be achieved. Hence it is important that the reinforcement fibres are aligned precisely in the directions of the major loads. The fibre alignment is greatly influenced during the preform production ( Fig. 1) as in this process step the single fabric layers are put in position. By the lay-up the dimension, the geometry and the mechanical properties of the composite part are determined. To ensure the maximum part performance, a quality control during this early process stage is vital. In particular, the cutting of the textile layers (1) and the preform lay-up (3) have to be controlled. Up to now, many FRP manufacturing ...

Laser light-section sensor automating the production of textile-reinforced composites

“…Since the lateral resolutions are approximately twice times lower than the distance-to-sensor resolution, the evaluation of the contour is more accurate and has already been examined in previous works at WZL ([21], [22]). The contour is defined through the layer's edges.…”

“…For the contour scan a higher camera resolution coming along with a short laser line and a small working distance is needed (specified in [21], [22]). For the surface scan the lateral uncertainty can be higher.…”

“…Hence one essential part of the present work is the determination of the expanded measurement uncertainty for the geometry scanning of complex FRP textiles after drapery. The examinations are based on previous works [22].…”

“…The sensors specifications are defined with regard to the task ( [22]). For a precise scanning of each fabric, a sensor with an adequate measurement area and a small uncertainty in measurement has to be deployed.…”

“…For knitted carbon fibre fabrics a strong contrast between the white seam and the black fibres occurs. This means that the inspection system has to cope with quite a range of different material properties ( [18], [19], [21], [22]). …”