Modelling Flexible Sheets for Automatic Handling and Lay-up of Composite Components

Abstract

Automating the manufacturing process associated with composite components from prepreg presents new engineering challenges. To design, implement and operate machinery to handle and lay-up prepreg sheet material requires a clear understanding of the processes involved. Manipulation of sheet material is an integral part of the lay-up procedure. This paper presents the main automation issues concerning the production processes and defines a mathematical model for predicting the shape of prepreg sheets for the purposes of manipulation. This provides an aid towards the control of shape during the process of lay-up. Critical mould parameters, which determine prepreg sheet shape, are presented. Lay-up trajectories for a multi-arm robotic system have been derived, utilizing the models formulated. Practical trials with an existing multi-arm robotic system have proved satisfactory control of the process.

Getting to grips with automated prepreg handling

“…There are requirements on contamination-free handling, positional accuracy of placed plies, requirements for gap/overlap, fiber angles, wrinkles and other deformations [7,[13][14][15][16][17]. • The systems must be designed to handle a multitude of ply shapes and sizes [14].…”

“…Although less expensive than AFP and ATL, implementation of pick and place systems has so far been unsuccessful in industry, and there are no commercially available alternatives to ATL and AFP for automated composite manufacturing [6]. The reason for the lack of industrial implementation has not been sufficiently investigated, but published results in the field of automated prepreg handling indicate that projects aim to automate layup onto contoured molds [7][8][9][10][11]. This, together with Elkington's [12] conclusion that layup of prepreg on a contoured mold is probably too complex to be automated using existing technologies, may indicate that the problem needs to be deconstructed in order to create truly efficient systems.…”

Automated layup and forming of prepreg laminates

“…Because the manufacturing steps taken before a composite product has cured have a particular impact on the quality of the final product, prepreg layup follows a highly controlled process. For the layup process, the plies must be stacked in the correct sequence and according to specifications on allowable gaps and overlaps between prepreg plies, and the position and orientation of the plies must also be to specification [3,[67][68][69][70][71]. There are also requirements on fiber orientation: the industrial norm generally allows a ±2° or ±3° fiber orientation deviation compared to the drawing nominal [16,67].…”

“…The distribution of the grip points is either spread out over the entire surface of the plies that the end effectors should be able to handle, or located along the edges or at the corners of the plies. The review indicates that a distribution over the surface is a more common approach, and it can be noted that many of the solutions that grip at the corners or edges of the plies use two or more robotic arms for the handling operation [70,112,113,122,123].…”

“…The next example of an automated layup system for prepreg was developed by Newell, Buckingham and Khodabandehloo, who from 1995 to 1996 published three papers [70,122,133] describing a system for automated layup of prepreg on a three-dimensional mold. The system, outlined in Figure 28, is designed for automated layup of prepreg onto double-curved molds and is tested using three different mold shapes as well as three different prepreg materials.…”