Modeling the robotic manipulation of woven carbon fiber prepreg plies onto double curved molds: A path-dependent problem

Abstract

This paper investigates the behavior of woven prepreg plies being placed on a weakly double curved mold by a robot. It is essential that the draped configuration is free from wrinkles. The baseline is a virtual draping environment that can plan and simulate robot draping sequences. It consists of a kinematic mapping algorithm for obtaining target points for the grippers on the mold surface. A simple motion planner is used to calculate the trajectories of the grippers. Here, two conceptually different draping strategies are employed. Finally, the two generated draping sequences are simulated using a transient, non-linear finite element model and compared w.r.t. their predicted wrinkle formations. Material data are obtained by means of tension, bias-extension and cantilever tests. The numerical examples show that the virtual draping environment can aid in developing the automatic draping system but that the generation of feasible draping sequences is highly path dependent and non-trivial.

Generation of feasible gripper trajectories in automated composite draping by means of optimization

“…In a previous study by Krogh et al [3], the prepreg material was characterized experimentally for the in-plane tension and shear and out-of-plane bending responses. This characterization was used as the basis for a nonlinear rate-dependent finite element (FE) model.…”

“…The basic idea is to preserve the fabric length in the fiber directions on the mold while allowing shearing. Details of the calculation of the target points can be found in Krogh et al [3].…”

“…As a validation of the cable model and in particular its ability to account for shearing, consider the example in Figure 16. The example is a comparison between the cable model and the non-linear ratedependent FE model from Krogh et al [3]. The latter will be the baseline for the comparison.…”

“…In Figure 18(a), the ply is in the initial configuration with the seed point gripper (2,1) located 50 mm above the seed point, and in Figure 18 Figure 18(f) is the final draped configuration where the grippers are located within 2 mm of their target points. The ply is in contact with the mold surface everywhere except for the concave region near gripper (3,2). Here the ply is bridging with a maximum distance to the mold of 3 mm.…”

“…A key issue related to the automation of the draping process, is the concept of draping strategies which for the robot system translates to its gripper trajectories. Handling of the prepreg ply by the FlexDraper robot system was previously studied by means of a nonlinear, rate-dependent finite element (FE) model [3]. It was found that the end result is highly dependent on the gripper paths and that wrinkles can easily form during draping.…”