Toolless out of build plane manufacturing of intricate continuous fiber reinforced thermoplastic composites with a 3D printing system
Date
2019
Authors
Bourgeois, Mark Elliott, author
Radford, Donald, advisor
Ma, Kaka, committee member
Maciejewski, Anthony, committee member
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Abstract
Continuous fiber reinforced composite materials are manufactured using a variety of techniques ranging from manual layup to highly automated tape and fiber placement, yet all of the processes require significant tooling to act as a form which gives the composite the desired shape until processing is complete. Once processed and rigid, the composite is removed from the tooling and the tooling is, usually, then prepared and another composite component shaped on the tool. Manufacturing on such tooling has the advantage of offering a repeatable shape in a large batch production of fiber reinforced composite parts; however, the tooling itself can be a significant time to manufacture and cost challenge. It may take a large volume of composite parts to effectively amortize the cost of the tooling, which has a finite service life. Further, once the tooling is produced, making geometry changes during a production cycle is almost impossible. Geometry changes need either remanufacture of the tooling or the development of completely new tooling sets. Thus, technologies which could reduce the required tooling for composites production are highly desirable. With the advent of additive manufacture, it has become commonplace to expect the development of components of very complex geometry built from a simple surface. However, unlike continuous fiber reinforced composites, these complex geometry 3D printed components have material properties which are, for the most part, non-directional. While fiber reinforced composites are produced in a layer-by-layer additive fashion, the key to the performance of this material family is the positioning and orientation of the continuous fiber over complex contours, which has resulted in a need for substantial tooling. Thus, if concepts related to 3D printing could be mapped into the continuous fiber reinforced composite manufacturing space, the potential may exist for a radical reduction in the amount of tooling required and a corresponding increase in the flexibility of manufacture. The current research effort implements concepts common to 3D printing to investigate an approach to producing continuous fiber reinforced structures which require no tooling. Sandwich panels are commonly used as structure based on fiber reinforced composites, with the goal of high flexural stiffness and low mass. It is most common to separate two high performance composite laminates (facesheets) with a low-density core material, generally in the form of a foam of honeycomb. A recent concept has been to replace these traditional core materials with fiber reinforced truss-like structures, with the goal of further reducing mass; however, a manufacturable solution for these truss core sandwich panels has not been developed and those processes that do exist are tooling intensive. In this work, a system was developed and demonstrated that can radically reduce the amount of tooling required for truss core sandwich panels. Pyramidal truss core sandwich panels were manufactured to test the positional fidelity of out of build plane, unsupported space manufacturing. Laminates with different lamina counts were manufactured on a substrate and in unsupported space and tested for consolidation quality. Lap shear specimens were manufactured on a substrate and in unsupported space and tested for interlaminar bond quality. Individual continuous fiber reinforced composite strand specimens were manufactured in unsupported space at varying temperatures and tested for stiffness. These truss core panels, manufactured without tooling, were compared to similar truss core panels produced by more traditional techniques. The outcome of the research performed indicates that structures could be manufactured, unsupported, in free space with good precision. The void content of laminates manufactured in unsupported space decreased by 15% as the laminate was built up while the laminate manufactured on the substrate had no significant change in void content. Unidirectional laminates placed in space showed no statistical difference in strength when compared to laminates placed on a substrate. Crossply laminates had a 33% reduction in strength compared to similar laminates placed on a substrate. Composite truss core sandwich panels manufactured with the system developed in this work were more precise than composite truss core sandwich panels manufactured with compression molding and heat fusion bonding. Increasing the placement temperature of continuous fiber reinforced thermoplastic strands increases the quality of the strand by up to 44%. Improvements to the MAGIC system have increased the composite quality by 25%. Thus, manufacturing techniques were implemented to place fiber not only within the build plane, X-Y, but also to place continuous fiber out of the build plane, X Y Z. Intricate continuous fiber reinforced thermoplastic composites were manufactured without the use of tooling. While the composites produced with the new system were less stiff than composites made with compression molding further improvements to the manufacturing system have closed the stiffness gap between the two manufacturing methods.
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Subject
commingled roving
3D printing
out-of-plane
toolless manufacturing
continuous fiber
thermoplastic composites