Problem Statement

A variety manufacturing methods are currently available to produce quality, high

strength-to-weight components. Continuous fiber composites, such as carbon or

aramid fiber composites, are some of the highest strength to weight material systems currently available that fit within the financially acceptable limits for their applica- tions. There are a handful of manufacturing processes available to manufacture these components, each with their strengths and limitations.

Figure 1.1: The web of technologies related to industrial 3D Printing with continuous fiber

One of the most common methods of manufacturing composites is highly manual:

hand layup and Vacuum or Pressure Assisted Resin Transfer Molding (RTM, figure

1.2a), where plies of fabric are manually draped over a mold, infused with a resin and then cured offer a low-cost step into the composite manufacturing world. For com- plex and highly 3 dimensional parts, these processes and methods may get relatively expensive, as they require significant man-hours and the potential curing equipment can become significant. More importantly and more relevant to this research topic, the shape of the structure that can be produced is limited, as composite structures require molds and tooling that need to be removable in most cases. Furthermore, they are mostly suitable for structures that are relatively simple in shape, as highly complex and 3D parts require tooling that comes at a steep pricetag.

More automated methods of composite manufacturing areAutomated Tape Laying

(ATL) and Automated Fiber Placement (AFP), as shown in figure 1.2b. Both are

similar rapid AM methods that require roller pressure to ensure the placed tape or

(a) (b)

Figure 1.2: Common composite manufacturing methods at the McNAIR Center: (1.2a) VARTM of two skin panels for a UAV and (1.2b) Automated Fiber Placement.

composite material is (quasi-)geodesically wound around a (rotating) mandrel can be used to manufacture high strength revolution-type objects, however the possible fiber paths can be quite constrained, depending on the base objects shape. A similar

drawback exists for compositeBraiding, a process that resembles filament winding in

the sense that now a braid, instead of a tape/tow, is overlayed onto a base mold. The most significant differences with winding are the process speed and fiber path angles. As with filament winding, for braiding, the mold is embedded in the composite after curing and, depending on the objects shape, may be very hard or even impossible to remove. Furthermore, ATL, AFP and filament winding are technologies perfected to rapidly produce relatively thin shell like structures in the build direction and, although some stiffener or grid generation is possible through clever path structuring, they struggle or generally lack the ability to manufacture highly complex non-shell 3D reinforced structures.

Whether one considers hand Layup, AFP, ATL or filament winding, all of these ex- isting additive manufacturing methods require one or multiple stiff and strong molds that are machined to tolerances and behave well under autoclave and in- and post- process pressures to ensure the part maintains it shape. These molds/tools allow the parts to be produced within acceptable tolerances and quality, however they are the source of high non-recurring expenses that can add a significant amount of overhead

and lead time on low volume production components. For some components, this may be a reason not to pursue Additive Manufacturing or composite manufacturing at all, which limits the engineer’s design freedom. There is thus a desire to expand the scope of manufacturing processes for mold/tool-less high strength-to-weight composites.

A secondary problem arises from the history and marketing of 3D Printing. 3D printing has gained a lot of traction as a rapid prototyping method, and is known to be a relatively young, but promising technology. Although the general consensus is slowly changing, many professionals and decision makers still consider 3D print- ing as a gimmick, and do not consider it a worthy option for the manufacturing of functional end-user components. An additional research problem is thus, through design for functionality, to prove the viability and technology readiness for functional components.

Through continued research, multi-axis continuous fiber reinforced 3D printing offers the opportunity to reduce manufacturing cost of highly three-dimensional com- posite structures. It has the potential to reduce non-recurring expenses as it is a tool-less, mold-less and largely automated process to make functional components. The ability to print with continuous fiber reinforced plastics can greatly increase the strength of the component within the layers, however having the anisotropy of a com- posite material system only enhances the already-inherent anisotropy of 3D printed components. To insure these printed components do not delaminate or underper- form, it is important to add reinforcement of the fiber along the build direction of the base layer in complex 3D parts. Fortunately, with careful design for modular- ity, FFF systems allow for continuous fiber deposition head to be integrated on a full 6-axis robotic platform. Continuous fiber reinforced additive manufacturing with multi-material deposition capabilities have the opportunity to fill this void in man- ufacturing processes, allowing for true 3D printing of 3D composites for a variety of applications and markets.