To address the industrial need for manufacturing advanced thermoplastic composite parts with less energy, waste, and time and at lower cost, the feasibility of automated fiber placement using ultrasonic consolidation (UC) is investigated as an alternative to hot gas torch, laser, and infrared (IR) heating. The flexural stiffness and strength of simple flat parts made using UC and also thermal pressing per manufacturer’s specifications are measured by three-point bending and compared. Whereas UC proved to be more effective in welding polyethylene terephthalate/carbon prepreg tape than thermal pressing for both unidirectional and quasi-isotropic layups, the opposite was true for high-density polyethylene/glass, although optimal welding process parameters may not have been used. Finally, a simple transient conduction model is used to predict temperature rise in the thickening laminate and is compared to experimental measurements.

The manufacture of natural fiber and core preforms for biocomposite sandwich structures that bound together with fungal mycelium-based polymer is investigated. The complete manufacturing process involves: (1) cutting individual textile plies; (2) impregnating multi-ply layups with natural glue conducive to mycelium growth; (3) simultaneously forming, sterilizing and setting impregnated skins; (4) filling formed skins with mycelium-laden agri-waste; (5) allowing mycelium to colonize and bind together core substrate and skins into a unitized preform; (6) high temperature drying that also inactivates fungus; and (7) infusing skins with bioresin using resin transfer molding. Aspects of steps 3–6 related to the preform shells and sandwich structure are the main focus of this paper. Three-point bending tests are performed on dry, natural glue-bonded, four-ply specimens in a full-factorial experimental design, and test results are analyzed by analysis of variance (ANOVA) to assess process parameter effects and sensitivities along with environmental condition effects. New specimens are then made using the optimized process and tested for beam bending in creep within an environmental chamber that mimics the actual mycelium growth environment for three days. Two- and six-ply specimens loaded to provide identical maximum tensile stress in flexure are tested, and useful conclusions are drawn based on all creep test results. Finally, preforms in the shape of a viable commercial product are filled with mycelium-inoculated substrate, grown and dried, and part quality is evaluated based on the amount of skin ingrowth and deviation between the measured and desired shapes.

Curing and consolidating thermoset composite laminates and sandwich structures typically involves vacuum bagging an uncured and formed layup over a thin-walled mold, placing it in an autoclave, and subjecting the entire unit to temperature, vacuum, and pressure cycles as prescribed by the manufacturer. Autoclaving is generally considered the major bottleneck in manufacturing advanced composite parts because of high capital and consumable costs, energy usage, waste generated, and process scalability. A new curing and consolidation process called “thermal press curing” is presented and demonstrated as an alternative to autoclaving. The process involves compressing a composite laminate between a special mold set––a heated metal mold and a matching rubber-covered mold made of an insulative material––designed to provide uniform temperature and pressure over the metal mold surface, that is, mimic the process conditions provided by an autoclave. The thermal press curing process is demonstrated for the first time using a mold set for a simple two-dimensional axisymmetric shape. An aluminum curing mold with embedded electric resistance cartridge heaters is heuristically designed to provide uniform temperature in operation across the mold surface within $1°C$ of the target value $(177°C)$. With the mold set compressing an eight-ply carbon/epoxy composite workpiece and well insulated on all sides, the power draw is at least one to two orders of magnitude less than a comparable autoclaving operation. The potential to significantly improve pressure uniformity from the compressed rubber mask is shown by changing the mask shape. Even without an optimized rubber layer shape and thickness, the eight-ply composite part was successfully cured. Finally, a plan for future work is described.

Specialized elastomeric tooling (SET) is a patented process that can replace autoclaving for consolidating and curing advanced thermoset and thermoplastic composite parts. The process mimics autoclave conditions of uniform pressure and temperature by clamping an uncured laminate or sandwich structure with known force between a temperature-controlled lower tool and an engineered, rubber-faced upper tool. Several published studies involving small- to medium-sized parts have shown that SET provides equal or better quality, but at fraction of the energy, waste, and capital and consumable costs. The elastomer of choice for the upper tool is a castable, platinum-catalyzed silicone rubber because of its high working temperature, high tear strength, and negligible shrinkage. To date, there is limited understanding about the properties of silicone rubber subjected to high temperature and compression for long periods of time over multiple cycles. This paper discusses recent work that characterizes silicone rubber under these conditions for design and simulation purposes. Compression testing performed per ASTM-D575 exhibited linear behavior at 125 °C (typical processing temperature for epoxy resins), whereas tensile testing (per ASTM-D412) at the same temperature exhibited strain softening. To show the repeated effect of compression on rubber properties (i.e., mimic multiple loading cycles on rubber mask) at typical process temperature (125 °C) and pressure, a fatigue testing apparatus was custom designed and fabricated. Over repeated cycles between 0 and 1.35 MPa (typical consolidation pressure for advanced composites), silicone rubber exhibited slight hysteresis and a minor stiffening effect that appears to plateau at a particular modulus. Static and kinetic frictional coefficients, also used in modeling, between silicone rubber and several materials commonly used in SET ranged from 0.5 to 2.4 (per ASTM-D1984). Finally, pressure injection and in-line mixing of uncured rubber resulted in significantly less entrained air bubbles (and resulting surface defects in contact with composite part) than the current standard practice of hand mixing. Results are applicable to both SET and any advanced composite forming or curing/consolidation processes involving rubber-faced tools.

A reconfigurable fixturing device (RFD) is a computer-controlled reconfigurable bed-of-pins used for holding a compliant workpiece during manufacturing operations. A new RFD design, based on controlled clamping of loose pins descending on a position-controlled platen, is much simpler in design and is estimated to be significantly less expensive to make than commercially available machines. A RFD prototype with a $5×5$ matrix of pins that can be individually clamped using custom-designed solenoids was prototyped to demonstrate the technology. A solenoid, which is considered the best method for clamping RFD pins, has not been used before in either commercial devices or prototypes discussed in the literature. Design models that predict stopping time and distance of pins clamped with a solenoid have also been developed along with a single pin experimental setup instrumented with linear encoders for model validation. The RFD prototype successfully demonstrated controlled clamping of the matrix of pins in either manual or computer-controlled mode. Another useful result was the validation of models for estimating solenoid force as a function of position, time for the solenoid plunger to impact the pin once energized, and distance the vertically descending pin drops before and immediately after impact by the plunger. Experimental data show that the models can accurately predict pin positioning performance with a solenoid as long as friction within the device is included. Since this RFD concept has been fully demonstrated by the prototype device, the next step in development will be a commercial machine. As such, the models for pin positioning can be used to predict shape accuracy of a particular RFD design and solenoid combination.

The capabilities of specialized elastomeric tooling (SET), a low-cost and low-energy autoclave alternative for consolidating and curing thermoset and thermoplastic composite parts made of “prepreg” material, are expanded to allow vacuum infusion of dry fiber preforms through a simple demonstration project. In this case, SET was designed to allow vacuum infusion of a flat five-ply, woven carbon fiber preform with epoxy resin, consolidate under uniform pressure in a press, and thermally cure while still under load. As expected, parts made using this process were thinner, showed slight increases in stiffness and strength, and had less surface voids as consolidation pressure was increased. Curing temperature/time has no significant effect on part quality. This expanded SET process was further characterized through a full-factorial set of experiments with replicates and quality metrics measured, such as stiffness, strength, surface roughness, and composite volume fractions. Future work will include the design and fabrication of tooling for a realistic part shape.