Author: [Bruce Zhou]
Affiliation: [Jota Machinery Composites Material Prepreg Solution]
Corresponding Author: [jotamachinery@gmail.com]
Published : December 16 , 2025
Abstract
Automated Fiber Placement (AFP) of thin-ply prepreg tapes presents a significant opportunity for weight reduction and mechanical tailoring in aerospace composite structures. However, the manufacturing behavior of low areal weight tows differs substantially from standard prepregs, leading to unique defect modes and process limitations. This paper examines AFP trials conducted on thin-ply carbon–epoxy materials with 70 g/m² and 30 g/m² tow forms, focusing on parameter optimization and defect characterization. Results demonstrate that 70 g/m² tows can achieve consistent placement quality with optimized heater output, compaction force, and feed rates, whereas 30 g/m² materials introduce challenges linked to material variability and hardware compatibility. The paper outlines the practical process windows, defect observations, and implications for prepreg feedstock preparation systems, including slitting quality and tape handling.
Keywords
Automated Fiber Placement; Thin-Ply Composites; Prepreg Slitting; Tow Width Consistency; Process Optimization; Aerospace Manufacturing
1. Introduction
Automated Fiber Placement has become an essential manufacturing method for high-performance aerospace composites due to its ability to deposit narrow unidirectional prepreg tapes with precision and repeatability. Traditional AFP has been validated on standard prepreg tow weights, typically ranging from 140 to 170 g/m². Recent research has explored the feasibility of AFP with thin-ply materials—prepregs with areal weights between 30 g/m² and 70 g/m²—motivated by the potential for weight reduction and improved mechanical performance, including delayed damage onset and enhanced ply orientation tailoring.
The transition to thin-ply introduces manufacturing challenges not previously encountered in standard AFP. Variations in tow width, differences in resin behavior, and increased sensitivity to process parameters can lead to defects such as tow wandering, gaps, overlaps, and hardware interactions that compromise laminate integrity. This paper evaluates key process parameters and defect mechanisms identified in NASA Langley Research Center thin-ply AFP trials, with the objective of defining actionable process windows and identifying upstream considerations for material preparation, including prepreg slitting quality.
2. Literature Review
Thin-ply composites have been extensively studied for their mechanical advantages. Earlier work has shown that reduced ply thickness can improve ultimate tensile strength and delay transverse cracking in composite laminates through mechanisms collectively referred to as the “thin-ply effect”. These studies highlighted the benefits of increased fiber orientation density within a given laminate thickness and reduced stress concentrations at ply interfaces.
Automated Fiber Placement has traditionally been applied to standard prepreg tows, with literature documenting common defect modes including gaps, overlaps, wrinkles, and tow misalignment. These defects are influenced by process parameters such as compaction force, heater output, feed rate, and tow tension, as well as by geometric considerations in complex tool paths.
Despite this, there is limited published work specifically addressing the manufacturing behavior of thin-ply in AFP environments. The NASA study provides empirical data linking process parameters with defect occurrence for two thin-ply forms, offering insights into the sensitivity and behavior of low areal weight materials during automated placement.
3. Methodology
3.1 Materials
Two thin-ply carbon–epoxy prepreg systems were evaluated:
- Toray 3900-2/T800S with 70 g/m² areal weight, 6.35 mm tow width.
- Hexcel IM7/8552 with 30 g/m² areal weight, 6.35 mm tow width.
These tow forms were selected to represent thin-ply classes with differing sensitivity to mechanical handling and resin distribution.
3.2 AFP Trials
Trials were conducted on an integrated AFP system capable of multi-tow placement, using standard compaction rollers and process controls. Variables adjusted during placement included:
- Heater output (expressed as a percentage of maximum)
- Compaction force (in pounds)
- Feed rate (as a percentage of maximum machine capability)
- Tow tension (nominal)
Flat panels and complex surface geometries were fabricated to assess the effect of curvature and steering on defect manifestation.
3.3 Defect Assessment
Defects were qualitatively assessed through visual inspection, including:
- Tow wandering
- Gaps and overlaps
- Surface roughness variations
- Jam events and hardware interaction
Defect rates and quality observations were correlated with parameter settings to identify practical process windows.
4. Results
4.1 Thin-Ply 70 g/m²
For the 70 g/m² material, consistent placement with minimal visible defects was achieved on both flat panels and complex surfaces. Optimized parameter sets included:
- Heater Output: ~200%
- Compaction Force: 50–100 lb
- Feed Rate: up to 400 ipm
- Tow Tension: ~1 lb
Flash tape was applied at the start of placements to reduce tow wandering by minimizing friction at the initiation zone. Under these conditions, gaps and overlaps were significantly reduced, and course continuity was maintained through multiple orientations.
4.2 Thin-Ply 30 g/m²
The 30 g/m² material presented persistent challenges. Tow width variation (e.g., measured deviations from 6.04 mm to 6.35 mm) contributed directly to inconsistent placement, with gaps forming where reduced geometry occurred. Additionally, the thin tow form required hardware adjustments, such as secondary backing take-up spools, to manage extra backing layers. Best results for this material were observed at lower feed rates (~200 ipm) with increased compaction, but placement quality remained inferior to the 70 g/m² case.
4.3 Hardware Sensitivities
Complex surface builds revealed additional sensitivities. Standard roller widths occasionally interfered with previously laid courses, particularly in concave regions, indicating the need for hardware adaptation when processing thin plies on contoured geometries.
5. Discussion
5.1 Process Parameter Impacts
The experimental data indicate that heater output and compaction force must be balanced such that resin tack activation and consolidation occur without excessive resin flow or thermal degradation. In the 70 g/m² case, maintaining 200% heater output with moderate compaction allowed continuous placement at high feed rates without significant defect introduction. For the 30 g/m² material, lower feed rates compensated for increased sensitivity to positional perturbations and geometry variation.
5.2 Tow Geometry and Slitting Considerations
A critical observation from the 30 g/m² trials is that tow width inconsistency directly translates into placement defects that cannot be corrected through AFP parameter tuning alone. This underscores the importance of upstream feedstock preparation, especially tape slitting quality. If slit tape width varies beyond narrow tolerances, the AFP head cannot constrain the tow sufficiently to maintain course alignment, particularly at ply starts and direction changes.
5.3 Implications for AFP Production
The results highlight that:
- Thin-ply AFP success is contingent on feedstock precision, not only on machine parameters.
- Hardware must be capable of handling lightweight tows without inducing jams or disruptive interactions.
- Process windows for thin-ply are narrower than for standard prepreg, requiring disciplined control of heating, force, and motion settings.
6. Conclusion
Automated Fiber Placement of thin-ply prepreg can be achieved with high quality for 70 g/m² materials when process parameters are optimized and course initiation friction is managed. Conversely, 30 g/m² materials remain challenging under existing AFP hardware due to tow geometry variation and hardware compatibility issues.
These findings emphasize the need for precise prepreg slitting and handling to support thin-ply AFP production. Effective thin-ply manufacturing will require coordinated control of feedstock attributes and AFP process settings to ensure placement stability and laminate consistency.
References
- Harik, R., Lovejoy, A., Yokan, C., & Jegley, D. (2020). Thin-Ply: Exploration and Manufacturing with Automated Fiber Placement. NASA Technical Report.
- Amacher, R., et al. (2014). Thin ply composites: Experimental characterization and modeling. Composite Science and Technology.
- Sihn, S., et al. (2007). Experimental studies of thin ply laminated composites. Composite Science and Technology.