I. Core Breakthroughs

Breakthrough 1 : Clearly define low-pressure heating ADFP The process is the optimal solution for homogenizing thin preforms.

Previously ADFP High-pressure compaction is commonly employed to achieve a high fiber content; this paper compares two processing regimes and demonstrates that high pressure combined with low temperature… MC1 Four corners of the precast element \(V_f\)" The difference can be as high as 4.3% , severe dispersion; MC2 Reducing the pressing force and simultaneously raising the temperatures of both the die and the strip material ensures more uniform binder activation, reducing the coefficient of variation in fiber content within a single preform to 1.3% Within this range, it perfectly addresses the industry‑wide challenge of uneven compaction at the initial laying stage of robotic fiber placement. It simultaneously optimizes molding uniformity and resin‑impregnation pathways, striking a balance between densification and infusion efficiency.

Breakthrough 2 : Revealing the nonlinear densification behavior of ultra-thin unidirectional tapes under cyclic compaction

Conventional thick‑fabric preforms have been extensively studied for compaction, whereas ultra‑thin plies and multilayer interfaces exhibit distinctive viscoelastic responses. Experimental results demonstrate that… 4~16 The layered preform has undergone 50  The subsequent depressurization cycle still fails to reach the compaction steady state, Previous 10 The subsequent cycle accounts for the vast majority of the increase in fiber volume. The fewer the layers, the greater the incremental densification per compaction cycle; in contrast, multi-layer preforms, subjected to repeated compression at the bottom layer, exhibit a higher initial degree of densification, thereby… CAPRI The controlled-pressure perfusion debonding process provides a quantitative basis for the number of cycles.

Breakthrough 3 : Upending the conventional understanding of unidirectional preform permeability

Traditional unidirectional fabrics exhibit extremely poor through-thickness permeability (poor). 2~3 an order of magnitude), this study found that ADFP The ultra-thin multilayer preform differs by only 1  At this scale, the resin can rapidly impregnate through the thickness; however, a staggered ply arrangement can block the interlayer microchannels, reducing the through-thickness permeability. This finding provides direct guidance for laminate layup path design, addressing… LCM Slow mold filling and internal bubble defects remain challenging issues.

Breakthrough 4 : Establish a complete “ Laying down -  Compact tightly -  Penetration -  Perfusion ”  Integrated Standardized Testing System

Integration of roller pressure calibration, infrared temperature monitoring, single / A comprehensive suite of testing methods, including bidirectional permeability testing, cyclic pressure‑relief simulation, and vacuum infusion‑molded component metallographic etching; a unified sampling and four‑quadrant partitioning scheme for characterization; and the ability to perform cross‑benchmarking of all data, thereby filling a critical gap. ADFP Thin paving layer LCM Gap in standardized testing of supporting processes

II. Technological innovation

Innovation 1 Dual-process gradient ADFP Prefabrication Preparation System

Establish two sets of controllable variable molding schemes:

• MC1 : to lay out 40℃ , mold 20℃ , compacted 375N (Traditional high-pressure, low-temperature)
• MC2 : to lay out 50℃ , mold 35℃ , compacted 250N (Optimized Low-Pressure Heating)

Uniform laying speed 200 mm/s , paired with three classic layups: orthogonal CP , Half-width staggered floor CPSS , quasi-isotropic QI , a comprehensive variable‑control matrix is established to isolate the influence of each individual variable. A corresponding calibration method for the pressure imprint of silicone rubber compaction rollers is developed, enabling precise measurement of the full‑field contact pressure distribution on the roller surface.

Innovation 2 Multidimensional Characterization Techniques for Prefabricated Components

• Quasi-static compaction test: A universal testing machine simulates vacuum pressure, and a power-law function is used to fit the pressure data. -\(V_f\) Curve, quantifying the densification response of different plies;
• Cyclic depressurization test: simulates the industrial degassing process under pressurization. - Holding pressure -  Complete pressure-relief cycle, capturing creep, springback, and permanent deformation of thin laminates;
• Bidirectional permeability testing: A custom‑designed permeation apparatus was used, with silicone oil employed as a surrogate for epoxy resin; permeability in the in‑plane and through‑thickness directions was determined separately in accordance with Darcy’s law.
• Vacuum infusion molding verification: using HexFlow RTM6 Aviation epoxy: fiber measurement by post‑curing ablation. /  Pore content and the distribution of bubbles within the microstructural observation layer.

Innovation 3 Method for Evaluating the Uniformity of Zonal Sampling

The single prefabricated block is uniformly divided into four quadrants for sampling, with comparisons made between the head, middle, and tail sections. \(V_f\)" • The disparity in penetration rate provides a direct quantitative measure of the spatial variability introduced by the robot’s laying path, enabling rapid assessment of whether equipment temperature and compaction parameters meet specifications, and serving as a standard quality‑inspection procedure for incoming materials on the production line.

Innovation 4 Viscoelastic Compaction Mechanism Model for Thin Layers

The ultra-thin laminate has a large number of layers and an enormous interlayer interface area; under pressure, fiber slippage and interfacial friction give rise to significant creep. During the hold‑pressure stage, densification continues, and upon pressure release, partial springback occurs—this springback diminishes with increasing layer count. A comprehensive explanation is provided for the mechanism by which the underlying structure gradually becomes uniform after repeated depressurization of a thin preform, thereby laying the groundwork for… LCM The duration of the pre-degassing process provides quantitative support.

III. Application Scenarios

• Lightweighting of Thin Aviation Flooring Layers L Structural Components (Core Scenarios)

Military aircraft fairings, small load-bearing bulkheads, and composite interior components of aerospace vehicles are manufactured using… ADFP Ultra-thin preform +  Vacuum infusion molding, with precisely engineered quasi‑isotropic layups that enhance impact resistance, leverages the low‑pressure process described herein to minimize internal porosity in the preform and reduce molding‑related bubble defects.

• Hydrogen energy V Type of hydrogen storage tank body without liner

Large-size curved dry fiber preforms, ADFP The robot precisely controls the fiber angle, in conjunction with… LCM Integral infusion molding; leveraging the advantage of thin-layer thickness for enhanced resin infiltration to shorten mold-filling time, improve the tank’s gas-tightness, and reduce the risk of hydrogen permeation.

• Small wind turbine blades, lightweight interior components for rail transit

Small-batch, complex-shaped composite components—no expensive autoclave required. ADFP After automated preform placement, low-temperature infusion is employed; staggered-layer stacking enhances the consistency of part thickness, thereby reducing post‑processing costs associated with grinding.

• Composite Materials Equipment Company ADFP Production line process commissioning

The new paving equipment has been parameter‑calibrated, and the dual‑process comparison and four‑zone partitioned testing procedure described in this paper have been reused to rapidly identify the optimal operating windows for temperature and compaction force, thereby shortening the process development cycle.

• Benchmark Experimental Study on Composite Material Forming in Higher Education Institutions

A standardized test protocol for thin‑layer intervention and liquid‑molding processes, enabling cross‑comparative studies across different binders and ribbon specifications.

IV. Summary of the Article

(1) Core Research Findings

• MC2 Low-pressure heating ADFP Craft ( 50℃/35℃/250N ) is the optimal solution for ultra-thin preforms, significantly reducing spatial variability in fiber content across individual components.
• The thin-layer preform exhibits continuous creep compaction, prior to… 10 The subsequent depressurization cycles achieve most of the densification, and the higher the number of layers, the initial… \(V_f\)" The higher;
• ADFP In the in-plane direction of the ultra-thin unidirectional preform, the permeability difference in the thickness direction is only… 1  At this scale, it outperforms conventional thick fabrics; however, the staggered layer arrangement can clog the interlayer channels and reduce thickness‑permeation capability.
• Porosity of castings produced by the existing process 2.5%~4.9% , not yet reached aviation ≤1% Standards require optimizing the pre‑degassing process and designing minimal interlayer gaps to enhance resin impregnation.

(II) Engineering Application Value

ADFP Automated intervention–based body coordination LCM It represents a low-cost, large‑size composite core technology pathway; however, uneven compaction of thin plies and slow mold filling have long constrained mass production. This paper proposes a temperature strategy that can be directly implemented. -  A pressure‑process window, laminate‑selection guidelines, and a comprehensive quality‑inspection and characterization workflow are provided, along with a quantified standard duration for the degassing cycle, significantly reducing trial‑and‑error during prototyping and enabling automated mass production of thin‑walled, integrated aerospace and hydrogen‑energy components.

(3) Current Research Limitations

Only using a single 79 g/m² Ultra-thin carbon ribbon, RTM6 Epoxy, non‑prepreg glass fiber, and high‑temperature thermosetting resin; only flat‑plate specimens were tested, with no verification of the compaction and impregnation characteristics of doubly curved preforms; fatigue and impact mechanical property tests were not conducted.

(4) Future Expansion Directions

• Develop prefabricated artificial micro‑gaps and perforation techniques to enhance thickness‑direction permeability and reduce molding porosity.
• Curved mold ADFP Preform compaction and grouting test;
• Coupled simulation setup “ Laying parameters -  Penetration rate -  Mold-filling time ”  Predictive model;
• Research on the formulation of new low-viscosity resins ADFP Thin preform forming process.

(5) Industry Insights

Ultra-thin ADFP The intervention‑based approach balances precise, controllable ply placement with the cost advantages of liquid molding; however, the choice of process is critical: while high pressure yields a higher fiber content in the short term, it also leads to severe preform disintegration, thereby increasing molding porosity. In contrast, a low‑pressure, temperature‑rising strategy strikes a balance between uniformity and permeation pathways. When designing the mold‑filling process, prioritizing orthogonal ply stacking enhances thickness‑wise permeation efficiency, while pairing this with thorough depressurization cycles helps optimize the preform’s density and uniformity—this is… LCM Core principles for enhancing quality and efficiency in thin-walled composite materials.

Image and Text Guide

Table 1.  Process parameters under different production conditions

Figure 1.  For out-of-plane permeability testing CP Schematic diagram of the preformed component. The colored square areas represent the four quadrants, with their numbering sequence indicated; the yellow dashed line denotes… 0 °, 45 ° and 90 The starting position for laying the layer; the red dashed line indicates − 45 ° The starting position for laying the layer.

Table 2 . Detailed information on sample preparation and terminology explanations

Figure 2. (A) Side-view image of the roller—showing the contact lengths corresponding to five discrete displacement points, with red line segments at the top and ink marks at the bottom. (B) Example frame images captured using a matrix camera, used to measure the effective gap width.

Table 3 . The contact area and corresponding pressure values for each of the five displacement points

Figure 3. (A) Schematic diagram of the saturated in-plane permeability testing apparatus: (1) An outlet reservoir placed on a mass balance; (2) Permeameter; (3) Pressure sensor; (4) A pressure vessel containing an inlet liquid storage tank; (5) Data Acquisition System (adapted from [41] ); (B) An infiltration apparatus for in-plane flow, with red and yellow dots indicating the locations of the inlet and outlet pressure sensors, respectively.

Figure 4. (A) Unidirectional lateral flow permeameter; (B) Cross-sectional view of the permeameter’s structural schematic; (C) Detail drawing of the lower perforated plate (including a double-clamp sealing structure)

Figure 5.  Compaction pressure versus time curve. Note: Point Yx Indicates belonging to the nth item. x A specific point in time within a loop Y ; Δ tinit set Refers to the time range of the initial settlement stage; Δ tcomp * Refers to the time range of the compaction phase in the first cycle; Δ test Refers to the time range of the settlement phase; Δ tdecomp Refers to the time range of the soil loosening stage; Δ trelax Refers to the time range of the relaxation phase; Δ tcomp Refers to the time range of the compaction stage.

Figure 6.  Schematic diagram of the resin vacuum infusion system, illustrating each component along with its corresponding power rating and target temperature.

Figure 7. VI_CP Schematic diagram of the laminate, showing the thickness‑removed and ablated specimens. The blue boxed area indicates the thickness distribution map, while the red rectangular area denotes the ablation test specimen; the yellow dashed line marks the microscopical analysis region. During analysis, a width of … was excluded. 15 The peripheral region in millimeters; the red arrow indicates the flow direction.

Table 4  In 100 kPa Fiber Volume Fraction Results Under Compaction Pressure

Table 5.   Power-law fitting coefficient

Figure 8. MC1 Sample (top) and MC2 Sample (bottom): Trend of fiber volume fraction as a function of increasing compaction pressure. The solid line denotes the experimental results, while the dashed line represents the power-law approximation curve. PL Represents a power-law function.

Table 6  In-plane permeability calculated for each quadrant in all directions of each laminate layer.

Table 7. Out-of-plane permeability calculated for each quadrant of the laminate’s ply orientations.

Figure 9.  Represented by blue, green, and yellow dots, respectively. IPP_CP 、  IPP_CPSS and IPP_QI Calculation of the quadrants for each sample Kx=y Value; the red icon represents the average permeability calculated for each sample orientation.

Figure 10.  Represented by blue, green, and yellow dots, respectively. OPP_CP 、  OPP_CPSS and OPP_QI Calculation of the sample’s quadrants Kz Value; the red icon represents the average permeability calculated for each sample orientation.

Figure 11. Displayed 100 kPa Calculated at the end of the settlement stage Vf Value ( Vf@tf = 785 N ) The relationship as a function of the number of compaction cycles. The figure shows results under different sample plot and layer conditions. CC_XX_CP Test results of the specimen: (A)4 layer, (B)8 layer, (C)12 Layer and (D)16 Layer.

Table 8.  Derived based on the number of cycles. Vf Mean @tf − 785N Numerical value

Table 9 . Final moment of the settlement phase (Δ Vf Mean @tf − 785N ) the change in fiber volume fraction, with data based on the …th 1 After the next iteration and each subsequent one 10 It is computed in the next iteration.

Figure 12. (A)4 layer, 8 layer, 12 Layer and 16 In the prefabricated component layer Q3 Calculation of Quadrant Samples Vf@tf − 785N Value; (B) The 1 Δ after the next iteration Vf@tf − 785N Value, each 10 The calculation is performed once per iteration.

Figure 13. 16 Layered sample ( CC_16L_CP ) Calculated in different quadrants Vf The evolution trend of the value as a function of the number of cycles; the solid line and the dash-dot line indicate the onset and termination of the settlement phase, respectively, while the dashed line and the dotted line denote the onset and termination of the relaxation phase, respectively.

Figure 14.  by VI Equipment production of VI_CP (A) 、  VI_CPSS (B) and VI_QI (C) Thickness distribution of the laminate. The mean and standard deviation are also provided.

Table 10.  Laminated material quality and fiber volume fraction ( Vf ( % ), resin volume fraction ( Rf ( % )) and porosity ( You ( % ) ) relationship

Figure 15.  Cross-sectional images obtained from impregnated laminated board samples; VI_CP (A) 、  VI_CPSS (B) and VI_QI 。