I. Core Breakthrough: Filling the Gap in Systematic Reviews within the Field and Clarifying Pain Points Across the Entire Value Chain

Breakthrough 1 : Establish a unified benchmark for comparison and quantify the strengths and weaknesses of traditional manufacturing versus additive manufacturing.

Previous studies have often examined only a single type. 3D Printing equipment or materials lack horizontal benchmarking. This paper systematically compares hand lay-up, RTM , autoclave, automated fiber placement ( AFP ) and other traditional crafts with FFF , multi-axis robotic deposition, LOM 、 CF3D For additive manufacturing processes, a quantitative comparison matrix has been established across six key dimensions—local fiber control, fiber volume fraction, defect types, tooling dependency, geometric complexity, and certification maturity—clearly highlighting the technology’s core advantages in localized fiber placement and reduced tooling requirements, while also exposing its inherent limitations, such as porosity, weak interlayer bonding, and performance variability.

Breakthrough 2 : Build “Craft” -  Microscopic -  A “performance” mapping framework that addresses the challenge of characterization standardization.

The industry has long lacked unified testing standards, making it difficult to conduct cross‑study comparisons of data from different papers. This paper integrates tensile, compressive, interlaminar shear, impact, and fatigue tests, among others. ASTM Standard test, paired with Micro-CT , ultrasound, SEM Using nondestructive micro‑scale inspection techniques, establish the correlation between processing parameters, microstructural defects (porosity, fiber waviness, interlaminar delamination), and macroscopic mechanical degradation. Clarify how printing path, compaction, and environmental conditions—temperature and humidity—directly give rise to property variability, thereby providing a standardized reference for subsequent experimental design.

Breakthrough 3 : A multi-dimensional summary of the simulation modeling framework, clarifying the applicable scope of various algorithms.

Successfully attempted a complete partition of the micro. /  Fine /  A macroscopic multi-scale simulation framework, compared with classical laminate theory and embedded fiber finite element methods, RVE Homogenization, AI The advantages and limitations of surrogate models, along with a clear distinction among different simulation‑tool selection logics tailored to early‑stage design screening, failure‑mode prediction, and large‑scale parameter optimization, address the industry’s persistent pain point: engineers often “don’t know which model to use.”

Breakthrough 4 : Incorporating sustainable circular manufacturing into the core research framework

Most reviews of composite materials focus solely on forming and mechanical properties. In contrast, this paper examines material energy consumption, waste generation, aging and durability, as well as the three major recycling pathways—mechanical… /  Pyrolysis /  Chemistry, as an independent core discipline, distinguishes between the thermoplastic recyclable closed-loop and the thermoset non-recyclable bottleneck, and proposes a life-cycle assessment approach tailored for additive‑manufactured composite materials. LCA ) The indicator system aligns with the development trend of lightweight, green manufacturing.

II. Technological Innovation: Systematic Review of Technologies Across Six Major Sectors and Key Areas of Reform

Innovation 1 : A Comprehensive Classification of Additive Manufacturing Processes Using Diverse Continuous Fibers

• Decomposition of the mainstream commercial roadmap: Desktop FFF Co-extrusion, industrial multi-axis robotic deposition, 9T Labs Hot-press fusion, UV In-situ curing CF3D , large-scale CFAM Granule +  Comparison of the operating principles, applicable materials, and forming accuracy of fiber‑printing and other additive manufacturing technologies;
• Summary of three fiber impregnation approaches—pre-impregnated filaments, in-nozzle impregnation, and in-situ co-deposition—highlighting their respective differences in interfacial bonding, porosity, and printability.
• Hardware innovation direction: single /  Double /  Multiple extrusion heads, 3/5/6 The robotic axis platform and the in-situ heating‑compaction module clearly demonstrate that multi‑axis printing is a key technology for overcoming the limitations of planar deposition and enabling the fabrication of curved components with spatially varying stiffness.

Innovation 2 : Standardized Material Selection System for Material Matching

Matrix material

• Low-temperature thermoplastic ( PLA/PETG ): Low cost, easy to print, and resistant to high temperature fluctuations;
• Engineering thermoplastics ( PA/PC/TPU ): It has high toughness, but absorbs moisture and easily develops porosity;
• High-temperature thermoplastic ( PEEK/PEI ): Aviation-grade performance, with high processing temperatures and stringent equipment requirements;
• Thermosetting epoxy / UV Resin: Molds at room temperature and cannot be repaired once molded.

Reinforcing fiber

• Carbon fiber (high stiffness and strength), glass fiber (low cost), aramid fiber (impact resistance), and natural fibers (green and low-cost), along with a general approach for fiber sizing and surface modification to enhance interfacial adhesion.

Innovation 3 : Two Cutting-Edge Technologies in Structural Design

• Cellular‑filler design: lattice structures such as honeycomb, diamond, and corrugated patterns balance lightweight construction with load‑bearing capacity; however, fiber bending at corners can readily reduce structural strength.
• Variable-Stiffness Topology Optimization: The algorithm generates spatially continuous fiber‑density and fiber‑orientation‑angle distributions, addressing the load‑misalignment issues inherent in conventional unidirectional layup. It also proposes methods to enforce additive‑manufacturing constraints, such as minimum bend radius and avoidance of fiber discontinuities.

Innovation 4 : Complete Multi-Scale Representation Technology Matrix

• Destructive testing: comprehensive suite of standards for statics, fatigue, creep, and impact;
• Nondestructive testing: Micro-CT Quantitative porosity, ultrasound /  Infrared nondestructive testing, SEM Fracture analysis;
• Core innovative insight: The interfilament gaps and fiber waviness introduced by additive manufacturing are unique defects that distinguish these materials from conventional composites, directly causing substantial reductions in stiffness and strength, and thus must be incorporated into performance assessments.

Innovation 5 : Layered Numerical Simulation Toolbox

• Macroscopic Fast Simulation: Classical Layered Theory, suitable for early-stage design screening;
• Fine-scale high-precision analysis: embedded fiber finite element modeling and voxel-based modeling accurately capture interfacial gaps and stress concentrations.
• Multiscale homogenization: RVE The unit connects the microfibers with the overall component;
• Data-driven AI Model: Neural Network for Rapid Process Fitting -  Performance relationships significantly reduce the cost of simulation iterations.

Innovation 6 : Sustainable Technologies for the Full Lifecycle of Composite Materials

• Manufacturing: Near-net-shape forming reduces material waste, while in-situ monitoring lowers the rate of scrap.
• Usage: Lightweight design reduces carbon emissions, and modular architecture facilitates maintenance.
• Recycling stage: mechanical recycling (low cost, but fiber shortening), thermal /  Chemical recycling (retains continuous fibers, suitable for high-end composites), thermoplastic 3D Composite materials offer the advantage of a closed-loop system that enables direct remelting and remanufacturing.

III. Application Scenarios (Covering High-End Manufacturing) + Smart Features + Green sector)

• Aerospace Lightweight Structures

Aircraft brackets, tooling fixtures, small load-bearing components, and satellite lattice structures; relying on… PEEK/PEEK High-temperature continuous fiber printing offers a lightweight alternative to metal, eliminates the need for tooling in small‑batch production of complex parts, and meets the iterative prototyping requirements of the aerospace industry.

• New Energy Vehicle Chassis and Functional Components

Battery pack frame, crash beam, and lightweight suspension; utilizing low-cost glass fiber. /  Carbon fiber PA Composite materials, with monolithic molding to reduce assembly, balance strength and enhance range.

• Robots and Soft Actuators

Multi-axis printing of continuous fiber components with variable stiffness, 4D Shape‑memory composites; electrically conductive carbon fibers can serve simultaneously as both a reinforcing skeleton and a heating element, enabling controllable deformation for use in soft robots and biomimetic mechanisms.

• Self-Sensing Smart Composite Materials

Continuous carbon fibers simultaneously serve as load-bearing and conductive materials; in lattice and laminated structures, the electrical resistance varies linearly under mechanical loading. Integrated‑structure health‑monitoring sensors eliminate the need for externally bonded sensing elements.

• Molds, Tooling, and Large-Scale Industrial Components

Large-sized CFAM Additive manufacturing equipment produces wind‑energy auxiliary tooling and forming molds, with chopped fibers. +  Continuous fiber hybrid deposition balances build speed with localized strength.

• Biomedical and lightweight civilian equipment

Natural fiber PLA Biocomposite scaffolds, sports equipment, and drone housings—balancing lightweight design, environmental sustainability, and low-cost mass production.

IV. Summary of the Article

(1) Industry Value Summary

This article is currently the most comprehensive review of additive manufacturing for continuous-fiber composites, synthesizing nearly a decade of cutting-edge global research and bridging the gap between equipment. -  Materials -  Design -  Characterization -  Simulation -  Application -  By covering the entire recycling value chain and breaking down information silos across different sub‑domains, this approach provides a systematic reference for university research topic selection, corporate process development, equipment procurement, and standard setting. At the same time, by benchmarking against conventional composite manufacturing processes, it clearly delineates the applicable scope and irreplaceable advantages of additive manufacturing—namely, the ability to freely and precisely control local fiber orientations and to rapidly fabricate complex structures with variable stiffness without the need for molds.

(II) Current Core Bottlenecks in the Industry

• Lack of standardization: There are no unified standards for printing, testing, and defect acceptance, resulting in poor data comparability; moreover, safety‑critical components such as those used in the aviation sector lack an official certification pathway.
• Inherent defects in the formed structure—such as interfilament porosity, fiber bowing, and weak interlaminar adhesion—result in significant variability in mechanical properties, making it difficult to achieve the performance levels of conventionally autoclave‑cured composites.
• Challenges in practical implementation: Multi-scale models are computationally expensive, data-driven models suffer from limited generalization, and there is a lack of integrated simulation tools that couple process‑physics models.
• Sustainability challenges: Thermoset continuous-fiber printed parts are costly to recycle, and a fully closed-loop recycling process has yet to be scaled up.
• Equipment and material limitations: High-end, high-temperature printing equipment is costly, and there are relatively few matrix resins specifically tailored for continuous fibers, as well as a limited range of modified fiber grades.

(III) The Five Major Core Research Directions for the Future

• Processes and Equipment: Multi-axis non-planar deposition, in-situ simultaneous heating and compaction, online laser processing /  Ultrasonic real-time defect monitoring system;
• Material optimization: development of a high‑wetting fiber sizing system, low‑moisture‑absorbing engineering thermoplastics, and recyclable thermoset matrices.
• Algorithm design: topology optimization that integrates additive manufacturing constraints, with automatic planning of continuous, smooth fiber paths.
• Simulation and AI : Process -  Defect -  Performance-coupled multi-scale modeling, coupled with machine learning for rapid prediction and parameter optimization;
• Green Circular Economy: Closed-loop remanufacturing of thermoplastic composites, low-cost chemical recycling of continuous fibers, and life-cycle‑wide low‑carbon process design.

(IV) Industry Development Outlook

Additive manufacturing of continuous-fiber composites will not completely replace it. RTM 、 AFP It complements conventional mass‑production processes, yet holds irreplaceable value in niche applications such as small‑batch manufacturing, complex freeform structures, variable‑stiffness designs, prototype parts, and multifunctional smart structures. As equipment costs decline, defect control improves, testing standards are refined, and recycling technologies mature, this technology is poised to penetrate key high‑end sectors—including aerospace, new energy, and advanced robotics—thereby advancing the industry’s goals of on‑demand fiber placement, lightweight integrated forming, and green manufacturing across the entire product lifecycle.

Image and Text Guide

Figure 1 | Traditional manufacturing methods for composite materials. (a) Wet lay-up method: Dry reinforcing materials are manually impregnated with resin in an open mold. (b) Resin Transfer Molding: Resin is injected into a closed mold containing the preformed part. (c) Autoclave prepreg lamination: Pre-impregnated plies are cured under hot‑press conditions. (d) Fiber winding: Continuous fiber bundles are wound onto a rotating mandrel under tension. (Adapted from) [23] , Copyright belongs to ( 2021 year), the author and MDPI All). (e) Pultrusion: After the fibers are impregnated, they are drawn through a heated die to form a uniform cross-sectional shape. (Adapted from) [24] , Copyright belongs to ( 2024 year), Elsevier B.V. Published). (f) Compression molding: Sheet material is compressed and molded within a heated die at a specified temperature. (Adapted from) [25] , Copyright belongs to ( 2024 year), the author and MDPI All).

Table 1 | Classified by parameter CFRP Manufacturing method (traditional) / Automated stacking process).

Figure 2 | Used for manufacturing CFRP Additive manufacturing methods for composite materials: (a) Layered Manufacturing ( LOM ), adapted from [37] , Copyright belongs to Elsevier Ltd. ( 2017 year); (b) Automated Fiber Placement ( AFP ), adapted from [38] , Copyright belongs to Elsevier Ltd. ( 2021 year); (c) Fused Deposition Modeling ( FFF ).

Table 2 | Divided according to parameters CFRP Classification of Manufacturing Methods (Additive Manufacturing)

Table 3 | Tradition CFRP Manufacturing processes and additive manufacturing–based ( AM ) of technology CFRP Comparison of composite material preparation methods.

Table 4 | CFRP Design factors influencing additive manufacturing.

Table 5 | Additive manufacturing CFRP A guide to selecting matrices and continuous fiber-reinforced materials in composite materials.

Table 6 | Additive manufacturing CFRP Common reinforcing fibers used in composite materials.

Figure 3 | CFRP Different types of feed fibers used in manufacturing: (a) Dry fiber, (b) Pre-impregnated fibers, and (c) Mixed fibers.

Table 7 | Additive manufacturing CFRP A commonly used matrix material in composite materials.

Figure 4 | CFRP Different structures in: (a) Fill mode, (b) Cellular structure, and (c) Topological design.

Figure 5 | Schematic diagram of topology optimization for a composite plate structure with holes. (a) A problem model that includes design parameters and geometric parameters; (b) An improved design scheme featuring spatially varying fiber volume fractions and optimized fiber orientations; (c) Computational results after applying the topology optimization algorithm; (d) 3D Visualization of printed samples [107] . Reprinted with permission. Copyright reserved. 2020 year Springer Nature Ltd 。

Figure 6 | The process flow of fused deposition modeling for continuous-fiber-reinforced polymers.

Figure 7 | Impregnation and Extrusion Principles: (a) The extrusion process of impregnated filament yarns; (b) Impregnation during the extrusion process; (c) In-situ impregnation after extrusion.

Figure 8 | Extruder head type: (a) Suitable for fiber and matrix materials with a single extrusion nozzle; (b) A dual-extrusion head, respectively applicable to fiber and matrix materials; (c) Multi-extruder head suitable for a variety of fibers and matrix materials.

Figure 9 | Advances in degrees of freedom: (a) A common linear‑type three‑degree‑of‑freedom printer configuration. (b) Five-axis 3D Printer [86] . Reprinted with permission. Copyright reserved. 2020 Year, author, and MDPI 。 (c) A robotic arm configuration with higher degrees of freedom. (d) A six-degree-of-freedom robotic arm equipped with deposition tools. [115] . Reprinted with permission. Copyright reserved. 2025 year Springer Nature Ltd 。

Table 8 | Overview of Selected Commercial Continuous-Fiber Additive Manufacturing (AM) Systems, Including Their Product Lines, Build Envelopes, Process Technologies, and Material Compatibility (Compiled Based on Publicly Available Manufacturer Specifications)

Table 9 | Standardized Methods for Destructive and Non-Destructive Characterization of Continuous Fiber-Reinforced Polymers (CFRP), with Examples of ASTM Standards and Typical Applications in Additively Manufactured Composites

Table 10 | Mapping of Process–Microstructure–Property Relationships in the Characterization of CFRP via Additive Manufacturing (AM)

Table 11 | Modeling Methods for Additively Manufactured CFRP Composites, with a Focus on Typical Applications, Advantages, and Limitations

Figure 10 | CFRP Various applications of composite materials. (a) Structural battery composite materials [180] . Reprinted with permission; copyright reserved. 2020 Year Elsevier Ltd 。 (b)4D Printable shape-memory polymers [19] . Reprinted with permission; copyright reserved. 2020 year Elsevier Ltd 。 (c) Fiber-reinforced actuator [181] . Reprinted with permission; copyright reserved. 2023 year Elsevier Ltd 。 (d) Fiber-reinforced structures with sensing capabilities [182] . Reprinted with permission; copyright reserved. 2022 year Elsevier Ltd 。 (e) Fiber-reinforced strain sensor [183] . Reprinted with permission; copyright reserved. 2022 year John Wiley & Sons Ltd 。 (f) Lightweight structure [184] . Reprinted with permission; copyright reserved. 2021 year Elsevier Ltd 。

Table 12 | Sustainability Scope of Additively Manufactured CFRP Composites, Highlighting Key Life-Cycle Stages, Quantifiable Metrics, and Feasible Improvement Measures

Figure 11 | CFRP Different recycling methods for composite materials. (a) Mechanical Recycling [195] . Reprinted with permission. Copyright. 2009 Year, Elsevier Ltd 。 (b) Thermosetting polymer matrix CFRP Recycling of [196] . Reprinted with permission. Copyright. 2016 Year, John Wiley & Sons Ltd 。 (c) Thermoplastic polymer matrix CFRP Recycling of [197] . Reprinted with permission. Copyright. 2017 Year, Elsevier Ltd 。