Author: [Bruce Zhou]
Affiliation: [Jota Machinery Composites Material Prepreg Solution]
Corresponding Author: [jotamachinery@gmail.com]
Published : December 01 , 2025

Abstract

Thermoplastic composites (TPCs) have advanced from niche usage to mainstream aerospace candidates due to their recyclability, weldability, and reduced manufacturing costs compared with thermoset systems. Welding technologies—ultrasonic, induction, resistance, infrared, laser, and microwave—enable solvent-free, fast assembly of high-performance laminates such as CF/PEEK and CF/PPS. The widely cited 2012 review by Costa et al. established foundational classifications and mechanisms but predated major developments in process automation, hybrid composite–metal joining, and in-situ monitoring. This updated assessment synthesizes post-2012 advances and positions ultrasonic welding as a leading candidate for aerospace due to its speed, absence of metallic implants, and capability for TPC–metal interfaces. Optimized ultrasonic lap joints now achieve shear strengths up to 90 MPa, although consistent weld quality requires tailored interfacial features such as energy directors. Induction and resistance welding remain essential for large-area aerospace panels, yet often rely on susceptors that may introduce corrosion risks or added weight. Laser welding offers geometric precision but depends heavily on absorptivity and colorant selection. Overall, fusion bonding continues to offer significant weight savings and recyclability advantages over mechanical fastening and adhesive bonding, though integration into primary aerospace structures demands continued process optimization, certification datasets, and robust monitoring strategies.

Keywords

Thermoplastic composites; ultrasonic welding; induction welding; resistance welding; laser joining; fusion bonding; aerospace structures; CF/PEEK; CF/PPS; hybrid interfaces.

1. Introduction

Thermoplastic composites (TPCs) have gained substantial traction in aerospace due to their high damage tolerance, low moisture uptake, rapid processing, and capacity for welding rather than adhesive or mechanical joining. High-performance semi-crystalline matrices—such as polyetheretherketone (PEEK), polyphenylene sulfide (PPS), and polyetherimide (PEI)—enable melt reprocessing, recyclability, and improved toughness compared with thermosetting systems.

The challenge of joining these materials remains central to their adoption in primary aircraft structures. Traditional mechanical fastening increases mass, introduces stress concentrations, and compromises fatigue performance. Adhesive bonding eliminates drilling but adds cure steps, surface preparation demands, and long-term durability uncertainties.

Fusion bonding (welding) melts thermoplastic interfaces, allowing polymer interdiffusion without chemical curing or added adhesives. The 2012 Costa et al. review synthesized classical welding methods for aerospace TPCs. Since then, significant progress has been recorded—particularly in ultrasonic, resistance, and induction welding—along with new research in hybrid thermoplastic–thermoset–metal assemblies and automation strategies relevant to next-generation sustainable aviation initiatives.

This paper revisits the earlier review with modern developments and evaluates the most promising welding technologies for aerospace composite structures.

2. Literature Review

2.1 High-performance thermoplastic matrices

TPCs used in aerospace largely employ high-melting semi-crystalline polymers:

PEEK: high modulus, excellent chemical resistance, crystallinity 30–35%.
PPS: inherently flame-retardant, used for aircraft clips and brackets.
PEI/PES: amorphous matrices with good toughness and lower processing temperatures.

Crystallinity affects joint performance—higher crystallinity improves modulus but reduces molecular mobility for interdiffusion. Weld quality therefore depends on precise thermal management.

2.2 Classical welding mechanisms (Costa et al., 2012)

The baseline classification separates welding processes by heat generation:

Friction-based (fusion) welding
Ultrasonic, vibration, and spin welding.
Electromagnetic welding
Induction, microwave, dielectric heating, resistance welding.
Thermal contact heating
Infrared, hot-plate, and laser welding.

The 2012 study emphasized that ultrasonic, induction, and resistance welding were the most promising for aerospace based on cycle time and mechanical performance.

2.3 Post-2012 advancements

Recent research (2013–2025) highlights several trends:

Ultrasonic welding matured dramatically with energy director (ED) control, achieving lap shear strengths of 70–90 MPa for CF/PEEK.
Induction welding advanced through improved susceptors and hybrid EM heating strategies suitable for large fuselage covers and stiffened panels.
Resistance welding remains widely studied in Europe (Delft, École Centrale Nantes, USP/UNESP), particularly for CF/PPS fuselage components.
Laser welding expanded in in-situ AFP consolidation and hybrid polymer–metal joining.
Microwave and dielectric heating remain experimental due to complex energy absorption profiles.

Automation integration—robotic welding heads, closed-loop thermography, and real-time acoustic monitoring—has emerged as a key enabling technology.

3. Methodology (Review Approach)

Following Costa et al.’s 2012 review structure, the present paper synthesizes developments across:

Peer-reviewed studies (2012–2025)
Aerospace programs (Airbus, Boeing, NASA, ESA, DLR)
Industrial initiatives (Tri-Mack, Victrex, Solvay, SABIC)
Academic groups (UNESP, USP, TU Delft, NTU Singapore)

Techniques are compared based on:

Heat generation mechanism
Cycle time
Process robustness
Equipment complexity
Mechanical performance
Suitability for primary/secondary aerospace structures
Compatibility with carbon fiber-reinforced PEEK/PPS systems
Weight and corrosion implications

No experiments were performed; this is a structured, evidence-based synthesis.

4. Results (Synthesis of Technologies)

4.1 Ultrasonic Welding

Heat mechanism: high-frequency vibration (15–70 kHz) generating interfacial friction.
Advantages:

Weld times of 1–3 seconds
No metallic implants
High strengths after ED optimization (up to 90 MPa lap shear)
Compatible with TPC–metal hybrid interfaces

Limitations:

Requires precise amplitude/frequency tuning
Effective mainly for small or medium components
ED designs needed for reproducibility

Aerospace relevance:
Extensively studied for CF/PEEK airframe clips, stiffeners, and stringers. Interest grows for hybrid welded assemblies in electric aviation.

4.2 Induction Welding

Heat mechanism: electromagnetic fields inducing Joule and hysteresis heating.
Advantages:

Non-contact
Suitable for large curved panels
Compatible with robotic automation

Limitations:

Requires metallic susceptors or conductive fibers
Susceptors may increase weight or introduce corrosion pathways

Applications:
Wing panels, UAV fuselage skins, large PPS/PEEK assemblies.

4.3 Resistance Welding

Heat mechanism: Joule effect through conductive meshes or carbon fibers.
Advantages:

Proven structural performance (shear strength >33 MPa)
Scalable for large joining lines
Low equipment cost

Limitations:

Implants remain in the structure
Risk of galvanic coupling in hybrid metal–carbon joints

Aerospace usage:
CF/PPS skin-to-stringer joints; USP/UNESP studies achieved strong, repeatable welds with controlled consolidation pressure.

4.4 Laser Welding

Heat mechanism: optical absorption at the interface (through-transmission).
Advantages:

High precision
Allows complex geometries
Potential for in-situ AFP consolidation

Limitations:

Material absorptivity/colorant sensitivity
High equipment cost

Applications:
Precision joining of PEEK/PPS components; advanced TPC-metal hybrid interfaces.

4.5 Infrared, Hot-Plate, and Microwave Welding

IR/Hot-plate advantages:

Robust for flat, large components
Good for automation lines

Limitations:

Surface overheating
Sensitivity to pigments and component thickness

Microwave welding:

Volumetric heating but highly material-dependent
Limited industrial deployment

5. Discussion

5.1 Dominant Processes for Aerospace

Recent publications and industrial programs converge on three leading methods:

Ultrasonic welding (high speed, hybrid capability)
Induction welding (large-scale, non-contact)
Resistance welding (high strength, scalable)

These methods support aerospace ambitions for automated, solvent-free joining with consistent quality.

5.2 Trade-offs in Process Selection

Ultrasonic offers unmatched speed but limited scalability.
Induction covers large panels but requires susceptors.
Resistance achieves reliable strength but introduces implants.
Laser provides geometric precision but sensitive to optical properties.

5.3 Need for Interfacial Design

Energy directors, pre-shaped interlayers, and tailored surface morphologies are critical for consistent weld quality in ultrasonic and laser welding.

5.4 Hybrid TPC–Metal–Thermoset Interfaces

Post-2018 research emphasizes hybrid joining for next-generation aircraft:

TPC-to-metal via ultrasonic or laser welding
TPC-to-thermoset via induction implants
Multi-material integration for hydrogen-powered aircraft

5.5 Automation and In-Situ Monitoring

Modern welding heads integrate:

IR thermography
Ultrasonic acoustic feedback
Pressure/temperature closed-loop control

These innovations enable certifiable, repeatable welding processes.

6. Conclusion

Thermoplastic composite welding technologies have advanced considerably since the foundational 2012 review. Ultrasonic welding has emerged as a leading aerospace candidate due to rapid cycle time, ED-assisted strength improvements, and applicability to hybrid joints. Induction and resistance welding remain vital for large-area structures, while laser welding gains importance for precision joining and in-situ AFP consolidation.

Challenges remain in uniform heating, scale-up, susceptor design, long-term durability, and certification for primary structures. Future progress will depend on integrated automation, multi-physics monitoring, optimized interfacial architecture, and sustainability-driven design enabling recyclability. The aerospace sector is now positioned to adopt welded TPC assemblies more broadly, aligning with global objectives for lighter, more efficient, and environmentally responsible aircraft.

References

(Curated for aerospace journals; can be expanded into complete list)

Costa, A.P. et al. A Review of Welding Technologies for Thermoplastic Composites in Aerospace Applications, JATM, 2012.
Liu, M. et al. “Developments and Future Prospects of Welding Technology for Carbon Fiber Thermoplastic Composites,” Composites Part A, 2025.
Jongbloed, B. et al. “Single- vs Multi-step Ultrasonic Welding of Carbon/PEEK Composites,” Composites Part A, 2022.
Martin, N. et al. “Resistance Welding of Thermoplastic Composites,” Journal of Manufacturing Processes, 2024.
Tsiangou, E. et al. “Sensitivity of Ultrasonic Welding of PEEK-based Composites to Heating Time,” Composites Part A, 2021.
Zhao, T. et al. “Ultrasonic Welding of Metal to Fiber-Reinforced Thermoplastic Composites,” Journal of Manufacturing Processes, 2019.