Project in the Spotlight: ENLIGHTEN: Advancing Integrated Thermoplastic Composite Structures for High-Volume Manufacturing

Key information

Project title: ENLIGHTEN: Enabling Integrated Lightweight Structures In High Volumes
Project in the Spotlight: N21010
Written by Martina Cuschieri

The transition towards more sustainable transport requires lightweight structural solutions that can be manufactured efficiently, reliably and at scale. Thermoplastic composites (TPCs) offer considerable potential in this respect, combining high specific mechanical properties with short processing cycles and good opportunities for direct recycling. However, while the manufacture of individual TPC components is relatively mature, the integration and assembly of these components into larger structural systems remains a significant technological challenge.

ENLIGHTEN – Enabling Integrated Lightweight Structures in High Volumes addresses this challenge by developing the scientific understanding, modelling capabilities and manufacturing technologies required for integrated thermoplastic composite structures. The programme focuses on fusion-bonding and integration technologies, including ultrasonic welding, induction welding and overmoulding, supported by process and performance modelling, inline monitoring and machine-learning approaches.

A central objective is to establish the processing–structure–performance relationships governing fusion-bonded TPC structures and to translate this knowledge into predictive tools and monitoring strategies. Ultimately, ENLIGHTEN aims to support a transition from predominantly empirical process development towards more predictive and controlled manufacturing of integrated composite structures.

Progress in process and performance modelling
Over the course of the programme, substantial progress has been made in understanding and modelling the physical phenomena governing TPC processing and structural performance.

Recent process-modelling activities have addressed crystallisation kinetics, transverse material flow and tool–ply friction, thermal expansion and process-induced distortion. A crystallisation model incorporating secondary crystallisation has been implemented for C/LM-PAEK and fitted to DSC data over a wide range of melting and cooling rates. Experimental studies have also investigated highly non-isothermal fusion bonding of LM-PAEK and PEEK, while squeeze-flow experiments and Digital Image Correlation have been used to characterise transverse flow behaviour under systematically varied boundary conditions.

These activities are complemented by developments in structural performance modelling. Multilevel modelling approaches have been further developed and validated for rate- and orientation-dependent behaviour of unidirectional thermoplastic composites. Cohesive and plasticity models have been combined to simulate fracture and fatigue in overmoulded sections, while a new cohesive approach has been developed for macroscale simulation of debonding in overmoulded panels in high-cycle fatigue.

The work has also generated relevant insights into the relationship between processing history and subsequent performance. For example, simulations indicate that plasticity, fibre migration and healing influence bond lifetime under cyclic loading and that boundary conditions can strongly affect the transferability of T-section test results to representative overmoulded rib-stiffened structures.

Machine-learning and surrogate-modelling approaches are being developed alongside these physics-based models. Neural-network-based surrogate models have demonstrated the ability to capture variations associated with macroscale uncertainties such as fibre misalignment and fibre concentration, providing a computationally efficient route towards incorporating manufacturing variability into process predictions.

Towards inline assessment of manufacturing quality
Inline monitoring constitutes another important element of ENLIGHTEN. The objective is to obtain information on process conditions and product quality during manufacturing, thereby reducing reliance on post-process inspection and contributing to first-time-right production.

For ultrasonic welding, passive infrared thermography has been investigated in combination with advanced data-processing methods. The results show that processed thermal data can distinguish between sound and defective welds in cases where this distinction is not apparent from the raw thermal signal. This demonstrates the potential of passive thermography for inline weld-quality assessment.

The monitoring concepts are also being implemented on larger-scale manufacturing equipment. Research on monitoring technologies at Delft University of Technology is being translated to manufacturing-scale implementation at SAM|XL, where acoustic sensing, laser line scanning and infrared thermography have been integrated into a robotic continuous ultrasonic welding setup. Initial investigations into correlations between sensor data and weld quality identified infrared measurements as particularly informative, leading to the installation of additional infrared cameras for more extensive temperature monitoring.

At TPAC, injection-moulding equipment has been instrumented with temperature, pressure and infrared sensors. Communication between the injection-moulding cell and the Kistler ComoNeo data-acquisition system has been established, enabling machine-data logging and control of the injection-moulding switch-over point. Instrumented overmoulding trials have subsequently been performed to validate the functionality of the integrated system.

Integration and validation through demonstrators
As ENLIGHTEN progresses towards its final stage, increasing emphasis is being placed on integrating the developments from the individual work packages in representative demonstrators and validation cases.

For induction welding, the University of Twente, TPRC, Toray Advanced Composites and Collins/DTC are collaborating on an L-stiffened demonstrator consisting of a thermoplastic composite stiffener welded onto a flat skin. Specimens obtained from the demonstrator will be mechanically characterised, with the resulting data potentially providing validation for the mechanical models developed within the programme.

In parallel, Envalior, Toray Advanced Composites and Victrex are working with TPRC, the University of Twente, Eindhoven University of Technology and Delft University of Technology on overmoulded validation specimens. These consist of short-fibre-reinforced ribs overmoulded onto continuous-fibre-reinforced laminates. Static and fatigue testing of the rib–laminate interface will provide experimental data for validation of the mechanical models developed within ENLIGHTEN.

The transfer of modelling developments towards industrial application has also started. TPRC has implemented melting and crystallisation models developed at the University of Twente in commercial software for use with industrial partners.

Together, these activities demonstrate the programme’s integrated approach: linking material characterisation and process physics with structural performance, process monitoring, data-driven modelling and manufacturing-scale validation.

Strengthening the link between research and application
ENLIGHTEN brings together complementary expertise from technical universities, universities of applied sciences, application and research centres, and industrial partners across the thermoplastic-composites value chain. The University of Twente, Delft University of Technology and Eindhoven University of Technology contribute research spanning process modelling, structural performance and inline monitoring, while the Universities of Applied Sciences and application centres such as TPRC, TPAC and SAM|XL provide an important link towards manufacturing-scale implementation and validation. Industrial partners contribute materials, manufacturing expertise and application requirements, helping to ensure that the scientific developments are evaluated in technologically relevant conditions.

During the latest reporting period, this collaboration included consortium and work-package meetings as well as direct cooperation on welding demonstrators, overmoulding validation specimens and monitoring technologies. Rather than treating modelling, experimental characterisation, monitoring and manufacturing as separate activities, these collaborations increasingly connect expertise across the consortium around common validation cases. The welding demonstrator, for example, brings together the University of Twente, TPRC, Toray and Collins/DTC, while overmoulding validation involves the University of Twente, Eindhoven University of Technology, Delft University of Technology, TPRC, Envalior and Toray.

The final phase of ENLIGHTEN will place further emphasis on demonstration, validation and knowledge dissemination. Inline-monitoring hardware and software will be implemented and evaluated on industry-scale equipment, while processing models developed within the programme are intended to be transferred to TPRC and/or Aniform for industrial use. Furthermore, the knowledge developed will be disseminated to a wide audience in a dedicated session during the upcoming ICMAC conference in June 2027.

The programme also provides a basis for continued development beyond ENLIGHTEN. Connections with the Dutch National Growth Fund programme Luchtvaart in Transitie offer opportunities for alignment of research activities and data exchange, while emerging interest in thermoplastic composites for defence applications could provide additional routes for further development and application.

ENLIGHTEN is therefore entering its final phase with a clear focus on connecting scientific understanding with manufacturing implementation. By combining process and performance modelling, inline sensing, machine learning and experimental validation, the programme is establishing the knowledge and tools required to make integrated thermoplastic composite structures more predictable, controllable and suitable for industrial-scale manufacturing.