New generation of manufacturing technologies: liquid print of composite matrices

Lead Research Organisation: University of Bristol
Department Name: Aerospace Engineering

Abstract

Composite industry exhibits a wide spectrum of efficient manufacturing methods spanning from cheap and robust liquid moulding processes to high quality expensive autoclaving. All the available methods have one feature in common: the continuously reinforced components, no matter how big or small, are produced in one curing/consolidation shot. Thus to achieve good dimensional tolerances and internal composite quality, a heavy tooling must be used: autoclaves, hot presses, double sided RTM moulds and other equipment that can provide high levels of applied pressure over large area.

Considerable efforts are required to design and monitor these manufacturing processes. It is difficult to introduce any correction once the process has started or to detect and mitigate the defect occurrence when it runs. All possible scenarios of the material formation have to therefore be considered in advance and any possible quality issues must be addressed prior to the material consolidation. There is also a very limited instrument pallete available to adjust the process as the overall manufacturing parameters do not determine the formation of local geometrical features directly. This makes these processes expensive and risky particularly for new applications and reinforcement systems.

This project introduces a new additive manufacturing concept which negates the need for heavy manufacturing equipment. The process is implemented through local deposition of liquid resin by means of a series of high precision injections through the thickness of a textile preform followed by local consolidation. In other words, the process is realised as 3D print of matrix into the reinforcement which maintains the liquid resin in the required position. The locality of the process guarantees its flexibility and sophisticated control over the geometry and properties. The current project looks at (a) optimisation of injection and consolidation process aimed at competitive rates of print, and (b) understanding effects of manufacturing parameters on the composite properties. In other words, this study offers new flexible high-quality composite manufacturing method tailored to the needs of property enhancement and the management of complex failure processes.

Planned Impact

Success of the proposed project has several aspects of impact. The major ambition is to introduce a new paradigm in composite design and manufacturing. The multi-scale manufacturing philosophy will make one more step in achieving a full potential of composites.

A number of attractive features guarantee a fast pick up of the technology by industry once proven competitive in terms of print rates and composite properties: (a) the locality of the process allows early stage detection and in-situ mitigation against forming defect, (b) the high efficiency and the compactness of the tooling gives obvious advantages compared to conventional technologies, (c) compatibility with conventional liquid moulding ensures that the local print can be used to enhance the properties locally, stabilise textile preforms, control the flow in liquid moulding processes. All these possibilities are beyond the capacity of any of the current manufacturing method.

These benefits are relevant for the entire spectrum of composite industries but the highest potential for the fast technology pick-up have the applications where high-quality multi-functional well-controlled materials are needed, e.g. the aerospace components. Apart from clear industrial benefits there is an important fundamental aspect of this project.

Understanding the role of locally enhanced material systems is critical for efficient design and properties such as toughness, stiffness, and damage resistance. Exploring opportunities by using the new tools for the new purposes maximises both the academic and industrial impact. In addition, expanding the limits makes textile composites more attractive to end users hence it serves as a catalyst for spreading these materials as well as taking a full advantage of these composites in existent applications. The current project provides an opportunity for material researchers to increase fundamental knowledge on this subject.

Publications

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Description The project aimed at developing a new manufacturing concept - Liquid Resin Print - an additive manufacturing approach to integrating matrices in composites with continuous reinforcement. The locality of the explored manufacturing technique grants a direct control on local composite features, allows accommodating different matrices in one component, and, in perspective, releases the need in heavy and expensive composite manufacturing equipment. The research revealed that Liquid Resin Print is a viable option for integrating composite matrices for textile composites. The key findings are:

1) The locality of resin delivery grants many process advantages but also presents with its own challenges. In contrast to conventional composites manufacturing, the print process is not vacuum assisted. It means that an unsaturated flow of locally injected resin through reinforcement results in the void entrapment. Upon cure, voids transform into pores and may negatively affect performance of composite structures. Various processing strategies have been tested in the project to address the issue. It was found that the most efficient way to tackle this problem is through a bespoke highly-instrumented consolidation procedure. In this process, injected resin is thermally treated to reach required rheological characteristics. When the resin is at a right state, a subsequent consolidation process successfully suppresses porosity. Essential development in this work is a model-based sensor tracking resin characteristics in real time. It allows to tailor pressure application to material properties of highly reactive systems. Demonstrators showing the relation between process parameters and morphology of printed patches were developed in the project.

2) Liquid Resin Print process introduces new material features not known in the previous generation of composites. Sequential integration of resin creates multiple internal fibre-bridged interfaces between printed domains. Understanding mechanical properties of printed composites with these features was identified as one of the project priorities. An extensive testing programme was conducted. Preliminary results show that these features do not have any impact on composite stiffness. On the other hand, these interfaces do influence damage and failure mechanisms and, when properly designed, can be beneficial for mechanical performance. Printing patches allows delocalize failure and absorb more energy through controlled damage accumulation. It was also found that the integration of enhanced resins around stress concentrators leads to an improvement in mechanical performance of composites.

3) One of the technological challenges associated with the implementation of the print concept is the manufacturing rates. The suggested process requires sequential curing of printed patches which eliminates the application of resins used for conventional composites processes (characteristic cure time - hours). New advanced snap cure resin systems (with the cycle time of minutes) were tested in the context of resin printing. These resins were found not only suitable for the process but through high-sensitivity to heat treatment allowed to tune and improve the consolidation process. A new end-effector with the in-situ mixing of two component resin systems, self-cleaning function, and instant pressure application was designed in the project reflecting the understanding developed within experimental trials.
Exploitation Route The project pursued the development of Liquid Resin Print concept as an alternative to existing composite manufacturing technologies. It pioneered printing of composite resins and addressed the most urgent challenges impeding the implementation of this manufacturing technique. The findings of the project demonstrated the potential of the concept, showed methods to implementation of the approach, identified the solutions to most critical challenges, and pave the way for further developments at a new Technology Readiness Level. Hence, the project prepared a ground for emerging technologies at the interface between Additive and Composites Manufacturing.
Sectors Aerospace, Defence and Marine,Manufacturing, including Industrial Biotechology

 
Description EPSRC Pump Priming Study for Engagement with The Sir Henry Royce Institute
Amount £8,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 01/2016 
End 05/2016
 
Description Pump Priming Bid, Novel patterned composites with revolutionary loading of functionalising additives by 3D printing
Amount £5,000 (GBP)
Organisation University of Bristol 
Sector Academic/University
Country United Kingdom
Start 10/2015 
End 06/2016
 
Description SIMulation of new manufacturing PROcesses for Composite Structures (SIMPROCS)
Amount £1,115,704 (GBP)
Funding ID EP/P027350/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 05/2017 
End 04/2022
 
Title CAD model of robotic end-effector implementing resin delivery and print of the fast-curing resin 
Description The CAD design presents a detailed operational model of a robotic end-effector, which takes into account the critical requirements to resin delivery and consolidation in one integrated system. The model considers high-pressure delivery of reactive resin, self-cleaning operations of the fast curing precursors, pressure/flow sensing and process control, in-situ mixing of resin components, fabric constraints and consolidation. The design takes into practice the main lessons derived from manufacturing print trials. 
Type Of Material Computer model/algorithm 
Year Produced 2016 
Provided To Others? No  
Impact The design of a functional robotic end-effector presents an essential development towards upscaling the Resin Print concept to higher Technology Readiness Level. It condenses the wealth of research experience on matrix printing to a design brief and summarises the main functionalities that a proper fully-automated print system must have. Because of the budget and time constraints of the project, the entire system was not implemented in full. More conventional resin dispensers were adopted to produce demonstrators. This design however create a good starting point for the next development of the idea in follow-up projects with industrial partners. 
 
Title Model-based sensor for monitoring state of printed resin in the process of pre-consolidation heat treatment 
Description The sensor presents a script, written in LabView, and hardware acquiring thermal data and calculating the resin characteristics by solving cure kinetics equations in real time. 
Type Of Material Data analysis technique 
Year Produced 2016 
Provided To Others? No  
Impact The optimisation of print process requires tailoring consolidation programme to the chemorheological characteristics of fast curing resin systems. The sensor calculates a theoretical state of the resin in real time based on live thermal input. The experimental trials showed the morphology of the printed patches can be significantly improved by using the data from the sensors for an actuation of consolidation programme. A paper describing the details of this work is progress. 
 
Description Gradient reinforcements and matrices for resilient feature-insensitive composites 
Organisation University of Manchester
Department Faculty of Life Sciences
Country United Kingdom 
Sector Academic/University 
PI Contribution The collaboration has started in the frame of a Feasibility Study funded as a Pump Priming Project within the frame of EPSRC grant for developing engagement with Sir Henry Royce Institute and University of Bristol (see the follow-up funding section). This study explores the feasibility of improving damage resilience around structural features in composite components through varying (a) the internal geometry of the reinforcement and (b) matrix properties. Introducing matrix gradients is implemented through a novel Liquid Resin Print technique which is applied through precise point-wise injections of dissimilar brittle and tough polymers into dry textile preforms prior to infusion. This is the concept that has been developed within the reported EPSRC grant. In addition, the University of Bristol manufactured samples, tested them and assessed the damage development in reference and modified materials.
Collaborator Contribution The innovative concepts of fibre steering through braiding and matrix grading through resin printing were explored to determine the potential for creating composites with better mechanical performance. While the University of Bristol focused on grading of matrix properties, the University of Manchester focused on fibre grading. The group of Prof Potluri manufactured and supplied novel braided preforms with the gradients in fibre architecture realised through varying the braiding angle. The in-kind contribution has no market estimate.
Impact The preliminary results of this work have been published in the conference proceedings of ECCM17 - 17th European Conference on Composite Materials, Munich, Germany, 26-30th June 2016. The paper called "MECHANICAL BEHAVIOUR OF PATTERNED MULTI-MATRIX COMPOSITES WITH GRADIENT PROPERTIES" was co-authored by David Stanier, Ian Gent, Sree Shankhachur Roy, Ian Hamerton, Prasad Potluri, and Dmitry S. Ivanov.
Start Year 2016
 
Description Novel patterned composites with revolutionary loading of functionalising additives by 3D printing 
Organisation Imperial College London
Department VIGILab
Country United Kingdom 
Sector Academic/University 
PI Contribution The collaborative study has been exploring the novel concept of incorporating nano-additives for fictionalisation and structural performance. This initial feasibility study, funded by the School of Engineering of University of Bristol brought, together two novel concepts in composites manufacture: Liquid Resin Print (explored within the reported grant) and a new form of nano-additives developed and created by research group of Prof Milo Shaffer, ICL. The contribution of Bristol's research group comprised implementation of Liquid Resin print with new form of additives integrated in the resin, sample manufacture, characterisation of the obtained composites.
Collaborator Contribution The contribution of ICL comprised manufacture and delivery of various form of the advanced additives, further characterisation of additives and samples manufactured in UoB.
Impact The collaboration resulted in an ongoing PhD project of Arjun Radhakrishnan, the student of EPSRC CDT in Advanced Composites, devoted to this topic. The project is multi-disciplinary and involves advanced chemistry for producing new additives, process analysis, functional and structural testing of produced composites.
Start Year 2015