PowerPoint presentation (6 MB file)

Resin infusion under flexible tooling (RIFT) covers a range of processes similar to Resin Transfer Moulding (RTM) where one of the mould faces is replaced by a polymer film or by a thin composite "splash" mould tool.  The process is reviewed in several papers [1-4].  Summerscales [3] proposed that four variants on the resin infusion process could be considered to form a continuum bridging the gap between RTM and prepreg/autoclave techniques:

• resin transfer moulding (RTM)
• RIFT1: in-plane flow parallel to the layers of reinforcement



Figure 1: Schematic representation of the resin infusion in-plane flow process [the bagging film (above) and mould tool (below) are omitted for clarity].

• RIFT2: through-plane flow from a flow medium or scored core



Figure 2: Schematic representation of the resin infusion flow medium and through-plane flow process [the bagging film (above) and mould tool (below) are omitted for clarity]

EADS Deutschland have developed the Vacuum Assisted Process, VAP^®, which is protected by several worldwide patents to enable the manufacture of cost-efficient primary aircraft structures. VAP^® technology uses the Gore Composite Manufacturing Membrane (GCM) which is a barrier to resin but permeable to gas and air, to allow uniform vacuum distribution and degassing during cure of the infused resin. This is claimed to result in a more robust process, minimal potential for dry spot formation, very low void content, more uniform part thickness and improved dimensional tolerances. VAP^® has been successfully applied in integrated stringer technology on the cargo door for the Airbus A400M military transport aircraft.



Figure 3: Schematic of the EADS VAP® technique before (top) and after (below) resin infusion (reproduced with the permission of EADS. Original image URL.)

• RIFT3: resin film infusion (RFI)



Figure 4: Schematic representation of the resin film infusion process [the bagging film (above) and mould tool (below) are omitted for clarity].

• RIFT4: partially pre-impregnated materials



Figure 5: Schematic representation of the ‘semi-preg’ infusion process [the bagging film (above) and mould tool (below) are omitted for clarity].

• prepreg/autoclave

A key feature of this process is that, unlike the fixed cavity in RTM, the thickness of the component normally varies with the local pressure.  The pressure is in turn is a function of the pressure history and the position of the resin flow front.  Williams et al [5] have reported some initial RIFT1 experiments to characterise this variation.

RIFT2 processes are commonly referred to as SCRIMP^TM (Seeman Composites Resin Infusion Molding Process: a process patented in the United States of America, but challenged by prior art in Europe).  A number of companies have signed up for SCRIMP^TM licences as the technical support costs can be justified against potential scrap costs without such help.  The Advanced Composites Manufacturing Centre has undertaken a similar role in guiding their clients to effective implementation of the process.

Govignon et al [6] have described a fully instrumented resin infusion to acquire experimental data while varying key parameters during both the filling and the post-filling stages. Full field thickness variations were monitored using digital speckle stereophotogrammetry. In-mould resin pressures, flow front progression, and incoming resin flow rate were also measured.  The system enabled the calculation of transient changes in local permeability across the preform.

Gardiner [7] has described a double-bag infusion technique with a "venting layer" between the bags developed by Russell Ermanis which, in combination with tight process control, is claimed to enable repeatable fibre volumes of 60-70% and low void volume fractions.

Gardiner and Brandis [8] explored the causes of resin volatilization and recommended the following process steps:

• pull full vacuum on the laminate stack perform.
• wait until all moisture and air in the preform are evacuated, evidenced by vacuum gauge reading -999 mbar.
• carry out a leak check starting with -985.3 mbar minimum and achieving a loss of no more than 33 mbar in 15 minutes.
• degas mixed resin under gauge vacuum pressure of -999 mbar for five minutes.
• infuse with controlled (throttled) resin feed 969 mbar minimum.
• try to maintain temperature between 21-30°C during and after the preform is wet out.
• measure mould temperature, consult water boiling point chart, and lower vacuum pressure accordingly to prevent resin/water boiling.
• clamp off resin supply.
• monitor resin temperature with an infrared thermometer, and adjust vacuum pressure if you observe boiling.
• maintain vacuum until resin gels.

Kessels et al [9] have presented a short overview of all previous modelling effort for RIFT processes.  They developed a fully transient 2½D flow model using Darcy’s law, a flexible CV height and different wet and dry preform compaction properties to predict mould filling.  A fluid presence function was used for flow front tracking and for pressure prediction in the partially filled cells.

Typical components produced by resin infusion processes include Lotus car bodies, the cab of the InterCity 125 train, bulkheads for Vosper Thornycroft mine sweepers/hunters, Westerly yachts, NEG Micon wind-turbine blades.

Double diaphragm infusion techniques

There is a technique whereby dry fabric is placed between two elastomeric membranes, resin is infused into the fabric and then the ‘sandwich’ is vacuum-formed over a mould. This is known as Double RIFT Diaphragm Forming (DRDF) [10, 11] or Resin Infusion between Double Flexible Tooling (RIDFT) [12-15].

Figure 6: Schematic representation of the Resin Infusion between Double Flexible Tooling (RIDFT). Reproduced from [11] with the permission of Okenwa Okoli.

Large structures

Infusion techniques have been used to produce large composite structures.  Large boat hulls include the 42-, 75- and 105-foot hulls at Princess Yachts and the Oyster OM125 superyacht [16] produced in partnership with RMK Yachts in Turkey which is claimed to be the largest one-shot infusion to date with 11 tonnes of reinforcement and 3 tonnes of balsa core infused with 6.3 tonnes of vinlyester resin and the 57m Christensen 186 all-composite motor yacht which was scheduled for launch in 2011.  Examples of infused bridge structures are the 22.6 m Moscow footbridge in Russia, the 44 m Madrid footbridge which won the Civil Engineering category of the JEC Innovation Awards 2011 and the 47 metre span Halgavor suspension bridge in Cornwall.

References

1. C D Williams, J Summerscales and S M Grove, Resin infusion under flexible tooling (RIFT): a review, Composites Part A: Applied Science and Manufacturing, July 1996, 27A(7), 517-524. Restricted: Download 1.21MB .pdf file
2. D Cripps, T J Searle and J Summerscales, Open Mould Techniques for Thermoset Composites, In R Talreja and J-A Månson (editors): Comprehensive Composite Materials Encyclopædia, volume 2: Polymer Matrix Composites,
   Elsevier Science, Oxford, July 2000, Chapter 21, pp 737-761. ISBN 0-08-043725-7.  UOP Library  Restricted: Download 1.24MB .pdf file. This text also covers hand lamination, vacuum bagging and spray techniques.
3. J Summerscales and T J Searle, Review: Low pressure (vacuum infusion) techniques for moulding large composite structures  Download 6.6MB .ppt file
   Proc IMechE Part L: Journal of Materials: Design and Applications, February 2005, L219(1), 45-58. Restricted: Download 793KB .pdf file
4. SW Beckwith, Resin Infusion Technology * Part 1 - Industry highlights * Part 2 - Process definitions and industry variations * Part 3 - A detailed overview of RTM and VIP infusion processing,
   SAMPE Journal, 2007, 43(1), 61 and 43(3), 46 and 43(4), 6 & 66-70.
5. CD Williams, SM Grove and J Summerscales, Compressive response of fibre reinforced plastics plates during manufacture by the resin infusion under flexible tooling method,
   Composites Part A: Applied Science and Manufacturing, 1998, 29A(1/2), 111-114.  Restricted: Download 441KB .pdf file
6. Q Govignon, S Bickerton, J Morris and PA Kelly, Full field monitoring of the resin flow and laminate properties during the resin infusion process, Composites Part A: Applied Science and Manufacturing, September 2008, 39(9), 1412-1426.
7. G Gardiner, Double bag infusion: 70% fiber volume?, Composites Technology, December 2010, 16(6), 54-56.
8. G Gardiner and S Brandis, Keeping liquids liquid, Professional BoatBuilder, August/September 2011, (132), 50-60.
9. JFA Kessels, AS Jonker and R Akkerman, Fully 2½D flow modeling of resin infusion under flexible tooling using unstructured meshes and wet and dry compaction properties,
   Composites Part A: Applied Science and Manufacturing, January 2007, 38(1), 51-60.
10. KJ Channer, W Cosgriff and GF Smith, DRDF (double RIFT diaphragm forming) volume automotive manufacture of structural composites. In Sixth International Conference on Automated Composites, Institute of Materials, Bristol, 23–24 September 1999, 273–279.
11. KJ Channer, W Cosgriff, GF Smith and OI Okoli, Development of the double RIFT diaphragm forming process, Journal of Reinforced Plastics and Composites, 2002, 21(18), 1629-1635.
12. JR Thagard, Investigation and development of the resin infusion between double flexible tooling (RIDFT) process for composite fabrication, PhD thesis, Florida State University, 2003.
13. JR Thagard, OI Okoli, Z Liang, H-P Wang and C Zhang, Resin Infusion between Double Flexible Tooling: prototype development, Composites Part A: Applied Science and Manufacturing, 2003, 34, 803–811.
14. JR Thagard, OI Okoli and Z Liang, Resin infusion between double flexible tooling: evaluation of process parameters, Journal of Reinforced Plastics and Composites, November 2004, 23(16), 1767-1778.
15. N Toro, OI Okoli and H-P Wang, In-mould coating of composites manufactured by resin infusion between double flexible tooling process, Journal of Reinforced Plastics and Composites, 2005, 24(7), 725-733.
16. U Ustunel, Signature marine projects and record-breaking super yacht, JEC Composites magazine, November-December 2011, (69), 12-13.

Recommended reading

1. Vacuum Infusion - The Equipment and Process of Resin Infusion, http://www.fibreglast.com/documents/361.pdf, accessed on Saturday 29 April 2006 16:42.
2. Vacuum infusion strategies for a yacht hull, http://www.lightweight-structures.com/index.php?option=com_content&task=view&id=29 accessed on 31 August 2006 at 17:01 (based on the paper by A Hoebergen, E van Herpt and M Labordus,
   The manufacture of large parts using the vacuum injection technique: practical strategies for boat building used in the manufacture of the Contest 55, 20th Jubilee International Conference of SAMPE Europe, Paris, 13-15 April 1999).