Neil ReynoldsWMG, University of Warwick, UK

Aims & BackgroundASF process outline

Details, pros & cons

Process studyMaterials, process monitoring,microstructure, partperformance

Towards implementation

To develop and demonstrate feasibility of manufacturing processfor manufacturing structural parts using thermoplastic compositesOne shot process for medium- to high-volume automotiveproduction

Inherent structural capability => based on stamp forming of aligned fibrereinforced TPC laminatesAdding function/removing parts through co-moulding of integrated flow-formed structureEconomical in terms of material and process costs – using existingmaterials and equipmentUnderstanding challenges of combining both low- and high-pressuremoulding processes within a single tool

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Engineering polymer based TPCs seeingincreased (semi-)structural usage in highvolume automotive applicationsAligned fibre reinforced net-shapeinserts used for injection moulded TPCparts:

Single polymer system (recyclable) withgreatly enhanced performanceSome benefits of aligned fibre composites,also with parts integration opportunity

BMW 5-series GT transmissionsupport, PA6-GF60

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Pre-laminated, pre-trimmed aligned fibre insert (e.g. organosheet)In some cases, pre-formed insert

Warm/molten insert placed in mould – mould closesInsert over-moulded with flow-formed material (generally IM)

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Ultimately, using ‘sticking plaster’ approach to improvepart performance…

Insert CM Insert IM

Pre-trimmed/consolidated insert Yes Yes

Net-shape parts from tool Yes Yes

In-mould pressure 10-20MPa >20MPa

Laminate drape – complexity/control Limited Limited

Fibre length in ribs >10mm - cont. <10mm

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Process details, pros & cons

Augmented stamp forming (ASF) ofTPCs:

Lower pressure aligned fibre reinforcedlaminate thermoforming/ drapingprocess

PLUSComplex high pressure random fibrereinforced flow-formed inner structure

Tooling without positive shut-off(flash edge condition)

Oil-heatedmatchedtooling

Oil-heated sprungblank holders

Random fibre reinforced flowmaterial (e.g. LFT/GMT)

Aligned fibre reinforced laminate(CFRTP)

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Tool loading

Preheated (molten) tailored blank:

Oversized laminate

Measured charge

Tool closes

Blank holder restrains laminate:

Assisting/controlling laminatedrape during forming

Full tonnage

Charge flows to fill cavity, laminatefreezes around trim-line

Hydrostatic pressure develops incavity

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Taking ‘from the ground up’ approach to the utilization ofstructural TPC materials

Insert CM Insert IM ASF

Pre-trimmed/consolidated insert Yes Yes No

Net-shape parts from tool Yes Yes No

In-mould pressure 10-20MPa >20MPa 10-20MPa

Laminate drape – complexity/control Limited Limited Yes

Fibre length in ribs structure >10mm - cont <10mm >10mm – cont

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Approach & materials, process monitoring,microstructure, part performance

Initial studies using a simple 2D U-profilecomponent design

Fully instrumented cavity (T & P)Contact heating of blank, manual transfer intotoolAnalyse resultant beam structuralperformance and microstructure

Materials:Laminate: CFR-TP PA6-GF60, 11-ply,(0/90/90/0)(0/90/0)(0/90/90/0) = 3mmlaminateRibs: PA6-GF40, injection moulded plates

450mm

WMG matched steelASF tooling

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Blank pre-heat: 250°C x 220sStack/transfer time: 20sTool temp: 130°CPress force: 950kN

(=190bar cavity pressure)

Stamping: 4sTLaminate/TProbe <Tm at t =>4s

Tool open: 90s(>10mm wall thickness at rib root)

Temperature/press force vs time for ASF process

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8x Kistler 6161AA piezo sensors3x rib structure (P1-P3)5x laminate (P4-P8)

Observations:Peak moulding pressure @ t=2.25s,coincides with peak press tonnagePressure on some areas of laminate(P4, P5) increases after materialfreeze-off

Shrinkage in rib structure transferspress tonnage onto laminate

In-mould pressure/press force vs time for ASF process

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Sensor over-range

Pribs across part =>170barOnly small variationUniform pressure in ribs

Plaminate > PribsPlaminate greatest in centre ofcavity (P5)Plaminate lowest at flange (P4)

Free edge/flash condition atmould periphery

Peak in-mould pressures for ASF process

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Average porosity is estimated at<1.5% v.f.

Thresholding analyses on >40xmicrographs = 1.21% v.f.

Flow structure leads to largethickness variations in laminate skin

Impingement/entrainment oflaminate skin into root of rib isexcellent opportunity for optimisedrib-skin adhesion mechanism

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Laminate flow mechanisms

2D part – intra & interlaminar shearLaminate inextensible along UD fibres

Laminate matrix percolation (plus bulkmovement of flow compound)Transverse flow

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3mm(11 plies)

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ASF beam performance evaluated instatic 3-point flexure:

Composite, steel and aluminiumbenchmarksExcellent mass-specific flexural stiffnessand strength behaviourIdeal failure mode: in laminate ontensile beam face

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ASF - PA6-GF60

PA6-GF60

AA5754

DP600

Specific flex load vs deflection comparisonDIC (major) strain map of ASF beam at peak flex load

ASF process delivers TPC parts with structural potentialProcess parameters, selected materials and flash edge conditiontooling design provides:

Uniform, moderate pressure in flow material (>170 bar)Pressure gradient away from centre towards part periphery inlaminate (270 – 120 bar)Some voids; but part static performance not adversely affectedPressure differentials at peak tonnage leading to incorporation oflaminate into root of moulded ribs => transverse flow

FP7 ENLIGHT project, 3D tool design

‘Enhanced lightweight design’Research into TS, TP and hybrid compositetechnologies (RTM, IM, CM, SF, ASF)48 months, within FP7 ‘SEAM’ cluster – 4connected projectsLed by Fraunhofer LBF (Darmstadt), 20+partnersMedium volume, lightweight, novel materialsTechnology demonstrated throughdevelopment of modules

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ASF process development anddemonstration:

Full-sized generic demonstratorEmploying bio-derived PA410-basedcomposites

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WP1: ModuleDesign

WP2: Simulation

WMG: Mechanical testing

WP3: MaterialDevelopment

WMG: ASF process development

WP4: Manufacturing

WMG: ASF Processdemonstration

Next stages of ASF process development:Large-scale fully instrumented tool in industrial1,700t press

Automated heat and transfer of blank

3D form – evaluation of drape (up to 60° shearangles in laminate)

Improved geometry, smaller drafts, thinner ribs

Ability to modify tool shut-off condition at partperiphery – control pressure profile in cavity

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ENLIGHT ASF tool in WMG’s EngelV-Duo 1700

Co-authors/contributors:Dr N Raath, Dr D Hughes, Dr V Goodship, Dr G Williams, Prof K Kendall

Thanks to:Technical support at WMG: D Stewardson & M Wilkins

HVM Catapult WMG centre

ENLIGHT consortium

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neil.reynolds@warwick.ac.uk

Mallick PK. Thermoplastics and thermoplastic-matrix composites for lightweight automotive structures. In: MallickPK, editor. Materials, design and manufacturing for lightweight vehicles: Woodhead Publishing; 2010. p. 174-207.Yilmazer, U. and M. Cansever (2002). "Effects of processing conditions on the fiber length distribution andmechanical properties of glass fiber reinforced nylon-6." Polymer Composites 23(1): 61-71.Rhode-Tibitanzl, M (2015). “Direct processing of long fiber reinforced thermoplastic composites and theirmechanical behavior under static and dynamic load”, PhD Thesis, Fakultät für Ingenieurwissenschaften, UniversitätBayreuthBrooks, R. (2007). Forming technology for thermoplastic composites. Composites forming technologies. A. C. Long,Woodhead Publishing Limited: 256-276.Biron, M. (2016). 2 - Thermoplastic Specific Properties. Material Selection for Thermoplastic Parts. Oxford, WilliamAndrew Publishing: 39-75.Emerson, D., et al. (2012). Using Unidirectional Glass Tapes to Improve Impact Performance of ThermoplasticComposites in Automotive Applications. 12th Automotive Composites Conference Exhibition, SPE.(2014). "Hybrid fibre thermoplastics bridge the performance gap." Reinforced Plastics 58(6): 12.Stanley, W. F. and P. J. Mallon (2006). "Intraply shear characterisation of a fibre reinforced thermoplasticcomposite." Composites Part A: Applied Science and Manufacturing 37(6): 939-948.

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