Compression RTM - A new process for manufacturing high volume continuous fiber reinforced composites

Compression RTM - A new process for manufacturing high volume continuous fiber reinforced composites 5 th International CFK-Valley Stade Convention 07-08 June 2011, STADEUM Stade, Germany Authors Raman Chaudhari, Michael Pick, Oliver Geiger, Dennis Schmidt, Prof. Dr.-Ing. Peter Elsner Prof. Dr.-Ing. Frank Henning

Contents Motivation and Goal of this Feasibility Study State of the art: Resin Transfer Molding (RTM) Process High Pressure RTM Processes Definition of process parameters Compression RTM process study Process equipment Experimental design Results and Discussion Summary and Outlook Acknowledgement

Motivation and goal of this feasibility study Applications for high performance composite parts in the automotive industry Floor structure Side frame Audi R8 Spyder Source:Alcan Bumper BMW M6 Roof BMW Project I CityCar Quelle: BMW

Motivation and goal of this feasibility study Development of a new processing strategy for the manufacturing of high-performance thermoset composite parts in shorter cycle time To overcome the issues of the standard resin transfer molding process The new process strategy should fulfill the following requirements Excellent material and part performance Nice surface of the parts Short cycle times Capable for the utilization of fast curing resins Large scale production capability

State of the art: Resin Transfer Molding (RTM) Process RTM Process cycle 3D Preform Preform production and fixing Preform handling Handling semi-finished i product Mold technology Resin Hardener Fixing 2D-semifinished fabric product Infiltration and curing Semi-finished fabric cuts 2D Component demolding and post-processing processing Textile product Mold cleaning RTM component Start of cycle End of cycle

State of the art: Resin Transfer Molding (RTM) Process RTM Process cycle Injection sequence The dry 3D fiber preform is placed into the open mold cavity and the mold cavity is closed completely (gap in the cavity = final wall thickness) Resin and hardener are mixed and then injected into the cavity Injected resin impregnates the preform Demolding of the part after curing Resin Hardener Dry 3D fiber preform in Resin injection, preform impregnation Demolding of the completely closed mold and curing of the part cured RTM part

State of the art: Resin Transfer Molding (RTM) Process Typical challenges and issues of the state of the art RTM process Typical injection pressure between 1 and 20 bar Higher pressure disturbs the fiber orientation in the preform Permeability of 3D fiber preform influences significantly the injection time Proper impregnation of complex shaped preforms is a challenge Required injection time does not allow the use of fast curing resin systems Typically long cycle times due to long injection and curing times Additional resin required to push trapped air out of the mold cavity Negative economical and ecological impact Probable solutions: High Pressure RTM processes

High pressure injection RTM Process (HP-IRTM) HP Injection RTM Process cycle Injection sequence The dry 3D fiber preform is placed into the open mold cavity and the mold cavity is closed completely (gap in the cavity = final wall thickness) Resin and hardener are mixed under high pressure and then injected into the cavity at leading to high pressure built up in the cavity Injected resin impregnates the preform mainly due to flow in in x-y plane Demolding of the part after curing Resin Hardener Dry 3D fiber preform in Resin injection, preform impregnation Demolding of the completely closed mold and curing of the part cured RTM part

High Pressure Compression RTM Process (HP-) Compression RTM Process cycle Injection sequence The dry 3D fiber preform is placed into the open mold cavity and the mold cavity is partially closed Resin and hardener are mixed and injected into the mold gap at low cavity pressure The mold is then closed completely, high pressure is applied and the preform is completely impregnated and cured before demolding of the part Resin Hardener Dry 3D fiber preform in Resin injection and partial Apply pressure, complete preform Demolding of the partially closed mold preform impregnation impregnation and curing of the part cured RTM part

High Pressure RTM Processes High Pressure Injection Resin Transfer Moulding HP-IRTM High Pressure Compression- Resin Transfer Moulding HP- Impregnation of preforms in x- and y- direction Impregnation of preforms in x-, y- and z- direction

High Pressure Compression RTM Process (HP-) Advantages and challenges of the Compression RTM process Increased permeability of fiber preform due to open mold gap Thus also reduced time for resin injection Significantly ifi reduced d time for preform impregnation through h high h pressure compression Fast injection and impregnation allows the use of fast curing resins Almost no additional resin required to push trapped air out of the mold cavity Positive economical and ecological impact Reduced cycle times (depending on part geometry, fiber architecture and resin) Challenge: Suitable mold technologies required (injection port, sealing etc.)

Definition of process parameters Important process parameters affecting process Fiber volume content It can strongly affects the required compression force and the impregnation quality Resin viscosity / Resin temperature It can influences the impregnation quality in the process Cavity pressure / Compression pressure It can affect the impregnation behavior in correlation to the resin viscosity and fiber volume content Mould gap and gap closure speed It can mainly influence the impregnation during injection (mould gap) and flow of the resin in the cavity (gap closure speed) and hence the impregnation behavior Injected resin amount It can mainly influence the impregnation during injection / degree of mould filling during injection

Compression RTM process study Literature research to eventually derive process parameters Literature Fiber volume Closing Mold Curing Resin Injection Injection Mold Cavity content speed temperature temperature temperature time pressure gap pressure [%] [mm/min] [ C] [ C] [ C] [s] [bar] [mm] [bar] Kang, M. [1999]: "Analysis of resin transfer compression molding process" 24 27 27 27 2 Chang, C. [2006]: "Effect of process variables on quality of " 25, 50, 75 80, 100, 120 25, 32, 40 1, 1.5, 2 1, 5, 10 1, 1.5, 2 lkegawa, N. [1996]: "Effect of compression process on void behavior in structural resin transfer molding" 33 5, 100 130 130 90 05 0,5 13 0, 3, 6, 12 PHAM, X. [1999]: "Simulation of for thin shells" 18, 33 15 1.5, 30 3.0, 7.5, 15, 30 90, 30-60, 14, 8, 8 -, 48 4.8, 2, 3.5, 7 5.1 3.1 (final thickn. )

Compression RTM process study Process equipments Injection equipment: Wolfangel two-component RTM mixing and dosing equipment Compression press: Dieffenbacher DYL 630/500 hydraulic press, 6,300 kn press force Compression RTM mold: Plate mold 830 mm x 210 mm x 3 mm

Compression RTM process study Materials Saertex non-woven fabric (S14EU960-01210-01300-487000) UD MC Sizing, 1218 g/m² Epoxy resin system Hexion RIM 935 and RIMH 936 Resin-/Hardener mixture: 100:29 (wt.-%) / 100:35 (Vol.-%) Resin mixture viscosity: 340 mpa*s

Compression RTM process study Experimental design Fibre orientation Resin temp. Resin amount Injection pressure Cavity pressure Mould gap Gap closure speed Mould filling time [ C] [g] [bar] [bar] [mm] [mm/s] [s] RTM [0 4 ] RT --- 6-10 bar --- --- --- 400 1 [0 4 ] RT 260 max. 6 60 1 02 0.2 30-3333 2 [0 4 ] RT 260 max. 6 60 2 0.2 30-33 RTM [0/90] s RT --- max. 6 --- --- --- 400 3 [0/90] s RT 260 max. 6 60 1 0.2 30-33 4 [0/90] s RT 260 max. 6 60 2 0.2 30-33

Compression RTM process study Materials characterization program ILSS samples Flexural test samples Fiber vol. content Tensile test samples 15mm x 30mm 15mm x 90mm Ø 30 mm 15mm x 250mm 3 3 2 1 2 2 4 1 3 1 2 3 4 5 5 4 3 1 2 6 5 4 3 2 1 1 ILSS samples away from injection point ILSS samples close to injection point

Results and discussions RTM experiments Non impregnated area Partially impregnated fabrics Non impregnated area It was not possible to obtain complete impregnation of the fibers even after 400s injection time in the classical RTM process at 6-10 bar injection pressure Hence it was not possible to characterize the mechanical properties of the plates manufactured by the classical RTM process

Results and discussions Tensile properties of the laminates 1200 Tensile strength Tensile modulus 50 45 1000 40 Tensile streng gth [MPa] 800 600 400 200 0 45,85 46,12 1147 1131 [0 4 ] [0 4 ] 596 [0/90] S 31,82 30,77 561 [0/90] S 1mm Gap 2mm Gap 1mm Gap 2mm Gap 35 30 25 20 15 10 5 0 lus [GPa] Tensile modul Fiber volum me content [Vol- -%] 80 70 60 50 40 30 Fiber volume content Part thickness 58,51 60,05 59,37 61,15 [0 4 ] 1mm Gap [0 4 ] 2mm Gap [0/90] S 1mm Gap 4 3 2 1 0 [0/90] S 2mm Gap s (mm) Part thickness Nearly equivalent part thickness and hence fiber volume content was observed in the laminates at 1 mm and 2 mm mold gap Almost identical tensile properties of the laminates

Results and discussions Flexural properties of the laminates 1400 50 Flexural strength Flexural modulus 45 1200 40 Flexural streng gth [MPa] 1000 800 600 400 200 1270 1228 37,27 37,51 1139 1037 33,58 33,51 35 30 25 20 15 10 5 Fiber volum me content [Vol- -%] 80 70 60 50 40 30 Fiber volume content Part thickness 58,51 60,05 59,37 61,15 [0 4 ] 1mm Gap [0 4 ] 2mm Gap [0/90] S 1mm Gap 4 3 2 1 0 [0/90] S 2mm Gap s (mm) Part thickness 0 [0 4 ] 1mm Gap [0 4 ] 2mm Gap [0/90] S 1mm Gap [0/90] S 2mm Gap 0 Almost identical flexural properties of the UD laminates at both mold gaps Flexural properties of [0/90] s laminates significantly high due to presence of UD layer from top and bottom side; a slight drop of flexural strength observed at 2 mm mold gap

Results and discussions 80 ILSS of the laminates ILSS Away from injection point 70 ILSS Close to injection point ILSS [MP Pa] 60 50 40 30 20 10 0 57,89 59,35 57,58 58,83 [0 ] 4 1mm Gap [0 ] 4 2mm Gap 32,71 34,87 33,45 29,45 [0/90] [0/90] S S 1mm Gap 2mm Gap Fiber volume content [Vol-%] 80 70 60 50 40 Fiber volume content (Away from Injection point) Fiber volume content (Close to Injection point) Part thickness (Away from Injection point) Part thickness (Close to Injection point) 58,92 60,39 63,77 58,34 59,86 60,08 58,08 59,41 30 0 [0 4 ] [0 4 ] [0/90] S [0/90] S 1mm Gap 2mm Gap 1mm Gap 2mm Gap 4 3 2 1 Part thickness [mm m] Almost identical ILSS properties for UD laminates at 1 mm and 2 mm mold gap observed near injection point and away from injection point At 2 mm mold gap the ILSS properties of bidirectional laminates dropped slightly for the samples away from injection point if compared to close to injection point

Summary The process was investigated using 1 mm and 2 mm mold gap The unidirectional ([0] 4 ) and bidirectional ([0/90] s ) laminate layup were used for investigating the effect of chosen mold gaps on the process The selection of 1 mm or 2 mm mold gap did not show any influence on the tensile and flexural properties of the UD and bidirectional laminates For bidirectional laminates at 1mm and 2 mm mold gap, depending on the degree of mold filling after injection step, roving displacement and bad impregnation quality was observed due to resin flow under compression force, solution reduction of resin viscosity it process utilizes only the required amount of the resin which has a direct impact on environment and process economy Due to very low resin injection time and impregnation time the process indicates high potential for high volume manufacturing

Outlook Ongoing activities Evaluation of different fabric architectures and fiber orientation on the process development Evaluation of effect of compression pressure on process development Use of highly reactive resins to manufacture laminates in less than 5 min cycle time in the mould Setting up automated Compression RTM infiltration setup using KraussMaffei High Pressure RTM equipment for industrial scale manufacturing

Outlook Ongoing activities Development of the industrial scale High Pressure Compression RTM process Prototype study: Resin injection time: 7.5 sec Impregnation time: 5-10 sec Cure cycle time: 4 min part size: 830x210x3 mm Fiber vol. content: ca. 57-60% Prototype sample

Acknowledgement "Dieses Vorhaben wird durch die Europäische Union - Europäischer Fonds für regionale Entwicklung - sowie das Land Baden-Württemberg gefördert. Verwaltungsbehörde des operationellen Programms RWB-EFRE ist das Ministerium für Ländlichen Raum, Ernährung und Verbraucherschutz h Baden-Württemberg. Weitere Informationen unter www.rwb-efre.baden-württemberg.de

Compression RTM - A new process for manufacturing high volume continuous fiber reinforced composites 5 th International CFK-Valley Stade Convention 07-08 June 2011, STADEUM Stade, Germany Thank you very much for your kind attention. Contact: Raman Chaudhari Fraunhofer ICT raman.chaudhari@ict.fraunhofer.de de