CompTest 2011 Monitoring key parameters during the elaboration of composite parts by resin transfer moulding process (RTM) Presented by Marc WARIS 15/02/2011, Lausanne (Switzerland) B. Tortech, E. Marin, A. Vautrin

Outline Context and process monitoring Development of a specific Optical Fiber Sensor (OFS) Monitoring Resin Transfer Moulding process (RTM) by OFS Conclusions and perspectives

Context and process monitoring 3 Context  Development of LCM process for complex part manufacturing (Project LCM Smart)  Today Empirical Approach  Realization of trial, geometric compensation mould  Problematics: the time and the cost development increase No information on the sensibility of the process  Towards a more scientific Approach  Development of the process knowledge through appropriated instrumentation  Modeling of the process First steps - Development of a specific optical fiber sensor (OFS) - Feasibility assessment of the instrumentation process (RTM)

Context and process monitoring 44 Why monitoring Resin Transfer Moulding Process (RTM)  To reduce the number of scrap parts  To have a better knowledge of the process :  Tooling design (Injection strategy)  Find the suitable parameters  To reduce the time development of new part Reduction development cost  To control the evolution of physical parameter during the elaboration  Evolution of temperature and strain inside the part Control of the thermal cycle  Control of the cure degree evolution Control of the time process cycle  Detection of the flow front Control of the filling stage Process improvement and their reliability

Context and process monitoring 55 Which sensor for monitoring process  Optical fiber sensor :  Monitoring of several parameters inside the preform  Which parameters can we measure?  Great tool for optimizing composite process Advantages : - Low dimension (250 µm diameter) - Multiplexing several sensors - Local measurement (in situ) Drawbacks : - Brittle - Connectivity Fiber Bragg Grating (FBG) Fresnel principle Two kinds of sensors Temperature and Strain inside the preform Output Data - to detect the resin presence - to monitor the curing stage of thermoset resin

Development of a specific optical fiber sensor 6  Objectives :  Assessment of the temperature and the strain with a resolution of 1°C and around 50 µε respectively  Minimizing the intrusivity of sensor  Problematic :  Discrimination of the temperature and the strain 1) temperature compensation with a thermocouple Carbon fiber 90° Conductor Weft Teflon Insulator Flaw Good resolution High intrusivity (600 µm) Difficult to multiplex Low intrusivity (125 µm) Easy to multiplex Limited resolution OFS 2) Dual grating method

Development of a specific optical fiber sensor 77  Dual grating method :  Two FBG inscribed side by side in the same optical fiber  Current limits : the conditionement of the matrix K the resolution of Bragg’s wavelength measure  Dual grating with different types of FBG :  FBG type I, IA and IIA Different sensitivities to the temperature FBG IA FBG IIA FBG I

Development of a specific optical fiber sensor 88 Assessment of sensor’s sensitivity  Tested with calibrate equipment  Temperature : GratingK T (pm/°C)K ε (pm/µε) FBG I FBG IA FBG IIA Sensivities

Development of a specific optical fiber sensor 99 Discrimination with FBG IA/ IIA  Errors analysis  Theorical approach Errors propagation  Experimental tests Results issued from equipment test Dual-Grating sensing scheme Temperature errors (°C/pm) Strain errors (µε/pm) FBG I / FBG IIA FBG IA / FBG IIA Interrogation system Sensor Dual-Grating sensing scheme Temperature errors (°C) Strain errors (µε) FBG IA / FBG IIA8120 Increase of errors caused by : - Some problem with equipment test (homogeneity of temperature along the fiber) - slow Interrogation system (1 min for one spectrum)

Monitoring RTM process by OFS 10 Case Study  Materials :  Woven [90 2,0 3,90 2 ] panel 430x430x4 mm  Resin RTM 6 Mono component  RTM process and instrumentation Process Parameters Injection Thermal cycle t (min) Ø (cc/min) Pl=3bar

Monitoring RTM process by OFS 11 Embedded sensor in rigid tool  RTM process harsh environment  High compaction of reinforcement  Relative High Pressure of injection (3 bars)  Shrinkage of the resin in the injection channel  Some requirements  Good alignment of optical fiber inside the preform  Perfect seal between the optical fiber and the mould  Two solutions - Groove with sealant - Sealed feedthrough Easy to implement in laboratory mould - Safety solution for industrial mould - Accurate sensor positioning

Monitoring RTM process by OFS 12 Preparation of surface mould Embedding of sensor in the middle of the preform Case Study in photos Final part after removal from the mould Compaction of the preform and injection

Monitoring RTM process by OFS 13 Response of sensor during the process  Evolution of Bragg’s wavelength

Monitoring RTM process by OFS 14 Response of sensor during the process  Evolution of the temperature - We noticed no variation of Bragg’s Wavelength during the injection  No detection of the flow front - No exothermic phenomena measured  thin plate

Monitoring RTM process by OFS 15 Response of sensor during the process  Evolution of strain  Influence of the mould during the RTM process  360 µε induced by the mould in the cooling stage Debonding between the part and the mould

Conclusion & Perspectives 16 Conclusions & Perspectives  Dual grating method is a good way to discriminate the temperature and the strain  Easy to multiplex several sensor along the same fiber  Less intrusive than a sensor with temperature compensation  Validation of RTM process instrumentation with reference model parts  Application of the OFS to complex shaped parts :  manufacturing of thick part and thickness variation  influence of process parameters upon the quality of the final part

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