UNIVERSITY OF DELAWARE CENTER FOR COMPOSITE MATERIALS intkhnanonaltr RECOCNiZED EXCELLENCE VARTM PROCESS VARIABILITY STUDY Solange Amouroux H. Deffor, M. Fuqua D. Heider, J. W. Gillespie UD-CCM 1 July 2003
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Outline Objectives and Motivation Approach Theory Experimental set-up Materials Process Cycle time Conclusions Future work
Objectives Achieve a repeatable VARTM process by: Identifying Understanding Evaluating Controlling the sources of process variations affecting the final part: Quality Dimensional tolerances Mechanical properties While maintaining a low cost process for composite parts dedicated to high-performance applications: Aerospace Naval applications
Motivation VARTM process: +/- Main advantages: low cost, high fiber volume fraction, large scale parts Still some limitations High variability compared to autoclave process From part to part In the same part Autoclave repeatability difficult to achieve with VARTM Comparison VARTM/Autoclave: VARTM Autoclave Fiber volume fraction gradient DVf ± 10% ± 1-3% Thickness gradient Dth F ± 10% ± 1-3%
VARTM vs. Autoclave Repeatability Goal VARTM Autoclave Property Weight A lower variation (higher repeatability) in properties improves the allowable design Actual Actual Cost Cost Following conditions have to be met to make VARTM viable for highperformance applications: Process as repeatable as autoclave (reference) Slightly lower properties but for a much lower cost
Sources of Variability Materials as well as the Process have an impact on the repeatability Preforming Fabric Inputs Cure Infusion Resin Inputs Incoming materials Infusion parameters Cure parameters Outputs Quality of the part Mechanical properties Outputs
Manual vs. Automated Set-Up Current industry practice Future industry practice: Variability identified Manual lay-up Manual infusion Manual control Manual lay-up Automated infusion Automated control SMART Molding Automated lay-up (laser cutting) Automated infusion Automated control NO Monitoring MONITORING SMARTMolding set-up
Approach Theory Identification of potential sources of variation Evaluation of the different degrees of influence Experimental Manufacture of a large number of panels (Statistical) Analysis of data Synthesis Model for prediction/optimization of the process variations Actions to control the real sources of variations
Theory 1) Gather parameters influencing VARTM variations Literature review 2) Screen the parameters For each critical parameter (Example: fiber volume fraction, V f ) 1) Identify contributing parameters Areal density of the fabric n Density of the fibers Vf = Final thickness of the part th 2) Evaluate their variations 3) Rank parameter contributions 3) Example: V V f f f = 2.5% < Vf = 3.34% < V f ρ A ρa ρ Rank 3 Rank 2 Rank 1 ρ V V f f f th F f = 5% Inputs Areal density of the fabric Final thickness Density of the fibers Outputs Vf
Experimental Set-Up System 24 oz. Woven fabric E-glass Dow Derakane Momentum 411-100 Materials Fabric : Weight, Size, Areal density, Permeability, Porosity Resin : Viscosity, Mix-ratio Consumables : Weight SMARTMolding processing Operator : Accuracy, Cycle time Processing variability : Vacuum leak, Infusion time, Gel time Injection lines Vent gate Preform layer Layer for permeability study Ref layer 12 48 6 12
Materials: Fabric Weight (source of variation: preform) Manual cutting Fabric weight = 2426 g ± 1.4% Frequency 4 3 2 Future work: Measurement of -Areal weight, Porosity (affect directly V f ) -Permeability 1 0 2380 2400 2420 2440 2460 2480 2500 Weight (g) Contributing parameters: Operator Areal density
Process: Arrival Time (source of variation: infusion) Infusion Focus on the 1 st part of the injection: Injection lines 1 2 3 4 5 The variations are almost constant with flow distance. : ttt R+ : fc m ttt ". n Vent gate Time (s) 600 500 400 300 200 Part43 Part44 Part45 Part46 Part47 Part49 Part53 172s Sensor number Sensors 1 Sensors 2 Sensors 3 Sensors 4 Sensors 5 Variability of the time (%) 18.8 17.1 14.8 14.4 14.6 100 0 1 2 3 4 5 Sensors number (6" between each sensor) Contributing parameters: Viscosity Permeability Porosity
Materials: Resin Viscosity (source of variation: infusion) Viscosity = 129.4 cp ± 11.5% Fill time at 60cm = 375s ± 14.9% 5 ln(m) = 146.69*1/T + 2.9531 (modelisation) 500 Viscosity m(cp) 4.9 4.8 4.7 Fill time (s) 400 300 200 100 100 cp 110 cp 120 cp 130 cp 140 cp 150 cp 4.6 3.30E-03 3.32E-03 3.34E-03 3.36E-03 3.38E-03 3.40E-03 Temperature (K -1 ) 0 0 10 20 30 40 50 60 Distance (cm) Contributing parameters: Temperature Mix-ratio
Weight of resin (g) Process: Resin Volume (source of variation: infusion) Injected resin vs. Sensor distance 900 600 300 0 Part43 Part44 Part45 Part46 Part47 Part49 Part53 1 2 3 4 5 Sensor number Variability is distance sensitive Fiber volume fraction: V f = f(part size) Thickness change [mm] Sensor number Sensors 2 Sensors 3 Sensors 4 Sensors 5 Variability of the amount of resin (%) 16.8 13.4 Other factors can include permeability (flow shape) of DM and preform 0.8 0.6 0.4 0.2 0-0.2-0.4-0.6-0.8-1 9 5.6 Location [mm] 0 200 400 600 800
Process: Cure Gel time: 1st approximation Gel time = 1:46 ± 21.7% Peak Half-peak half-peak time 8000 NB:Infusion time» 1500 s Voltage Gel time (s) 7000 6000 5000 Time (hr:min:s) Approximated gel time time 4000 70 75 80 85 Temperature (F) Contributing parameters: - Ambient temperature - Exothermic reaction - Mix-ratios Future work will include: -K. M. England & M. B. Dorairaj prediction of gel time -Monitor and control of mix-ratios
Process: Final Part Weight (final part) = 3320 g 1.7% Fiber weight fraction = 73% 0.55% 4 5 3 4 Frequency 2 3 2 1 1 0 3240 3280 3320 3360 3400 3440 Weight (g) 0 0.725 0.73 0.735 0.74 Fiber weight fraction (g) Contributing parameters: Initial fabric weight Final thickness Future work: Quality of the part (Void content, Fiber volume fraction), Mechanical properties.
Cycle Time Variability Operator Automated VARIATIONS SOLUTIONS Mold prep + lay-up : 0:46:02 ± 97% "Kitting of material is key" Bagging : 0:42:35 ± 120% "Reusable bagging" Vacuum check : 0:09:30 ± 57% "Reusable bagging" Infusion : 0:26:23 ± 18% Gel time : 1:46:04 ± 22% Time (hr:min:s) 2:24:00 2:18:22 2:09:36 1:55:12 1:40:48 1:26:24 1:12:00 0:57:36 0:43:12 0:28:48 0:14:24 0:00:00 Part number Average 41 2003 University 42 of 43 Delaware 44 All rights reserved 45 46 47 49 53
Conclusions Initiation of the first set in characterizing VARTM variations, Part-to-part only. Development of an experimental set-up to study incoming materials Identification of a first set of variations Among the inputs Materials - Fabric (weight) - Resin (viscosity) Process parameters - Injection (time to reach the sensors, amount of injected resin) - Cure cycle (gel time)
Current and Future Work (1/2) Include: Distribution media contribution to the variability of the process Determine the variations of: - Permeability - Porosity - Areal density Measure: - Void content - Fiber volume fraction - Mechanical properties Create larger experimental data set for meaningful statistical results Variability increases with complexity of the part Manufacture of panels with more complicated shapes (stiffener, 3D) Measure "in-part" variations Show benefits of automation
Current and Future Work (2/2) Long term objectives Create interaction between the quality of the part and the variations of the inputs Modeling (prediction) Inputs For given allowables, the variation of contributing parameters can be calculated Quality variations Other materials Carbon fibers High-temperature resins
Description of the Parameters Exhaustive list Preform Resin Infusion df Diameter of the fibers ρf Density of the fibers R tow Radius of the tows S tow Saturation of the tows Vf tow Fiber volume fraction of the fiber tows K tow Permeability of the fiber tows ρ A Areal density of the fabric φ Porosity of the fabric K Permeability Cp Compressibility C Compaction th i Thickness of the final preform Vf PW Fiber volume fraction - Wet fibers Vf PD Fiber volume fraction - Dry fibers n debulk Number of debulking cycles P debulk Pression of the debulking cycles Binder Presence of binder µ R Viscosity of the resin Er Young's modulus of the resin θ Contact angle Degassing pressure P deg t deg Tg Degassing time Glass transition temperature Cure kinetics Vf F Vv F th F TS F CS F part OHCS F Resulting σ fsf ILLS Kc E F K DM V Q t infusion tgel Tgel xv,yv Permeability of the DM Vacuum pressure Flow rate Infusion time Gel time Gel temperature Vent location Final fiber volume fraction Final void content Final thickness Tensile strength Compression strength Open hole compression strength Flexural strength Interlaminar shear strength Toughness Young's modulus