CONTROL OF LAMINATE QUALITY FOR PARTS MANUFACTURED USING THE RESIN - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS CONTROL OF LAMINATE QUALITY FOR PARTS MANUFACTURED USING THE RESIN INFUSION PROCESS Q. Govignon, S.M.R. Kazmi, C.M.D. Hickey, S. Bickerton* Centre for Advanced Composite Materials, The University of Auckland, New Zealand * Corresponding author (s.bickerton@auckland.ac.nz) Keywords : VARTM, Process control, Experimental 850 g/m 2 ; the EB, is a [0/90] stitched glass 1 Introduction reinforcement with an areal weight of 825 g/m 2 ; and Resin infusion (aka. VARTM) is a member of the liquid composite moulding (LCM) family of the EDB is a double bias stitched glass with processes, in which a dry fibrous preform is orientation of [+45/-45] and areal weight of 800 g/m 2 . The three reinforcements are pictured in Fig. 1. enclosed into a mould and impregnated with a reactive liquid resin. Resin Infusion, as compared to From this figure it can be observed that the EB other LCM processes such as resin transfer fabric contains the biggest fibre bundles, and the moulding, offers the advantage of requiring neither widest gaps between the tows. It is reasonable to supplied positive pressure nor rigid matched mould. expect that this reinforcement will produce panels The tooling forces and mould costs can be kept to a with lower V f , and result in faster fill times as minimum, but the processing time may be longer compared to the other two. The EB also seems to than for other LCM processes. It is therefore a very present the most variability in its architecture. The attractive process for the manufacture of medium to EQ appears to have slightly bigger tows than the large sized parts in small to medium quantities. EDB, and displays a little more variability. However, While being widely used in the marine and wind for both the EQ and EDB, the tows are placed very energy industries, the perceived lack of control of close to each other with minimal gaps available to laminate quality and fibre volume fraction ( V f ) has act as resin transfer channels. hindered the spread of this technique in the EQ EB EDB aerospace industry. This paper presents an experimental study into control of fibre volume fraction and laminate quality of panels manufactured using the resin infusion process. A study of the compaction behaviour of a selection of fibre reinforcements is presented, providing a guideline for estimating the potential for controlling the V f of manufactured parts. Following this, an experimental study into the selection of process parameters on the Fig. 1: Photograph of the glass reinforcement used in quality of manufactured parts is presented. this study. The resin used in this study is PRIME TM 20 low 2 Materials viscosity infusion epoxy produced by Gurit, applied Three different non-crimp glass fibre reinforcement using a mass ratio of 10% fast and 90% slow materials were used in this study. The three hardener [1]. Consumables used include a 80 g/m 2 reinforcements were chosen to have a comparable Nylon peel ply, a Knitflow 40 distribution mesh, and areal weight but different architecture. Due to the a 50 μ m thick heat stabilised PA6 vacuum bag; all differences in architecture, these reinforcements consumables being supplied by SP-High Modulus. display different permeability and compaction behaviour. The fabric referred to here as EQ is a 3 Compaction Characterization stitched quadriaxial glass reinforcement with 3.1 Procedure orientation of [90/45/0/-45], with an areal weight of

The procedure for studying the compaction Fig. 2 presents the compaction traces for the three behaviour of fibrous reinforcement during the resin reinforcements. Four nominally identical samples infusion process is detailed in [2]. Specimens were were prepared and tested under identical conditions. cut and placed between two parallel plates mounted Some variability is observed in the compaction in an Instron universal testing machine. A response, which can be attributed to variability in compaction load was applied and ramped up to an the reinforcement architecture, as well as variation equivalent compaction pressure of 1.0 bar on the dry in the inter-layer nesting of the reinforcement stack. reinforcement. The preform was then saturated with The EB fabric appears to present the largest mineral oil, and the load was decreased down to an controllable V f range out of the three fabrics, with a equivalent compaction pressure of 10 mbar, before range from 0.44 to 0.486 if varying the compaction being ramped up again to an equivalent pressure of pressure between 0 and 1 bar. However, these 1.0 bar. This second compaction phase, which values are significantly lower than those achieved replicates the compaction occurring during the post with either EQ or EDB fabric. Both of these filling stage, can serve as a basis to determine the reinforcements have a very similar range of range of fibre volume fraction achievable through achievable V f under resin infusion conditions, control of the resin infusion process. ranging from 0.49 to 0.53. 3.2 Results a) 1000 Compaction stress (mbar) EQ2 Cameras for stereophtogrammetry 800 EQ3 and flow front tracking EQ4 600 Panel measurements 400 Average 200 Temperature controlled enclosure 0 0.45 0.46 0.47 0.48 0.49 0.5 0.51 0.52 0.53 0.54 0.55 Fibre volume fraction b) 1000 Compaction stress (mbar) EB1 800 EB2 EB3 600 EB4 400 Panel measurements Average 200 Laminate 0 0.42 0.43 0.44 0.45 0.46 0.47 0.48 0.49 0.5 0.51 0.52 Fibre volume fraction c) 1000 Compaction stress (mbar) EDB1 800 EDB2 EDB3 600 Vent pot Inlet pot EDB4 Panel measurements 400 Average Fig. 3: Experimental setup for monitoring resin 200 infusion. 0 0.47 0.48 0.49 0.5 0.51 0.52 0.53 0.54 0.55 0.56 0.57 4 Resin Infusion Control Fibre volume fraction Fig. 2 : Traces of the secondary compaction for the 4.1 Experimental Setup three reinforcements studied; a) EQ, b) EB, c) EDB. The experimental setup presented in Fig. 3 is a development of the setup presented in [3]. The

CONTROL OF LAMINATE QUALITY FOR PARTS MANUFACTURED USING THE RESIN INFUSION PROCESS infusion experiments were performed in an Table 1: Plan of experiments . enclosure permitting accurate control of ambient temperature. The laminate thickness and flow front Inlet / Vent Inlet / Vent Material (# of progression were monitored using a pair of cameras condition condition during repeats) mounted above the mould, and resin pressures were during filling post-filling measured at three positions along the panel length Atmospheric / Full vacuum/ full EQ(3); EB(2); using pressure transducers mounted below the full vacuum vacuum EDB(2) mould. The inlet and vent pots were equipped with Atmospheric / 500 mbar/ 500 EQ(2); EB(1); pressure regulators as well as pressure transducers. full vacuum mbar EDB(1) Atmospheric / 900 mbar / 900 EQ(3); EB(1); Pos1 Pos2 Pos3 Pos4 Pos5 Pos6 full vacuum mbar EDB(2) Atmospheric / Clamped / full EQ(1); EB(1); full vacuum vacuum EDB(1) 500 mm 650 mbar / full Full vacuum/ full EQ(1) vacuum vacuum 650 mbar / full 500 mbar/ 500 EQ(1) vacuum mbar 125 mm 5 mm 125 mm 125 mm 125 mm 125 mm 650 mbar / full 900 mbar / 900 EQ(1) 1000 mm vacuum mbar Distribution Transducer/ Distribution Glass Reinforcement media hole tape Fig. 4: Schematic of the laminate and consumables 4.3 Observations during Resin Infusion layout. Table 2 presents the average fill time for each The preforms were cut using a press and cutting reinforcement, together with the standard deviation template to a dimension of 230 x 450 mm. The expressed in percent of the fill time. For the EQ materials lay-up and position of the pressure reinforcement, the tests in which the inlet pressure transducers is depicted in Fig. 4; the distribution was reduced to 650 mbar during filling are treated media was cut 30 mm narrower than the glass separately. It appears that the EQ generates the reinforcement and was placed to stop 50 mm short longest fill times, and also the most variability in fill of the end of the preform towards the vent; a further times. EB, despite being the reinforcement visually 50 mm gap was left between the end of the presenting the most variability in architecture, reinforcement and the vent, with only peel ply to act appears to present very little variability in fill time. as a break region. Table 2: Fill time and variations for each reinforcement. 4.2 Control Parameters The processing parameters considered for the Reinforcement Mean fill Standard control of laminate quality are the pressure applied (Inlet pressure) time (s) deviation (%) at the inlet and vent during both filling and post- 645 20.1 EQ (1000mbar) filling, and the action of clamping the inlet as 1385 18.9 EQ (650mbar) opposed to turning the inlet into a vent at the onset 312 2.7 EB (1000mbar) of post-filling. Table 1 presents the plan of resin 480 8.7 EDB (1000mbar) infusion experiments, which has been designed to demonstrate the effect of varying the filling and post-filling conditions. All other parameters were kept constant throughout the study. Care was taken to use a consistent pre-filling procedure, with respect to cycling of the applied vacuum levels, and timing of the resin mixing and degassing. All panels were manufactured at a constant ambient temperature of 25°C, with the resin, hardener, and preform stabilized at that temperature beforehand. 3