Polymer Matrix Thermosetting (TS) polymers are the most common matrix materials Principal TS polymers are: Phenolics – used with particulate reinforcing phases Polyesters and epoxies - most closely associated with PMCs Thermoplastic molding compounds include fillers or reinforcing agents Nearly all rubbers are reinforced with carbon black
MATERIAL SUITABILITYDepending on the applications.Not all materials are suitable for all applications.Knows the pros and cons of the materials before using it for certain applications.
Factors to be consider :-Structural (stiffness, strength, toughness)ThermalElectrical (conduct electricity or not ?)Chemical (resistance)Aesthetic (will the materials achieve the required look?)
FACTORS IN PROCESS SELECTION• Materials – matrix and reinforcing(fibres) system• Reinforcing architecture required• Complexity of part geometry• Number to be manufactured• How quickly they are to be manufactured
Open Mold PMC Processes1. Hand lay‑up2. Spray‑up3. Vacuum Bagging – uses hand-lay-up, uses atmospheric pressure to compact laminate.4. Filament Winding The differences are in the methods of applying the laminations to the mold, alternative curing techniques, and other differences
Open Mold ProcessesFamily of FRP shaping processes that use a single positive or negative mold surface to produce laminated FRP structuresThe starting materials (resins, fibers, mats, and woven rovings) are applied to the mold in layers, building up to the desired thicknessThis is followed by curing and part removalCommon resins are unsaturated polyesters and epoxies, using fiberglass as the reinforcement
Hand Lay‑Up MethodOpen mold shaping method in which successive layers of resin and reinforcement are manually applied to an open mold to build the laminated PMC composite structureLabor‑intensiveFinished molding must usually be trimmed with a power saw to size outside edgesOldest open mold method for PMC laminates
Hand Lay-Up MethodFigure 15.4 Hand lay‑up : (1) mold is treated with mold release agent; (2) thin gel coat (resin) is applied, to the outside surface of molding; (3) when gel coat has partially set, layers of resin and fiber are applied, the fiber is in the form of mat or cloth; each layer is rolled to impregnate the fiber with resin and remove air; (4) part is cured; (5) fully hardened part is removed from mold.
Products Made by Hand Lay‑UpGenerally large in size but low in production quantity - not economical for high productionApplications: Boat hulls Swimming pools Large container tanks Movie and stage props Other formed sheets
SPRAY UPSuitable in making boats, transportation components, tub/shower units in a large variety of shapes and sizes.Chopped laminated – good comfortability and faster than hand lay-up.Operator – control thickness and consistencyOperator dependant compared to hand lay-up.Low production per volume but can produce more when using multiple molds.
Spray‑Up MethodLiquid resin and chopped fibers are sprayed onto an open mold to build successive FRP laminationsAttempt to mechanize application of resin‑fiber layers and reduce lay‑up timeAlternative for step (3) in the hand lay‑up procedure
Products Made by Spray‑UpBoat hulls, bathtubs, shower stalls, automobile and truck body parts, recreational vehicle components, furniture, large structural panels, and containersMovie and stage props are sometimes made by this methodSince products made by spray‑up have randomly oriented short fibers, they are not as strong as those made by lay‑up, in which the fibers are continuous and directed
VacuumBaggingUse atmospheric pressure to suck air from under vacuum bag, to compact composite layers down and make a high quality laminate (image from cgi.ebay.com). Layers from bottom include: mold, mold release, composite, peel-ply, breather cloth, vacuum bag, also need vacuum valve, sealing tape.
Filament Winding Resin‑impregnated continuous fibers are wrapped around a rotating mandrel that has the internal shape of the desired PMC product; the resin is then cured and the mandrel removed The fiber rovings are pulled through a resin bath immediately before being wound in a helical pattern onto the mandrel The operation is repeated to form additional layers, each having a criss-cross pattern with the previous, until the desired part thickness has been obtained
Closed Mold ProcessesPerformed in molds consisting of two sections that open and close each molding cycleTooling cost is more than twice the cost of a comparable open mold due to the more complex equipment required in these processes
Classification of Closed MoldProcesses Three classes based on their counterparts in conventional plastic molding: 1. Compression molding 2. Transfer molding 3. Injection molding 4. Resin transfer molding 5. Pultrusion The terminology is often different when polymer matrix composites are molded
Compression Molding PMC ProcessesA charge is placed in lower mold section, and the sections are brought together under pressure, causing charge to take the shape of the cavityMold halves are heated to cure TS polymer When molding is sufficiently cured, the mold is opened and part is removedSeveral shaping processes for PMCs based on compression molding The differences are mostly in the form of the starting materials
Injection Molding PMC ProcessesInjection molding is noted for low cost production of plastic parts in large quantitiesAlthough most closely associated with thermoplastics, the process can also be adapted to thermosetsProcesses of interest in the context of PMCs: Conventional injection molding Reinforced reaction injection molding
Pultrusion ProcessesSimilar to extrusion (hence the name similarity) but workpiece is pulled through die (so prefix "pul‑" in place of "ex‑")Like extrusion, pultrusion produces continuous straight sections of constant cross sectionDeveloped around 1950 for making fishing rods of glass fiber reinforced polymer (GFRP)A related process, called pulforming, is used to make parts that are curved and which may have variations in cross section throughout their lengths
PultrusionContinuous fiber rovings are dipped into a resin bath and pulled through a shaping die where the impregnated resin curesThe sections produced are reinforced throughout their length by continuous fibersLike extrusion, the pieces have a constant cross section, whose profile is determined by the shape of the die openingThe cured product is cut into long straight sections
Pultrusion ProcessFigure 15.11 Pultrusion process
Materials and Products in PultrusionCommon resins: unsaturated polyesters, epoxies, and silicones, all thermosetting polymersReinforcing phase: E‑glass is most widely, in proportions from 30% to 70%Products: solid rods, tubing, long flat sheets, structural sections (such as channels, angled and flanged beams), tool handles for high voltage work, and third rail covers for subways.
Resin Transfer Molding (RTM)intermediate volume molding processinject resin under pressure into a mold cavitycan be automated and is capable of producing rapid cycle timesVacuum assist can be used to enhance resin flow in the mold cavity.
resin is injected under pressure, using mix/meter injection equipment, and the part is cured in the moldThe reinforcement can be either a preform or pattern cut roll stock material
can be done at room temperatureproduces parts with two finished surfaces.laying up reinforcement material dry inside the mold, any combination of materials and orientation can be used, including 3-D reinforcementsPart thickness is determined by the tool cavity