1ENG 4793: Composite Materials and Processes1Compression Moldingver 2ENG 4793: Composite Materials and Processes2ENG 4793: Composite Materials and Processes3ENG 4793: Composite Materials and Processes4Schematic of a Compression Molding PressENG 4793: Composite Materials and Processes5Matched Die MoldENG 4793: Composite Materials and Processes62ENG 4793: Composite Materials and Processes7Typical products• Front and rear end automobile panels• Hoods• Roofs•Scoops• Fenders• Spoilers• Air deflectors• Lift gates• Battery traysENG 4793: Composite Materials and Processes8>100 SMC parts450 lb/truck114 million lb, 1996■Lightweight■Durable■Aerodynamic stylingENG 4793: Composite Materials and Processes9Car parts by SMC - ProwlerENG 4793: Composite Materials and Processes10Advantages and disadvantages• Advantages:– Short cycle time (typically 1-6 minutes)– High volume production– Class A (high quality) surfaces• Disadvantages:– High initial capital investment– Labor intensive– Secondary operations are sometimesrequiredENG 4793: Composite Materials and Processes11Three Thermoset Material Types• Preform Molding– Shaped dry reinforcement– Binder– Matrix as liquid or powder• BMC (Bulk Molding Compound) Molding– Fibers < 30 % and < 1 inch– Resin about 25 %– Filler about 40 %– Log or rope form• SMC Molding– Fibers 30-50 % by weight (Fibers 1-3 inches to continuous)– Resin about 25 %– Filler 25-45 %– Thin, flat Sheet Molding CompoundENG 4793: Composite Materials and Processes12Thermoplastic SMC•Azdel–PP matrix– glass fiber mat (30-40% by weight)• continuous• chopped• directionalized3ENG 4793: Composite Materials and Processes13ENG 4793: Composite Materials and Processes14ENG 4793: Composite Materials and Processes15ENG 4793: Composite Materials and Processes16SMC manufacture using a configuration that can make chopped-fiberSMC-R; continuous fiber SMC-C; or continuous, random SMC-C/RmaterialENG 4793: Composite Materials and Processes17SMCComponentWeightPercentFunctionStyrene13.4Reactive monomers that provide across-linking structurePolyester10.5Reactive monomers that provide across-linking structureGlass fiber30.0 ReinforcementCalciumcarbonate40.0Filler--increases bulk volumeandreduces part costLow profileagent (LPA)3.45Controls part shrinkage--athermoplastic additiveInitiator1.00Provides free radicals to initiatepolymerizationMagnesiumhydroxide0.70 Increases viscosityZinc stearate1.00 Lubricant / mold release agentENG 4793: Composite Materials and Processes18High Strength SMC4ENG 4793: Composite Materials and Processes19Polyester• Polyesters can be thermosets orthermoplastics.– Thermoset polyesters, such as those used incompression molding, are formed from linear,unsaturated, thermoplastic polyesters which arecrosslinked during a cure reaction.• Special features of polyester resins:– Does not emit gases (byproducts) during cure– Most commonENG 4793: Composite Materials and Processes20Epoxy• Do not emit gases during cure• Compared to polyesters:– Higher mechanical properties– Longer cycle times– Less desirable surface appearanceENG 4793: Composite Materials and Processes21Other resins• Phenolic•Urea•Melamine• All three of these emit gases(condensation products) during cure.Gas emission can lead to voids in thefinal product, an obvious disadvantage.ENG 4793: Composite Materials and Processes22Molding processENG 4793: Composite Materials and Processes23SMC cycleENG 4793: Composite Materials and Processes24Geometry factors• Wall thickness of part• Charge area vs. mold area• Charge placement (location)• Single or multiple charges5ENG 4793: Composite Materials and Processes25Manufacturing Factors• Mold wall heating• Closing rate• Maximum clamping force• Gel time (Mold filling should becomplete before the resin gels)• De-molding time (Time to attain asufficient degree of cure to demold thepart)ENG 4793: Composite Materials and Processes26Curing Time vs. Mold Temperature forSMC sheetsENG 4793: Composite Materials and Processes27Viscosity variation of an SMC before and duringthe compression molding operationENG 4793: Composite Materials and Processes28Flow of various layers of an SMC charge duringcompression moldingENG 4793: Composite Materials and Processes29Fiber orientation• Planar (two-dimensional) fiberorientation• Fibers aggregate to form bundles• Compaction of bundles to produce"swirling"• Principal direction changes throughoutplaque because flow direction varies• Most affected by amount of flowENG 4793: Composite Materials and Processes30Fiber orientation6ENG 4793: Composite Materials and Processes31Effect of cure time on the development of flexural strengthin a compression molded SMC-R laminateENG 4793: Composite Materials and Processes32Various defects in a compression-moldedSMC partENG 4793: Composite Materials and Processes33Common Surface Defects in CompressionMolded SMCENG 4793: Composite Materials and Processes34 Matched Die Molding Evaluation• Investment– High Capital equipment– High tooling• Materials– Fast cure preferred– Low or no volatiles– New for thermoplastics– Mostly chopped fibers• Processing– Fast (1-10 min cycles)– Low labor (automated)– Hazards remote (moldclosed)– High Pressure (> 1,000psi, 7 MPa)• Quality– Smooth surfaces (bothsides)– Voids, cracking common– Consistent parts– Properties modest• Products– High volume– Low cost– Small projected areas– Fairly complex shapes(avoid undercuts)ENG 4793: Composite Materials and