composite tech&tech

8/14/2019 Composite Tech&Tech

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Cover


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Definition of Composites......................1

What are FRP/Composites?.................2

Benefits and Features

of FRP/Composites..............................3

Fibers and Resins....................................4

FRP Composite MoldingMethods..................................................11

The FRP/Composite

Design Process......................................17

Guide to Design Details......................20

Molded Fiber Glass Companies 2003

his manual is an overview of the Fiber ReinforcedPlastic/Composite (FRP/Composite) material system.

Materials and processes are presented along with designguidelines and comparisons to alternate materials. Because

of the versatility of FRP/Composites, the designer isencouraged to collaborate with a molder and/or materialsupplier to optimize the application.


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Composites are a combination of two or more materialsyielding properties superior to those of the individualingredients. One material is in the form of a particulate orfiber, called the reinforcement or discrete phase. The otheris a formable solid, called the matrix or continuous phase.

The region where the reinforcement and matrix meet iscalled the interface. Composite properties are determined bychemical and mechanical interaction of the combined materials.

Wood and concrete are composites under this definition.

This document is limited to the application of the subset ofcomposites called Fiber Reinforced Plastic (FRP) thatcombine fibers of glass or other materials (the reinforcement)

with thermoset and/or thermoplastic resins (the matrix).

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The plastic resin systems determinechemical, electrical, and thermalproperties. Fibers provide strength,

dimensional stability, and heatresistance. Additives provide colorand determine surface finish, andaffect many other properties suchas weathering and flame retardance.

Processing of FRP/Compositesinvolves complex chemical reactions.

iberglass reinforced plastic,commonly known as

fiberglass, was developed commerciallyafter World War II. Since that time,the use of fiberglass has grown rapidly.

The term fiberglass describes athermoset plastic resin that isreinforced with glass fibers.In this manual, the more generalterms Fiber Reinforced Plastic/Composites or FRP/Compositeswill be used to describe theseextremely useful material systems.

Plastic resins come in two different

classes - thermosets andthermoplastics. From a practicalperspective, its easy to rememberthat thermosets maintain their moldedshape at higher temperatures andcannot be melted and reshaped.Thermoplastics will melt at a giventemperature and can be solidifiedinto new shapes by cooling toambient temperatures. Thermosetsand thermoplastics are describedwith more detail in the ResinSystems section of this document.

Reinforcing fibers include glass, carbon,aramid and other man-made and naturalmaterials that are further described inthe Reinforcement section of thisdocument. These are used in a varietyof forms and combinations to providethe required properties.

Final properties are determined bymany factors including the type,amount, and composition of the

resin systems and reinforcements.In addition, the use of additives cangreatly affect the FRP/Compositeproperties.


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There can be many benefitsobtained by the use of FRP/Composites. These benefits and

characteristics should be consideredearly in the design process.

Corrosion Resistance

FRP/Composites do not rust, corrodeor rot, and they resist attack frommost industrial and householdchemicals. This quality has been

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responsible for applications incorrosive environments such asthose found in the chemical processingand water treatment industries.Resistance to corrosion provideslong life and low maintenance inmarine applications from sailboatsand minesweepers to seawalls andoffshore oil platforms.

High Strength, LightweightFRP/Composites provide highstrength to weight ratios exceedingthose of aluminum or steel. Highstrength, lightweight FRP/Compositesare a rational choice whenever weightsavings are desired, such as componentsfor the transportation industry.

Dimensional Stability

FRP/Composites have highdimensional stability under varying

physical, environmental, and thermalstresses. This is one of the most usefulproperties of FRP/Composites.

Parts Consolidation andTooling Minimization.

A single FRP composite moldingoften replaces an assembly ofseveral metal parts and associatedfasteners, reducing assembly andhandling time, simplifying inventory,and reducing manufacturing costs.A single FRP/Composite tool can

replace several progressive toolsrequired in metal stamping.

High Dielectric Strength andLow Moisture Absorption

The excellent electrical insulatingproperties and low moistureabsorption of FRP/Composites

qualify them for use in primarysupport applications such as circuitbreaker housings, and where lowmoisture absorption is required.

Minimum Finishing Required

FRP/Composites can be pigmentedas part of the mixing operation orcoated as part of the moldingprocess, often eliminating the needfor painting. This is particularlycost effective for large componentssuch as tub/shower units. Also, oncritical appearance components, aclass A surface is achieved.

Low to Moderate Tooling Costs

Regardless of the molding methodselected, tooling for FRP/Compositesusually represents a small part ofthe product cost. For eitherlarge-volume mass-production or

limited runs, tooling cost is normallysubstantially lower than that of themultiple forming tools required toproduce a similar finished partin metal.

Design Flexibility

No other major material systemoffers the design flexibility ofFRP/Composites. Presentapplications vary widely. They rangefrom commercial fishing boat hullsand decks to truck fenders, from

parabolic TV antennas to transitseating, and from outdoor lamphousings to seed hoppers. Whatthe future holds depends on theimagination of todays designengineers as they develop evenmore innovative applications forFRP/Composites.

Corrosion Resistance

High Strength, Lightweight

Dimensional Stability

Parts Consolidation and

Tooling Minimization

High Dielectric Strength and

Low Moisture Absorption

Minimum Finishing Required

Low to Moderate Tooling Costs

Design Flexibility


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Much of the strength ofFRP/Composites is due tothe type, amount andarrangement of the fiberreinforcement. While over

90% of the reinforcements in use

are glass fibers, other reinforcementshave established a critical niche.

E-glass is the most commonly usedfiber reinforcement. It is strong,has good heat resistance, and highelectrical properties. For morecritical needs, S-Glass offers higherheat resistance and about one-thirdhigher tensile strength (at a highercost) than that of E-glass.

Carbon Fibers (graphite) are

available in a wide range of propertiesand costs. These fibers combinelight weight with very high strengthand modulus of elasticity. Themodulus of elasticity is a measureof the stiffness or rigidity in amaterial. For high stiffnessapplications these reinforcementsare hard to beat, with a modulus ofelasticity that can equal steel. FRP/Composites with carbon fiberreinforcement also have excellentfatigue properties. The primary useof carbon fibers is in aircraft andaerospace, in which weight savingsare a major objective. While its costlimits carbons use in commercialapplications, it is used extensively wherematerial content is low, such assporting equipment.

Aramid, or aromatic polyamidefibers (Kevlar or Twaron)provide high strength and lowdensity (40% lower than glass) aswell as high modulus. These fibers

can be incorporated in manypolymers and are extensively usedin high impact applications, includingballistic resistance.

Natural Fibers such as Sisal, Hempand Flax have been used for manyapplications with low strengthrequirements. They are limited toapplications not requiring resistanceto moisture or high humidity.

Arrangement of the glass fibers -how the individual strands arepositioned determines bothdirection and level of strengthachieved in a molded FRP/Composite.The three basic arrangements of glassfiber reinforcement are unidirectional,bidirectional and multidirectional.

Unidirectional arrangements providethe greatest strength in the directionof the fibers. Unidirectional fibers canbe continuous or intermittent,depending on specific needs

determined by part shape andprocess used. This arrangementpermits very high reinforcementloading for maximum strengths.The fibers in a bidirectional arrangementare in two directions usually at 900

to each other, thus providing thehighest strength in those directions.The same number of fibers neednot necessarily be used in bothdirections. High fiber loading canbe obtained in woven bidirectionalreinforcements.

Multidirectional or randomarrangements provide essentiallyequal strength in all directions of thefinished part.

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Kevlar is a registered trademark of E.I. du Pont de Nemours and Company

Twaron is a registered trademark of Teijin Twaron, BV.


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additives to prepare moldingcompounds for compression orinjection molding and otherprocesses. Various surface treatmentsare applied to ensure optimumcompatibility with different resinsystems.

The matrix or resin is the othermajor component of an FRP/Composite. Resin systems areselected for their chemical, electricaland thermal properties. The twomajor classes of resins are thermosetsand thermoplastics.

Thermoset Resins

Thermosetting polymers are usuallyliquid or low melting point solidsthat can easily combine with fibers

or fillers prior to curing. Thermosetsfeature cross-linked polymer chainsthat become solid during a chemicalreaction or cure with the applicationof a catalyst and heat. The highlevel of cross-linking providesfor reduced creep compared tothermoplastics. The thermosetreaction is essentially irreversible.

Among the thermoset resins forFRP/Composites, the family ofunsaturated polyesters is by far themost widely used. These resins aresuitable for practically every moldingprocess available for thermosets.

Polyesters offer ease of handling,low cost, dimensional stability, anda balance of good mechanical,chemical, and electrical properties.

Reinforcements are supplied inseveral basic forms to provideflexibility in cost, strength,compatibility with the resin system,and process requirements.Regardless of the f inal fo rm, allfibe r reinforcements originate as

single filaments. A large numberof filaments are formedsimultaneously and gathered into astrand. A surface treatment is thenapplied to facilitate subsequentprocessing, maintain fiber integrity,and provide compatibility withspecific resin systems. After thistreatment, the strands are furtherprocessed into various forms ofreinforcements for use in moldingFRP/Composites.

Continuous Strand RovingThis basic form of reinforcement issupplied as untwisted strandswound into a cylindrical packagefor further processing. Continuousroving is typically chopped forspray-up, preform or sheet moldingcompounds. In the continuous form,it is used in pultrusion andfilament-winding processes.

Woven Roving

Woven from continuous roving,this is a heavy, drapable fabricavailable in various widths, thicknessesand weights. Woven roving costs lessthan conventional woven fabric andis used to provide high strength in largestructural components such as tanksand boat hulls. Woven roving is usedprimarily in hand lay-up processing.

Woven Fabrics

Made from fiber yarns, wovenfabrics are of a finer texture thanwoven roving. They are available ina broad range of sizes and inweights from 21/2 to 18 oz./sq. yd.Various strength orientations arealso available.

Reinforcing Mat

Made from either continuousstrands laid down in a swirl patternor from chopped strands, reinforcingmat is held together with a resinousbinder or mechanically stitched.These mats are used for medium-strength FRP/Composites.Combination mat, consisting ofwoven roving and chopped strandmat bonded together, is used tosave time in hand lay-up operations.Hybrid mats of glass and carbon

and aramid fibers are also available forhigher-strength reinforced products.

Surfacing Mat

Surfacing mat or veil is a thin fibermat made of monofilament and isnot considered a reinforcingmaterial. Rather, its purpose is toprovide a good surface finishbecause of its effectiveness inblocking out the fiber pattern ofthe underlying mat or fabric.Surfacing mat is also used on the

inside layer of corrosion-resistantFRP/Composite products toproduce a smooth, resin-richsurface.

Chopped Fibers

Chopped strands or fibers areavailable in lengths from 1/8 to 2for blending with resins and

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They can be formulated for highresistance to acids, weak alkalies andorganic solvents. They are notrecommended for use with strongalkalis. Other formulations aredesigned for low or high-temperature processing, for roomtemperature or high-temperaturecure, or for flexible or rigid endproducts.

Vinylesters provide excellentresistance to water, organic solventsand alkalis, but less resistance toacids than polyesters. Vinylestersare stronger than polyesters andmore resilient than epoxies. Moldingconditions for vinylesters are similarto those for polyesters.

Epoxies are another family ofthermoset resins used in FRP/Composites. They have excellent

adhesion properties and are suitedfor service at higher temperatures some as high as 500oF. Epoxy-matrixFRP/Composites are processed by anyof the thermoset methods. Epoxiesare more expensive than polyesters,and cure times are longer, but theirextended range of properties canmake them the cost/performancechoice for critical applications.Epoxy/fiber structures have generallyhigher fatigue properties than polyesters.

Polyurethanes are a family of resinsthat offer very high toughness, highelongation, faster cure times andgood coupling to a variety ofreinforcements. Polyurethanes areeasily foamed in a controlled process toproduce a wide range of densities.

Additives are easily incorporatedinto resin systems to providepigmentation, flame retardance,weather resistance, superior surfacefinish, low shrinkage and otherdesirable properties.

Gel coats consisting of a specialresin formulation provide anextremely smooth next-to-moldsurface finish on FRP/Composites.

They are commonly applied inhand lay-up and spray-up processesto produce a tough, resilient,weather-resistant surface. Gel coats,which may be pigmented, are sprayedonto the mold before thereinforcement and resin areintroduced.

Other thermosetting resin systems,generally formulated with choppedstrand or milled fiber reinforcementfor compression or transfer

molding are:Phenolics-Good acid resistance,good fire/smoke, and thermalproperties.

Silicones -Highest heat resistance,low water absorption, excellentdielectric properties.

Melamines -Good heat resistance,high impact strength.

Diallyl phthalates -Good electricalinsulation, low water absorption.

Thermoplastic Resins

Thermoplastic polymers can softenand become viscous liquids whenheated for processing and thenbecome solid when cooled. Theprocess is reversible allowing areasonable level of process waste

and recycled material to be reusedwithout significant effect on theend product. Thermoplastic resinsallow for faster molding cycle timesbecause there is no chemicalreaction in the curing process.Parts may be formed as fast as heatcan be transferred into and out ofthe molding compound.

Polypropylene and polyethylene arethe most common thermoplasticresins used in FRP/Composites.They have excellent resistance to

acids and alkalies and have goodresistance to organic solvents. Theirrelatively low melting points allowfor rapid processing at lower cost.

Nylon and Acetal are highlyresistant to organic solvents andmay also be used where increasedmechanical properties are required.

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FRP/Composite simulator screens provide a stable close-tolerance spherical projectionsurface in military and commercial flight trainers


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The molding experience of thousandsof applications in the past fivedecades has enabled FRP/Composites polymer chemists todevelop a number of standardresin-reinforcement-additivecombinations that are used for most

production needs. Industryresearch teams also stand ready tocustom design new blends ofmaterials to provide the exact needsof new applications. Because mosthigh production-volume FRP/Composite parts are made bycompression molding, severalready-to-mold material forms havebeen developed to facilitate andspeed the molding process. Eachof these forms is designed to bestproduce a specific type of finishedproduct and provide a distinctive set ofproperty and appearance features.

Liquid Composite Molding (LCM)

A fiber preform of the part is producedby forming fibers and a resin binderin a controlled manner to the sameshape as the part to be molded.The combination is cured toprovide physical integrity duringhandling and molding operations.

Parts molded using LCM with

preforms are particularly suited forboxlike, deep-drawn shapes inFRP/Composite parts. The fibersstay in place during molding andalso ensure good wet-out of thematrix resin, which is added at thepress. The result is uniform propertiesin the plane of the part walls becausethere is no flow of reinforcementduring molding. The fiber contentof preform-molded parts can becontrolled from 15 percent to a

maximum of approximately 50 percentby weight. Fiber lengths vary from1/2 to 3.

Fiberglass preforms are produced by robotically choppingglass fibers and resin emulsion on to a metal screen thesame size and shape as the part to be molded.

Another form of reinforcementused with LCM as well as mostother molding processes is calledmat. This material is a randomdistribution of fibers in roll orsheet form. Its use is limited toparts that are relatively flat, havecurvature in only one plane, or havea slight compound curvature.

FRP/Composite Compound FormsA few ready-to-mold compoundforms have been developed to supportthe highest volume productionwhile maintaining good mechanicalproperties in complicated parts.Of these, sheet molding and bulkmolding compounds (SMC/BMC)are based on thermoset resins whilethermoplastic resins are used inglass mat thermoplastic and longfiber-reinforced thermoplastic

(GMT/LFTP).

Sheet Molding Compound (SMC)

SMC contains long glass fibers (1to 2) dispersed in a resin matrix.The fiber arrangement can bedirectional, random, or a combinationof both. SMC is manufactured in ahighly automated, continuous flowprocess. The compound takes theform of a flexible, leather-like sheetthat is easily cut, weighed and placed inthe mold for curing to the desired

part configuration.

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A continuous process creates a sandwich of glass and resin paste between sheets of film in SMC production.

Standard SMC contains up to 35percent of randomly oriented fibersby weight. Because there is nomixing or extruding involved inpreparing sheet molding compound, thefibers remain undamaged and at their

original lengths. This plus the higherfiber loading provides very goodmechanical properties in compres-sion-molded SMC parts, especiallythose having relatively thin crosssections.

FRP/Composite parts molded fromSMC are characterized by high strength,very smooth surfaces and excellent detailin complex shapes. However, becauseSMC flows in the mold, fiber orientationand properties can vary throughout apart, particularly in deep-drawn shapes.

Several variations of SMC are available.One contains 8 to 12 unidirectionalfibers and another contains continuousunidirectional fibers. Other versions havehigher fiber contents of up to 65 percentby weight and are used for structuralapplications.

Bulk Molding Compound (BMC)

BMC is a mixture of short (1/8 to1/2 in.) fibers with resin containingfiller, a catalyst, pigment and otheradditives required by the application.

The premixed material, having theconsistency of modeling clay, isusually extruded into rope or logshapes for easy handling.

The strength of BMC-molded FRP/Composite is lowest of those madefrom ready-to-mold forms becausethe mixing operation degrades thefibers and the fiber content is lowest.In addition, properties are subject tofiber orientation because the compoundmust flow to fill the mold. However,

BMC is economical and satisfies awide variety of high-volume,compression-molded parts requiringfine finish, dimensional stability,complex features, and moderateoverall mechanical properties.

Compression-Molded ReinforcedThermoplastic

Reinforced thermoplastics can becompression molded into many partsusing processes similar to those forSMC and BMC. There are twomaterial forms available for such molding.

Glass Mat Thermoplastic (GMT) is a

fiberglass reinforced sheet that hasbeen available for many years. It istypically 30% 50% glass fiber in apolypropylene matrix. When heatedabove its melting point, GMT can becompression molded very similar toSMC.

Long Fiber-reinforced Thermoplastic(LFTP) is a process that has morerecently been commercialized. Thisprocess uses a special thermoplasticextruder to compound thermoplasticpellets with long fibers of up to 2inches. The melted resin/fiber material isejected from the extruder as a charge thatis immediately compression molded,very similar to BMC.

The properties of these moldingsvary depending on the fiber fractionand type of thermoplastic used.Typically such materials are lowerweight and have high impact resistance,but have lower modulus and lower

heat resistance than those usingthermoset resin.

The most common thermoplasticresins are polypropylene andpolyethylene; however, engineeringplastics such as thermoplasticpolyesters or nylon can be used toachieve higher properties.

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Matched Die MoldingMatched die molding methodsproduce highly consistent, net-shapeand near-net shape parts with twofinished surfaces and low labor cost.These methods include compression;low pressure, low temperaturecompression; transfer compression;resin transfer, injection; andstructural reaction injection molding.

Compression Molding

Compression molding is the primarychoice for most high-volume FRP/Composite parts made from BMC,SMC, Liquid Composite (preform),GMT, or LFTP. The high-pressuremolding process produces high-strength, complex parts in a widevariety of sizes. Matched metal moldsare mounted in a hydraulic ormechanical molding press. The materialcharge is placed in the open mold.The heated mold halves are closed,and pressure is applied. Molding

time, depending on part size andthickness, ranges from about one tofive minutes. Inserts and attachmentscan be molded in.

Compression-molded FRP/Composites are characterizedby net size and shape, two excellent

esponding to the requirementsof a demanding marketplace, the FRP/Compositeindustry is ever on the move

developing new resin systems, newtypes of reinforcements, and newcombinations of these materials.And in keeping with theseadvancements, processes continueto be improved, refined and furtherautomated to provide better outputwhile reducing handling time andcosts. Todays presses feature ever-closer control of processing times,temperatures and pressures, as wellas part dimensions. Overall part sizecapability continues to increase,permitting the commonplace

production of sizes and weights ofFRP/Composites not possible just afew years ago.

In addition to the wide variety ofmaterial combinations, there aremany choices available for processingFRP/Composite products. Thesechoices provide for even greaterflexibility in optimizing the shape,

properties and production cost ofFRP/Composite components.Matched die molding, contact moldingand more specialized molding methodsrepresent the top-level choices. Thedesigner is encouraged to collaboratewith a molder and/or materialsupplier to optimize the application.

finished surfaces, and outstandingpart to part repeatability. Trimmingand finishing costs are minimal.

Low Pressure-Low TemperatureCompression Molding

This method uses composite ornickel-shell molds that may not be

heated, but usually are constructed withcoils to heat or control mold temperature.

The molding process is an economicalcompression molding method formanufacturing intermediate volumesof parts using a low-pressure cureand inexpensive molds.

Preform or mat reinforcement isplaced on the lower mold half anda resin/filler mixture is added.The mold is closed under moderate

pressure of 20 to 200 psi, and theFRP/Composite part cures. This issuited mainly for relatively simpleshapes, without ribs or bosses.

Transfer Compression Molding

This process is characterized bymolding operations using a transfercylinder that is usually built into thetool. The material charge made ofresin, reinforcement and additives ismoved to the transfer cylinder and

subsequently forced into the closedmold cavity or cavities by thetransfer piston. It is best suited forvery thick parts, like transformerbobbins, and is very effective formultiple-cavity molds.

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Resin Transfer Molding (RTM)

Suitable for medium-volume productionof rather large FRP/Compositecomponents, resin transfer molding isusually considered an intermediateprocess between the relatively slowspray-up with lower tooling costs andthe faster compression-moldingmethods, which require higher toolingcosts. RTM parts, like compression-molded parts, have two finishedsurfaces, but molded parts requiresecondary trimming. Gel coats maybe used to provide a high-quality,

durable finish. Reinforcement mat orwoven roving is placed in the mold,which is then closed and clamped.Catalyzed, low-viscosity resin ispumped in under pressure, displacingthe air and venting it at the edges,until the mold is filled. Molds forthis low-pressure system areusually made from FRP/Compositesor nickel-shell faced FRP/Composite construction.

Injection Molding

Reinforced thermoset moldingcompounds can be injection

durability. For structural applications,however, the low temperature andpressure characteristics of SRIM makelarge structural shapes practical.

Contact Molding Methods

Contact, or open mold methodsprovide a lower tooling cost whenonly one finished surface is required.These methods also allow for a

shorter product development cyclebecause of the simplified toolingfabrication process.

Hand Lay-Up

The simplest and oldest of thefabrication processes for FRP/Composites, hand lay-up, is used inlow-volume production of largecomponents such as boat hulls andassociated parts.

A pigmented gel coat is first sprayedonto the mold for a high-quality surface.When the gel coat has cured, glassreinforcing mat and/or wovenroving is placed on the mold, andthe catalyzed resin is poured,

brushed or sprayed on. Manualrolling then removes entrapped air,densifies the FRP/Composite andthoroughly wets the reinforcementwith the resin. Additional layers ofmat or woven roving and resin areadded for thickness. A catalyst oraccelerator initiates curing in theresin system, which hardens theFRP/Composite without external heat.

molded in similar equipmentcommonly used for thermoplasticresins. The principle difference liesin the temperatures maintained invarious areas of the system. Withthermoplastics, the injection screwand chamber are maintained at arelatively high temperature, and thedie is cooled so the molded part setsup. In contrast, for a thermoset

FRP/Composite, the screw andchamber are cooled so the resindoes not cross-link and gel, and thedie is heated so it does cross-linkand cure. Injection molding offershigh-speed production and lowdirect labor costs. Combined withthe excellent mechanical propertiesavailable from a long-fibered BMC,the result is a capability for highvolumes of complex parts withproperties approaching those ofcompression or transfer molded parts.

Structural Reaction InjectionMolding (SRIM)

This method is suitable for medium-to-high volume FRP/Composite partsrequiring superior strength with no lossin toughness or flexibility. The SRIMprocess also produces parts with highimpact resistance and lower weight, andis excellent for larger part sizes.

Like injection molding, resin is

injected into a closed mold. However,the SRIM process utilizes a preform orreinforcing mat, which is placed intothe mold prior to closure, resulting ineven distribution of glass and uniformmechanical properties.

SRIM parts offer two finished surfaces,but the polyurethane systems typicallyused do not provide a good cosmeticsurface or a high level of dimensional

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Resin Forced into Mold Under Pressure


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relatively high glass content. Fibercontent is determined by fiberarchitecture and pressure. Thisprocess is environmentally friendlysince there is no resin exposure.

Autoclave Molding

Autoclave molding is a furthermodification of vacuum bag. Theprocess produces denser, void-freeFRP/Composites because higherheat and pressure are used in thecure. Autoclaves are essentiallyheated pressure vessels (usuallyequipped with vacuum systems)

into which bagged lay-ups, on theirmolds, are cured at pressures of 50to 100 psig. Autoclaves are normallyused to process high-performancecomponents based on epoxy-resinsystems for aircraft and aerospaceapplications.

Other Significant Molding Methods

Filament Winding

Vacuum Bag Molding

Vacuum bag processing uses avacuum to eliminate entrapped airand excess resin from a lay-up formon either a male or female mold. Anon-adhering film (usually polyvinylalcohol or nylon) is placed over thelay-up and sealed at its edges. Avacuum is drawn on the bag formedby the film, and the FRP/Composite iscured, either at room temperatureor with moderate heat to speed theprocess. Compared to hand lay-up,the vacuum method provides higher

reinforcement concentration andbetter adhesion betweenreinforcement layers.

Vacuum Infusion Molding

The infusion process differs fromvacuum bag molding in that all thereinforcements are placed in themold dry, often combined with cores orother special inserts. Vacuum is thenapplied to compact the reinforcementand eliminate air. Resin is introducedwith the vacuum drawing the resin

throughout the reinforcement.Very large parts can be made by thismethod although it requires a verylow viscosity resin and a relativelylong fill time as well as bleeder filmand other venting.The resin infusion process results invery low void content and excellentmechanical properties due to the

Spray-Up

Similar to hand lay-up in simplicity,spray-up offers greater shape complexityand faster production. It too uses alow-cost open mold (one finished partsurface), room temperature curingresin, and is suited for producing

large FRP/Composite parts such astub/shower units and vent hoods inlow to moderate quantities. Cure isusually at room temperature, butcan be accelerated by application ofmoderate heat.

Chopped fiber reinforcement andcatalyzed resin are deposited in themold from a combination chopper/spray gun. As with lay-up, manualrolling removes entrapped air and wetsthe fiber reinforcement. Woven

roving is often added in specific areasfor thickness or greater strength.Pigmented gel coats can be used toproduce a smooth, colorful surface.

Flexible Film

Edge Bleeder

Seal

Vacuum

Heat Source

Laminate

Mold

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Hand lay-up offers low-cost tooling,simple processing and a wide range ofpart size potential. Design changes aremade easily. Parts have one finishedsurface and require secondary trimming.

Insulated Shell

Air Distribution Shroud Heating Elements

QuickOpeningDoor

Bagged Composites

on Molds CirculatingAir Fan

Resin Trough

(Wet Method)

Mandrel


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CutoffSaw

Pull RollsHeated

Steel DiesFluorocarbonForming Block

Roving/Mat/

SurfaceVeil

Resin TankFinishing Pultrusion

Continuous, resin-impregnatedfibers or roving are wound on arotating mandrel in a predeterminedpattern, providing maximumcontrol over fiber placement anduniformity of structure. In the wetmethod, the fiber picks up thelow-viscosity resin either by passingthrough a trough or from a meteredapplication system. In the dry

method, the reinforcement isimpregnated with resin prior to winding.

Integral fittings and vessel closingscan be wound into the structure.When sufficient layers have beenapplied, the FRP/Composite iscured on the mandrel and themandrel is removed.

Filament winding is traditionallyused to produce cylindrical andspherical FRP/Composite products

such as chemical and fuel storagetanks and pipe, pressure vessels androcket motor cases. However, thetechnology has been expanded, andwith computer-controlled windingmachines, other shapes are nowbeing made. Examples are helicoptertail booms and rotor blades, windturbine blades and aircraft engine cowls.

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Pultrusion

Constant section-reinforced FRP/Composite shapes, such as structuralI-beams, channels, solid rod, pipe,and ladder rails are produced incontinuous lengths by pultrusion.The reinforcement, consisting of acombination of roving, mat, clothand surfacing veil, is pulled througha resin bath to wet-out the fibers,then drawn through a formingblock that sets the shape of the

composite and removes excessresin, and through a heated steel dieto cure the resin. The finishedshape is cut to lengths by a travelingcutoff saw.

Very high strengths are possible inpultruded shapes because of highfiber content (to 75 percent) andorientation parallel to the length ofthe FRP/Composite shape.Pultrusion is easily automated, andthere is no practical limit to productlength manufactured by the process.

Continuous laminating

Sheet FRP products, such as clearor translucent glazing panels, flatand corrugated construction panelsand electrical insulation panels, aremade by a continuous laminatingprocess. Chopped rovings, reinforcingmat and fabric are combined with

resin and sandwiched between twocarrier film sheets. The materialthen passes between steel rollers toeliminate entrapped air and to establishfinished laminate thickness, thenthrough a heated zone to cure theresin. Wall thickness can be closelycontrolled.

A wide variety of surface finishesand textures can be applied, and

panel length is unlimited. Corrugationsare produced by molds or by rollersjust prior to the curing stage.

Technical drawings reprinted from Machine Design, October 22, 1987. Copyright, 1987, by Penton Publishing Inc., Cleveland, OH.

Precision robotic waterjet cutting is usedto ensure part to part trimming accuracy.

Strong, lightweight FRP/Composite domes use self-supporting sandwich construction to protect sensitiveelectronic equipment from the Sahara to Antactica whileremaining transparent to the electromagnetic signals.


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iber reinforced plastics can beformulated to withstand avariety of service environmentsand to satisfy many specific

end-use requirements. These can

include a broad service temperaturerange, electrical insulation properties,corrosion resistance, abrasion resistanceand flammability. Many applicationsrequire considerable strength tensile, flexural, compressive orimpact. Surface finishes can behighly refined or they may be textured.In many cases, color can be moldedin. Parts can be large or small,simple or complex. Because of theversatility of FRP/Composites andthe many material and process

choices, the designer is encouragedto collaborate with a molder and/or material supplier to optimize thedesign process and its end product.

Consideration of many of theserequirements leads to the choice ofreinforcement, resin system andprocessing method. These decisionsare governed by the three basicprinciples of designing with FRP/Composites:

Mechanical strength depends onthe amount and arrangement ofthe glass fiber reinforcement.

Chemical, electrical and thermalperformance depend on theformulation of the resin system.

Molding process is determined byproduction requirements, and size,shape and complexity of parts.

Now, in addition to these factors, afourth principle must be considered:

Total value received results fromgood design based on judiciousselection of materials and process.

The following section provides astep-by-step method for optimizing

cost/performance in FRP/Compositemolded parts.

The design process starts withdetermining the functionalrequirements of the component

or assembly being designed.These considerations include:

MechanicalProperties

Tensile, compressiveand flexural strength;

elongation andimpact resistance.

PhysicalProperties

Hardness and density;dielectric strength;volume resistivity andarc resistance; thermal

conductivity, heat distortionand heat resistance;

flammability and thermalexpansion coefficient.

17

ChemicalProperties

Resistance to acids,alkalies and

organic solvents;water absorption;resistance to ozone,

ultraviolet radiationand weathering.

Fitness forService

Surface quality andcosmetic appearance;dimensional stability,

fabrication and end-usetolerancing, and

compatibility with othermaterials.

Other function-related requirementsmay involve machinability, abrasionresistance and properties needed tomeet Underwriters Laboratory,National Sanitary Foundationstandards or other code authority.

The next step in the design processis to establish cost targets. Evaluation ofthe economics of a specific applicationrequires a systems approach so theFRP/Composite component(s) isviewed in the context of its totalcontribution to the end use. This,of course, broadens the design processbeyond a simple comparison of materialcosts between FRP/Composites and


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The purpose of initial sketches isto help design engineers focus theirbasic concepts and to make theseconcepts consistent with end-userequirements. Keeping in mind thebasic attributes of FRP/Compositematerials and processes help avoidproducing a direct copy of a part asit might be designed to suit thecharacteristics of metals or ofunreinforced plastics. This isespecially important if the othermaterials are highly cost-competitive

and where the savings of a fewounces of material per part can addup to a significant amount over alarge production run.

The designer must decide on anapproach that will produce a partsufficiently strong to meet mechanicalrequirements, with the chemical,thermal and electrical properties, aswell as appearance qualities to meetspecifications. Initial sketches arenecessary to perform stress analysis

and start the detail empirical design.High-performance FRP/Compositeproducts usually result fromeffective use of both disciplines,validated with laboratory testing.

Stress analysis involves usingengineering equations for calculatingstresses at critical areas, resulting inthe determination of optimumconfiguration and minimum partthickness for those areas. Such

other candidates. Such considerationsshould include at least these items:

Tooling cost, including peripheralequipment such as cooling fixtures,machining fixtures andassembly tools.Process capabilities compared withgeneral fabrication and end-usetolerancing. Tolerances outsideof normal process capabilities

add cost premium. Secondary operations, such as

machining and assembling. Finishing cost, such as trimming,

sanding, polishing, platingand painting.

Other cost-producing operationsthat require studying and comparinginclude packaging, storing, qualitycontrol, inventory control andshipping. Such a thorough economicevaluation of the proposed FRP/

Composite application providesthree valuable benefits: First, it presents a true picture

of the total systems cost, makingsubsequent design decisionsmore cost effective.

Second, it reveals other cost-savingsareas (such as parts consolidation)that may not have been obviousinitially savings that can bedesigned into the product.

And third, it enables the designer todetermine exactly how much

performance is worth buying,in keeping with present orprojected selling prices andother market considerations.

With functional and economicrequirements established, the designercan now proceed to this most criticalstage of the FRP/Composite design

design may have had only one ortwo of these basics as its objective,opportunities to reduce cost andimprove product performance inother areas are often brought tolight by considering them allonce again.

process. The designer who understandsthe wide range of material and processoptions will use this step to add agreat deal of value to the end product.Coincidentally, good choices herewill also minimize project risk andcost during the development andproduction cycles. The unique synergyof the FRP/Composite part design,materials and molding methods atthis point will effectively define the

product economics and performanceover the long term.

Partnering with a molder and materialsuppliers throughout the designprocess will reward the project engineerregardless of his or her experiencelevel, but this step may represent thesingle most significant opportunity foroptimizing performance and cost.

In many cases, material and processinvolve a single selection. Forexample, if sheet molding compound is

chosen as the most suitable material,compression molding is the logicalprocess. In some cases, however,two or more processes are available,even though definite reinforcementand resin selections have beenmade. For instance, polyester bulkmolding compound can be eithercompression or injection molded.In such a situation, other factors,such as part configuration, fabricationand end-use tolerances, and productionvolume, may determine theoptimum process.

In all cases, cost/performanceevaluation should be the decidingfactor. Cost of materials, toolingand labor must all be consideredand measured against performance.And each candidate productionmethod must be considered todetermine the best choice.

Finally, the basic advantages offeredby FRP/Composites should bereviewed. Although the initial

18


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the most efficient production flowconcepts will form the basis fornear- and long-term economic benefitsduring the production life cycle.

As detailed drawings are completed,a final economic analysis should beprepared to confirm the preliminaryeconomic study, to calculate investmentand return on investment, and toestablish the total delivered cost ofthe FRP/Composite component.

A mock-up or simulation may behelpful to establish the technicalfeasibility of the initial design concept.This need not be an exact prototype ordetailed replica of the part to bemolded. An approximation can aidvisualization of the finished FRP/Composite part and its relationshipto parts associated with it in thefinal product. In addition, a mock-uphelps visualize possible problemsinvolving tooling, assembly, inspectionor handling. Correcting such problemsat this stage is much less expensivethan later in the production program.

A working prototype one that closely

duplicates the expected final designin configuration and performance isthe next step. The best FRP/Composite prototype is one producedfrom partially completed productionmolds because it will be almostidentical to a production part. Thismay be facilitated with the help ofmolders that are skilled in low-volumeFRP/Composite processes that are

studies are often performed usingfinite element analysis methods andspecial computer programs thateliminate the tedious manualcalculations. This design approach isused for FRP parts where performancerequirements are severe and wherematerial cost considerations arecritical. Empirical design is basedon the designers familiarity with

FRP/Composite materials andprocesses in related applications.Assumptions are made concerningpart thickness, surface finish andother features and characteristics,based on past experience with similarparts plus all additional availableinformation. A preliminary costestimate is usually made to determinewhether the design approach meetsall production requirements.

In committing the design toproduction drawings, many detailsmust be considered and resolved.As elsewhere in the design effort,consulting with a reliable custommolder at this point is a wise movefor advice concerning designdetails, such as radii, holes, inserts,ribs, bosses, as well as for guidanceon surface finish, molded-in color,reduced stress concentration, andother features and refinements.

This is also a critical point to considercurrent design and manufacturingmethods such as:

Design for Six SigmaDesign for ManufacturabilityLean Manufacturing

Collaboration with a custom molder tooptimize tolerances for cost andperformance and to help develop

particularly suited for producingprototype parts economically.

The easiest prototypes to fabricateare those for applications involvingcontact molding processes.Such prototypes are readily checkedagainst performance and dimensionalrequirements. They are thenadapted, or the mold is modifiedand another prototype molded.

The mold or the processingtechnique is adjusted until asatisfactory part is produced.

Through molding and testing a seriesof prototypes and gradually refining thedesign, the final configuration anddimensions are established. Theprocess produces an FRP/Compositepart that provides the requiredfunction and uses the minimummaterial commensurate with designobjectives of strength, dimensional

stability and surface finish.

As the prototypes undergo finalrefinements to meet design objectives,the tooling is completed and thedesign is ready for pilot production.Provisions for heating or coolingare added, and surface finishes areapplied to facilitate part release.Duplicate tools may be built if

production volume dictates.During tool tryout runs, it isimportant to control closely thevariables of temperature, pressureand cycle times so the parts producedcan be evaluated in terms of end-useobjectives. Such control is alsonecessary to ensure reproducibilityof production run parts.

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ComparisonsHow Reinforcing Systems Compare in Compression-Molded FRP Parts

Best for uniform wall componentswith deep-drawn shapes. Parts can be

several feet long or in diameter.

Best for complex configurations.Bosses and ribs are easily formed

because the compound flows duringmolding. Parts can be several feet

long or wide.

Best for moderate-sized (1-2),bulky, thick-walled parts with

complex configurations such asribs and bosses.

Part

Complexity,

Wall

Thickness

Highest strength of the resin/fiber

systems. Reinforcing fibers do notflow during molding but maintain

their random orientation. Propertiesare isotropic in plane of part walls.

Moderate strength, which can be

increased with higher glass content toas much as 65 percent for structural

parts. Nonuniformity of propertiesis a function of composite flow

during molding.

Least strong of the choices;

relatively poor strengthuniformity because reinforcing

fibers become oriented duringmolding as the material flows.

Strength

Glass pattern can be minimized with

use of fillers such as calciumcarbonate and surfacing veils (to

provide resin richness at the surface).Class A automotive surfaces can be

achieved with no long-term waviness.

Very smooth surfaces are possible,

requiring minimal secondaryoperations to produce Class A

automotive-type finishes.However, large parts often have

long-term waviness.

Very smooth surfaces are

possible, similar to thoseof SMC parts, but usually

with a higher degree oflong-term waviness.

Surface Finish

Typically molded at 200 - 500 psi,

lower cost tools acceptable, usuallyrequires more work than SMC to trim

flash and finish parting line. Can bein-mold coated.

Requires up to 1000 psi for molding,

excellent quality tooling and pressesrequired, in-mold coating possible,

minimal flash and part line finishingnecessary.

Requires 800 to 1500 psi, high

quality tooling essential, can beinjection molded, minimal flash

and part l ine finishing necessary.

Molding

Characteristics

Good process for medium to very

large parts; excellent application forlarge vertical walls and deep draws.

Good application for medium to large

parts; part size limited by availablemolding pressure. Not recommended

for deep drawn parts.

Small but heavy parts; not

well-suited for deep drawn parts.Part Size

Deep tub or boxlike shapes such ashousings for industrial electrical

equipment; large, smooth componentssuch as automobile hoods and truck roofs.

Complex ribbed parts such asautomobile front-end panels,

business-machine housing,instrument bases.

Blocky electrical insulators,under-hood automotive

components.

TypicalApplications

Characteristicor Property

Preform SMC BMC

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Design Details

Compression Molding

PreformMolding

SheetMolding

Compound

ResinTransferMolding

Cold PressMolding

BulkMolding

Compound

Spray-Up& HandLay-Up

Minimum InsideRadius, in.

Molded-in holes

Trimmed-In Mold

Core Pull & Sides

Undercuts

Minimum Recommended

Draft (no in-mold coating )

Minimum PracticalThickness, in.

Normal ThicknessVariation, in.

Maximum ThicknessBuild-Up, Heavy Build-Upand Increased Cycle

Corrugated Sections

Metal Inserts

Bosses

Ribs

Molded-In Labels

Maximum PracticalThickness, in.

Raised Numbers

Finished Surfaces(Reproduces Mold Surface)

* Parallel or perpendicular to ram action only. *** Can be 0.060 in. if glass content is less than 20 percent.** With slides in tooling or split mold.

21

Minimum Recommended

Draft (in-mold coating )

1/81/16

1/161/4

1/41/4

yes* yes* yes* no no no

yes yes yes no no no

no yes yes no no no

no yes yes** yes** no yes**

1/4 in. to 6 in. depth: 2 o to 3 o 2o 2o 1o

6 in. depth and over: 3 o or as required 3o 3o

4oor as required not applicable

0.045 0.080 0.060 0.080*** 0.080 0.060

1/41/2 1

1/21/2 no limit

0.010 0.010 0.010 0.020 0.020 0.030

2-to-1 as as 2-to-1 2-to-1 asmax. required required max. max. required

yes yes yes yes yes yes

yes yes no no yes

no yes yes yes

yes yes yes



two two two two two one

not

recommended

not

recommended

not

recommended

not

recommended

not

recommended

not

recommended

4o or as required not applicable


24/28


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Unreinforced

Thermoplastics

ABS

1.05

0.036

6.0

0.30

5.0

11.0

0.32

10.0

4.4R107-115

HB

Acetal

1.42

0.050

8.8

0.41

40.0

13.0

0.40

16.0

1.3M78-80

HB

Nylon6

1.14

0.041

11.8

0.38

38.0

15.7

0.40

13.0

1.0

R119

HB

Nylon6/6

1.13

0.041

11.8

0.40

60.0

17.0

0.41

15.0

0.9

R120

V-2

Polycarbonate

1.14

0.041

9.0

0.34

110.0

13.5

0.33

12.5

12.0

M70

V-2

Polyester(PBT)

1.31

0.047

8.5

0.28

50.0

12.0

0.34

8.6

1.2M68-78

HB

Polyester(PET)

1.34

0.048

8.5

0.40

50.0

14.0

0.40

11.0

0.7M94-101

HB

Polyphenyleneether(PPO)

1.06

0.038

9.5

0.38

50.0

12.8

0.36

12.0

5.0

R115

V-1

Polyphenylenesulfide

1.30

0.047

9.5

0.48

1.0

14.0

0.55

16.0

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