copyright joseph greene 20011 manufacturing methods for composites professor joe greene csu, chico

Copyright Joseph Greene 2001 1

Manufacturing Methods for Composites

Professor Joe Greene

CSU, CHICO


Objectives • Identify the major manufacturing methods for composites • Discuss the advantages and disadvantages of each• Contrast and compare methods for thermoplastic and thermoset

composites• Identify areas of work for improvements in manufacturing

methods


Overview • Manual lay-up

– Wet and – Prepreg

• Vacuum Bagging• Autoclave curing• Filament winding• Pultrusion• Matched-Die Molding

– SMC and BMC– Preform molding– SRIM and RTM

• Spray-up• Thermoplastic Composite molding


Manual lay-up• Manual lay-up

– Simplest technique and is called lay-up molding, wet lay-up, laminating

– Fabric or mat is saturated with a liquid resin and the lay-up is made by building layer upon layer to obtain the desired thickness

• Prepreg– Wet the reinforcement with resin and partially cure the resin– Careful control is taken to insure desired rein/fiber ratio

• Both methods have the layers placed onto a shaped surface (mold) by hand.– Pressure in normally applied by hand rolling, wiping with a squeegee,

or using vacuum bagging to remove trapped air and provide better uniformity.

– Part is cured at room temperature or at elevated temperature with heat gun or in an autoclave or oven


Manual lay-up• Wet lay-up– Oldest method, though rarely used today because of difficulty in handling

wet sheet of reinforcement and high labor costs.

– Mold release is added to prevent resin from sticking to the mold• Wax, PVOH, silicone, fluorocarbon, or plastic film

– Gel coat is added to the mold so that the fibers can be hidden on painted part.• Gel coat is a layer of catalyzed resin that is applied to the release coated mold and

allowed to cure before composite lay-up

• Gel coats improve flexibility, blister resistance, strain resistance, weatherability, and toughness.

– Surface veil glass is added to the composite lay-up on the top and bottom layers to provide better surface finish and hide the glass fiber read through.

– Vacuum bagging is used to remove the voids in the part.

– Parts are removed manually from the mold with the help of flat plastic, wooden, or metal wedges


Manual lay-up• Molds for wet-layup– Molds can be made of any materials though usually composite materials (epoxy

or polyester with glass fiber)or aluminum or steel. • The choice depends upon the maximum number of parts desired.

– The parts can be made from one side of the mold, either the outside of the part (female mold) or the inside of the part (male mold). The side of the part that you want the best finish decides whether you use the male or female maold.

• For bathtubs you want the best surface finish on the inside of the part so you use a male mold.

• For Boats, you want the best surface finish on the outside of the part so you use a female mold.

• Curing of wet lay-up– Typically done at room temperature with the use of a promoter to speed up the

reaction.– Never mix the promoter with the catalyst together at the same time

• Mix the catalyst in the resin, then the promoter in the resin.


Manual lay-up• Prepreg method– Prepreg method is an extension of the wet lay-up method.

• Pre-wetting outside of the mold and then laying-up the composite.

– Fibers are arranged in a unidirectional tape or a woven fabric and are impregnated with initiated resin (partially cured), rolled for shipment

– Prepreg method is more precise than wet lay-up method– Requires vacuum bagging and autoclaving for heat and pressure.– Dimensions

• Prepreg is supplied in rolls of widths from 3” to 72 “ (usually 12” to 24”)• Cut to fit mold and layed-up layer by layer until desired thickness is achieved.

– Prepregs have limited shelf life due to partially cured resin.• Usually several days to weeks at room temperature.

– For unidirectionl prepreg, the strength in the cross-fiber direction is essentially the strength of the resin alone.

• To achieve strength in all directions, the prepreg layers are oriented in different directions, e.g., 0° (fiber direction), 90°, +45°,-45°,-45°,+45°,90°,0°

• Fiber ply direction lay-up should be symmetrical (same number top to bottom)


Manual lay-up• Advatages of Wet Lay-up– Tooling can consist of any material that will hold its shape under minimal

pressure.– Tooling can be changed easily for engineering changes.– Investment in pressure devices such as press, autoclave, or vacuum pump is not

required. The pump can improve the quality of parts.– Curing ovens are not needed

• Disadvantages of Wet Lay-up– Only addition-type cross-linking resin can be used, because condensation

polymerization can cause bubbles and voids in part, which requires pressure.– Product is nonuniform and voids are common– Mechanical properties are low in comparison to other methods– Tight weave fabrics are difficult to saturate with high viscosity resins– Resin rich areas are common causing fracture points and shrinkage.– Only one finished surface


Manual lay-up• Advatages of Pre-preg Method

– Resin/initiator (hardener) ratio is more accurately controlled.

– Resin distribution is more controlled resulting in more uniform part.

– Fewer health and safety concerns due to lack of liquid resin

– Automation can improve output.

– Higher fiber content, better part definition, and better consolidation

• Disadvantages of Pre-preg Method– Methods are slow and labor intensive compared to automated

methods

– High reject rate because of faulty bagging procedures.

– Difficult to bag complex shapes

– Curing equipment (autoclaves) are expensive

– Inside surfaces are not satisfactory as in matched-die molding.


Manufacture of Lay-up Materials • Manufacture of Prepreg Materials

– Solvent impregnation: • Fiber bobbins are placed on a pay-off device such as creel, • Fibers are collimated into a ribbon• Ribbon is passed through a resin/solvent bath.• Resin/fiber is squeezed through nip rollers for proper ratio.• Resin/fibers are heated to remove solvent and cure resin.• Pre-preg is wound onto drum and stored at 0°F.

– Hot melt impregnation:• Resin is calendered (rubber mixing rollers) or cast into a film.• Collimated fibers are sent to hot rollers with hot resin applied to them.• Tape and resin are heated and pressed in rollers.• Roll is cooled and stored.

– Sizes• Prepreg are available in styles of fabric up to 72” (1.83 m) wide• Sizes range from 12 to 48” are most common• Sizes from 3, 6, or 12” are used in automated lamination

– Narrow tapes have tighter tolerances on width, longer defect free lengths, and lower and more repeatable tack.


Manufacture of Lay-up Materials • Manufacture of Prepreg Materials (ref: http://www.calitzler.com/cistyp.html)


Manufacture of Lay-up Materials • Manufacture of Prepreg Materials (ref: http://www.calitzler.com/cistyp.html)

• Companies (ref: http://www.compositesworld.com/sb/browse/488) » Aeroform Ltd.; Automated Dynamics

» Brenner International ; Composite Matrix Corporation» Diaphorm; Eurocarbon BV» Gerber Technology Inc.; Magnum Venus Products - M.V.P.» Mikrosam; Owens Corning

» Sutherland & Assoc. of Los Angeles

http://www.calitzler.com/cistyp.html


Manufacture of Automated Tape Lamination• Ref: http://claymore.engineer.gvsu.edu/eod/manufact/manufact-

257.html#pgfId-513476

• New machines and concepts can speed-up the lay-up process.• An overhead gantry moves a tape application head across the mold, and up

inclined faces to apply a prepreg tape, 3" width is typical.

• Cutting and trimming is done automatically.

• NC programs direct the tape layup, often in geodesic paths.

– Advantages• Time and labor savings

• More uniform parts due to more consistent lay-up pressures.

• Lower stresses in fibers during lay-down.

– Disadvantages• Cost to program the machine plus cost of the machine

• Presence of consistent gap between adjacent paths; Restricted to simple parts.

• Long production time for small parts.


Manufacture of Lay-up Materials

• Cutting of Uncured Composite Materials– Manual cutting of uncured composite parts has been a major method

for many years.• Utility knives, carbide disc cutters (pizza cutters), shears (powered or manual)

– Template is used to guide the cut on a soft urethane, rubber, plywood, or aluminum sheet that is placed on a hard cutting table.

– Multiple sheets can be cut at the same time to reduce costs and increasing consistency.

– Automated cutting can be used for high volume parts and more relatively simple (planar) parts.

• Ultrasonics, water jets (care is required not to wet the materials), die cutting, laser cutting

• Punch Presses


Vacuum Bagging

• Application of a vacuum to the resin helps eliminate residual materials/gas trapped in the uncured resin, e.g., air pockets, solvents, and low molecular weight resin components

http://claymore.engineer.gvsu.edu/eod/manufact/manufact-259.html#pgfId-513508


Vacuum Bagging• Procedure

– Coat the mold with mold release agent to allow the part to easily separate later.

– Remove prepreg materials from the freezer. Allow the materials to warm to room temperature to reduce condensation which can contaminate the polymer materials.

– Build up the prepreg layers of the part. Inserts, ribs, can be placed in mold.

– Put a layer of release film on the part. This allows resin to flow out under vacuum, and leaves a good bonding surface for subsequent composite layers.

– Add the bleeder layer. This layer will soak up excess resin. It is typically a mat of cotton, polyester felt, or fiberglass (with teflon coat), etc.

– Add a layer of barrier to prevent resin movement to the vacuum valve, but allow air movement. A resin trap should be used in the vacuum system if this step is omitted.

– Add a layer of breather material. This will act as a buffer between the wrinkles in the bag, and the part surface. It also allows better distribution of the vacuum.

– Apply a sealant around the edges of the part. This can be a foam tape.

– Put the vacuum bag over the part, and seal at the edges. A typical material is nylon. The vacuum is then applied, and possibly a curing oven is used to accelerate curing.

•


Autoclave• An oven that allows for high pressures to be used.

• Composites cure under heat and pressure provides a superior part because the voids are reduced due to the pressure.

• Process– The part is placed in the pressure vessel, and heated, pressure is applied

simultaneously.

– Vacuum bagging can be used in an autoclave.

– Thermoset composites are crosslinked.

– Thermoplastics are melted.

• Advantages– The pressure helps bond composite layers, and remove more voids in the matrix.

– Very large parts can be made with high fiber loadings.

– Properties are improved.

– Many different parts can be cured at the same time.

• Disadvantages– Autoclaves are expensive


Filament Winding

• Filament Winding Process Fig 5-1– For Round or Cylindrical parts

– A tape of resin impregnated fibers is wrapped over a rotating mandrel to form a part.

– These windings can be helical or hooped.

– There are also processes that use dry fibres with resin application later, or prepregs are used.

– Parts vary in size from 1" to 20‘

– Winding direction• Hoop/helical layers

• Layers of different material

– High strengths are possible due to winding designs in various direction

– Winding speeds are typically 100 m/min and Typical winding tensions are 0.1 to 0.5 kg.

Ref: http://www.eha-maschinenbau.de/


Filament Winding• Demolding

– To remove the mandrel, the ends of the parts are cut off when appropriate, or a collapsible mandrel (e.g., low melt temperature alloys ) is used.

– Curing in done in an Autoclave for thermoset resins (polyester, epoxy, phenolic, imide, silicone) and some thermoplastics (PEEK)

– Fibers are E-glass, S-glass, carbon fiber, and aramids (toughness and lightweight) – Inflatable mandrels can also be used to produce parts that are designed for high pressure

applications, or parts that need a liner, and they can be easily removed. • Advantages

– Good for wide variety of part sizes – Parts can be made with strength in several different directions – Very low scrap rate – Non-cyclindrical parts can be formed after winding – Flexible mandrels can be left in as tank liners– Reinforcement panels, and fittings can be inserted during winding – Due to high hoop stress, parts with high pressure ratings can be made

• Disadvantages – Viscosity and pot life of resin must be carefully chosen – NC programming can be difficult – Some shapes can't be made with filament winding – Factors such as filament tension must be controlled

Ref: http://www.eha-maschinenbau.de/


Laminating• EHA - Coating machines are used for the manufacture:

– paper and plastic coating – manufacture of flexible abrasives – slitting and cross-cutting of webs – application of glue – laminating – manufacture of PVC floors – special scopes of application in the field of coating technology

http://www.eha-maschinenbau.de/


Pultrusion

• Manufacturing– Fibers are brought together over

rollers, dipped in resin and drawn through a heated die. A continuous cross section composite part emerges on the other side.

Ref: http://claymore.engineer.gvsu.edu/eod/manufact/manufact-262.html#pgfId-513483

• Design (Fig 5-4)· Hollow parts can be made using a mandrel that extends out the exit side of the die.

· Variable cross section parts are possible using dies with sliding parts.

· Two main types of dies are used, fixed and floating. Fixed dies can generate large forces to wet fiber. Floating dies require an external power source to create the hydraulic forces in the resin. Multiple dies are used when curing is to be done by the heated dies.

· Very low scrap. Up to 95% utilization of materials (75% for lay-up).

· Rollers are used to ensure proper resin impregnation of the fiber.

· Material forms can also be used at the inlet to the die when materials such as mats, weaves, or stitched material is used.

· For curing, tunnel ovens can be used. After the part is formed and gelled in the die, it emerges, enters a tunnel oven where curing is completed.

· Another method is the process runs intermittently with sections emerging from the die, and the pull is stopped, split dies are brought up to the sections to cure it, they then retract, and the pull continues. (Typical lengths for curing are 6" to 24")

–


PultrusionRef: http://claymore.engineer.gvsu.edu/eod/manufact/manufact-262.html#pgfId-513483

• Materials – Most fibers are used (carbon, glass, aramids) and Resins must be fast curing because of process speeds.

(polyester and epoxy)

• Processing– speeds are 0.6 to 1 m/min; thickness are 1 to 76 mm; diameters are 25mm to 5m – double clamps, or belts/chains can be used to pull the part through. The best designs allow for continuous operation for production.– diamond or carbide saws are used to cut sections of the final part. The saw is designed to track the part as it moves.– these parts have good axial properties.

• Advantages– good material usage compared to lay-up – high throughput and higher resin contents are possible

• Disadvantages– part cross section should be uniform.– Fiber and resin might accumulate at the die opening, leading to increased friction causing jamming, and breakage.– when excess resin is used, part strength will decrease – void can result if the die does not conform well to the fibers being pulled – quick curing systems decrease strength

–


Matched Die Molding• Matched die molding involves molding of composites with two

sided molds. • Materials

– The molds are typically steel molds and

• Production rates– Used for high volume production (up to 1 million parts per year)

• Processes– SMC molding- compression molding with polyester and glass.– BMC molding- similar to SMC but with a lot of filler.– GMT molding- compression molding of thermoplastic PP and glass.– Preform molding- spray process of polyester with chopped glass.– SRIM molding- molding of liquid polyurethane resin and glass

preform. – RTM molding- molding of polyester resin and glass preform.


BMC Materials

• BMC- Bulk Molding Compound– Materials

• BMC is a combination of chopped glass strands with resin as a bulk prepreg.

• Unlike SMC, it is not necessary to have recourse to a maturation step, and consequently, BMC prepreg formulations contain higher filler contents.

• The reinforcements are essentially chopped glass strands of 6 or 12mm.

– The reinforcement content is generally between 10 and 20%.

– The filler is usually calcium carbonate with consequent economic benefit.

• The resins are polyester, vinyl ester, epoxy, urea, melamine, phenolic, or polyurethane

– Processing • BMC is suitable for either compression or injection molding.

– Design• Injection molding of BMC can produce complex components such as electrical

equipment, car components (headlamps), housings for electrical appliances and tools in large industrial volumes.


Sheet Molding Compound (SMC)• SMC is the paste that is compression molded

– 33% polyester resin and styrene, which polymerizes and crosslinks

– 33% glass fibers (1” fibers)

– 33% Calcium Carbonate


Sheet Molding Compound (SMC)• Materials

– Resins: polyester; Fibers: 0.5” to 1” E-glass; Filler: Calcium Carbonate– Body panel Class ‘A’ material- Phase epsilon from Ashland Company has less glass– Structural material- Has more glass fibers (up to 50%)– SMC Lite- Lower density SMC that has glass bubbles in it to lower density to 1.2 g/cc

• Processing – SMC is produced in paste form and made into a roll which is kept for 1 month to allow for viscosity and

molecular weight increases.– SMC is cut off the roll and cut into charges (2” x 8” strips typically)– SMC strips are placed in a hot mold at strategic locations (charge pattern) and then compression molded at

400F for 1 minute.– SMC molded parts typically have blisters and areas of defects at the edge of the parts that need to be

sanded

• Design– SMC Alliance

• Any information you may desire about SMC and BMC thermoset, crosslinking composite systems will be available from the Web site of the European Alliance for SMC.

http://www.smc-alliance.com/


Sheet Molding Compound (SMC)• Design http://www.smc-alliance.com/welcome/welcome.html


Sheet Molding Compound (SMC)• Design

Compression Molding Processes

Bulk Molding Sheet Molding Thick Molding SMC Random Fiber

SMC-Chop/Continuous

RTM with Preform

Bosses & Ribs Yes Yes Yes Yes No NoCosmetic Appearance Good Good Good Fair Fair Fair

Type of Part Casting Stamping Cast & Stamping Casting Casting StampingSize of Part Small Large Medium Large Large LargeTensile Strength (psi) 5,000 12,000 10,000 23,000 55,000 14,000Flexural Strength (psi) 15,000 26,000 22,000 37,000 85,000 28,000Specific Gravity 1.9 1.75 2 1.85 1.8 1.2

Comparison to SteelSheet Molded Compound

IM Thermoplastic Aluminum

Part Consolidation Excellent Excellent FairMass Reduction from steel 25% 30% 25%Corrosion Resistance Best Better GoodImpact Resistance Best Better PoorTooling Cost Reduction 60% 40% 0%Stiffness Ratio to steel 6% 2% 30%Thermal Expansion to steel 100-130% 600-1000% 170-200%

http://www.amalgacomposites.com/prod_cm.htm


Compression Molding Process• Materials

•Thermosets: Polyester, Vinyl ester, or Epoxy resins with glass fiber •Sheet Molding Compound (SMC), Bulk Molding Compound (BMC)

•Thermoplastics: Polypropylene, polyester, or others with glass fibers•Glass Mat Thermoplastic (GMT), thermoplastic BMC

•Elastomers: Thermoplastic or Thermoset rubbers•Thermoplastic Olefin (TPO), Thermoplastic Elastomer (TPE), Thermoplastic Rubber (TPR)•Thermoset Styrene Butidiene Rubber

Thermoplastic:Heat Plastic

prior to molding

Thermosets:Heat Mold

during molding


GMT Compression Molding• GMT: Glass Mat Thermoplastic• Materials

– Products: General Electric Company- Azdel– AZDEL Laminate, GMT

• Resin: thermoplastic polypropylene – 60% by weight• Glass: continuous glass mat- 40% by weight• Five layer composite of glass fiber and thermoplastic resin. • Usually compression molded in a process similar to SMC, this material may also be

thermoformed using several industry standard methods of production.• Typically used in more structural applications where surface finish is not an issue.• Typical applications include vehicle bumper beams, underbody shields, etc.• Available in three types of glass fiber mat: Chopped, Random & Uni-directional.

– AZDEL SuperLite®• A low pressure, thermoformable composite of polypropylene and long chopped fiber

combined with outer layers as needed for the application (i.e.; adhesive film, barrier film, tough PP film, non-woven, reinforcing, or just the bare surface.)

• A sheet product that is primarily thermoformed into shape.• Typically used in less demanding structural applications where a high stiffness-to-weight

ratio is required.• Typical applications include vehicle interior substrates (headliners, shelves, etc.)

http://www.azdel.com/Products.htm


AZDEL GMT Material Applications

• Azdel– AZDEL is a global leader in the manufacture and supply of high-performance

thermoplastic composite materials serving a wide variety of markets and industries including automotive, large truck, materials handling, HVAC, and building & construction.

– AZDEL is a joint venture company between GE Advanced Materials (PP plastic) and PPG, Inc.(glass-fiber technology)

– Products• Bumper beams, seat backs, instrument panels, interior parts, roof racks, A/C housings

http://www.azdel.com/Products.htm


Processing of Composites• Open Mold processes

– Lay-up on one-sided molds• Resin is added to fiber preform

– Pultrusion• Fiber are drawn through bath

before being pulled through a profile shape.

– Filament winding• Fibers are dipped in resin before

winding to shape

– Spray-up of glass and resin• Resin is sprayed like paint as the

fibers are chopped onto a screen with vacuum to form the part.

• Fiber-resin combination is heated for 5 to 10 minutes to cure and crosslink the resin.

• Part is removed from screen and then is trimmed of the flash.


Preform Molding: RTM and SRIM

• Closed mold processing– Place fiber preform inside two sided molds and inject resin onto fiber

preform, heat to cure resin, demold, and trim part of flash

• Materials– Resin: polyester, epoxy, polyurethane liquid thermoset resins

– Reinforcements: Continuous: glass, carbon fiber, kevlar; Discontinuous: chopped glass

• Processing– RTM: Resin Transfer Molding

– VARTM: Vacuum assisted RTM

– RIP: Resin infusion process

– SCRIMP: Seeman composites resin infusion process

– SRIM: Structural Resin Injection Molding


Resin Transfer Molding• In the RTM process, dry (i.e.,non-impregnated ) reinforcement

is pre-shaped and oriented into skeleton of the actual part known as the preform which is inserted into a matched die mold.

• The heated mold is closed and the liquid resin is injected• The part is cured in mold.• The mold is opened and part is removed from mold.

http://islnotes.cps.msu.edu/trp/liquid/rtm/intro.html


Polyurethane Processing• Polyurethane processed by

– Casting, painting, foaming• Iso and polyol are mixed under low

pressure and injected into open mold.

– Reaction Injection Molding (RIM)• Iso and polyol are mixed under high

pressure and flow into closed mold

RIM mixing RIM flow into mold

Foam machine


Processing of Composites• Open Mold processes

– Vacuum bag, pressure bag, SCRIMP– VARTM, Vacuum Assisted Resin Transfer Molding

– autoclave: Apply Vacuum Pressure and Heat in an oven which can be 5 feet to 300 feet long


VARTM

• Vacuum Assisted Resin Transfer Molding


Structural RIM• Fiber preform is placed into mold.• Polyol and Isocyanate liquids are injected into a closed mold

and reacted to form a urethane.


Injection MoldingGlass Reinforced Composites

• Plastic pellets with glass fibers are melted in screw, injected into a cold mold, and then ejected.

Glass filled resin pellets


Thermoset Reacting Polymers

• Process Window– Temperature and pressure must be set to produce chemical reaction

without excess flash (too low a viscosity), short shot (too high a viscosity), degradation (too much heat)


Tooling• Molds are cheaper than equivalent steel stamping dies• Materials

– Soft- polyester resin with glass mat (like the skateboard)• Low cost- typically $20,000 and 2 weeks for a bumper beam mold.• Low production runs of 20 to 200 parts depending upon the quality.

– Kirksite: Zn (94%) and Al (6%) cast alloy; machinable and weldable• Low cost- typically $40,000 and 6 weeks for a bumper beam mold.• Medium production runs of 500 to 2,000 parts depending upon the quality.

– Aluminum• Moderate cost- typically $80,000 and 6 weeks for a bumper beam mold.• Medium production runs of 5,000 to 20,000 parts depending upon the quality.

– Steel (typically P-20)• Moderate cost- typically $250,000 and 12 weeks for a bumper beam mold.• Medium production runs of 1 million parts depending upon the quality.

• Comparison to Steel stamping tooling of $1.5 Million and 24 weeks for bumper beams.

copyright joseph greene 20011 manufacturing methods for composites professor joe greene csu, chico

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