Lecture 9: Composite Manufacturing Techniques

What are some composite manufacturing methods?

-Spray up

-Resin Transfer Molding (RTM)

-Vacuum-assisted Resin Transfer Molding (VaRTM)

-Filament winding

-Automated tape laying

-Fiber placement

-Pultrusion

-Resin infusion

-Resin Film Infusion

What is spray up manufacturing technique?

-Spray gun applies reinforcements and resin

Spray up manufacturing technique advantages

-Cheap tooling and material

-Good for small to medium volume

Spray up manufacturing technique disadvantages

-Hard to control fiber volume fraction

-Lower structural performance

-Good surface finish only on one side

Fibers and resin used in SPray Up

Fibers: usually 10-40 mm glass fiber rovings and Kevlar

Resin: usually polyester and DCPD polyester

SPray up applications

-Used to make bathtubs, swimming pools, boat hulls

-Makes small and large parts in small to medium quantities

What is Resin Transfer molding (RTM) manufacturing technique

Composites made by injecting liquid resin under pressure into a closed mold filled with dry reinforcing fibers

Resin Transfer Molding advantages

-Good dimensional accuracy / surface finish

-high fiber volume

RTM Disadvantages

-Requires experimentation / flow simulation

-Tooling / equipment costs are higher then hand lay-- up

-Tool design is complex

RTM resin and fibers

Resin: Thermoset resin + catalyst, low viscosity and adequate pot life important

Reinforcement: Variety of them can be used

RTM Applications

-Automotive, aerospace, consumer goods (like helmets, doors, and bikes)

-Makes small to large parts in small to medium quantities

Vacuum assisted Resin Transfer Molding (VaRTM)

Uses vacuum pressure to pull resin into preform

RTM vs VaRTM: RTM

-Higher pressure

-Better control

-Higher fiber volume

-More expensive tooling

RTM vs VaRTM: VaRTM

-Vacuum pressure

-Cheaper tooling

-Large parts

-Lower fiber volume

-Lower viscosity (although both have low viscosity)

WHat is filament winding?

Continuous fibers are wound under tension around a rotating mandrel to produce bodies of revolution

What are the three main filament winding patterns?

Helical, polar and hoop

What are the advantages of filament winding?

-High-rate process

-Continuous fibers

-Controlled fiber orientation.

Disadvantages of filament winding?

-Cannot wind concave contours

-Fiber angle is limited by slippage

-Mandrel must be removable after curing.

What fibers and resins are used in filament winding?

Fibers: Glass, aramid, and carbon

Resins: Epoxy is most common, polyester and vinyl ester also used

Filament winding applications

Bodies of revolution: Cylinders, shafts, spheres

What is Automated Tape Laying (ATL)

A gantry-stye machine automatically lays wide, unidirectional composite tape to fabricate large, mostly flat parts.

What is the reinforcement form used for ATL?

Unidirectional tape

Advantages of ATL

-Can make large flat parts

-Can make parts with small contours

What is fiber placement?

A manufacturing method that combines features of filament winding and tape laying by placing individual fiber tows. Tows can be steered.

What are the advantages and important features of fiber placement?

-Allows true 0 degree plies

-Tows can be steered

-Little material is wasted

-Gaps / overlaps can be tightly controlled

What reinforcement is used in fiber placement?

Individual tows are used. Typical machines have 12, 24, or 32 tows, with tow widths of about 0.125 - 0.182 in

Applications of fiber placement

-Fuselage sections

-Pressure tanks

-Inlet ducts

What is pultrusion?

Fibers are continuously pulled through a resin bath and then a heated die, which controls the shape / resin content and cures the final profile

What are the advantages of pultrusion?

-Fast and economical

-Accurate resin control

-Aligned fibers

WHat are the limitations of pultrusion?

-Limited to constant or nearly constant cross sections

-Heated dies are expensive

What resins and reinforcements are used in pultrusion?

Resins: Epoxy, polyester, vinyl ester, phenolic

Reinforcement: Various reinforcements can be used

Pultrusion applications

-Beams

-Bridges

-Ladders

Resin infusion molding

A closed-mold process where vacuum draws liquid resin into a dry fiber laminate sealed beneath a rigid or flexible membrane

What are the advantages of resin infusion?

-Good resin properties

-Low void content

-Less dry areas

-Clean lay-up

What are disadvantages of Resin Infusion Molding?

-Not widely proven except for airplanes

-Expensive tooling

-Requires vacuum bagging

What is resin film infusion?

Dry fabrics laid with semi-solid resin films. Vacuum removes air, then heating melts the resin so it flows into the fiber and cures

What resin and reinforcement are used in resin film infusion?

Resin: Epoxy Resin

Reinforcement: Various

Resin film infusion applications

-Aircraft radomes

-Submarine sonar domes