resin transfer molding (rtm)

Resin Transfer Molding

KAMLESH JAKHAR

Introduction Resin transfer molding in which fiber preform or dry fiber reinforcement is packed

into a mold cavity that has the shape of the desired part and then supply the matrix material to form the product.

Resin transfer molding is a closed molding process.It is also knows as liquid transfer molding process.Molding unit has two halves namely upper half mold (core) and lower half

mold(cavity).In this technique, resin is transferred over the already placed reinforcement.

Raw MaterialsReinforcing materials:-

Glass fiber, carbon fiber, aramid fiber, natural plant fibers (sisal, banana, nettle, hemp, flax etc.)

- These fibers are used either individually or in combined form (hybrid) as a woven mat, unidirectional mat or copped strand mat.

- Minerals fillers may also be added to improve surface finish, Fire retardants, Accelerator, U V stabilizers, Release agent.

Matrix:-

Thermosets :- Epoxy resin, Methyl Methacrylate, polyester, polyvinyl

ester, phenolic resin, polyurethane resin, silicone, alkyd, thermoset

polyamides.

Thermoplastics :- Nylon, PP, PE, Styrene resin, Thermoplastic polyester,

fluoropolymer, Liquid crystal polymers and thermoplastic

elastomers.

Resin transfer molding procedure

• Reinforcement in terms of either woven mat or strand mat form is placed on the surface of lower half mold.

• A release gel is applied on the mold surface for easy removal of the composite.

• The mold is properly closed and the mold halves clamped together.

• The resin is pumped in by repeated stroking of the metering cylinders until a predetermined volume has been delivered into the mold.

• Air is displaced through other vents.

• The uniformity of resin flow can be enhanced by using a catalyst as an accelerator and vacuum application.

• After curing, the mold is opened and composite product is taken out.

Process

Process• There are two separate containers for resin and catalyst.

• Resin container is larger than the catalyst container.

• Both the containers have separate outlets which pass through pumping unit and opens in mixing chamber.

• Pumping unit transfers the resin and catalyst to the mixing chamber.

• Resin and catalyst is mixed thoroughly(properly) in the mixing chamber.

• Resin injector is used to inject the mixture to the mold cavity.

• Molding unit has two halves namely upper half mold and lower half mold.

• Heating arrangement is integrated with molding unit.

• Vents are provided to release the gases in the mold cavity during clamping.

• End of process the molding unit is open and eject the product.

ComponentsResin and catalyst containerPumping unitMixing chamberResin injectorMolding unit like lower halves and upper halves.

Controlling ParameterResin viscosityInjection timeInjection pressureTemperature in the mold

• The viscosity of the resin plays an important role in resin transfer molding process.

• Injection time depends upon viscosity of the resin.

• If viscosity of resin is high, high pressure is required which may cause displacement of fibers knows as fiber wash.

ApplicationComplex structure can be produced.Automotive body parts, big containers, bathtubs, helmet etc.Vehicle panels Boat hulls.Wind turbine blades.Aerospace parts.

Advantage• Good surface finish on both surface of the product.

• Fast cycle time can be achieved through temperature control device.

• Higher production rate is associated with process automation.

• The process does not require high injection pressure.

• Wide range of reinforcement.

• Process can be manual control, semi-automatic or highly automated.

• Ability to incorporate insert and other attachment into molding.

• Parts are easily painted.

• Composite part thickness is uniform which is determined by the mold cavity.

• Low capital investment.

Disadvantage

• Limited to smaller components.

• Tolling cost expansive.

• There is limitation on reinforcing materials due to the flow and resin saturation of fibers.

• Mold maintenance is high than compression tools.

• It is produce higher volume waste because of a large pad with sprues.