FIBER REIFORCED PLASTICS PROCESSING

Alakananda P MMary NeenuSumi M Nair

Vivek V Shenoy

IMPORTANT METHODS Hand Lay-up Spray up method Filament winding Match die molding Pultrusion Resin transfer molding Reaction injection molding

HAND LAYUP METHOD• Open mold shaping method in which

successive layers of resin and reinforcement are manually applied to an open mold.

• Labor-intensive • Finished molding must usually be trimmed

with a power saw to size outside edges.

• Advantages: • Low cost tools• Wide range of products• Good surface finish• Unlimited size

• Disadvantages: • Time consuming• Easy to form airbubbles and disorientation• Inconsistency• Low production rate

SPRAY UP METHOD• In this technique, a spray gun is used to

spray pressurized resin and reinforcement which is in the form of chopped fibers.

• The deposited materials are left to cure under standard atmospheric conditions.

• Advantages: – Continuous process – Any materials can be used as mold.– Error can be corrected by re-spraying.

• Disadvantages: – Slow.– inconsistency.– No control of fiber orientation.– Only one side finished.– Environmental unfriendly

PULTRUSION

• Continuous fiber rovings are dipped into a resin bath and pulled through a shaping die where the impregnated resin cures

• The sections produced are reinforced throughout their length by continuous fibers .

• Like extrusion, the pieces have a constant cross section, whose profile is determined by the shape of the die opening

• The cured product is cut into long straight sections .

ADVANTAGES• This can be a very fast, and therefore economic,

way of impregnating and curing materials.• Resin content can be accurately controlled.• Fibre cost is minimised since the majority is taken

from a creel.•   Structural properties of laminates can be very

good since the profiles have very straight fibres and high fibre volume fractions can be obtained.

• Resin impregnation area can be enclosed thus limiting volatile emissions.

DISADVANTAGES• Limited to constant or near constant cross-section

components•  Heated die costs can be high.

FILAMENT WINDING• Resin-impregnated continuous fibers are wrapped

around a rotating mandrel that has the internal shape of the desired FRP product; the resin is then cured and the mandrel removed

• The fiber rovings are pulled through a resin bath immediately before being wound in a helical pattern onto mandrel

• The operation is repeated to form additional layers, each having a criss-cross pattern with the previous, until the desired part thickness has obtained.

ADVANTAGES• This can be a very fast and therefore economic method of

laying material down.•  Resin content can be controlled by metering the resin onto

each fibre tow through nips or dies. • Fibre cost is minimised since there is no secondary process to

convert fibre into fabric prior to use.•  Structural properties of laminates can be very good since

straight fibres can be laid in a complex pattern to match the applied loads.

DISADVANTAGES• The process is limited to convex shaped components.•  Fibre cannot easily be laid exactly along the length of a

component.• Mandrel costs for large components can be high. • The external surface of the component is unmolded, and

therefore cosmetically unattractive.• Low viscosity resins usually need to be used with their

attendant lower mechanical and health and safety properties.

RESIN TRANSFER MOLDING• Here resin is transferred over the already placed

reinforcement• 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 clamped. • The resin is pumped into the mold through ports

and air is displaced through other vents.• After curing, the mold is opened and composite

product is taken out.

ADVANTAGES• Good surface finish.• Any combination of reinforced materials

(including 3D) in any orientation can be achieved.

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

• Uniform part thickness.DISADVANTAGES• Mould cavity limits the size of the

composite. • High tooling cost.

REACTION INJECTION MOULDING• Here two reactive ingredients are mixed and

injected into a mold cavity where curing and solidification occur due to chemical reaction.

• If reinforcing agents are added to the mixture then the process is known as reinforced reaction injection moulding (RRIM).

ADVANTAGES AND DISADVANTAGES•  Quick cycle times compared to typical vacuum cast

materials.

•  The bi-component mixture injected into the mold has a much lower viscosity than molten thermoplastic polymers, therefore large, light-weight,flexible and thin-walled items can be successfully RIM processed.

• This thinner mixture also requires less clamping forces, which leads to smaller equipment and ultimately lower capital expenditure.

• Another advantage of RIM processed foam is that a high-density skin is formed with a low-density core.

• The disadvantages are slow cycle times, compared to injection moulding, and expensive raw materials.

MATCHED –DIE FORMING• The composite material is pressed between

heated matched dies• Pressure required depends on the flow

characteristics of the feed materials• The feed materials flows into the contours

of the mould and cures at high temp There are three types of matched die forming• Perform moulding• Sheet molding compound• Dough/bulk molding compound (DMC

ADVANTAGES• Both interior and exterior surfaces are finished• Production rate can be high • Labour cost are low• Minimum trimming of parts are moulded• Product has good mechanical properties and closed

part toleranceDISADVANTAGES• More equipment is needed than layup• Mould and tooling are costly than layup moulds• Transparent parts are not possible with SMC and

BMC• Moulding problems may cause surface

imperfections• SMC and BMC have limited shelf life .