FRP PROCESSING METHODS

GEETHU C.THOMASJEFF JOSE

KESIYA GEORGEKRISHNAPRIYA M.P

Group 3

IMPORTANT METHODSHand Lay-upSpray up methodFilament windingMatch die molding PultrusionResin transfer moldingReaction injection molding

1)HAND LAY-UP METHOD

• Hand Lay-Up is well suited for low volume production of product.

• This method can be used for both corrosion barrier and the structural portion.

• A mold must be used for hand lay-up parts unless the composite is to be joined directly to another structure.

• The mold can be as simple as a flat sheet or have infinite curves and edges.

• For some shapes, molds must be joined in sections so they can be taken apart for part removal after curing.

• Reinforcement fibers can be cut and laid in the mold. – It is up to the designer to organize the type,

amount and direction of the fibers being used. • Resin must then be catalyzed and added

to the fibers. • A brush or roller can be used to

impregnate the fibers with the resin. – The lay-up technician is responsible for

controlling the amount of resin and the quality of saturation.

Hand lay‑up : (1) mold is treated with mold release agent; (2) thin gel coat (resin) is applied, to the outside surface of molding; (3) when gel coat has partially set, layers of resin and fiber are applied, the fiber is in the form of mat or cloth; each layer is rolled to impregnate the fiber with resin and remove air; (4) part is cured; (5) fully hardened part is removed from mold.

Materials used for hand layup • Resins:

– Any, e.g. epoxy, polyester, vinyl ester, phenolic.

• Fibres: – Any, although heavy aramid fabrics can be

hard to wet-out by hand.

Advantages:• i) Widely used for many years.• ii) Simple principles to teach. • iii) Low cost tooling, if room-temperature

cure resins are used. • iv) Wide choice of suppliers and material

types. • v) Higher fibre contents, and longer fibers

than with spray lay-up.

Disadvantages • Resin mixing, laminate resin contents, and laminate

quality are very Dependent On The Skills of laminators. Low resin content laminates cannot usually be achieved without the incorporation of excessive quantities of voids.

• ii) Health and safety considerations of resins. The lower molecular weights of hand lay-up resins generally means that they have the potential to be more harmful than higher molecular weight products. The lower viscosity of the resins also means that they have an increased tendency to penetrate clothing etc.

• iii) Resins need to be low in viscosity to be workable by hand. This generally compromises their mechanical/thermal properties due to the need for high diluents levels.

• Generally large in size but low in production quantity - not economical for high production

• Applications:– Boat hulls– Swimming pools– Large container tanks– Movie and stage props– Other formed sheets

• The largest molding ever made was ship hulls for the British Royal Navy: 85 m (280 ft) long

2)Spray up method

• Fibre is chopped in a hand-held gun and fed into a spray of catalysed resin directed at the mould. The deposited materials are left to cure under standard atmospheric conditions.

• Materials Options: Resins: Primarily polyester. Fibres: Glass roving only.

• 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.

3) PULTRUSION

• Fibres are pulled from a creel through a resin bath and then on through a heated die.

• The die completes the impregnation of the fibre, controls the resin content and cures the material into its final shape as it passes through the die.

• This cured profile is then automatically cut to length.• Fabrics may also be introduced into the die to provide

fibre direction other than at 0°. • Pultrusion is a continuous process, producing a profile of

constant cross-section, a variant known as 'pulforming' allows for some variation to be introduced into the cross-section.

Main Advantages:• i) This can be a very fast, and therefore

economic, way of impregnating and curing materials. ii) Resin content can be accurately controlled. iii) Fibre cost is minimised since the majority is taken from a creel. iv) Structural properties of laminates can be very good since the profiles have very straight fibres and high fibre volume fractions can be obtained. v) Resin impregnation area can be enclosed thus limiting volatile emissions.

Main Disadvantages:

• i) Limited to constant or near constant cross-section components ii) Heated die costs can be high.

• Typical Applications:

Beams and girders used in roof structures, bridges, ladders, frameworks.

4) FILAMENT WINDING

• This process is primarily used for hollow, generally circular or oval sectioned components, such as pipes and tanks.

• Fibre tows are passed through a resin bath before being wound onto a mandrel in a variety of orientations, controlled by the fibre feeding mechanism, and rate of rotation of the mandrel.

Main Advantages• i) This can be a very fast and therefore

economic method of laying material down. ii) Resin content can be controlled by metering the resin onto each fibre tow through nips or dies. iii) Fibre cost is minimised since there is no secondary process to convert fibre into fabric prior to use. iv) Structural properties of laminates can be very good since straight fibres can be laid in a complex pattern to match the applied loads.

Main Disadvantages• i) The process is limited to convex shaped

components. ii) Fibre cannot easily be laid exactly along the length of a component. iii) Mandrel costs for large components can be high. iv) The external surface of the component is unmolded, and therefore cosmetically unattractive. v) Low viscosity resins usually need to be used with their attendant lower mechanical and health and safety properties.

5) Resin transfer moulding

• Resin transfer molding is a closed molding process

• In this technique, as the name indicates, 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 clamping can be done either perimeter clamping or press clamping mechanism

• 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

Raw materials

Advantage• Composite part produced with this method has good

surface finish on both side surface of the product.• Any combination of reinforced materials (including 3D) in

any orientation can be achieved.• Fast cycle time can be achieved through temperature

control tooling device. • Process can be manual control, semi-automated or

highly automated. • Composite part thickness is uniform which is determined

by the mold cavity.• The process does not require high injection pressure

Disadvantages• Mould cavity limits the size of the

composite. • High tooling cost. • There is limitation on reinforcing materials

due to the flow and resin saturation of fibres.

6) Reaction injection moulding• Reaction injection molding (RIM) is

similar to injection molding except thermosetting polymers are used, which requires a curing reaction to occur within the mold.

• First, the two parts of the polymer are mixed together.

• The mixture is then injected into the mould under high pressure using an impinging mixer.

• The mixture is allowed to sit in the mole long enough for it to expand and cure.

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

• Common reinforcing agents include glass fibers and mica. This process is usually used to produce rigid foam automotive panels

Advantages and disadvantages• Reaction injection molding can produce strong, flexible,

lightweight parts which can easily be painted•  It also has the advantage of 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, 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 expenditures.

• 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.

7) Matched die forminga) Matched-die molding (Acuan

Terpadan)-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)• These three molding technique utilize

same type of high pressure molding equipment but differ in the form of the material that is placed inside the mold to form the part

a) Sheet molding compound (SMC)Sheet of resin-fiber blend which contains additives (curing agent, release agent & pigments). Clean to be used & give good consistency in properties

b) Dough molding compound (DMC)Blends (in dough forms) of all the necessary constituents (but only short fibers are used)

Sheet molding compound (SMC)

• SMC moulding is a sheet material that is made by chopped glass fibres on to a sheet of plastic film on which a resin-initator-filler mixture has been doctored

• Another film which also has the resin mixture applied onto it, is placed on the top and then the sandwich of resin mixture and the chopped glass is passed between the compaction rolls to wet the fibres and mix the constituents

• The material is then cured and rolled up for shipment

• A typical SMC incorporates about 30-50%fibres ,25%resin,25-45%filler

Bulk moulding compound

• BMC is a dough like mixture of chopped fibreglass resin initiator and fillers that has a composition similar to that of SMC

• The resulting material is called a premix• The fibreglass mixture is about 5-10% lower

than SMC • BMC is moulded by placing a weighed amount

of material onto the lower mould• The mod are then closed under

pressure ,temperature

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 tolerance

Disadvantages • 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

REFERENCE• Handbook of Composite

Reinforcements -By Stuart M. Lee• http://www.frprawmaterial.com/frp-process.

html• Handbook of Composite Fabrication- by

G Akovali• Introduction to Composite Materials and

Structures Nachiketa Tiwari Indian Institute of Technology Kanpur