EMAC 270 Quiz 4 - Composite Processing Methods

hand lay-up molding

a reinforcement in a form of a cloth or mat is placed on a mold and liquid resin is painted on it.
advantages: versatile, fast mold-making, low capital investment, can align long fibers with controlled orientation for high strength applications.
disadvantages: labor intensive, high scrap rate (thermosets w/ bubbles & polymer deficient areas), low productivity.
examples: aerospace composite products, boats, bath tubs

spray-up molding

continuous fiber is chopped at the spray-up gun and the short fibers are sprayed onto the mold surface along with the initiator. usually used for 1 of a kind products.
advantages: improved productivity than hand lay-up, mold design flexibility
disadvantages: still labor intensive, high scrap rate (hard to maintain constant thickness), low productivity, catastrophic failure of the product (due to short length of filament strands, gradual breakdown. not made for life-dependent applications).

compression molding

a material is placed on a heated platen and squeeze the material with a powerful hydraulic unit using an open mold approach.
advantages: good/mid-range productivity, most versatile processing method (you can use any form of composite). large shapes can be made, fairly automated.
disadvantages: intricately shaped objects cannot be molded, some labor is needed to clean the flash, energy intensive.

transfer molding

improved version of compression molding. a fiber/resin mixture is transferred from a reservoir into mold cavity by a press. A long-fiber reinforced composite cannot be made.
advantages: a closed mold can be utilized, preventing flash.

resin transfer molding (RTM)

same as ordinary transfer molding; a polymer resin is transfer molded into a mold cavity, but a fiber fabric called preform is placed in a mold beforehand. a preform is placed in a closed mold into which a liquid resin is injected and later polymerized.
advantages: a large product can be made in 1 shot, energy efficient.
disadvantages: resin must be low viscosity, intricately shaped object cannot be molded

vacuum assisted resin transfer molding (VARTM)

same as RTM, except for the added vacuum to help pull the viscous resin to enter the platform cavity by evacuating air ahead of the resin flow front. can be used to mold much larger objects than RTM.

extrusion/injection molding

thermoplastic polymer pellets are placed in a hopper. the pellets drop into heated barrel where a reciprocating screw rotates to melt and homogenize the pellets. the molten plastic is then injected into a closed mold.
most intensively used method for processing short-fiber reinforced thermoplastics. extensive fiber damage.
advantages: very intricate object can be molded, high productivity, low scrap rate, highly automated
disadvantages: energy intensive (due to high viscosity), capital intensive

(plunger type injection molding)

less fiber damage occurs than injection molding. because the plunger-type injection molding machine does not achieve a high degree of mixing in the machine, the raw materials must be thoroughly mixed prior to feeding.

(extrusion)

the basic hopper, screw, and barrel of injection molding make the main elements of an extruder. a die is then placed on the end, where the polymer melt is forced through to make various shapes. for example, a circular die can be used to make piping, while a flattened die is used to make sheets. can make products with a constant cross section.

reaction injection molding

liquid A and B are designed to polymerize very rapidly upon contact. then A and B are pumped into a mixing head where a very fast impingement mixing takes place. the mixed liquid quickly starts polymerizing while the mixture is injected into a closed mold.
water applications - jet ski, snowmobile, etc.
if a reinforcing filler is mixed into those individual components, this type of RIM is called reinforced RIM. If preform is used in the mold cavity, the method is called structural RIM.
advantages: very rapid cycle time, low energy need
disadvantages: limited # of polymers can be made (commercially, only several polymerize fast enough), chemicals can be air or water sensitive

pultrusion

fibers wet with liquid resin are pulled through a heated die where the resin gels and vitrifies.
advantages: very high mechanical strength, only continuous process for continuous fiber reinforced polymers, low labor cost.
disadvantages: only composites w/ constant cross-sectional area can be made

filament winding

a mandrel is wound with fibers wet with a liquid resin. the wound mandrel is then heated to polymerize the resin. upon solidification, the mandrel is pushed out to leave the composite.
advantages: the strongest composite of all processing methods
disadvantages: low productivity, expensive.

highly-automated processes:

pultrusion, filament winding, injection molding, extrusion

can be used for nanocomposite processing:

compression molding, injection molding, extrusion

a life size statue of yourself

spray-up molding

an arrow used for archery

pultrusion

HDPE pipe

extrusion

a high pressure railway tank car

filament winding

composite processing technique suitable for the highest strength composites

filament winding

the processing method for the most versatile design flexibility of the mold shape using continuous fiber reinforcement

hand lay-up

best method for processing a very intricately shaped object with a thermoplastic polymer

injection molding