Manufacturing: Chapter 14

filament winding

resin-impregnated continuous fibers are wrapped around a rotating mandrel that has the internal shape of the desired FRP product resin is then cured and the mandrel removed fiber rovings are pulled through a resin bath before being wound in a helical pattern around the mandrel the operation is repeated to form additional layers, each having a crisscross pattern with the previous, until the desired part thickness has been obtained

woven roving

similar to cloth, but consists of untwisted filaments rather than yarns

pultrusion processes

similar to extrusion but workpiece is pulled through die like extrusion, pultrusion produces continuous straight sections of constant cross section a related process, called pulforming, is used to make parts that are curved and which may have variations in cross section throughout their lengths

PMC shape processing

slow and labor intensive

polymer matrix

thermosetting polymers are the most common matrix material thermoplastic: most TP molding compounds include fillers or reinforcing agents on a regular basis

conventional injection molding

used for both thermoplastics and thermosets type FRPs virtually all TPs can be reinforced with fibers chopped fibers must be used during injection into the mold cavity, fibers tend to become aligned as they pass through the nozzle

compression molding PMC processes

charge is placed in lower mold section, and the mold sections are brought together under pressure, forcing charge to take the shape of the cavity mold halves are heated to cure thermosetting polymer several shaping processes for PMCs based on compression molding

transfer molding PMC processes

charge of thermosetting resin with short fibers is placed in a pot or chamber, heated, and squeezed by ram action into one or more mold cavities mold is heated to cure the resin the name of the process derives from the fact that the fluid polymer is transferred from a pot into a mold

fibers as the reinforcing phase

common fiber materials: glass, carbon, and Kevlar in some fabrication processes, the filaments are continuous, while in others, they are chopped into short lengths most familiar form of continuous fiber is cloth: a fabric of woven yarns woven roving

materials and products in pultrusion

common resins: unsaturated polyesters, epoxies, and silicones, all thermosetting polymers reinforcing phase: E-glass is most widely used, in proportions from 30% to 70% products: solid rods, tubing, long flat sheets, structural sections, tool handles for high voltage work, and third rail covers for subways

polymer matrix composite (PMC)

composite material consisting of a polymer imbedded with a reinforcing phase such as fibers or powders

pultrusion

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

reinforced reaction injection molding

conventional reaction injection molding (RIM): two reactive ingredients are mixed and injected into a mold cavity where curing and solidification occur reinforced reaction inject molding (RRIM): similar to RIM but includes reinforcing fibers, typically glass fibers, in the mixture advantages: similar to RIM but with fiber-reinforcement products: auto body and truck body parts

curing in open mold processes

curing is required of all thermosetting resins used in FRP laminated composites curing cross-links the polymer, transforming it from its liquid or highly plastic state into a solid product three principal process parameters: time, temperature, pressure

curing at room temperature

curing normally occurs at room temperature for the thermosetting resins used in hand lay-up and spray-up procedures

open mold processes

family of FRP shaping processes that use a single positive or negative mold surface to produce laminated FRP structures starting materials are applied to the mold in layers, building up to the desired thickness this is followed by curing and part removal common resins are unsaturated polyesters and epoxies, using fiberglass as the reinforcement

mats and preforms as reinforcements

fibers can also be in a mat form: a felt consisting of randomly oriented short fibers held loosely together with a binder during molding, the resin impregnates the preform and then cures, thus yielding a fiber-reinforced part

prepregs

fibers impregnated with partially cured thermosetting resins to facilitate shape processing available as tapes or cross-piled sheets or fabrics curing is completed during and/or after shaping advantage: prepregs are fabricated with continuous filaments rather than chopped random fibers, thus increasing strength and modulus

open mold FRP processes

hand lay-up spray-up automated tape-laying machines

injection molding PMC processes

injection molding is noted for low cost production of plastic parts in large quantities although most closely associated with thermoplastics, the process can also be adapted to thermosets processes of interest in the context of PMCs: conventional injection molding and reinforced reaction injection molding

spray-up method

liquid resin and chopped fibers are sprayed onto an open mold successive FRP laminations attempt to mechanize application of resin-fiber layers and reduce lay-up time products: boat hulls, bathtubs, shower stalls, truck body parts, furniture, structural panels, containers since products have randomly oriented short fibers, they are not as strong as those made by lay-up, in which fibers are continuous and directed

automated tape-laying machines

machines that operate by dispensing a prepreg tape onto an open mold following a programmed path typical machine consists of overhead gantry to which the dispensing head is attached

molding compounds

most are thermosetting polymers since they are designed for molding, they must be capable of flowing

two approaches to combining matrix reinforcement

1. the starting materials arrive at the fabrication operation as separate entities and are combined into the composite during shaping 2. the two component materials are already combined into some starting form that is convenient for use in the shaping process

hand lay-up method

open mold shaping method in which successive layers of resin and reinforcement are manually applied to an open mold to build the laminated FRP composite structure labor-intensive either with wet or dry lay-up finished molding usually trimmed with power saw to size outside edges 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

closed mold processes

performed in molds consisting of two sections that open and close each molding cycle tooling cost is more than twice the cost of a comparable open mold due to the more complex equipment required in these processes advantages: good finish on all part surfaces, higher production rates, closer control over tolerances, and more complex three-dimensional shapes are possible three categories: compression molding, transfer molding, injection molding

reinforcing agent

possible materials: ceramics, metals, other polymers, or elements such as carbon or boron possible geometries: fibers, particles, and flakes