SHAPING PROCESSES FOR POLYMER MATRIX COMPOSITES 1 Starting

Overview of PMC Technology A polymer matrix composite (PMC) is a composite material consisting

PMC Shape Processing O Many PMC shaping processes are slow and labor intensive O

Categories of FRP Shape Processes O Open mold processes - some of the original

Classification of FRP Processes Figure 15. 1 Classification of manufacturing processes for fiber reinforced

Video © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern

Starting Materials for PMCs O In a PMC, the starting materials are: O A

Polymer Matrix O Thermosetting (TS) polymers are the most common matrix materials O Principal

Reinforcing Agent O Possible geometries - fibers, particles, and flakes O Possible materials -

Fibers as the Reinforcing Phase O Common fiber materials: glass, carbon, and Kevlar (a

Fibers as the Reinforcing Phase O The most familiar form of continuous fiber is

Mats and Preforms as Reinforcements O Fibers can also be in a mat form

Combining Matrix and Reinforcement 1. The starting materials arrive at the fabrication operation as

Molding Compounds FRP composite molding compounds consist of the resin matrix with short randomly

Prepregs Fibers impregnated with partially cured TS resins to facilitate shape processing O Available

Open Mold Processes Family of FRP shaping processes that use a single positive or

Open Mold FRP Processes 1. Hand lay‑up 2. Spray‑up 3. Automated tape‑laying machines O

Hand Lay‑Up Method Open mold shaping method in which successive layers of resin and

Hand Lay-Up Method Figure 15. 4 Hand lay‑up : (1) mold is treated with

Products Made by Hand Lay‑Up O Generally large in size but low in production

Spray‑Up Method Liquid resin and chopped fibers are sprayed onto an open mold to

Spray-Up Method Figure 15. 5 Spray‑up method © 2007 John Wiley & Sons, Inc.

Products Made by Spray‑Up O Boat hulls, bathtubs, shower stalls, automobile and truck body

Automated Tape‑Laying Machines Automated tape‑laying machines operate by dispensing a prepreg tape onto an

Figure 15. 6 Automated tape‑laying machine (photo courtesy of Cincinnati Milacron). © 2007 John

Curing in Open Mold Processes O O O Curing is required of all thermosetting

Curing at Room Temperature O Curing normally occurs at room temperature for the TS

Curing Methods Based on Heating O Oven curing provides heat at closely controlled temperatures;

Thanks © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern

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Overview of PMC Technology A polymer matrix composite (PMC) is a composite material consisting of a polymer imbedded with a reinforcing phase such as fibers or powders O The importance of PMC processes derive from the growing use of this class of material, especially fiber‑reinforced polymers(FRPs) O FRP composites can be designed with very high strength‑to‑weight and modulus‑to‑weight ratios O These features make them attractive in aircraft, cars, trucks, boats, and sports equipment © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

PMC Shape Processing O Many PMC shaping processes are slow and labor intensive O In general, techniques for shaping composites are less efficient than for other materials Why? O Composites are more complex than other materials, consisting of two or more phases O For FRPs, there is the need to orient the reinforcing phase O Composite processing technologies have not been the object of refinement over as many years as processes for other materials © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Categories of FRP Shape Processes O Open mold processes - some of the original O O FRP manual procedures for laying resins and fibers onto forms Closed mold processes - much the same as those used in plastic molding Filament winding - continuous filaments are dipped in liquid resin and wrapped around a rotating mandrel, producing a rigid, hollow, cylindrical shape Pultrusion - similar to extrusion only adapted to include continuous fiber reinforcement Other - operations not in previous categories © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Classification of FRP Processes Figure 15. 1 Classification of manufacturing processes for fiber reinforced polymer (FRP) composites © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Starting Materials for PMCs O In a PMC, the starting materials are: O A polymer O A reinforcing phase O They are processed separately before becoming phases in the composite © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Polymer Matrix O Thermosetting (TS) polymers are the most common matrix materials O Principal TS polymers are: O Phenolics – used with particulate reinforcing phases O Polyesters and epoxies - most closely associated with FRPs O Thermoplastic molding compounds include fillers or reinforcing agents O Nearly all rubbers are reinforced with carbon black © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Reinforcing Agent O Possible geometries - fibers, particles, and flakes O Possible materials - ceramics, metals, other polymers, or elements such as carbon or boron O Particles and flakes are used in many plastic molding compounds O Of most engineering interest is the use of fibers as the reinforcing phase in FRPs © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Fibers as the Reinforcing Phase O Common fiber materials: glass, carbon, and Kevlar (a polymer) O In some fabrication processes, the filaments are continuous, while in others, they are chopped into short lengths O In continuous form, individual filaments are usually available as rovings - collections of untwisted continuous strands, convenient form for handling O By contrast, a yarn is a twisted collection of filaments © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Fibers as the Reinforcing Phase O The most familiar form of continuous fiber is a cloth ‑ a fabric of woven yarns O Similar to a cloth is a woven roving, a fabric consisting of untwisted filaments rather than yarns O Woven rovings can be produced with unequal numbers of strands in the two directions so that they possess greater strength in one direction O Such unidirectional woven rovings are often preferred in laminated FRP composites © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Mats and Preforms as Reinforcements O Fibers can also be in a mat form ‑ a felt consisting of randomly oriented short fibers held loosely together with a binder O Mats are commercially available as blankets of various weights, thicknesses, and widths O Mats can be cut and shaped for use as preforms in some of the closed mold processes O During molding, the resin impregnates the preform and then cures, thus yielding a fiber‑reinforced molding © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Combining Matrix and Reinforcement 1. The starting materials arrive at the fabrication operation as separate entities and are combined into the composite during shaping O Filament winding and pultrusion, in which reinforcing phase = continuous fibers 2. The two component materials are combined into some starting form that is convenient for use in the shaping process O Molding compounds O Prepregs © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Molding Compounds FRP composite molding compounds consist of the resin matrix with short randomly dispersed fibers, similar to those used in plastic molding O Most molding compounds for composite processing are thermosetting polymers O Since they are designed for molding, they must be capable of flowing O Accordingly, they have not been cured prior to shape processing O Curing is done during and/or after final shaping © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Prepregs Fibers impregnated with partially cured TS resins to facilitate shape processing O Available as tapes or cross‑plied sheets or fabrics O Curing is completed during and/or after shaping O Advantage: prepregs are fabricated with continuous filaments rather than chopped random fibers, thus increasing strength and modulus © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Open Mold Processes Family of FRP shaping processes that use a single positive or negative mold surface to produce laminated FRP structures O The starting materials (resins, fibers, mats, and woven rovings) are applied to the mold in layers, building up to the desired thickness O This is followed by curing and part removal O Common resins are unsaturated polyesters and epoxies, using fiberglass as the reinforcement © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Open Mold FRP Processes 1. Hand lay‑up 2. Spray‑up 3. Automated tape‑laying machines O The differences are in the methods of applying the laminations to the mold, alternative curing techniques, and other differences © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

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 O Labor‑intensive O Finished molding must usually be trimmed with a power saw to size outside edges O Oldest open mold method for FRP laminates, dating to the 1940 s when it was © 2007 Johnfirst Wiley &used Sons, Inc. for M P Groover, boat Fundamentals hulls of Modern Manufacturing 3/e

Hand Lay-Up Method Figure 15. 4 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. © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Products Made by Hand Lay‑Up O Generally large in size but low in production quantity - not economical for high production O Applications: O Boat hulls O Swimming pools O Large container tanks O Movie and stage props O Other formed sheets O The largest molding ever made was ship hulls for the British Royal Navy: 85 m (280 ft) long © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Spray‑Up Method Liquid resin and chopped fibers are sprayed onto an open mold to build successive FRP laminations O Attempt to mechanize application of resin‑fiber layers and reduce lay‑up time O Alternative for step (3) in the hand lay‑up procedure © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Products Made by Spray‑Up O Boat hulls, bathtubs, shower stalls, automobile and truck body parts, recreational vehicle components, furniture, large structural panels, and containers O Movie and stage props are sometimes made by this method O Since products made by spray‑up have randomly oriented short fibers, they are not as strong as those made by lay‑up, in which the fibers are continuous and © 2007 Johndirected Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Automated Tape‑Laying Machines Automated tape‑laying machines operate by dispensing a prepreg tape onto an open mold following a programmed path O Typical machine consists of overhead gantry to which the dispensing head is attached O The gantry permits x‑y‑z travel of the head, for positioning and following a defined continuous path © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Curing in Open Mold Processes O O O 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 condition into a hardened product Three principal process parameters in curing: 1. Time 2. Temperature 3. Pressure © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Curing at Room Temperature O Curing normally occurs at room temperature for the TS resins used in hand lay‑up and spray‑up procedures O Moldings made by these processes are often large (e. g. , boat hulls), and heating would be difficult due to product size O In some cases, days are required before room temperature curing is sufficiently complete toofremove the part © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals Modern Manufacturing 3/e

Curing Methods Based on Heating O Oven curing provides heat at closely controlled temperatures; some curing ovens are equipped to draw a partial vacuum O Infrared heating - used in applications where it is impractical to place molding in oven O Curing in an autoclave, an enclosed chamber equipped to apply heat and/or pressure at controlled levels O In FRP composites processing, it is usually a large horizontal cylinder with doors at either end © 2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e