CONTENTS –MANUFACTURING OF COMPOSITES Preparation of moulding compounds Prepregs Hand lay up method Autoclave method Filament winding method Compression moulding Reaction Injection moulding
PREPARATION OF MOULDING COMPOUNDS High polymer material is mixed with 4 to 10 ingredients each of which discharges a useful function during moulding or impart some useful property to the finished artifact
TYPES OF MOULDING COMPOUNDINGINGREDIENTS 1.Resin 2.Plasticizer 3.Fillers 4.Lubricants 5.Catalyst Or Accelerators 6.Stabilizers 7.Colouring Materials
TYPES OF MOULDING COMPOUNDING INGREDIENTS- 1.RESIN It is a binder which holds different constituents together Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives and food glazing agents
1.RESIN Synthetic resins are viscous liquids that are capable of hardening permanently. Otherwise, chemically they are very different from the various resinous compounds secreted by plants
1.RESIN Some are thermosetting plastics in which the term "resin" is loosely applied to the reactant or product, or both. "Resin" may be applied to one of two monomers in a copolymer (the other being called a "hardener", as in epoxy resins). For those thermosetting plastics which require only one monomer, the monomer compound is the "resin.
TYPES OF MOULDING COMPOUNDING INGREDIENTS 2.PLASTICIZERS Plasticizers are materials that are added to resins to increase their plasticity and flexibility They neutralise the part of the intermolecular forces of attraction between macromolecules of resins They impart a greater freedom of movement between the polymeric macro molecules of resin there by increasing the flexibility and plasticity of the compound material.
2.PLASTICIZERS Phthalate esters are plasticizers used in polyvinyl chloride (PVC) to soften the hard PVC by “lubricating” the areas between polymer strands so that it can be used in consumer products like inflatable pools and food packaging.Almost 90% of the market for plasticizer is for PVC, giving thismaterial improved flexibility and durability.Plasticizers work by embedding themselves between the chains ofpolymers, spacing them apart (increasing the "free volume"), andthus significantly lowering the glass transition temperature for theplastic and making it softer.
2.PLASTICIZERS Plasticizers evaporate and tend to concentrate in an enclosed space; the "new car smell" is caused mostly by plasticizers evaporating from the car interior.
3.FILLERS Fillers are added to give the final plastic better hardness , tensile strength , finish and workability. Advantages : Reduces cost Reduces shrinkage Reduces brittleness Examples : Carborundum,Quartz,Mica to provide extra hardness Barium salts to make plastic impervious to X-rays Addition of asbestos provides heat and corrosion resistance .
4.LUBRICANTS Added to make moulding of plastic easier. To impart a flawless , glossy finish to the products . Prevents plastic material from sticking to the fabricating equipment. Eg: Waxes , Oils , soaps etc
5.CATALYSTS OR ACCELERATORS Are added only in case of thermosetting plastics. Accelerates the polymerization of fusible resin during moulding operation into crosslinked infusible form . Eg: Hydrogen peroxide Acetyle sulphuric acid Benzoyl peroxide
6. STABILIZERS Improve thermal stability during processing Eg : Vinyl chloride UV light stabilizers are used frequently in plastics, including cosmetics and films. The primary function is to protect the substance from the long-term degradation effects from light, most frequently ultraviolet light.
7.COLOURING MATERIAL Used in high polymer artifacts Eg: Organic dystuffs Opaque inorganic pigments
PREPREGS Prepreg is the industry term for high quality reinforced fibers , which are preimpregnated with a resin system and partially cured to B-stage. B-stage is an intermediate cure stage of a thermosetting resin that lies between the completely uncured stage and a completely cured stage. Ready to mold or cure material in sheet form which may be tow , tape , cloth or mat impregnated with resin.
ADVANTAGES Consistent quality and consistent resin to reinforcement ratio Few rejections Less variance in mechanical properties . Finest quality material. Reduce the handling damage to dry fibers. Increased curing pressure reduces voids and improves fiber wetting
PREPREGS A prepreg consists of a reinforcement material preimpregnated with a resin matrix in controlled quantities. The resin is partially cured to a B-stage, and in this form is supplied to the fabricator, who lays up the finished part and completes the cure with heat and pressure. The required heat and pressure will vary with the resin system and the intended application.
METHODS OF PRODUCING PREPREG 1.Solvent Solution Pre-impregnation Process or Solution Coating 2.Hot Melt Pre Impregnation Procedure. Solution coating saturates the reinforcement with resin dissolved in carrier solvent. Hot melt coating uses heat and pressure to impregnate the fibers with resin. The prepreg is typically laid against the paper or polyethylene film separator called interleaf so that the preperg don’t stick on to itself and is wound around a core.
1.SOLVENT SOLUTION PRE-IMPREGNATION PROCESS Woven fabric or fiber yarn is passed through a resin rich solution . Prepreg is then dried to remove the solvent Excess resin is then removed via doctor blade or metering rolls Then the product is staged to the cold stable prepreg form (B-Stage )
HOT MELT PREIMPREGNATION PROCEDURE It replaces solvent method because of environmental concerns and a need to exert better control over the amount of resin on the fiber . Issues with Solvent method : Stringent Air emission control regulations and liabilities . High cost of maintaining solution ovens .
HOT MELT PREIMPREGNATION PROCEDURE In this process woven fabric or fiber yarn is passed over a series of rollers . The molten polymeric resin wets the fibers and then the resin impregnated sheet of fibers is compacted over a sheet of release paper and subsequently wrapped on rolls for storage .
HOT MELT PREIMPREGNATION PROCEDURE At the hot melting machine , the fibers go through a metered comb to maintain their parallel integrity for even spreading , and are laid on a release film containing a controlled amount of resin . Another role of release film , either dry or film coated , is positioned above the fibers. The fibers sandwiched between the films are pulled along the tape line with pull rollers as pressure is applied from sets of heated compaction rolls metered to the prepreg thickness
HOT MELT PREIMPREGNATION PROCEDURE The compaction ensures that the fibers are evenly spread apart and wet out . Once through the heated compaction area , the sandwich typically passes through cooling rolls before the carrier paper is removed. Great care is taken to control the temperature Trimming is done at both sides of the prepreg to exact width is down just before rewinding At the end of the tapeline , windup rolls remove one layer of carrier film and reroll it for disposal.
PREPREG CLASSIFICATION 1.Bleed System 2.No Bleed or Net Resin Content System
BLEED SYSTEM The bleed system Prepregs are those, which contain excess matrix that is bled off during the cure cycle by the use of BLEEDER PILES. Bleeder piles are the layers of fiber glass cloth or other highly absorbent material
NO BLEED SYSTEM Curing of prepreg takes place under heat and pressure Bleeder piles are generally not required for no bleeding system
DISADVANTAGES OF PREPREGS Shelf Life Since the epoxy is in a B-stage, it is required to be stored either refrigerated or frozen prior to use. Additionally, the overall shelf life can be low.
DISADVANTAGES OF PREPREGS Cost Prohibitive When manufacturing composites through a process such as vacuum infusion, the raw fiber and resin are combined on site. However, when using prepregs, the raw material must first be prepregged. This is most often done off-site at a specialized company that focuses on prepregs. This added step in the manufacturing chain can add increased cost, and in some instances close to double the material cost.
WET/HAND LAY UP METHOD 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.
WET/HAND LAY UP METHOD 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.
MATERIALS USED FOR HAND LAYUP Resins: Any, e.g. epoxy, polyester, vinylester, phenolic. Fibres: Any, although heavy aramid fabrics can be hard to wet-out by hand.
HAND LAY UP METHOD ADVANTAGES 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.
Hand Lay-Up MethodFigure 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.
HAND LAYUP METHOD - 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.
HAND LAYUP METHOD - DISADVANTAGES 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.
TYPICAL APPLICATIONS Standard wind-turbine blades Production boats, Architectural moldings
PRODUCTS MADE BY HAND LAY-UP 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
Filament winding processFilament winding is automated processes forcreating parts of simple geometry whereincontinuous resin impregnated fibres are woundover a rotating male tool called mandrel.
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 the mandrel. The operation is repeated to form additional layers, each having a criss-cross pattern with the previous, until the desired part thickness has been obtained.
TYPES OF FILAMENT WINDING PROCESS (i) The Polar Or Planer Method (ii) The High Helical Pattern Winding.
THE POLAR OR PLANER METHOD A winding in which the filament path passes tangent to the polar opening at one end of the chamber and tangent to the opposite side of the polar opening at the other end. The polar or planer method of winding utilizes a fixed mandrel and a shuttle that revolves around the longitudinal axis of the part to form longitudinal winding patterns. This type of winding is used if the longitudinal fibres are required with angle less than 25° to the mandrel axis.
HELICAL WINDING PROCESS A winding in which the filament or band advances along a helical path, not necessarily at a constant angle except in the case of a cylindrical article.In the high helical pattern winding, the mandrel rotates while the shuttle transverses back and forth. Both the mandrel rotation and shuttle movement are in the horizontal plane. By controlling the mandrel rotation and shuttle speed, the fibre angle can be controlled. .
HELICAL WINDING PROCESSAngles of 25°-85° to the mandrel rotation axis arepossible
HELICAL WINDING PROCESS After completion of the winding, the filament wound structure is cured at room temperature or in an oven. The mandrel is removed after the curing. The mandrel, which determines accurate internal geometry for the component, is generally the only major tool.
FILAMENT WINDING PROCESS Low cost mandrel materials such as cardboard or wood can be used for winding low cost routine parts. For critical parts requiring close tolerances, expensive mandrels designed for long term use may be required. For high temperature cure 315°C (600°F), graphite mandrels with low thermal expansion may be advantageous. However, attention should be paid for potential difficulties for mandrel removal.
TYPES OF MANDRELS Mandrels are either REMOVABLE or NON- REMOVABLE. Removable mandrels are classified according to the removal techniques as: • Entirely removed. • Collapsible. • Breakable or soluble.
THE SELECTION OF MANDREL1. Part size and complexity2. Size of openings3. Resin system and its curing4. The number of components to be fabricated.
THE REQUIREMENTS FOR A MANDREL It must be stiff and strong enough to support its own weight and the weight of the applied composite while resisting the fibre tension pressure from winding and curing. It must be dimensionally stable and should have thermal coefficient of expansion greater than the transverse coefficient of the composite structure.
MATERIALS USED FOR CONSTRUCTION OFMANDREL. Low melting temperature alloys used for small diameter applications. Sand, soluble plaster and eutectic salts used for irregular shapes. Inflatable material used in applications where sometimes the mandrel remains a part of the structure. Segmented metal used for high production rates, and where the mandrel can be withdrawn through a small hole in the part.
This process utilises large tonnage presses wherein the part is cured between two matched steel dies under pressure and high temperature. The moving platen is heated either by steam or electricity to promote thermal curing.
Curing of the part is affected by the following factors: Size of platen, which determines the length and width of the part, which can be cured. Total tonnage of the press, which determines the pressure to be exerted on the projected surface area of the part.
After placing the laminate to be cured called the charge in the core of the mold, the cavity is then closed at a rate of usually 4-12 mm/sec. In most cases the mold is heated to 150°C (302°F), which causes the charge viscosity to be reduced. With increasing mold pressure as the mold is closed, the charge flows towards the cavity extremities, forcing air out of the cavity.
The molding pressure based on projected part area ranges from 0.7 to 9 MPa (100 to 1200 psi). Higher molding pressure causes sink marks, while lower pressure cause scumming of the mold and porosity.
The curing time is usually between 25 sec to 3 minutes depending on several factors including resin-initiator-inhibitor reactivity part thickness component complexity mold temperature.
ADVANTAGE OF THE COMPRESSION MOLDING The primary advantage of the compression molding is its ability of producing large number of parts with little dimensional variations A wide variety of shapes, sizes and complexity can be produced by compression molding.
DRAWBACKS High tooling cost Need for large heated presses. Thus, this method is not practical for low volume production.
Sheet moulding compound (SMC) or sheet moulding composite is a ready to mould fibre- reinforced polyester material primarily used in compression moulding. The sheet is provided in rolls weighing up to 1000 kg.
SHEET MOULDING COMPOUND(SMC) It refers to both material and process for producing glass fiber reinforced polyester resin items . SMC is a totally integrated compound in sheet form that incorporates all reinforcements resin , chemical thickness , fillers , mould release agents and other ingredients . Also includes pigments and shrink control agents
SHEET MOULDING COMPOUND(SMC A SMC processing machine produces molding compound in sheet form. The glass fibre is added to a resin mixture that is carried onto a plastic carrier film. After partial cure, the carrier films are removed. The sheet molding material is cut into lengths and placed onto matched metal dies under heat and pressure
ADVANTAGES OF SMC MOLDING PROCESS High volume production. Excellent part reproducibility. Minimum material scrap. Excellent design flexibility. Parts consolidation.
BMC is a combination of chopped glass strands and Resin in the form of a bulk pre-preg. BMC is suitable for either compression or injection molding. Injection molding of BMC is used to produce complex components such as electrical equipment, car components, housings for electrical appliances and tools, in large industrial volumes.
BULK MOULDING COMPOUND Unlike SMC, it is not necessary to include a maturation stage. Consequently, BMC pre-preg formulations contain higher filler contents. The chopped glass strands vary in length depending on the level of performance required. Reinforcement content generally ranges between 15 and 20 percent; however, it may reach 25 percent for the highest performance. BMC uses a lower reinforcement content than SMC and permits higher filler loadings with lower costs.
APPLICATIONS OF BULK MOLDING COMPOUND Pump housing A/C components Circuit Breakers Computer components Power Tools Gear cases Electrical insulators
WET SYSTEM COMPRESSION MOULDING Matrix ( Liquid Resin ) is pumped to dry reinforcement in press mounted and heated matched metal moulds Hydraulic pressure forces the liquid resin to flow through the reinforcement and hold the material in place until cure is completed at the cure temperature of 120C to 180C
WET SYSTEM COMPRESSION MOULDING The equipment used for WCM is same as the BMC. Matrix material is thermosetting polyester vinylester and epoxy , resins filled with inert materials such as clay , calcium carbonate and alumina , catalyst and pigment to form a complete liquid system which require only the addition of heat for curing Reinforcement is chopped strand mats and continuous strand mats
REINFORCED THERMOPLASTIC SHEET COMPRESSION MOULDING Utilizes precombined sheet of thermoplastic resin and glass fiber reinforcement These sheets are cut into blanks which are preheated to a specified temperature and loded into matched metal compression mould. Under pressure , heat softened blanks flow and fill the mould. The mould is maintained at a temperature which causes the sheet to solidify and allows demoulding of the part
CLAMPING - the moving andfixed platens of the injectionmoulding machine holds the DWELLING - after the moltenmould tool together under plastic has been injected into thepressure. mould pressure is applied to ensure all cavities are filled.INJECTION - the molten plastic COOLING - the plastic parts arethat has been melted from pellet then allowed to solidify in theform in the barrel of the moulding mould.machine is injected underpressure into the mould.
OPENING - the moving platen moves away from the fixed platen separatingthe mould tool.EJECTION - rods, a plate or air blast then aids ejection of the completedplastic moulding from the injection mould tool.The length of time from closing the mould to ejecting the finished plasticmoulding is the cycle
PROCESS CHARACTERISTICS Utilizes a ram or screw-type plunger to force molten plastic material into a mold cavity . Produces a solid or open-ended shape that has conformed to the contour of the mold. It is ideal for producing high volumes of the same object
INJECTION MOULDING wire spools, packaging, bottle caps, automotive dashboards, pocket combs, , one-piece chairs and small tables, storage containers, mechanical parts (including gears), and most other plastic products available today. Injection molding is the most common method of part manufacturing...
ADVANTAGES OF INJECTION MOLDING high production rates repeatable high tolerances the ability to use a wide range of materials low labor cost minimal scrap losses little need to finish parts after molding
DISADVANTAGES expensive equipment investment potentially high running costs the need to design moldable parts.
REACTION INJECTION MOLDING It is similar to injection moulding except thermosetting polymers which requires a curing reaction to occur within the mold. The RIM Process involves a chemical reaction between the two liquid components. Initially, the liquids are held in separate, temperature-controlled feed tanks. The chemicals are fed through supply lines to metering units that precisely meter both chemicals, at high pressure, to a mixhead device.
RIM parts are created through a process that begins when two liquid reactants - an Isocyanate component and a Polyol resin mixture - are held in separate tanks at an elevated temperature with agitators. These liquids are fed through supply lines at high pressure to the mixhead.
When the injection begins, valves open in the mixhead and the liquids enter a chamber in the mixhead at high pressures (usually between 1,500 and 3,000 psi) and high speeds. Here they are mixed by high-velocity impingement. From the mix chamber, the mixed liquid flows into the mold at atmospheric pressure and undergoes an exothermic chemical reaction, forming a polymer in the mold.
Reaction time is usually expressed in seconds. For extremely large parts the reaction time can be extended to allow for proper filling of the mold.
ADVANTAGES strong, flexible, lightweight parts which can easily be painted. 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.
The disadvantages are slow cycle times, compared to injection molding, and expensive raw materials.