060070103-Rifat Yılmaz- 7th Week Definitions

Pulforming (previous) GROUP: Manufacturing Method

             This process was developped for the NASA shuttle stiffener ring. reinforcing fibres are drawn through a tank for resin impregnation and then through a die.pulforming may be curved or straight. a composite hammer handle is made on straight pulforming equipment.

(handbook of polymer blends and composites,A.K. Kulshrestha,Cornelia Vasile, p.29)

Pulforming (New)(Better)

Pulforming - is similar to pultrusion  except that it produces parts of nonuniform cross section. Tool handles and plastic leaf springs are two common products produced. Instead of pulling the preformed material through an extrusion-like die to create a constant cross section, it is placed in a mold. Additional material may be added where needed. The heated mold is closed, curing the resin-reinforcement mix to the desired shape. Although the process does not produce constant cross sectional shapes, parts produced often have only minor changes in shape along their length. Fig. 4G12 presents an example of the process.

(James G. Bralla, Handbook of Manufacturing Process, pages  180-181)

Continuous Laminating (previous) GROUP: Manufacturing Method

Continuous Laminating Fiber Reinforced plastic panels, sometimes translucent and/or corrugated, are used in construction.The process to produce them consist of (1) impregnating layers of glass fiber mat or woven fabric by dripping in liquid resin or by passing beneath a doctor blade; (2) gathering between cover films(cellophane,polyester, or other polymer); and (3) compacting between sequeeze rolls and curing.Corrugation (4) is added by formed rollers or mold shoes.

(Mikell P. Groover,Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, p.342)

Continuous Laminating (new)(better)

In the continuous laminating process, roving is chopped onto a film of resin which has been doctored onto, and is supported by, a cellophane or other suitable carrier sheet. The sheet is initially passed through a kneading device to eliminate entrapped air. then is covered with a second sheet and passed through squeeze rollers to establish a closely controlled, finished panel thickness. Finally, the laminate passes through a curing oven (93-149 ᵒC), which may contain shaping rollers for corrugations. Panels are then stripped of the carried sheets and cut to length. In continuous electrical sheet manufacture, mat of fabric passes through a bath of resin followed by a roller application of carrier sheets and curing (figure 6.16).

( Güneri Akovali, Handbook of Composite Fabrication, page 156)

Conventional Injection Molding (in PMC) (Previous) GROUP: Manufacturing Method

In PMC shape processing, injection molding is used for both TP- and TS-type FRPs. In the TP category, virtually all thermoplastic polymers can be reinforced with fibers. Chopped fibers must be used; if continuous fibers were used, they would be reduced anyway by the action of the rotating screw in the barrel. During injection from the chamber into the mold cavity, the fibers tend to become aligned during their journey through the noozle. Designers can sometimes exploit this feature to optimize directional properties through part design, location of gates, and cavity orientation relative to the gate.

Whereas TP molding compounds are heated and then injected into a cold mold, TS polymers are injected in to a heated mold for curing. Controll of the process with thermosets is trickier because of the risk of premature cross-linking in the injection chamber. Subject to the same risk, injection molding can be applied to fiber-reinforced TS plastics in the form of pelletized molding compound and dough molding compound.

(Groover M.P., Fundamentals of Modern Manufacturing: Materials, Processes and Systems, pg. 337, Kayra Ermutlu)

Conventional Injection Molding (in PMC) (New)(Better)

Injection molded parts begin with a plastic material in granular form, most commonly a thermoplastic. The granulated material passes from a hopper to a heated cylinder, where it changes from the heat into a mass. (Most plastics, when heated, do not melt into a full liquid, but change into a mass with a consistency similar to that of peanut butter.) The pasty mass is moved forward with a screw feed, by plunger, or both, and, under pressure, is injected into a mold. (Rotation of the screw mixes the

material and provides frictional heating; axial movement of the screw forces the material into the mold.) The mold is normally a steel cavity, made from at least two pieces, tightly clamped together.

The cavity has the same shape as that of the final part. Multiple cavities per mold are very common.

With thermoplastics, the mold is cooler than the cylinder from which the plastic was injected, cool

enough so that the plastic, after it enters and fills the mold, cools and solidifies. A typical temperature of the material in the machine cylinder is 400°F. (200°C) and, in the mold, 180°F (80°C). The machine cylinder is heated electrically and the mold temperature is regulated with circulating water. The process is normally fully automatic. Cycle times range most commonly from about 15 to 45 seconds, the time being dependent on the wall thickness and size of the part and many other process factors. Figure 4C 1 illustrates the injection molding process. Injection molding is by far the most common process used in the manufacture of parts from plastics. It is almost an ideal mass production method.

Parts can be complex and can have color and surface texture molded in (with no need for costly

secondary operations). They can have such features as hinges, springs, screw threads, and bearings

incorporated fairly easily. Many companies that have made significant DFM (Design for Manufacturability) improvements in their products have done so by combining a number of separate

parts and fasteners in a fewer number of injectionmolded plastic parts that snap together without

external fasteners. Some typical injection molded parts are the following: housings for various products such as computers, home entertainment products, telephones, caps for containers, pails, handles, laundry baskets, toys, and parts for automobiles and

refrigerators.

(James G. Bralla, Handbook of Manufacturing Process, pages  156-157)

Mandrel(Previous)-GROUP: Composite manufacturing tool part

The mandrel is the special tooling that determines the geometry of the filament-wound part. Mandrels must be capable of collapsing after winding and curing, for part removal. Various mandrel designs are possible, including inflatable/deflatablle mandrels, collapsible metal mandrels, and mandrels made of soluble salts or plasters.

(Mikell P. Groover,Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, p.338)

Mandrel(New)(Better)

The mandrel for filament winding can be of any material that will resist the winding tension, the heat of curing, the potential deformations caused by the weight of the product and the mandrel weight, can be made to the necessary tolerances, and has sufficient durability. They have ranged from cardboard t stainless steel. The basic requirement is that they can be removed (extracted) from the wound component unless, in some applications such as pressure vessels, the mandrel remains in the component as a liner. Some of the alternate approaches are shown subsequently.

Filament-Wound Mandrel

A filament-wound vessel with fibers at ±54,75° will, under internal pressure, expand in both directions, and the wind angle will remain the same. When the angle is ±60°. the fibers move toward a ±54.75° angle. This movement decreases (he diameter and increases the length of the vessel (Fig. 6.13). The filament winding mandrel uses (his fact to simplify extraction of a filament-wound pipe that was wound onto il. The mandrel is fabricated by overwinding both ends of a dissolvable mandrel or a 2 to 4 lb (1 to 2 kg) compressible foam mandrel. Center shafts are used with end-pressure connections. The mandrel surface can be machined by the filament winding machine using a tool postgrinder on the winder carriage. Machining does not significantly reduce the internal pressure capabilities. Plastic film can be spirally wrapped with a slight overlap as a release system. Resin for the mandrel should be cured at a temperature at least 50 °F (28 °C> greater than the cure temperature of the filament-wound product. The extraction pressure force for the mandrel is as low as 50 psi (345 kPa) and up to several hundred pounds per square inch. Trial windings and analysis can determine the most suitable mandrel wind angle. The filament  winding mandrel can be repeatedly used.

(Stan Peters,Composite Filament Winding, pages 71-72)

Reinforced Reaction Injection Molding (RRIM) (Previous) GROUP: Manufacturing Method

The principle of the RRIM process centers on bringing together two fast reacting liquids into a mixing chamber and then into a mold cavity. Relatively low clamping force pressure is used, and external heat is not normally used on the surface of the mold. The rate of polymerization reaction between two liquids gives a cycle time of typically less than 60 s in the mold. The chemical reaction starts immediately when the two liquids are combined through a mixing chamber and progresses as material flows into the mold cavity.

In general, RRIM has been developed using polyurethane formulations, with one reactant stream being a polypl and the other benig a di-isocyanate. The glass reinforcement normally used in the RRIM process is milled fiber added to the polyol stream. An alternative processing method involves placing a glass fiber preform into the mold cavity and then injecting the two liquids into the mold cavity. While polyurethanes are the dominant resin matrix used in this process, other matrix materials such as phenolics are used to achieve specific property requirements.

(Fiberglass and Glass Technology: Energy-Friendly Compositions and Applications, Frederick T. Wallenberger,Paul A. Bingham, p.144)

(Figure, taken from: Structural Composite Materials, F. C. Campbell)

Reinforced Reaction Injection Molding (New)(Better)

The development of RRIM systems with better properties has followed the use of reinforcing fillers in urethane, especially glass in bead and fibre form. Both glass beads, hammer milled glass are commonly used (0.8-2 mm random length) and chopped strand glass (1.5-3 mm precision lengths) which are processed as 'slurries' in the liquid urethane components. As good wetting and preferably bonding between urethane and glass matrices is considered desirable, the glass is often surface treated with chemical coupling agents. However, with longer fibres and higher loadings, e.g. the 3 mm fibres and greater than 6 ph of the 1.5 mm variety, the fibres are distributed in both polyol and diisocyanate components due to viscosity limitations. Settlement and high viscosity can be overcome by raising the polyol and diisocyanate temperature and it is observed that there exists a so-called "suspension equilibrium temperature' range over which filler settlement is not a problem.

The principal advantage of RIM is the ability to process low-viscosity liquid rcactants. typically 0.1-1.0 Pa-s, using low temperature and pressures, particularly during the mould-filling stage. This means that small-scale hydraulic equipment and lighter weight and lower cost moulds can be used, facilitating short production runs and prototype applications. Low-viscosity reactant systems also facilitate composite materials production, so called reinforced RIM (RRIM) composites (Figure 1.7), in which continuous fibre reinforcement mats are preplaced ni mould cavities prior to injection. Capital investment and operational costs in RIM are therefore much less than those for conventional injection moulding.

Mix-activated copolyurethanes (PU), copoly (urethanc-ureas) (PUU)and copolyureas(PUr) arc the most common systems used in RIM, and constitute over 95% of RIM materials produced. Unsaturated ester-urethanes (acrylamates), polyepoxidcs, unsaturated polyesters and phenolics have been developed for use mainly as thermosetting matrices for RRIM composites.

RKIM is similar to RIM in its intensive resin mixing procedures and its reliance on fast resin reaction rates. It is also similar to resin transfer moulding (RTM) in using preforms that are placed in the cavity of a compression mould to obtain optimum composite mechanical properties.

The overwhelming advantages of RRIM are highlighted in Table 1.8.

(A. K. Kulshreshtha,Cornelia Vasile, Handbook of Polymer Blends and Composites, pages 18-19-20-21)