Hakan YORULMUŞ 030070111 Week 7

1)Film stacking process (Group: manufacturing)
(previous)
Film stacking consists of interleaving layers of reinforcement fibres inthe form of tape or fabric with layers of thermoplastic polymer films or powder. Wetting of the fibres is achieved during the consolidation process. To obtain a high quality laminate (low void and good impregnation of the fibres), the stack has to be consolidated under severe conditions (high pressure and temperature, and a protracted molding cycle).
(Sylvie Béland, High Performance Thermoplastic Resins and Their Composites, p.101)

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In film stacking, alternale layers of reinforcement and polymer films arc stacked and molded. The impregnation takes place by applying heat and pressure, where the pressure must be sufficient to force the polymeric melt to flow into the reinforcement. The most important factor affecting the melt impregnation process is the rale at which the molten polymer penetrales the fibrous preform. Depending on the fiber architecture, the polymer wets individual fiber filaments to produce a void-free composite. The Darcy's law and Carmen-Kozeny equations, discussed in Section 6.3.2. are also applicable to determine the wet-out of a film stacked preform.

( Uday Vaidya; Composites for Automotive, Truck and Mass Transit: Materials, Design,2011,page197)

2)Spray Lay Up: (Group: moulding)

(previous)

This represents an attempt to mechanize the application of resin-fiber layers and to reduce the time for lay-up. It is an alternative for step 3 in the hand lay-up procedure. In the spray-up method, liquid resin and chopped fibers are sprayed onto an open mold to build successive FRP laminations, as in Figure 15.5. The spray gun is equipped with a chopper mechanism that feeds in continuous filament rovings and cuts them into fibers of length 25-75 mm (1-3 in) that are added to the resin stream as it exits the nozzle. . The mixing action results in random orientation of the fibers in the layer—unlike hand lay-up, in which the filaments can be oriented if desired. Another difference is that the fiber content in spray-up is limited to about 35% (compared to a maximum of around 65% in hand lay-up). This is a shortcoming of the spraying and mixing process.

Spraying can be accomplished manually using a portable spray gun or by an au­tomated machine in which the path of the spray gun is preprogrammed and computer controlle'd. The automated procedure is advantageous for labor efficiency and environ­mental protection. Some of the volatile emissions from the liquid resins are hazardous, and the path-controlled machines can operate in sealed-off areas without humans present. However, rolling is generally required for each layer, as in hand lay-up.

Products made by the spray-up method include boat hulls, bathtubs, shower stalls, automobile and truck body parts, recreational vehicle components, furniture, large struc­tural panels, and containers. Movie and stage props are sometimes made by this method. 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 directed.

(Mikell P. Groover,Fundamentals of Modern Manufacturing,4th Edition,pg.325-326)

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In this technique, glass fibre roving is fed continuously through a chopping unit, which cuts it to a convenient length (e.g. Sem); the resulting chopped strands are projected on the mould in conjunction with an atomized polymer jet (Fig. 2.29). Often this method makes use of a multiple-headed gun which blasts chopped glass fibres, polymer and catalyst or hardener simultaneously from one of its three heads. This spray is directed by the moulder to apply a uniform buildup over the entire mould surface. After the desired thickness has been piled up, the exposed product area is hand-rolled, to obtain a smooth surface, to remove air and consolidate the composite. Curing is achieved by one of the aforementioned contact moulding processes.

The spray-up method is a semiautomatic process which proves economical in many manufacturing operations; labour costs are greatly reduced by this process, and it makes use of an inexpensive material, glass roving.

It is a practical method for producing structural building panels, tank linings, large bodies, pools, roofs, etc. The advantages and disadvantages of spray lay-up are (2.81):

Advantages

(1)    Spray equipment is portable.

(2)    Capital outlay is small compared with other mechanized techniques.
(3)    Rovings are used, the least expensive form of reinforcement.

    (4) Production rales can be higher lhan with hand lay-up since

    shorter gel limes can be tolerated. 

    (5) Reduced   labour   costs   are   obtained   wlih   high   volume production.

Disadvantages

(1)  Mouldings have only one smooth surface.

(2)  Uniformity of lay-up depends, even more than with hand lay-up. on the skill of the operator.

(3)  Spray lay-up is uneconomical for small volume production.

(4)  An even spray pattern is difficult to achieve on small moulds.

Hand lay-up and spray-up techniques are relatively simple and low tooling cost can result in considerable versatility from the designer point of view. Very large mouldings arc done by these methods.

(Dorel Feldman, Polymeric Building Materials,1989 ,page 167)

3) Thermoset Dough Molding Compound (DMC) (Group: material)

Dough molding compound is same with bulk molding compound (BMC). BMC name is commonly used is US and DMC is used in Europe. DMCs are completely formulated preim-pregnant fiberglass reinforced plastics molding materials that are either prepared by the molder or are purchased from a compounder. They can be chemically thickened, in which case generally it is important to control the storage environment to minimize the maturation period of reaction time. When thermoplastic additives are included to control surface finish or surface appearance, the material generally is referred to as low shrink or low profile DMC. 

(Raymond W. Meyer; Handbook of Polyester Molding Compounds and Molding Technology; pg. 2)

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A popular material increasingly used in ther-mosel injection molding is polyester reinforced with glass or other fibers. This material gen­erally is referred to as bulk molding compound (BMC) in the United States and as dough mold­ing compound (DMC) in Europe. Because it is doughlike in consistency at room temperature, it does not feed from a hopper but requires a special slutling mechanism on the injection ma­chine for automatic molding.

Although BMC often is molded by using a conventional reciprocating screw, many BMC injection machines use a simple plunger to force the material from the barrel to the mold. The plunger is used (o lessen shear degradation of the fibers as well as to prevent back slippage of material during the injection and hold part of the cycle.

The stuffer mechanism includes a loading chamber, which is generally manually loaded with up to several hundred pounds of com­pound. The stuffer chamber has a large-diam­eter piston, air- orhydraulically driven, to force the room-temperature material into the injec­tion barrel upstream of the reciprocating screw or downstream of the plunger, depending on which injection method is used.

Because the BMC is already plasticized at room temperature, it needs a minimum of heat­ing in the barrel and relatively low pressures, 6000 to 10,000 psi, for rapid injection. Also, because BMC reaches the molder from the sup­plier in a fully homogenized state, no mixing in the barrel is necessary.

(Michael L. Berins, SPI Plastics Engineering Handbook of the Society of the Plastics Industry, Inc;1991; page: 247-248)

4)Thermoset Bulk Molding Compound (BMC) (Group: manufacturing)

BMC consists of similar ingredients as those in SMC, but the compounded polymer is in billet form rather than sheet. The fibers in BMC are shorter, typically 2-12 mm, because greater fluidity is required in the molding operations for which these materials are designed. Billet diameter is usually 25-50 mm. The process of BMC is similar to that SMC, except extrusion is used to obtain the final billet form. 

(Mikell P. Groover; Fundamentals of Modern Manufacturing Materials, Processes, and Systems 3rd Edition; pg.323)

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BMC has been defined as 'a fiber reinforced thermoset molding compound not requiring advancement of cure, drying of volatile, or other processing after mixing to make it ready for use at the molding press⁰. BMC can be molded without reaction byproducts under only enough pressure to flow and compact the material. BMC is usually manufactured by combining all the ingredients in an intensive mixing process. Recent advances in BMC technology dictate that both the dry ingredients and wet ingredients be batch mixed separately and then combined together in an intensive mixer. The BMC is usu­ally in a fibrous putty form when it comes out of the mixer and resembles 'sauerkraut'. It is usu­ally compacted and extruded into bars or logs' of simple cross section.

The earliest BMCs were probably made about 1950, employing a process of impregnat­ing roving strands with blend of resin, filler, etc. and chopping them to a length in the wet stage. Since wetting glass fibers with a resin contain­ing much filler is difficult and slow, these premixes had a high glass content. The first high volume commercial BMC was made with sisal fibers and used in molding automobileheater housings. Improvement in the binder chemistry of glass fibers, development of a chemical thickening system and thermoplastic low profile additives help BMC to attain strength, chemical resistance and to overcome surface irregularities. Consequently, BMC was accepted for use in the electrical, chemical and appliance industries.

Today, BMCs are accepted as high perfor­mance engineering thermoset molding compounds and used extensively in the elec­trical, automotive and consumer goods industries. BMC is increasingly injection molded to take advantage of the automation and reproducibility afforded by the process, although it is also both transfer molded and compression molded. (George Lubin; Handbook of Composites;1998;page: 379-380)




5)Hot marking (Group: manufacturing)

A plastic film with metallic deposits in inserted between a heated die punch and the piece to be decorated.The pattern, machined in relief on the die, is transferred by pressure and heat onto the piece(which may be plastic, for example).This procedure is fast, simple, and economical.Hot marking is often used to obtain 'gold' and 'silver' logos on cosmetic cases or flocked packaging.Gilding(with gold leaf) when done on luxury leather objects is similar to this thechnique.

(materiology by Daniel kula and elodie ternaux p.307)

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A dry process used to apply a coating of metal to a plastics substrate, by transferring the metal, usually aluminium, from a metallized foil to the substrate using a heated die. Also known as hot stamping, gold stamping, gold blocking, pro-duet marking, hot-press marking and dry priming. See metal­lizing.

(Tony Whelan, Polymer Technology Dictionary;1994;page 191)