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IE370Lecture14

IE370Lecture14 - 14.1 Introduction Chapter 14 Fabrication...

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1 Chapter 14: Fabrication of Plastics, Ceramics, and Composites 14.1 Introduction square6 Plastics, ceramics, and composites have different structure and properties than metals square6 Principles of material selection and manufacturing are different square6 Large, complex shapes can be formed as a single unit square6 Processes can produce a near perfect shape and surface product 14.2 Fabrication of Plastics square6 A successful plastic product is manufactured so that it satisfies the various mechanical and physical property requirements square6 The preferred manufacturing method is determined by the desired size, shape, and quantity square6 There are three main different types of polymers: thermoplastics, thermosets, and elastomers Casting square6 Simplest of the shape- forming processes square6 No fillers and no pressure is required square6 Thermoplastics are the main type of polymer that can be casted boxshadowdwn Acrylics, nylons, urethanes, and PVC plastisols square6 Some thermosets can also be cast Figure 14-1 Steps in the casting of plastic parts using a lead shell mold.
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2 Blow Molding square6 Thermoplastics can be converted to hollow-shape containers such as bottles square6 The preform is heated and placed between the two mold halves square6 The mold closes and the preform is expanded from air or gas pressure square6 The mold is then cooled, halves separated, and the product is removed square6 Flash, extra material, is trimmed from the part and recycled Blow Molding Figure 14-2 Steps in blow molding plastic parts: (1) a tube of heated plastic is placed in the open mold; (2) the mold closes over the tube, simultaneously sealing the bottom; (3) air expands the tube against the sides of the mold; and (4) after sufficient cooling, the mold opens to release the product. Compression Molding or Hot- Compression Molding square6 Solid granules or preformed tablets of unpolymerized plastic are placed into an open, heated cavity square6 A heated plunger applies pressure to the plastics, melting it and making it turn into a fluid square6 The pressure in the cavity is maintained until the material is set Figure 14-3 The hot-compression molding process: (1) solid granules or a preform pellet is placed in a heated die; (2) a heated punch descends and applies pressure; and (3) after curing (thermosets) or cooling (thermoplastics), the mold is opened and the part is removed. Compression Molding or Hot- Compression Molding square6 Costs for compression molding are much lower than complete processing square6 High dimensional precision and high surface finishing square6 Typical parts are gaskets, seals, exterior automotive panels, and aircraft fairings square6 Manufacturing equipment typically consists of a hydraulic or pneumatic press
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3 Transfer Molding square6 Reduces turbulence and uneven flow that occurs often in high pressure, hot- compression molding square6 The material is first heated until molten and then is forced into the cavity by a plunger square6 The temperature and pressure are maintained
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