Ch. 14 - 2/24/2010 Chapter 14: Fabrication of Plastics,...

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2/24/2010 1 Chapter 14: Fabrication of Plastics, Ceramics, and Composites 14.1 Introduction Plastics, ceramics, and composites have different structure and properties than metals Principles of material selection and manufacturing are different Large, complex shapes can be formed as a single unit Processes can produce a near perfect shape and surface product
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2/24/2010 2 14.2 Fabrication of Plastics A successful plastic product is manufactured so that it satisfies the various mechanical and physical property requirements The preferred manufacturing method is determined by the desired size, shape, and quantity There are three main different types of polymers: thermoplastics, thermosets, and elastomers Casting Simplest of the shape- forming processes No fillers and no pressure is required Thermoplastics are the main type of polymer that can be casted Acrylics, nylons, urethanes, and PVC plastisols 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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2/24/2010 3 Blow Molding Thermoplastics can be converted to hollow-shape containers such as bottles The preform is heated and placed between the two mold halves The mold closes and the preform is expanded from air or gas pressure The mold is then cooled, halves separated, and the product is removed 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.
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2/24/2010 4 Compression Molding or Hot- Compression Molding Solid granules or preformed tablets of unpolymerized plastic are placed into an open, heated cavity A heated plunger applies pressure to the plastics, melting it and making it turn into a fluid 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 Costs for compression molding are much lower than complete processing High dimensional precision and high surface finishing Typical parts are gaskets, seals, exterior automotive panels, and aircraft fairings Manufacturing equipment typically consists of a hydraulic or pneumatic press
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2/24/2010 5 Transfer Molding Reduces turbulence and uneven flow that occurs often in high pressure, hot- compression molding The material is first heated until molten and then is forced into the cavity by a plunger The temperature and pressure are maintained until the thermosetting resin
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This note was uploaded on 01/19/2012 for the course IE 230 taught by Professor Xangi during the Spring '08 term at Purdue University-West Lafayette.

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Ch. 14 - 2/24/2010 Chapter 14: Fabrication of Plastics,...

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