IE370Lecture14 - 14.1 Introduction Chapter 14: Fabrication...

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1 Chapter 14: Fabrication of Plastics, Ceramics, and Composites 14.1 Introduction s Plastics, ceramics, and composites have different structure and properties than metals s Principles of material selection and manufacturing are different s Large, complex shapes can be formed as a single unit s Processes can produce a near perfect shape and surface product 14.2 Fabrication of Plastics s A successful plastic product is manufactured so that it satisfies the various mechanical and physical property requirements s The preferred manufacturing method is determined by the desired size, shape, and quantity s There are three main different types of polymers: thermoplastics, thermosets, and elastomers Casting s Simplest of the shape- forming processes s No fillers and no pressure is required s Thermoplastics are the main type of polymer that can be casted b Acrylics, nylons, urethanes, and PVC plastisols s Some thermosets can also be cast Figure 14-1 Steps in the casting of plastic parts using a lead shel mold.
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2 Blow Molding s Thermoplastics can be converted to hollow-shape containers such as bottles s The preform is heated and placed between the two mold halves s The mold closes and the preform is expanded from air or gas pressure s The mold is then cooled, halves separated, and the product is removed s 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 s Solid granules or preformed tablets of unpolymerized plastic are placed into an open, heated cavity s A heated plunger applies pressure to the plastics, melting it and making it turn into a fluid s 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 pel et 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 s Costs for compression molding are much lower than complete processing s High dimensional precision and high surface finishing s Typical parts are gaskets, seals, exterior automotive panels, and aircraft fairings s Manufacturing equipment typically consists of a hydraulic or pneumatic press
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3 Transfer Molding s Reduces turbulence and uneven flow that occurs often in high pressure, hot- compression molding s The material is first heated until molten and then is forced into the cavity by a plunger s The temperature and pressure are maintained until the thermosetting resin has cured Figure 14-4 Diagram of the transfer molding process. Molten or softened material is first
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This note was uploaded on 09/23/2009 for the course IE 370 taught by Professor Chunghorng,r during the Spring '08 term at Purdue University-West Lafayette.

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IE370Lecture14 - 14.1 Introduction Chapter 14: Fabrication...

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