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21st Century Manufacturing Episode 2 Part 8

Tham khảo tài liệu '21st century manufacturing episode 2 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 334 Plastic-Products Manufacturing and Final Assembly Chap. 8 8.3 PROCESSING OF PLASTICS I THE INJECTION MOLDING METHOD 8.3.1 Overview Injection molding is a key production method for the casings of consumer products. It is cheap reliable and reduces the device s weight compared with metals. The ST Microelectronics Touchchip the case study in Chapter 2 and the InfoPad casings the case study in Chapter 6 were made in this manner. A very wide array of consumer products ranging from toys to telephones to automobile parts is also made through this process. In Figure 8.4 some general features of the mold are shown. A simple bucket or cuplike component could be made in the gap between the core and the cavity shown at the bottom right. In this case the parting plane shown on the bottom left could be at the lip of the bucket. For other products the parting plane might be less conveniently located. Thus a ridge is often visible around plastic toys and simple appliances where the parting plane has been located. Further finishing by hand might be desửable for such parts. Hand finishing might also be needed a for the injection s gate marks that may be visible as tiny pimples on the surface of a part and b for the ejector-pin marks that for a relatively small object like a cellular phone casing are usually about 6 mm about 0.25 inch in diameter. The reader might be interested in picking up any familiar plastic consumer product and searching for these inevitable markings. However these are often located in noncosmetic areas of the part because of the cost involved in finishing operations. Not surprisingly they are often found on the bottom or base of the object. Injection molding is shown in Figure 8.5. Pellets of the desừed thermoplastic are loaded into the hopper on the right side and heated as they are pushed by a screw direction Undercut Parting direction z Principal directions Parting plane Figure 4 Basic mold description including slider for an undercut. 8.3 Processing of