Tooling_English_模具英语.ppt

模具专业英语 Lesson 1 The Injection Molding and Machine The injection molding 　　Injection molding is principally used for the production of the thermoplastic parts, although some progress has been made in developing a method for injection molding some thermosetting materials. 　　The problem of injecting a melted plastic into a mold cavity from a reservoir of melted material has been extremely difficult to solve for thermosetting plastics which cure and harden under such conditions within a few minutes①. 　　 　　The principle of injection molding is quite similar to that of die-casting. 　　The process consists of feeding a plastic compound in powdered or granular form from a hopper through metering and melting stages and then injecting it into a mold②. 　　After a brief cooling period, the mold is opened and the solidified part ejected. 　　Injection-molding machines can be arranged for manual operation, automatic single-cycle operation, and full automatic operation. The advantage of injection molding are: 　　(i) a high molding speed adapted for mass production is possible; 　　(ii) there is a wide choice of thermoplastic materials providing a variety of useful properties; 　　(iii) it is possible to mold threads, undercuts, side holes, and large thin sections. The injection-molding machine 　　Several methods are used to force or inject the melted plastic into the mold. The most commonly used system in the larger machines is the in-line reciprocating screw, as shown in Figure 1-1. 　　The screw acts as a combination injection and plasticizing unit. As the plastic is fed to the rotating screw, it passes through three zones as shown: feed, compression, and metering. 　　After the feed zone, the screw-flight depth is gradually reduced, forcing the plastic to compress. 　　The work is converted to heat by shearing the plastic, making it a semifluid mass. In the metering zone, additional heat is applied by conduction from the barrel surface. 　　As the chamber in front of th