【正文】 文獻(xiàn) 編號： 畢業(yè)設(shè)計(jì) (論文 )外文翻譯 院 （系）： 應(yīng)用科技學(xué)院 專 業(yè)： 機(jī)械設(shè)計(jì)制造及其自動化 學(xué)生姓名： 學(xué) 號： 指導(dǎo)教師單位 ： 姓 名： 職 稱： 2020 年 5 月 20 日 文獻(xiàn) The Injection Molding The Introduction of Molds The mold is at the core of a plastic manufacturing process because its cavity gives a part its shape. This makes the mold at least as criticaland many cases more sofor the quality of the end product as, for example, the plasticiting unit or other ponents of the processing equipment. Mold Material Depending on the processing parameters for the various processing methods as well as the length of the production run, the number of finished products to be produced, molds for plastics processing must satisfy a great variety of requirements. It is therefore not surprising that molds can be made from a very broad spectrum of materials, includingfrom a technical standpointsuch exotic materials as paper matched and plaster. However, because most processes require high pressures, often bined with high temperatures, metals still represent by far the most important material group, with steel being the predominant metal. It is interesting in this regard that, in many cases, the selection of the mold material is not only a question of material properties and an optimum pricetoperformance ratio but also that the methods used to produce the mold, and thus the entire design, can be influenced. A typical example can be seen in the choice between cast metal molds, with their very different cooling systems, pared to machined molds. In addition, the production technique can also have an effect。 for instance, it is often reported that, for the sake of simplicity, a prototype mold is frequently machined from solid stock with the aid of the latest technology such as puteraided (CAD) and puterintegrated manufacturing (CIM). In contrast to the previously used methods based on the use of patterns, the use of CAD and CAM often represents the more economical solution today, not only because this production capability is available pinhouse but also because with any other technique an order would have to be placed with an outside supplier. Overall, although highgrade materials are often used, as a rule standard materials are used in mold making. New, stateofthe art (highperformance) materials, such as ceramics, for instance, are almost pletely absent. This may be related to the fact that their desirable characteristics, such as constant properties up to very high temperatures, are not required on molds, whereas their negative characteristics, e. g. low tensile strength and poor thermal conductivity, have a clearly related to ceramics, 文獻(xiàn) such as sintered material, is found in mild making only to a limited degree. This refers less to the modern materials and ponents produced by powder metallurgy, and possibly by hot isocratic pressing, than to sintered metals in the sense of porous, airpermeable materials. Removal of air from the cavity of a mold is necessary with many different processing methods, and it has been proposed many times that this can be acplished using porous metallic materials. The advantages over specially fabricated venting devices, particularly in areas where melt flow fronts meet, I, e, at weld lines, are as obvious as the potential problem areas: on one hand, preventing the texture of such surfaces from being visible on the finished product, and on the other hand, preventing the microspores from quickly being clogged with residues (broken off flash, deposits from the molding material, socalled plate out, etc.). It is also interesting in this case that pletely new possibilities with regard to mold design and processing technique result from the use of such materials. A. Design rules There are many rules for designing molds. These rules and standard practices are based on logic, past experience, convenience, and economy. For designing, mold making, and molding, it is usually of advantage to follow the rules. But occasionally, it may work out better if a rule is ignored and an alternative way is selected. In this text, the most mon rules are noted, but the designer will learn only from experience which way to go. The designer must ever be open to new ideas and methods, to new molding and mold materials that may affect these rules. B. The basic mold 1. Mold cavity space The mold cavity space is a shape inside the mold, “excavated” in such a manner that when the molding material is forced into this space it will take on the shape of the cavity space and, therefore, the desired product. The principle of a mold is almost as old as human civilization. Molds have metals into sand forms. Such molds, which are still used today in foundries, can be used only once because the mold is destroyed to release the product after it has solidified. Today, we are looking for permanent molds that can be used over and over. Now molds are made from strong, durable materials, such as steel, or from softer aluminum or metal alloys and even from certain plastics where a long mold life is not required because the planned production is small. In injection molding the plastic is injected into the cavity space with high pressure, so 文獻(xiàn) the mold must be strong enough to resist the injection pressure without deforming. 2. Number of cavities Many molds, particularly molds for larger products, are built for only cavity space, but many molds, especially large production molds, are built with 2 or more cavities. The reason for this is purely economical. It takes only little more time to inject several cavities than to inject one. For example, a 4cavity mold requires only one