【正文】 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 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 onefourth of the machine time of a singlecavity mold. Conversely, the production increases in proportion to the number of cavities. A mold with more cavities is more expensive to build than a singlecavity mold, but not necessarily 4 times as much as a singlecavity mold. But it may also require a larger machine with larger platen area and more clamping capacity, and because it will use 4 times the amount of plastic, it may need a large injection unit, so the machine hour cost will be higher than for a machine large enough for the smaller mold. 3. Cavity shape and shrinkage The shape of the cavity is essentially the “negative” of the shape of the desired product, with dimensional allowance added to allow for shrinking of the plastic. The shape of the cavity is usually created with chipremoving machine tools, or with electric discharge machining, with chemical etching, or by any new method that may be available to remove metal or build it up, such as galvanic processes. It may also be created by casting certain metals in plaster molds created from models of the product to be made, or by casting some suitable hard plastics. The cavity shape can be either cut directly into the mold plates or formed by putting inserts into the plates. C. Cavity and core By convention, the hollow portion of the cavity space is called the cavity. The matching, often raised portion of the cavity space is called the core. Most plastic products are cupshaped. This does not mean that they look like a cup, but they do have an inside and an outside. The outside of the product is formed by the cavity, the inside by the core. The alternative to the cup shape is the flat shape. In this case, there is no specific convex portion, and sometimes, the core looks like a mirror image of the cavity. Typical examples for this are plastic knives, game chips, or round disks such as records. While these items are simple in appearance, they often present serious molding problems for ejection of the product. The reason for this is that all injection molding machines provide an ejection mechanism on the moving platen and the products tend to shrink onto and cling to the core, from where they are then 文獻 ejected. Most injection molding machines do not provide ejection mechanisms on the injection side. Polymer Processing Polymer processing, in its most general context, involves the transformation of a solid (sometimes liquid) polymeric resin, which is in a random form (., powder, pellets, beads), to a solid plastics product of specified shape, dimensions, and properties. This is achieved by means of a transformation process: extrusion, molding, calendaring, coating, thermoforming, etc. The process, in order to achieve the above objective, usually involves the following operations: solid transport, pression, heating, melting, mixing, shaping, cooling, solidification, and finishing. Obviously, these operations do not necessarily occur in sequence, and many of them take place simultaneously. Shaping is required in order to impart to the material the desired geometry and dimensions. It involves binations of viscoelastic deformations and heat transfer, which are generally associated with solidification of the product from the melt. Shaping includes: twodimensional operations, . die forming, calendaring and coating。m, and a feed of 50 mm/min. The surface roughness Raof the specimen can be improved from about 181。m by using the optimal parameters for surface grinding. Surface roughness Ra can befurther improved from about 181。m by using the ball burnishing process with the optimal burnishing the optimal surface grinding and burnishing parameters sequentially to a ?nemilled freeform surface mold insert,the surface roughness Raof freeform surface region on the tested part can be improved from about 181。m. Keywords Automated surface ?nishing Grinding process Taguchi’s method 1 Introduction Plastics are important engineering materials due to their speci?c characteristics, such as corrosion resistance, resistance to chemicals, low density, and ease of manufacture, and have increasingly replaced metallic ponents in industrial applications. Injection molding is one of the important forming processes for plastic products. The surface ?nish quality of the plastic injection mold is an essential 文獻 requirement due to its direct effects on the appearance of the plastic product. Finishing processes such as grinding, polishing and lapping are monly used to improve the surface ?nish. The mounted grinding tools (wheels) have been widely used in conventional mold and die ?nishing industries. The geometric model of mounted grinding tools for automated surface ?nishing processes was introduced in [1]. A ?nishing process model of spherical grinding tools for automated surface ?nishing systems was developed in [2]. Grinding speed, depth of cut, feed rate, and wheel properties such as abrasive material and abrasive grain size, are