【導(dǎo)讀】畢業(yè)設(shè)計(論文)外文翻譯

　　

【正文】 The temperature of the part often exceeds the temperature of the mold. When the reaction is sufficiently advanced for the part to be rigid (even at a high temperature) the cycle is plete and the part is ejected. Design considerations The mold and process design for injection molding of reactive materials is much more plex because of the chemical reaction that takes place during the filling and postfilling stages. For instance, slow filling often causes premature gelling and a resultant short shot, while fast filling could induce turbulent flow that creates internal porosity. Improper control of moldwall temperature and/or inadequate part thickness will either give rise to moldability problems during injection, or cause scorching of the materials. Computer simulation is generally recognized as a more costeffective tool than the conventional, timeconsuming trialanderror method for tool and process debugging. Structural foam injection molding Overview Structural foam molding produces parts consisting of solid external skin surfaces surrounding an inner cellular (or foam) core, as illustrated in Figure 1 below. This process is suitable for large, thick parts that are subject to bending loads in their enduse application. Structural foam parts can be produced with both low and high pressure, with nitrogen gas or chemical blowing agents. Thinwall molding 文獻 Overview The term thinwall is relative. Conventional plastic parts are typically 2 to 4 mm thick. Thinwall designs are called advanced when thicknesses range from to 2 mm, and leadingedge when the dimension is below mm. Another definition of thinwall molding is based on the flowlengthtowallthickness ratios. Typical ratios for these thinwall applications range from 100:1 to 150:1 or more. Typical applications Thinwall molding is more popular in portable munication and puting equipment, which demand plastic shells that are much thinner yet still provide the same mechanical strength as conventional parts. Processing Because thinwall parts freeze off quickly, they require high melt temperatures, high injectio speeds, and very high injection pressures if multiple gates or sequential valve gating are not an optimized ramspeed profile helps to reduce the pressure requirement. Due to the high velocity and shear rate in thinwall molding, orientation occurs more readily help minimize anisotropic shrinkage in thinwall parts, it is important to pack the part adequately while the core is still molten. Injection molding machine Components For thermoplastics, the injection molding machine converts granular or pelleted raw plastic into final molded parts via a melt, inject, pack, and cool cycle. A typical injection molding machine consists of the following major ponents, as illustrated in Figure 1 below. 文獻 Machine function Injection molding machines can be generally classified into three categories, based on machine function: Generalpurpose machines Precision, tighttolerance machines Highspeed, thinwall machines Auxiliary equipment The major equipment auxiliary to an injection molding machine includes resin dryers, materialshandling equipment, granulators, moldtemperature controllers and chillers, partremoval robots, and parthandling equipment. Automated surface ?nishing of plastic injection mold steel with spherical grinding and ball burnishing processes Abstract This study investigates the possibilities of automated spherical grinding and ball burnishing surface ?nishing processes in a freeform surface plastic injection mold steel PDS5 on a CNC machining center. The design and manufacture of a grinding tool holder has been acplished in this optimal surface grinding parameters were determined usingTaguchi’s orthogonal array method for plastic injection moldingsteel PDS5 on a machining center. The optimal surface grinding parameters for the plastic injection mold steel PDS5 were the bination of an abrasive material of PA Al2O3, a grinding speed of 18 000 rpm, a grinding depth of 20 181。m, and a feed of 50 mm/min. The surface roughness Raof the specimen can be improved from about 181。m to 181。m by using the optimal parameters for surface grinding. Surface roughness Ra can befurther improved from about 181。m to 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 to 181。m. Keywords Automated surface ?nishing Ball burnishing process Grinding process Surface roughness 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 the