外文翻译--一个描述电铸镍壳在注塑模具的应用的技术研究 英文版

桂林电子科技大学毕业设计（论文）外文翻译译文 第 1页 共 28页 technical note on the characterization of electroformed nickel shells for their application to injection molds aUniversidad de Las Palmas de Gran Canaria, Departamento de Ingenieria Mecanica, Spain Abstract The techniques of rapid prototyping and rapid tooling have been widely developed during the last years. In this article, electroforming as a procedure to make cores for plastics injection molds is analysed. Shells are obtained from models manufactured through rapid prototyping using the FDM system. The main objective is to analyze the mechanical features of electroformed nickel shells, studying different aspects related to their metallographic structure, hardness, internal stresses and possible failures, by relating these features to the parameters of production of the shells with an electroforming equipment. Finally a core was tested in an injection mold. Keywords: Electroplating； Electroforming； Microstructure； Nickel 1. Introduction One of the most important challenges with which modern industry comes across is to offer the consumer better products with outstanding variety and time variability (new designs). For this reason, modern industry must be more and more competitive and it has to produce with acceptable costs. There is no doubt that combining the time variable and the quality variable is not easy because they frequently condition one another； the technological advances in the productive systems are going to permit that combination to be more efficient and feasible in a way that, for example, if it is observed the evolution of the systems and techniques of plastics injection, we arrive at the conclusion that, in fact, it takes less and less time to put a new product on the market and with higher levels of quality. The manufacturing technology of rapid tooling is, in this field, one of those technological advances that makes possible the improvements in the processes of designing and manufacturing injected parts. Rapid tooling techniques are basically composed of a collection of procedures that are going to allow us to obtain a mold of plastic parts, in small or medium series, in a short period of time and with acceptable accuracy levels. Their application is not only included in the field of making plastic injected pieces 1, 2 and 3, however, it is true that it is where they have developed more and where they find the highest output. This paper is included within a wider research line where it attempts to study, define, analyze, test and propose, at an industrial level, the possibility of creating cores for 桂林电子科技大学毕业设计（论文）外文翻译译文 第 2页 共 28页injection molds starting from obtaining electroformed nickel shells, taking as an initial model a prototype made in a FDM rapid prototyping equipment. It also would have to say beforehand that the electroforming technique is not something new because its applications in the industry are countless 3, but this research work has tried to investigate to what extent and under which parameters the use of this technique in the production of rapid molds is technically feasible. All made in an accurate and systematized way of use and proposing a working method. 2. Manufacturing process of an injection mold The core is formed by a thin nickel shell that is obtained through the electroforming process, and that is filled with an epoxic resin with metallic charge during the integration in the core plate 4 This mold (Fig. 1) permits the direct manufacturing by injection of a type a multiple use specimen, as they are defined by the UNE-EN ISO 3167 standard. The purpose of this specimen is to determine the mechanical properties of a collection of materials representative industry, injected in these tools and its coMParison with the properties obtained by conventional tools. Fig. 1. Manufactured injection mold with electroformed core. The stages to obtain a core 4, according to the methodology researched in this work, are the following: (a) Design in CAD system of the desired object. (b) Model manufacturing in a rapid prototyping equipment (FDM system). The material used will be an ABS plastic. (c) Manufacturing of a nickel electroformed shell starting from the previous model that has been coated with a conductive paint beforehand (it must have electrical conductivity). (d) Removal of the shell from the model. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 3页 共 28页(e) Production of the core by filling the back of the shell with epoxy resin resistant to high temperatures and with the refrigerating ducts made with copper tubes. The injection mold had two cavities, one of them was the electroformed core and the other was directly machined in the moving platen. Thus, it was obtained, with the same tool and in the same process conditions, to inject simultaneously two specimens in cavities manufactured with different technologies. 3. Obtaining an electroformed shell: the equipment Electrodeposition 5 and 6 is an electrochemical process in which a chemical change has its origin within an electrolyte when passing an electric current through it. The electrolytic bath is formed by metal salts with two submerged electrodes, an anode (nickel) and a cathode (model), through which it is made to pass an intensity coming from a DC current. When the current flows through the circuit, the metal ions present in the solution are transformed into atoms that are settled on the cathode creating a more or less uniform deposit layer. The plating bath used in this work is formed by nickel sulfamate 7 and 8 at a concentration of 400 ml/l, nickel chloride (10 g/l), boric acid (50 g/l), Allbrite SLA (30 cc/l) and Allbrite 703 (2 cc/l). The selection of this composition is mainly due to the type of application we intend, that is to say, injection molds, even when the injection is made with fibreglass. Nickel sulfamate allows us to obtain an acceptable level of internal stresses in the shell (the tests gave results, for different process conditions, not superior to 50 MPa and for optimum conditions around 2 MPa). Nevertheless, such level of internal pressure is also a consequence of using as an additive Allbrite SLA, which is a stress reducer constituted by derivatives of toluenesulfonamide and by formaldehyde in aqueous solution. Such additive also favours the increase of the resistance of the shell when permitting a smaller grain. Allbrite 703 is an aqueous solution of biodegradable surface-acting agents that has been utilized to reduce the risk of pitting. Nickel chloride, in spite of being harmful for the internal stresses, is added to enhance the conductivity of the solution and to favour the uniformity in the metallic distribution in the cathode. The boric acid acts as a pH buffer. The equipment used to manufacture the nickel shells tested has been as follows: Polypropylene tank: 600 mm 400 mm 500 mm in size. Three teflon resistors, each one with 800 W. Mechanical stirring system of the cathode. System for recirculation and filtration of the bath formed by a pump and a polypropylene filter. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 4页 共 28页 Charging rectifier. Maximum intensity in continuous 50 A and continuous current voltage between 0 and 16 V. Titanium basket with nickel anodes (Inco S-Rounds Electrolytic Nickel) with a purity of 99%. Gases aspiration system. Once the bath has been defined, the operative parameters that have been altered for testing different conditions of the process have been the current density (between 1 and 22 A/dm2), the temperature (between 35 and 55 C) and the pH, partially modifying the bath composition. 4. Obtained hardness One of the most interesting conclusions obtained during the tests has been that the level of hardness of the different electroformed shells has remained at rather high and stable values. In Fig. 2, it can be observed the way in which for current density values between 2.5 and 22 A/dm2, the hardness values range from 540 and 580 HV, at pH 4 0.2 and with a temperature of 45 C. If the pH of the bath is reduced at 3.5 and the temperature is 55 C those values are above 520 HV and below 560 HV. This feature makes the tested bath different from other conventional ones composed by nickel sulfamate, allowing to operate with a wider range of values； nevertheless, such operativity will be limited depending on other factors, such as internal stress because its variability may condition the work at certain values of pH, current density or temperature. On the other hand, the hardness of a conventional sulfamate bath is between 200250 HV, much lower than the one obtained in the tests. It is necessary to take into account that, for an injection mold, the hardness is acceptable starting from 300 HV. Among the most usual materials for injection molds it is possible to find steel for improvement (290 HV), steel for integral hardening (520595 HV), casehardened steel (760800 HV), etc., in such a way that it can be observed that the hardness levels of the nickel shells would be within the mediumhigh range of the materials for injection molds. The objection to the low ductility of the shell is compensated in such a way with the epoxy resin filling that would follow it because this is the one responsible for holding inwardly the pressure charges of the processes of plastics injection； this is the reason why it is necessary for the shell to have a thickness as homogeneous as possible (above a minimum value) and with absence of important failures such as pitting. Fig. 2. Hardness variation with current density. pH 4 0.2, T = 45 C. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 5页 共 28页 5. Metallographic structure In order to analyze the metallographic structure, the values of current density and temperature were mainly modified. The samples were analyzed in frontal section and in transversal section (perpendicular to the deposition). For achieving a convenient preparation, they were conveniently encapsulated in resin, polished and etched in different stages with a mixture of acetic acid and nitric acid. The etches are carried out at intervals of 15, 25, 40 and 50 s, after being polished again, in order to be observed afterwards in a metallographic microscope Olympus PME3-ADL 3.3/10. Before going on to comment the photographs shown in this article, it is necessary to say that the models used to manufacture the shells were made in a FDM rapid prototyping machine where the molten plastic material (ABS), that later solidifies, is settled layer by layer. In each layer, the extruder die leaves a thread approximately 0.15 mm in diameter which is compacted horizontal and vertically with the thread settled inmediately after. Thus, in the surface it can be observed thin lines that indicate the roads followed by the head of the machine. These lines are going to act as a reference to indicate the reproducibility level of the nickel settled. The reproducibility of the model is going to be a fundamental element to evaluate a basic aspect of injection molds: the surface texture. The tested series are indicated in Table 1. Table 1. Tested series Series pH Temperature (C) Current density (A/dm2) 1 4.2 0.2 55 2.22 2 3.9 0.2 45 5.56 3 4.0 0.2 45 10.00 4 4.0 0.2 45 22.22 Fig. 3 illustrates the surface of a sample of the series after the first etch. It shows the roads originated by the FDM machine, that is to say that there is a good reproducibility. It cannot be still noticed the rounded grain structure. In Fig. 4, series 2, after a second etch, it can be observed a line of the road in a way less clear than in the previous case. In Fig. 5, series 3 and 2 etch it begins to appear the rounded grain 桂林电子科技大学毕业设计（论文）外文翻译译文 第 6页 共 28页structure although it is very difficult to check the roads at this time. Besides, the most darkened areas indicate the presence of pitting by inadequate conditions of process and bath composition. Fig. 3. Series 1 (150), etch 1. Fig. 4. Series 2 (300), etch 2. Fig. 5. Series 3 (300), etch 2. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 7页 共 28页This behavior indicates that, working at a low current density and a high temperature, shells with a good reproducibility of the model and with a small grain size are obtained, that is, adequate for the required application. If the analysis is carried out in a plane transversal to the deposition, it can be tested in all the samples and for all the conditions that the growth structure of the deposit is laminar (Fig. 6), what is very satisfactory to obtain a high mechanical resistance although at the expense of a low ductibility. This quality is due, above all, to the presence of the additives used because a nickel sulfamate bath without additives normally creates a fibrous and non-laminar structure 9. The modification until a nearly null value of the wetting agent gave as a result that the laminar structure was maintained in any case, that matter demonstrated that the determinant for such structure was the stress reducer (Allbrite SLA). On the other hand, it was also tested that the laminar structure varies according to the thickness of the layer in terms of the current density. Fig. 6. Plane transversal of series 2 (600), etch 2. 6. Internal stresses One of the main characteristic that a shell should have for its application like an insert is to have a low level of internal stresses. Different tests at different bath temperatures and current densities were done and a measure system rested on cathode flexural tensiometer method was used. A steel testing control was used with a side fixed and the other free (160 mm length, 12.7 mm width and thickness 0.3 mm). Because the metallic deposition is only in one side the testing control has a mechanical strain (tensile or compressive stress) that allows to calculate the internal stresses. Stoney model 10 was applied and was supposed that nickel substratum thickness is enough small (3 m) to influence, in an elastic point of view, to the strained steel part. In all the tested cases the most value of internal stress was under 50 MPa for extreme conditions and 2 MPa for optimal conditions, an acceptable value for the required application. The conclusion is that the electrolitic bath allows to work at different conditions and parameters without a significant variation of internal stresses. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 8页 共 28页7. Test of the injection mold Tests have been carried out with various representative thermoplastic materials such as PP, PA, HDPE and PC, and it has been analysed the properties of the injected parts such as dimensions, weight, resistance, rigidity and ductility. Mechanical properties were tested by tensile destructive tests and analysis by photoelasticity. About 500 injections were carried out on this core, remaining under conditions of withstanding many more. In general terms, important differences were not noticed between the behavior of the specimens obtained in the core and the ones from the machined cavity, for the set of the analysed materials. However in the analysis by photoelasticiy (Fig. 7) it was noticed a different tensional state between both types of specimens, basically due to differences in the heat transference and rigidity of the respective mold cavities. This difference explains the ductility variations more outstanding in the partially crystalline materials such as HDPE and PA 6. Fig. 7. Analysis by photoelasticity of injected specimens. For the case of HDPE in all the analysed tested tubes it was noticed a lower ductility in the specimens obtained in the nickel core, quantified about 30%. In the case of PA 6 this value was around 50%. 8. Conclusions After consecutive tests and in different conditions it has been checked that the nickel sulfamate bath, with the utilized additives has allowed to obtain nickel shells with some mechanical properties acceptable for the required application, injection molds, that is to say, good reproducibility, high level of hardness and good mechanical resistance in terms of the resultant laminar structure. The mechanical deficiencies of the nickel shell will be partially replaced by the epoxy resin that finishes shaping the core for the injection mold, allowing to inject medium series of plastic parts with acceptable quality levels. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 9页 共 28页 References 1 A.E.W. Rennie, C.E. Bocking and G.R. Bennet, Electroforming of rapid prototyping mandrels for electro discharge machining electrodes, J. Mater. Process. Technol. 110 (2001), pp. 186196. 2 P.K.D.V. Yarlagadda, I.P. Ilyas and P. Chrstodoulou, Development of rapid tooling for sheet metal drawing using nickel electroforming and stereo lithography processes, J. Mater. Process. Technol. 111 (2001), pp. 286294. 3 J. Hart, A. Watson, Electroforming: A largely unrecognised but expanding vital industry, Interfinish 96, 14 World Congress, Birmingham, UK, 1996. 4 M. Monzn et al., Aplicacin del electroconformado en la fabricacin rpida de moldes de inyeccin, Revista de Plsticos Modernos. 84 (2002), p. 557. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 10页 共 28页5 L.F. Hamilton et al., Clculos de Qumica Analtica, McGraw Hill (1989). 6 E. Julve, Electrodeposicin de metales, 2000 (E.J.S.). 7 A. Watson, Nickel Sulphamate Solutions, Nickel Development Institute (1989). 8 A. Watson, Additions to Sulphamate Nickel Solutions, Nickel Development Institute (1989). 9 J. Dini, Electrodeposition Materials Science of Coating and Substrates, Noyes Publications (1993). 10 J.W. Judy, Magnetic microactuators with polysilicon flexures, Masters Report, Department of EECS, University of California, Berkeley, 1994. (cap. 3). How Surface Treatments Keep Molds Operating Longer Important tips and information about mold coatings to help you achieve the level of production that you and your customers desire. By Steven . Bales Mold making technology January 2006 Abstract Theres an awful lot to know these days about molding plastic and how to get the very best performance from the valuable tools you build or run. This guide has been written to provide important tips and information about mold coatings. After reading this, you should have a very good idea of what coatingsfrom the very traditional to the very latestwill help you to achieve the level of production you and your 桂林电子科技大学毕业设计（论文）外文翻译译文 第 11页 共 28页customers desire. After all, these tools are an investment and they need to be protected for the life of the products they mold. Key Words mold coatings preventive maintenance (PM) program benefit nickel Cobalt diamond-chrome nickel-PTFE nickel-boron nitride electroless nickel texture The Key Role of Coatings Before introducing you to the wide range of coatings on the market today, its important to note the role coatings can play in an effective preventive maintenance (PM) program. PM is really the key to protecting your tooling, your investment. Why? Because it saves time and money. Once you invest in a mold coating to improve tool performance, then a PM program is always a good idea to ensure you get the maximum benefit. These two steps should be a given in any shop. Remember, no coating lasts forever, and producing substandard parts from a mold with a worn coating is no way to win customers and stay profitable. PM is probably the most cost-effective strategy you can put in place. The key is to educate your personnel on how mold coatings wear during production. Every coating is different, so its of benefit to have employees learn how to tell when the coating is showing deterioration, especially in high-wear areas such as gates and runners. For example, wear in and around gate areas plated with hard chrome is the first sign that your mold needs servicing. How can you tell there is wear? The chrome coating is approximately 20 RC points harder than the base steel, so exposed steel will wear much faster than the coated surfaces surrounding it, causing a slight or pronounced edge or “step” on the surface. Conversely, nickel will wear almost evenly, causing a kind of feathering effect, making it more difficult to recognize wear. A more identifiable difference will be the color because when nickel coating wears, it produces a shadow or halo effect on the steel. No step or edge will be evident. The steel also will have a more silver appearance compared to the somewhat tarnished look of the nickel coating. This knowledge makes pulling a mold for maintenance before the coating wears through an ultra important aspect of a PM program. To miss important wear signals means more costly repairs and additional polishing expense. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 12页 共 28页Measuring Wear A recommended tool for measuring the wear level of any coating is an electronic thickness gauge that uses a combination of magnetism and eddy current to accurately measure surface thickness. When the mold first arrives in your plant, take the time to measure the surface thicknessespecially in high-wear areasusing this specialized tool. As you run production on the mold, occasionally pause to re-measure those areas. When you have determined that the finish is wearing to a critical level, pull the mold and send it out for maintenance. Part Counts Be sure to record the measurements taken with the thickness gauge and use the notes to create a history of maintenance requirements for the tool. A cycle counter installed on the mold will allow your tooling engineer to record wear levels as compared to piece part counts, thereby doubling the effectiveness of your PM program. Part counts are a great way to determine maintenance needs, especially with high-volume molding projects. From the very first time you run the mold, keep an accurate piece count until it is ready for its first maintenance work. Use that count as a gauge for when the next maintenance is due. Because you know approximately when the mold will be ready to be refurbished, you can arrange the service in advance with your coating vendor. This not only gives him ample time to schedule your mold maintenance, but it also allows you to optimize the use of the mold and the machine thats running it. Coating Challenges Even today, there are those who question the benefits of using fancysometimes more expensivecoatings to prolong tooling life or enhance performance. To some, the tried and true hard chrome or electroless nickel are all theyll ever need to accomplish those goals. But we all know that todays engineered plastic materials can be pretty rough on injection molds. Challenges to mold maintenance extend beyond glass- and mineral-fillers to include rice hulls, wood fibers, metal powders, flame retardants and other additivesnot to mention the resins themselves. In addition, outgassing and moisture acidity often accompany abrasive wear, taking an even bigger toll on expensive tooling. In addition, growing complexity in mold design involves tinier, more intricate flow passages and more frequent use of moving cores and slides. All of these circumstances have prompted the development of a wider variety of mold coatings that can keep molds operating longer between repairs. New Coating Science 桂林电子科技大学毕业设计（论文）外文翻译译文 第 13页 共 28页If you are molding highly intricate parts using glass-filled materials, you might think using hard chrome will be sufficient because it is a classic, reliable way to protect your mold from both corrosion and abrasion. However, hard chrome, for all its benefits, does not tend to plate uniformly in detailed areas like ribs and bosses. There is a newer solutiona nickel-cobalt alloy coating that can overcome that limitation. Nickel Cobalt Nickel-cobalt can be an economical alternative to hard chrome. Hard chrome requires construction of a conforming anode to coat the mold. The more detail in the mold, the more time it takes to build the anode and the more expensive the process becomes. This nickel-cobalt alloy coating requires no anode, and because of its electroless properties, it plates much more uniformly. The cobalt gives it good abrasion resistance, but its hardness is 62 RC, 10 points lower than hard chrome. Is it worth paying extra for hard chromes superior wear protection? You have to consider the material being run in the mold. Whats the percentage of glass? Is corrosion a greater concern than abrasion? Diamond Chrome Hard chrome and a nickel-cobalt alloy coating offer two very good solutions for abrasion resistance, but for very high-wear conditions, an even newer product called diamond-chrome offers exceptional protection. It has an RC rating greater than 85 and is a chromium-matrix composite coating with a dispersion of nanometer-size, spherical diamond particles. Since diamonds are unmatched for hardness, this coating offers protection beyond the norm. Though their Rockwell ratings are comparable, diamond-chrome outperforms titanium nitride (TiN) coating because it wont compromise the dimensional integrity of the plated tool. The difference is that it is applied at only about 130oF while TiN requires application temperatures of 800oF or higher. Diamond-chrome can plate prehardened, heat-treated or nitrided steel and other base materials such as aluminum, beryllium-copper, brass and stainless steel. Recommended uses include cores, cavities, slides, ejector sleeves, and rotating and unscrewing cores. Its anti-galling properties are advantageous on moving cores and slides. Diamond-chrome also is very strippable and has no adverse effect on the base material, saving time and money when maintenance is needed. TiN is strippable as well, but it can take up to several days to remove with a peroxide-based solution. Diamond-chrome can be stripped in minutes using reverse electrolysis in a caustic solution. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 14页 共 28页In addition, diamond-chrome can be deposited at any controlled thickness from 20 millionths of an inch to 0.001 in. TiN is generally only applied in thin deposits of a few millionths of an inch. Diamond-chrome can coat complex details, while TiN has very limited coverage of complex details. While TiN is very lubricious, with a coefficient of friction (COF) of 0.4 (against steel), diamond-chrome has a COF of 0.15nearly three times more lubricious. Nickel-Boron Nitride When it comes to molders needs for a specialty coating that offers excellent release properties and high resistance to wear, heat, and corrosion, an electroless nickel-phosphorus matrix containing boron nitride particles should be considered. It has a very low COF (0.05 against steel) and an RC hardness of 54, which can be increased to 67 RC after heat treatinga unique characteristic. Nickel-boron nitride can be applied to any substrate at only 185oF and can be easily stripped without compromising the base material. Though it is approximately 20 percent more expensive than nickel-PTFE, this coating will outperform nickel-PTFE at up to 1250oF, which far surpasses the 500oF maximum limit for all PTFE-based coatings. Because applying nickel-boron nitride is an autocatalytic process, it requires no anode, therefore saving time and money. In addition, it will not compromise thermal conductivity of the mold. Applications include unscrewing cores for closures, where reduced cycle times are essential. Where lubricity is needed for better release from deep ribs, zero-draft cores, textured surfaces and “sticky” polymers, a nickel-PTFE composite will greatly improve part release and enhance resin flow by as much as 4 to 8 percent for shorter cycle times. COF is 0.10 against steel. It should be noted that applying pure PTFE to the mold adds high lubricity, but only a very short-term benefit. PTFE by itself has no hardness, so it wont last. But a dispersion of 25 percent PTFE by volume in a co-deposit with nickel results in 45 RC hardness for added wear and corrosion protection. Tried and True Despite the new coating science, we cannot throw out the old, reliable coatings such as like hard chrome or electroless nickel just yet. Theres no question that they still have their uses. Hard Chrome For example, hard chromes top advantage is that it has a hardness of 72 Rockwell C (RC) and is applied at the low temperature of 130oF. When applied in its purest form, it allows you to achieve any SPI finish on your tooling. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 15页 共 28页Hard chrome is often a good choice for electrical circuit-breaker molds since they use materials containing as much as 40 percent glass. To help combat erosion and prevent severely damaging gates and surrounding mold areas, it is usually recommend to use a high-diamond polish, followed by a hard-chrome coating of 0.0003 to 0.0005 inches for added protection. The downside can be cost, since chrome plating is limited to areas accessible by an anode. If your mold has complex details, it could require extra conforming anode construction and that adds time and expense to the project. Another possible drawback is chromes environmental impactchromium is a carcinogen. Some companies are attempting to develop better, cleaner alternatives, but so far nothing matches hard chromes benefits from a tooling perspective. Electroless Nickel Like hard chrome, electroless nickel has been used successfully for years, particularly to protect molds where corrosive off-gassing is created by materials such as PVC or halogenated fire retardants. It is not uncommon to see such resins produce an orange rust, corroding the unprotected mold almost right before your eyes. Products molded of such materials for the electronic or medical industry often cannot tolerate the presence of any oxidation byproducts. Electroless nickel does an excellent job of resisting oxidation because it plates very uniformly in thin deposits of 0.0002 to 0.0003 inches. Even in tight areas of detailed parts, electroless nickel at 50 RC hardness is ideal for corrosion protection. It can be deposited in very accurate thicknesses of 0.002 to 0.003 inches and can be ground or EDMed. Thus, electroless nickel often is used for dimensional build-ups under flash chrome and for enlarging threaded cores and inserts or precisely sizing cavities. It also works very well on entire mold bases, A and B plates, ejector-base housings, pin plates and pillar supports, providing years of low-maintenance, rust-free operation. Know Your Mold Finishes Before determining what coating to useif one is neededthe mold finish must be taken into account because, as noted earlier, certain finishes may actually increase the need for a mold coating, and some combinations work extremely well together improving lubricity and release properties. There are four standard SPI finishes: diamond, stone, paper and blast. Each gives the molding surface a different appearance, from a glossy, mirror-like surface (A-1 Diamond) to a fairly rough, gritty texture (from blasting with glass beads or aluminum oxide). Each of the four finishes has three grades as well. Diamond The A-1 Diamond finish is the most perfect finish available, which means it has the lowest RA value (roughness average). There are no high or low ridges. For example, a 桂林电子科技大学毕业设计（论文）外文翻译译文 第 16页 共 28页paper scratch on steel can rate a 2 to 4 RA finish, whereas an A-1 Diamond is lens-quality smoothness, generally 1 RA or less. Roughness is almost immeasurable. But a number of plastic materials tend to stick like glue to the flawless, mirror-like finish, making such perfect smoothness almost detrimental in many molding applications. One good example is molding polystyrene on a polished straight-wall core with 1d or less draft. Streak or drag lines can appear on the parts. This can be solved by flash-chrome plating the core, which creates a surface with micro-cracks. Impregnating those cracks with PTFE and then re-establishing the A-1 Diamond finish solves the problem in more than 95 percent of cases. In thin-wall molding applications such as these, a light bead-blast finish is appliedjust enough to very slightly interrupt the flawless A-2 Diamond surface. The surface is buffed again, leaving just a bit of almost invisible stipple. This finish plus a coating of nickel-PTFE will greatly improve part release and enhance mold filling. Phenolics and other thermosets almost demand a perfect polish and work extraordinarily well with a diamond finish. Combine that with a hard, protective coating like chrome or diamond-chrome, and you will strengthen the molds surface and optimize release. Phenolics and other thermosets almost demand a perfect polish and work extraordinarily well with a diamond finish. Combine that with a hard, protective coating like chrome or diamond-chrome, and you will strengthen the molds surface and optimize release. Texture and Release There are many textured surfaces today, including faux leather for automobile dashboards, wood grains, geometric patterns and stipple patterns found on pagers, cell phones and computer components. A plated mold coating is often essential to obtaining a textured surface with adequate lubricity. Textured surfaces require protection. The peaks of the textured surfaces are the first areas of mold detail to experience wear, making it very important to check the mold periodically with a profilometer to measure grain depth and peak counts. Mold coatings help decrease the frequency of repairs and refurbishment by maintaining the integrity of the textured surface. If a diamond finish presents release problems, a blast finish can be the answerparticularly when molding textured parts using materials such as silicone rubber, flexible PVC, TPES and some soft polypropylenes. These products tend to cling to a polished finish, but breaking up the surface with a light blasting improves release. Add a coating of nickel-PTFE and you get even better release. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 17页 共 28页Hard chrome and electroless nickel plating will help protect textured surfaces, as will a nickel-cobalt coating. Unlike hard chrome, electreless nickel-cobalt plates uniformly, which makes it ideal for very detailed molds with deep ribs and bosses. It combines the corrosion protection and lubricity of electroless nickel with the strength of cobalt. Summary If youre looking for enhanced performance in your molds, the proper combination of surface treatment and finish can provide additional benefit by extending production times between preventive maintenance. Your coatings vendor can be a valuable resource for educating your personnel on how coatings you use will wear over time, as well as a way to reduce downtime and cut costs. Automated surface finishing 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 finishing processes in a freeform surface plastic injection mold steel PDS5 on a CNC machining center. The design and manufacture of a grinding 桂林电子科技大学毕业设计（论文）外文翻译译文 第 18页 共 28页tool holder has been accomplished in this study. The optimal surface grinding parameters were determined using Taguchis orthogonal array method for plastic injection molding steel PDS5 on a machining center. The optimal surface grinding parameters for the plastic injection mold steel PDS5 were the combination of an abrasive material of PA Al2O3, a grinding speed of 18 000 rpm, a grinding depth of 20 m, and a feed of 50 mm/min. The surface roughness Ra of the specimen can be improved from about 1.60 m to 0.35 m by using the optimal parameters for surface grinding. Surface roughness Ra can be further improved from about 0.343 m to 0.06 m by using the ball burnishing process with the optimal burnishing parameters. Applying the optimal surface grinding and burnishing parameters sequentially to a fine-milled freeform surface mold insert, the surface roughness Ra of freeform surface region on the tested part can be improved from about 2.15 m to 0.07 m. Keywords Automated surface finishing Ball burnishing process Grinding process Surface roughness Taguchis method 1 Introduction Plastics are important engineering materials due to their specific characteristics, such as corrosion resistance, resistance to chemicals, low density, and ease of manufacture, and have increasingly replaced metallic components in industrial applications. Injection molding is one of the important forming processes for plastic products. The surface finish quality of the plastic injection mold is an essential requirement due to its direct effects on the appearance of the plastic product. Finishing processes such as grinding, polishing and lapping are commonly used to improve the surface finish. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 19页 共 28页The mounted grinding tools (wheels) have been widely used in conventional mold and die finishing industries. The geometric model of mounted grinding tools for automated surface finishing processes was introduced in. A finishing process mode of spherical grinding tools for automated surface finishing systems was developed in. Grinding speed, depth of cut, feed rate, and wheel properties such as abrasive material and abrasive grain size, are the dominant parameters for the spherical grinding process, as shown in Fig. 1. The optimal spherical grinding parameters for the injection mold steel have not yet been investigated based in the literature. Fig.1. Schematic diagram of the spherical grinding process In recent years, some research has been carried out in determining the optimal parameters of the ball burnishing process (Fig. 2). For instance, it has been found that plastic deformation on the workpiece surface can be reduced by using a tungsten carbide ball or a roller, thus improving the surface roughness, surface hardness, and fatigue resistance. The burnishing process is accomplished by machining centers and lathes. The main burnishing parameters having significant effects on the surface roughness are ball or roller material, burnishing force, feed rate, burnishing speed, 桂林电子科技大学毕业设计（论文）外文翻译译文 第 20页 共 28页lubrication, and number of burnishing passes, among others. The optimal surface burnishing parameters for the plastic injection mold steel PDS5 were a combination of grease lubricant, the tungsten carbide ball, a burnishing speed of 200 mm/min, a burnishing force of 300 N, and a feed of 40 m. The depth of penetration of the burnished surface using the optimal ball burnishing parameters was about 2.5 microns. The improvement of the surface roughness through burnishing process generally ranged between 40% and 90%. Fig. 2. Schematic diagram of the ball-burnishing process The aim of this study was to develop spherical grinding and ball burnishing surface finish processes of a freeform surface plastic injection mold on a machining center. The flowchart of automated surface finish using spherical grinding and ball burnishing processes is shown in Fig. 3. We began by designing and manufacturing the spherical grinding tool and its alignment device for use on a machining center. The optimal surface spherical grinding parameters were determined by utilizing a Taguchis orthogonal array method. Four factors and three corresponding levels were then chosen for the Taguchis L18 matrix experiment. The optimal mounted spherical grinding parameters for surface grinding were then applied to the surface finish of a freeform surface carrier. To improve the surface roughness, the ground surface was further burnished, using the optimal ball burnishing parameters. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 21页 共 28页 Fig. 3. Flow chart of automated surface finish using spherical grinding and ball burnishing processes 桂林电子科技大学毕业设计（论文）外文翻译译文 第 22页 共 28页2 Design of the spherical grinding tool and its alignment device To carry out the possible spherical grinding process of a freeform surface, the center of the ball grinder should coincide with the z-axis of the machining center. The mounted spherical grinding tool and its adjustment device was designed, as shown in Fig.4. Schematic illustration of the spherical grinding tool and its adjustment device Fig. 4. The electric grinder was mounted in a tool holder with two adjustable pivot screws. The center of the grinder ball was well aligned with the help of the conic groove of the alignment components. Having aligned the grinder ball, two adjustable pivot screws were tightened； after which, the alignment components could be removed. The deviation between the center coordinates of the ball grinder and that of the shank was about 5 m, which was measured by a CNC coordinate measuring machine. The force induced by the vibration of the machine bed is absorbed by a helical spring. The manufactured spherical grinding tool and ball-burnishing tool were mounted, as shown in Fig. 5. The spindle was locked for both the spherical grinding process and the ball burnishing process by a spindle-locking mechanism. 桂林电子科技大学毕业设计（论文）外文翻译译文 第 23页 共 28页 Fig.5. (a) Photo of the spherical grinding tool (b) Photo of the ball burnishing tool 3 Planning of the matrix experiment 3.1 Configuration of Taguchis orthogonal array The effects of several parameters can be determined efficiently by conducting matrix experiments using Taguchis orthogonal array. To match the aforementioned spherical grinding parameters, the abrasive material of the grinder ball (with the diameter of 10 mm), the feed rate, the depth of grinding, and the revolution of the electric grinder were selected as the four experimental factors (parameters) and designated as factor A to D (see Table 1) in this research. Three levels (settings) for each factor were configured to cover the range of interest, and were identified by the digits 1, 2, and 3. Three types of abrasive materials, namely silicon carbide (SiC), white aluminum oxide (Al2O3, WA), and pink aluminum oxide (Al2O3, PA), were selected and studied. Three numerical values of each factor were determined based on the pre-study results. The L18 orthogonal array was selected to conduct the matrix experiment for four 3-level factors of the spherical grinding process. Table1. The experimental factors and their levels 桂林电子科技大学毕业设计（论文）外文翻译译文 第 24页 共 28页3.2 Definition of the data analysis Engineering design problems can be divided into smaller-the better types, nominal-the-best types, larger-the-better types, signed-target types, among others 8. The signal-to-noise (S/N) ratio is used as the objective function for optimizing a product or process design. The surface roughness value of the ground surface via an adequate combination of grinding parameters should be smaller than that of the original surface. Consequently, the spherical grinding process is an example of a smaller-the-better type problem. The S/N ratio, , is defined by the following equation: =10 log10(mean square quality characteristic) =10 log10 ni iyn121 where: yi : observations of the quality characteristic under different noise conditions n: number of experiment After the S/N ratio from the experimental data of each L18 orthogonal array is calculated, the main effect of each factor was determined by using an analysis of variance (ANOVA) technique and an F-ratio test. The optimization strategy of the smaller-the better problem is to maximize , as defined by Eq. 1. Levels that maximize will be selected for the factors that have a significant effect on . The optimal conditions for spherical grinding can then be determined. 4 Experimental work and results The material used in this study was PDS5 tool steel (equivalent to AISI P20), which is commonly used for the molds of large plastic injection products in the field of automobile components and domestic appliances. The hardness of this material is about HRC33 (HS46). One specific advantage of this material is that after machining, the mold can be directly used for further finishing processes without heat treatment due to its special pre-treatment. The specimens were designed and manufactured so that they could be mounted on a dynamometer to measure the reaction force. The PDS5 specimen was roughly machined and then mounted on the dynamometer to carry out the fine milling on a three-axis machining center made by Yang-Iron Company (type MV-3A), equipped with a FUNUC Company NC-controller (type 0M). The pre-machined surf