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Journal of Materials Processing Technology 176 (2006) 273277 Abstract procedure the metallographic with K 1. industry with this iti doubt able the to in the the a ity field, the turing composed us in Their 0924-0136/$ doi: A technical note on the characterization of electroformed nickel shells for their application to injection molds Mario D. Monzon, M. Dolores Marrero, A. Nizardo Benitez, Pedro M. Hernandez, J. Francisco Cardenes Universidad de Las Palmas de Gran Canaria, Departamento de Ingenieria Mecanica, Spain Received 19 November 2003; received in revised form 14 January 2006; accepted 11 April 2006 The techniques of rapid prototyping and rapid tooling have been widely developed during the last years. In this article, electroforming as a to make cores for plastics injection molds is analysed. Shells are obtained from models manufactured through rapid prototyping using FDM system. The main objective is to analyze the mechanical features of electroformed nickel shells, studying different aspects related to their structure, hardness, internal stresses and possible failures, by relating these features to the parameters of production of the shells an electroforming equipment. Finally a core was tested in an injection mold. 2006 Elsevier B.V. All rights reserved. eywords: Electroplating; Electroforming; Microstructure; Nickel Introduction One of the most important challenges with which modern comes across is to offer the consumer better products plastic injected pieces 13, 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 outstanding variety and time variability (new designs). For reason, modern industry must be more and more compet- ve and it has to produce with acceptable costs. There is no that combining the time variable and the quality vari- is not easy because they frequently condition one another; technological advances in the productive systems are going permit that combination to be more efficient and feasible a way that, for example, if it is observed the evolution of systems and techniques of plastics injection, we arrive at conclusion that, in fact, it takes less and less time to put new product on the market and with higher levels of qual- . The manufacturing technology of rapid tooling is, in this one of those technological advances that makes possible improvements in the processes of designing and manufac- injected parts. Rapid tooling techniques are basically of a collection of procedures that are going to allow to obtain a mold of plastic parts, in small or medium series, a short period of time and with acceptable accuracy levels. application is not only included in the field of making E-mail address: mmonzondim.ulpgc.es (M.D. Monzon). attempts trial starting an equipment. forming cations w parameters rapid rate method. 2. through epoxic core ing see front matter 2006 Elsevier B.V. All rights reserved. 10.1016/j.jmatprotec.2006.04.003 to study, define, analyze, test and propose, at an indus- level, the possibility of creating cores for injection molds from obtaining electroformed nickel shells, taking as initial model a prototype made in a FDM rapid prototyping It also would have to say beforehand that the electro- technique is not something new because its appli- in the industry are countless 3, but this research ork has tried to investigate to what extent and under which the use of this technique in the production of molds is technically feasible. All made in an accu- and systematized way of use and proposing a working Manufacturing process of an injection mold The core is formed by a thin nickel shell that is obtained the electroforming process, and that is filled with an resin with metallic charge during the integration in the plate 4 This mold (Fig. 1) permits the direct manufactur- by injection of a type a multiple use specimen, as they are 274 Processing defined specimen tion and tools. researched (a) (b) (c) (d) (e) The formed platen. process ca 3. which when bath an made the the cathode sulf (10 703 to molds, sulf stresses conditions, around also is amide also permitting of to harmful ti distrib has M.D. Monzon et al. / Journal of Materials Fig. 1. Manufactured injection mold with electroformed core. by the UNE-EN ISO 3167 standard. The purpose of this is to determine the mechanical properties of a collec- of materials representative industry, injected in these tools its coMParison with the properties obtained by conventional The stages to obtain a core 4, according to the methodology in this work, are the following: Design in CAD system of the desired object. Model manufacturing in a rapid prototyping equipment (FDM system). The material used will be an ABS plastic. 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). Removal of the shell from the model. 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. injection mold had two cavities, one of them was the electro- core and the other was directly machined in the moving Thus, it was obtained, with the same tool and in the same conditions, to inject simultaneously two specimens in vities manufactured with different technologies. Obtaining an electroformed shell: the equipment Electrodeposition 5,6 is an electrochemical process in a chemical change has its origin within an electrolyte passing an electric current through it. The electrolytic is formed by metal salts with two submerged electrodes, anode (nickel) and a cathode (model), through which it is to pass an intensity coming from a DC current. When current flows through the circuit, the metal ions present in solution are transformed into atoms that are settled on the creating a more or less uniform deposit layer. The plating bath used in this work is formed by nickel amate 7,8 at a concentration of 400 ml/l, nickel chloride g/l), boric acid (50 g/l), Allbrite SLA (30 cc/l) and Allbrite (2 cc/l). The selection of this composition is mainly due the type of application we intend, that is to say, injection even when the injection is made with fibreglass. Nickel amate allows us to obtain an acceptable level of internal ha ha temperature ifying 4. tests formed Fig. v from of perature 560 con operate Technology 176 (2006) 273277 in the shell (the tests gave results, for different process not superior to 50 MPa and for optimum conditions 2 MPa). Nevertheless, such level of internal pressure is a consequence of using as an additive Allbrite SLA, which a stress reducer constituted by derivatives of toluenesulfon- and by formaldehyde in aqueous solution. Such additive favours the increase of the resistance of the shell when a smaller grain. Allbrite 703 is an aqueous solution biodegradable surface-acting agents that has been utilized reduce the risk of pitting. Nickel chloride, in spite of being for the internal stresses, is added to enhance the conduc- vity of the solution and to favour the uniformity in the metallic ution in the cathode. The boric acid acts as a pH buffer. The equipment used to manufacture the nickel shells tested 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. 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 Elec- trolytic Nickel) with a purity of 99%. Gases aspiration system. Once the bath has been defined, the operative parameters that ve been altered for testing different conditions of the process 2 ve been the current density (between 1 and 22 A/dm ), the (between 35 and 55 C) and the pH, partially mod- the bath composition. Obtained hardness One of the most interesting conclusions obtained during the has been that the level of hardness of the different electro- shells has remained at rather high and stable values. In 2, it can be observed the way in which for current density alues between 2.5 and 22 A/dm 2 , the hardness values range 540 and 580 HV, at pH 4 0.2 and with a temperature 45 C. If the pH of the bath is reduced at 3.5 and the tem- is 55 C those values are above 520 HV and below HV. This feature makes the tested bath different from other ventional ones composed by nickel sulfamate, allowing to with a wider range of values; nevertheless, such opera- Fig. 2. Hardness variation with current density. pH 4 0.2, T =45 C. Processing Technology 176 (2006) 273277 275 ti stress tain hand, 200250 is the most steel (520595 a nick materials of filling for plastics shell minimum pitting. 5. current ples (perpendicular preparation, ished acid 15, observ PME3-ADL article, the the layer approximately zontal Thus, the going the be molds: T T Series 1 2 3 4 Fig. 3. Series 1 (150), etch 1. Fig. 4. Series 2 (300), etch 2. M.D. Monzon et al. / Journal of Materials vity will be limited depending on other factors, such as internal because its variability may condition the work at cer- values of pH, current density or temperature. On the other the hardness of a conventional sulfamate bath is between HV, much lower than the one obtained in the tests. It necessary to take into account that, for an injection mold, hardness is acceptable starting from 300 HV. Among the usual materials for injection molds it is possible to find for improvement (290 HV), steel for integral hardening HV), casehardened steel (760800 HV), etc., in such way that it can be observed that the hardness levels of the el shells would be within the mediumhigh range of the for injection molds. The objection to the low ductility the shell is compensated in such a way with the epoxy resin that would follow it because this is the one responsible holding inwardly the pressure charges of the processes of injection; this is the reason why it is necessary for the to have a thickness as homogeneous as possible (above a value) and with absence of important failures such as Metallographic structure In order to analyze the metallographic structure, the values of density and temperature were mainly modified. The sam- were analyzed in frontal section and in transversal section to the deposition). For achieving a convenient they were conveniently encapsulated in resin, pol- and etched in different stages with a mixture of acetic and nitric acid. The etches are carried out at intervals of 25, 40 and 50 s, after being polished again, in order to be ed afterwards in a metallographic microscope Olympus 3.3/10. Before going on to comment the photographs shown in this it is necessary to say that the models used to manufacture shells were made in a FDM rapid prototyping machine where molten plastic material (ABS), that later solidifies, is settled by layer. In each layer, the extruder die leaves a thread 0.15 mm in diameter which is compacted hori- and vertically with the thread settled inmediately after. in the surface it can be observed thin lines that indicate roads followed by the head of the machine. These lines are to act as a reference to indicate the reproducibility level of nickel settled. The reproducibility of the model is going to a fundamental element to evaluate a basic aspect of injection the surface texture. The tested series are indicated in Table 1. able 1 ested series pH Temperature ( C) Current density (A/dm 2 ) 4.2 0.2 55 2.22 3.9 0.2 45 5.56 4.0 0.2 45 10.00 4.0 0.2 45 22.22 first that still a less etch is dark conditions Fig. 3 illustrates the surface of a sample of the series after the etch. It shows the roads originated by the FDM machine, is to say that there is a good reproducibility. It cannot be noticed the rounded grain structure. In Fig. 4, series 2, after second etch, it can be observed a line of the road in a way clear than in the previous case. In Fig. 5, series 3 and 2 it begins to appear the rounded grain structure although it very difficult to check the roads at this time. Besides, the most ened areas indicate the presence of pitting by inadequate of process and bath composition. Fig. 5. Series 3 (300), etch 2. 276 Processing and model for deposition, ditions what although abo sulf non-laminar v ture the SLA). ture current 6. application Dif ties tensiometer with width only sile stresses. nick in tested for acceptable is tions stresses. M.D. Monzon et al. / Journal of Materials Fig. 6. Plane transversal of series 2 (600), etch 2. This behavior indicates that, working at a low current density a high temperature, shells with a good reproducibility of the and with a small grain size are obtained, that is, adequate the required application. If the analysis is carried out in a plane transversal to the it can be tested in all the samples and for all the con- that the growth structure of the deposit is laminar (Fig. 6), is very satisfactory to obtain a high mechanical resistance at the expense of a low ductibility. This quality is due, ve all, to the presence of the additives used because a nickel amate bath without additives normally creates a fibrous and structure 9. The modification until a nearly null alue of the wetting agent gave as a result that the laminar struc- was maintained in any case, that matter demonstrated that determinant for such structure was the stress reducer (Allbrite On the other hand, it was also tested that the laminar struc- varies according to the thickness of the layer in terms of the density. Internal stresses One of the main characteristic that a shell should have for its like an insert is to have a low level of internal stresses. ferent tests at different bath temperatures and current densi- were done and a measure system rested on cathode flexural method was used. A steel testing control was used a side fixed and the other free (160 mm length, 12.7 mm and thickness 0.3 mm). Because the metallic deposition is in one side the testing control has a mechanical strain (ten- or compressive stress) that allows to calculate the internal Stoney model 10 was applied and was supposed that el substratum thickness is enough small (3H9262m) to influence, an elastic point of view, to the strained steel part. In all the cases the most value of internal stress was under 50 MPa extreme conditions and 2 MPa for optimal conditions, an value for the required application. The conclusion that the electrolitic bath allows to work at different condi- and parameters without a significant variation of internal 7. moplastic has dimensions, cal by core, between the materials. it of ence e crystalline noticed core, around 8. check has erties that good structure. be core plastic Refer Technology 176 (2006) 273277 Fig. 7. Analysis by photoelasticity of injected specimens. Test of the injection mold Tests have been carried out with various representative ther- materials such as PP, PA, HDPE and PC, and it been analysed the properties of the injected parts such as weight, resistance, rigidity and ductility. Mechani- properties were tested by tensile destructive tests and analysis photoelasticity. About 500 injections were carried out on this remaining under conditions of withstanding many more. In general terms, important differences were not noticed the behavior of the specimens obtained in the core and ones from the machined cavity, for the set of the analysed However in the analysis by photoelasticiy (Fig. 7) was noticed a different tensional state between both types specimens, basically due to differences in the heat transfer- and rigidity of the respective mold cavities. This difference xplains the ductility variations more outstanding in the partially materials such as HDPE and PA 6. For the case of HDPE in all the analysed tested tubes it was a lower ductility in the specimens obtained in the nickel quantified about 30%. In the case of PA 6 this value was 50%. Conclusions After consecutive tests and in different conditions it has been ed that the nickel sulfamate bath, with the utilized additives allowed to obtain nickel shells with some mechanical prop- acceptable for the required application, injection molds, is to say, good reproducibility, high level of hardness and mechanical resistance in terms of the resultant laminar The mechanical deficiencies of the nickel shell will partially replaced by the epoxy resin that finishes shaping the for the injection mold, allowing to inject medium series of parts with acceptable quality levels. ences 1 A.E.W. Rennie, C.E. Bocking, G.R. Bennet, Electroforming of rapid pro- totyping mandrels for electro discharge machining electrodes, J. Mater. Process. Technol. 110 (2001) 186196. 2 P.K.D.V. Yarlagadda, I.P. Ilyas, P. Chrstodoulou, Development of rapid tooling for sheet metal drawing using nickel electroforming and stereo lithography processes, J. Mater. Process. Technol. 111 (2001) 286294. M.D. Monzon et al. / Journal of Materials Processing Technology 176 (2006) 273277 277 3 J. Hart, A. Watson, Electroforming: A largely unrecognised but expand- ing vital industry, Interfinish 96, 14 World Congress, Birmingham, UK, 1996. 4 M. Monzon, et al., Aplicacion del electroconformado en la fabricacion rapida de moldes de inyeccion, Revista de Plasticos Modernos. 84 (2002) 557. 5 L.F. Hamilton, et al., Calculos de Qumica Analtica, McGraw Hill, 1989. 6 E. Julve, Electrodeposicion 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 Develop- ment 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. www.bsac.eecs.berkeley.edu/arhive/masters/jjudy/chapter3.pdf (cap prime . 3).