【文章內(nèi)容簡(jiǎn)介】 e specimen, as they are defined by the UNEEN 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. (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 ing 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 position 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 surfaceacting 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. ? Charging rectifier. Maximum intensity in continuous 50 A and continuous current voltage between 0 and 16 V. ? Titanium basket with nickel anodes (Inco SRounds 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 55 176。C) and the pH, partially modifying the bath position. 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 and 22 A/dm2, the hardness values range from 540 and 580 HV, at pH 4 177。 and with a temperature of 45 176。C. If the pH of the bath is reduced at and the temperature is 55 176。C those values are above 520 HV and below 560 HV. This feature makes the tested bath different from other conventional ones posed by nickel sul