Rapid Electroforming Tooling
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ABSTRACT A method of rapid electroforming tooling for the production of metal tools including molds, dies, and electrical discharge machining electrodes is developed. Geometry and material of the solid freeform fabricated part, properties of the electroformed metal, and process parameters are significant factors that cause inaccuracy in the manufactured tools. Thermomechanical modeling and numerical simulation are used to simulate thermal stresses induced during the burnout process that removes the rapid prototyping part from the electroform. The analysis demonstrates that appropriate design of the rapid prototyping part geometry and selection of electroform thickness not only reduce thermal stress, thus improving tooling accuracy, but also minimize manufacturing time and cost.
INTRODUCTION Electroforming is the use of electrodeposition of metal onto a part that is subsequently separated from the deposit to produce a metal shell. This can be used to make molds and dies for replicating the part [I]. The metalized part, which has the required shape, dimensions, accuracy and roughness, is sinked into an electrolyte bath as the cathode and deposited a layer of metal, normally copper or nickel, for a specified thickness. The part is then separated from the metal shell. The shell is then backed with other materials to form a mold cavity or an EDM (electric discharge machining) electrode. A nickel electroformed part can be used for a prototyping tool or even a production tool [2], and a copper electroformed part can be used as an EDM electrode [3]. Metals deposited by electroforming have distinct properties [4]. Dimensional tolerances can be very good, often up to 0.0025 mm, and surface finishes of 0.05 jtm can be obtained quite readily if the master part is adequately smooth [5]. Solid freeform fabrication (SFF), or rapid prototyping (RP), is being increasingly used in industry for prototyping, tooling and manufacturing applications [6, 71. Rapid tooling is the process of directly or indirectly employing RP technologies to fabricate castings, dies, molds and EDM electrodes. Currently used rapid hard tooling processes such as 3D Keltool [8], 3dimensional printing (3DP) [9] and RapidTool [10], first bind metal powders by various techniques to generate a green part. Afterwards the part is debinded, sintered, and infiltrated with copper or other metals to produce functional metal parts. The powder metallurgy approaches involve random noise shrinkage during the sintering process and thus the generated metal parts suffer dimensional uncertainty and they usually have rough surface finish. The emergence of SFF has brought about new opportunities for electroforming in rapid tooling [11]. Since electroforming can closely copy the geometry and surface quality of an RP part, the accuracy and 57 Mat. Res. Soc. Symp. Proc. Vol. 625 © 2000 Materials Research Society
surface finish of the produced tool is largely determined by the accuracy and surface finish of the RP part. This paper first describes the tooling process and case stud
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