Fundamental Research On Prototyping Metal Part By Using Laminated Template Electro-deposition

Rapid Prototyping Manufacture (RPM) is an important fabrication technology using the concept of discrete-piling. It produces complicated parts or moulds in the manner of laminated fabrication. Since introduction of RPM in early 1980s, direct and economical production of metal parts satisfying market demand has been always pursued by RPM researchers worldwide. Electroforming is another widely accepted fabrication technology that employs electro-deposition, a non-contact processing method, to form metallic article, hence being advantaged in the following aspects including high accuracy to replicating sample mould, strong adaptability and solid mechanical behavior of the electroformed parts because of none of mechanical contact between tool and workpiece, therefore avoiding such defects as deformation, stress, tool-loss or heat-affected zone. Resultingly, in the engineering of small-sized and involuted metal parts, electroforming is more competent than conventional machining processes if dealing with operational difficulty and production cost.In this thesis, by systematically integrating the electroforming method with Laminated Object Manufacturing (LOM), the core concept of RPM, a novel technique to form metal part, namely laminated template electro-deposition (LTE) is presented. According to mechanism, the designated operational sequence of this technique begins with slicing of the target-part in STL format in order to make a series of patterned shielding templates. In the next step metal ion selectively deposits, layer by layer, into blank areas that templates determine and, finally, forms metal parts within templates inside-wall. LTE shares a few of properties with both RPM and electro-deposition, for instance, strong ability of producing complex metal articles, well behavior of finished products as well as low maintenance cost. As a valuable exploration into the field of metal part forming via special process, it is intentionally focused on the millimeter-scaled metallic structure production.In this thesis, the experimental research into producing copper parts are carried out and the major research works are as follows:1. The strategy combining LOM with electro-deposition method to form metal part and the mechanism of LTE were originally put forward. On the basis of understanding of the electrochemical theory, rapid prototyping technology and electrodeposition method, a set of feasible processing way and process route was drafted in line with current experimental conditions.2. In consideration of characteristics in LTE, an experimental system capable of fullfilling LTE requirement was constructed through updating the current electrochemical lab workbench and adding specially-built devices to this platform. This experimental system consists of three major parts: servo-control feed unit, electrolyte refreshing unit and electro-deposition unit.3. A slicing software that embeds an appropriately-selected hierarchical algorithm was achieved by programming tool. The software fully takes LTE requirement into account and allows any 3-d CAD model in STL-format for slicing. The study of software interface linking sliced files with NC machining system and the compatibility in data transmission were illustrated. The procedure of template-material selection, cutting process of patterned template and template configuration manner in experiment were repectively introduced.4. An experimentally-oriented computational model was established through finite element analysis software to estimate electric field distribution. Based on it, the dependence of experimental conditions such as electrode dimension, position of auxiliary cathode as well as template thickness on the electric field was analyzed and some potential problems were pre-analyzed to provide reference on the real operation of LTE.5. Studies of main technological problems in LTE experiment were demonstrated. The key obstacle was considered as how to avoid extremely uneven thickness of metal deposit layer, which is commonly generated by nonuniform electric-field distribution in planar deposition. A few of additional measures and assistant apparatus concerning the change of test environment, were tried, which includes setting rotating cathode and auxiliary cathode, variation of current parameters as well as adopting pulse current and reversing pulse current. Especially for reversing pulse current, the parameters such as pulse frequency of anodic and catholic, pulse width, the working time, off time and current density were variously modulated for optimization. The mechanism how the negative pulse current works to improve deposit uniformity was discussed. Experimental results reveal that these applied approaches favor formation of uniform and smooth deposit layer to some extent.6. The fabrication of a group of copper parts in varied shapes and thickness were presented to demonstrate the feasibility of using this method as an alternative small-sized metal part manufacturing technique. Mechanical tests and precision measurement were conducted on these samples, showing that the finished parts have well mechanical property. Methodology and solution for the improvement were proposed on the basis of imperfection analysis regarding this method.