Conversion of Rapid Prototyping Models into Metallic Tools by Ceramic Moulding—an Indirect Rapid Tooling Process

摘要

A process to convert models made by rapid prototypi ng techniques like SL (stereolitography) and LOM (laminated object manufacturing) or by conventional techniques (silicones, resins, wax, etc.) into metallic mould s or tools has been developed. The main purpose of this technique is to rapidly obtain the first prototypes of parts, for plastics injection, forging or any oth er manufacturing process using the tools produced by casting a metal into a cera mic mould. Briefly, it can be said that the ceramic moulds are produced by mixing in variab le proportions, depending on the type of ceramics employed, strength and roughne ss desired, a ceramic mixture composed by alumina and/or zirconium silicates bon ded with silica coming from a liquid binder, based on ethyl silicate. A catalyst is added to the slurry in order to produce a sol-gel reaction. The liquid slur ry is poured into the box containing the mould to be reproduced. After a short p eriod of time, controlled by the amount of gelling agent, the ceramic mixture ac quires a rubber consistency. The pattern is removed from the ceramic mould, whic h is fired to stop the gelation reaction. After this stabilization the ceramic m ould is sintered at high temperatures in order to generate an inert mould wi th the desired strength in which almost all metallic alloys can be cast. The effect of ceramic materials (shape, granulometric distribution, chemical com position, etc.), processing parameters (proportion binder/ceramic/catalyst, sint ering conditions, etc.) and casting conditions (mould pre-heating temperature a nd pouring temperature) were studied in order to obtain metallic moulds or tools with tailored properties (high dimensional accuracy, low roughness and high mec hanical strength).