Design, simulation and manufacturing of new rotational bimaterial mould made by additive manufacturing and electroforming

Abstract

Rotational molding is a unique manufacturing technique for the production of hollow plastic parts manufacturing. The cavity needed is commonly manufactured by machining, where intricate geometries and textures cannot be reproduced. One alternative method to manufacture this metallic cavity is electroforming which, starting from a pattern model (made by rapid prototyping, CNC machining, etc) manufactures a metallic shell, by electrolytic deposition of ions of metal onto the surface of model , which is later released. As metal is deposited ion by ion, it allows reproducing geometries and textures that cannot be obtained by machining or other conventional technologies, and obtaining thin moulds mechanically appropriate instead of machined moulds with higher wall thickness, improving thermal conductivity thus reducing process cycle times. Moreover, by electroforming it is possible to deposit different materials, even on the same part, so on the same shell it is possible to combine properties as hardness of nickel (into the mould to avoid erosion of the plastic particles inside) and good thermal properties in terms of heat conduction in contact with the hot air into the oven. The approach of this research work is to improve the global thermal conductivity of the mould by combining electrodeposited materials such as nickel and copper, using a pattern model obtained by rapid prototyping (SLS) to assure high dimensional accuracy. Several molds have been analyzed by Computational Fluid Dynamics (CFD) software and compared to experimental moulds heated into an oven. Results show significant reduction of cycle time (measured by the internal air temperature curve) related to conventional thick aluminum moulds. Also the developed moulds are suitable to be standardized by innovative and interchangeable shell-holders.