Metal solid freeform fabrication using semi-solid slurries

A new process for the direct solid freeform fabrication (SFF) of metallic prototypes and components offers a significant advantage over most other metal-SFF processes: it does not involve the use of powders, thus minimizing porosity and shrinkage distortion. This process utilizes the unique rheological and thermophysical properties of semi-solid-metal (SSM) slurries to build a near-netshape metallic component in one step, without the need of sintering, molds, roughmachining, or post-processing operations. A stream of semi-solid is deposited over a moving substrate that follows a three-dimensional pattern. The high viscosity of semi-solid slurries and their particular rheology allows the stream to be deposited over previous layers in a controlled fashion, without traces of an interface. Because the rate of deposition is an order of magnitude faster than in other SFF processes, manufacturing is also faster. In addition, distortion problems characteristic of other processes involving fully molten metal are significantly reduced because the material deposited is already partially solid. In this paper, the first implementation of this technology is presented in detail. Eventually, this process could be useful in the production of a small series of large metallic components that would otherwise be produced by casting or machining. Those processes cost more and result in lower-quality components.