Metal solid freeform fabrication using semi-solid slurries

A new process for the direct solid freeform fabrication (SFF) of metallic p rototypes and components offers a significant advantage over most other met al-SFF processes: it does not involve the use of powders, thus minimizing p orosity and shrinkage distortion. This process utilizes the unique rheologi cal and thermophysical properties of semi-solid-metal (SSM) slurries to bui ld a near-net-shape metallic component in one step, without the need of sin tering, molds, rough-machining, or post-processing operations. A stream of semi-solid is deposited over a moving substrate that follows a three-dimens ional pattern. The high viscosity of semisolid slurries and their particula r rheology allows the stream to be deposited over previous layers in a cont rolled fashion, without traces of an interface. Because the rate of deposit ion is nit order of magnitude faster than in other SFF processes, manufactu ring is also faster. In addition, distortion problems characteristic of oth er processes involving fully molten metal are significantly reduced because the material deposited is already partially solid. In this paper, the firs t implementation of this technology is presented in detail. Eventually, thi s process could be useful in the production of a small series of large meta llic components that would otherwise be produced by casting or machining. T hose processes cost more and result in lower-quality components.