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A manufacturing technique for the production of aluminum components is described. A resin-bonded part is formed by a rapid prototyping technique and then debound and infiltrated by a second aluminum alloy under a nitrogen atmosphere. During thermal processing, the aluminum reacts with the nitrogen and is partially transformed into a rigid aluminum nitride skeleton, which provides the structural rigidity during infiltration. The simplicity and rapidity of this process in comparison to conventional production routes, combined with the ability to fabricate complicated parts of almost any geometry and with high dimensional precision, provide an additional means to manufacture aluminum components.
Aluminum components are traditionally fabricated from molten metal by casting into a mold, from solid metal by mechanical forging, pressing, or extrusion or from powdered metal by sintering. All of these technologies require tooling or dies to shape the part that is expensive and time-consuming to produce, delays the introduction of new products, and increases their cost. Parts can also be machined from solid material in a process similar to carving, but this is time-consuming and produces a large amount of scrap material. An alternative production strategy produces three-dimensional objects directly from computer-aided design models through the use of additive processes as opposed to conventional, subtractive means such as machining (1). These rapid prototyping and rapid manufacturing techniques all operate through the sequential delivery of energy and/or material to specified points to produce a solid. Parts of any shape can be produced directly from a computer model without the need for expensive tooling or machining.
These techniques have been used to fabricate objects made from a variety of materials, including polymers, ceramics, and metals: notably steel (2, 3) and more recently aluminum (4-6). These aluminum parts are fabricated as a polymer-aluminum powder composite and post-processed by burning out the polymer and sintering the remnant metal powder to full or near-full density. However, it is extremely difficult to maintain dimensional accuracy during sintering of such a powder preform and, therefore, only small aluminum parts on the order of 1 cm^sup 3^ can be made this way (7, 8).
The dimensional problem is much reduced by infiltration, in which a loosely formed powder body is lightly pre-sintered and then infiltrated by a liquid. Because there is little...