Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Introduction
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Figure 10 Shape Deposition Manufacturing (SDM): Functional metal parts or tools can
be formed in layers by repeating three basic steps repetitively until the part is completed.
Hot metal droplets of both primary and sacrificial support material form layers by a thermal
metal spraying technique (a). They retain their heat long enough to remelt the
underlying metal on impact to form strong metallurgical interlayer bonds. Each layer is
machined under computer control (b) and shot-peened (c) to relieve stress buildup
before the work is returned for deposition of the next layer. The sacrificial metal supports
any undercut features. When deposition of all layers is complete, the sacrificial metal is
removed by acid etching to release the completed part.
metal. The support material protects the part layers from the deposition
steps that follow, stabilizes the layer for further machining operations,
and provides a flat surface for milling the next layer. This SDM cycle is
repeated until the part is finished, and then the sacrificial metal is etched
away with acid. One combination of metals that has been successful in
SDM is stainless steel for forming the prototype and copper for forming
the support structure
The SDM Laboratory investigated many thermal techniques for
depositing high-quality metals, including thermal spraying and plasma
or laser welding, before it decided on microcasting, a compromise
between these two techniques that provided better results than either
technique by itself. The metal droplets in microcasting are large enough
(1 to 3 mm in diameter) to retain their heat longer than the 50-mm
droplets formed by conventional thermal spraying. The larger droplets
remain molten and retain their heat long enough so that when they
impact the metal surfaces they remelt them to form a strong metallurgical
interlayer bond. This process overcame the low adhesion and low
mechanical strength problems encountered with conventional thermal
metal spraying. Weld-based deposition easily remelted the substrate