Selective Separation Shaping
Selective separation shaping (SSS) is a novel powder based additive manufacturing method that can build parts of various scale out of polymers, metals, ceramics and composites including cementitious materials. This is achieved at relatively high speed and with minimal machine complexity. In the SSS process, a thin wall of a separator powder material (S-powder) is deposited within the base material powder (B-powder) of which the part would be made by means of a narrow nozzle which emerges into the powder at the depth of one layer to form a barrier on the boundary of each layer. The nozzle has a slot at its outlet with the height of one layer through which the S-powder flows out under the vibration effect generated by a piezo element. The deposited barrier creates a physical separation between the part and surrounding material, which allows for the separation of the part from the surrounding powder after consolidation by fusing, sintering or bonding is complete. In case of sintering, which applies to printing metallic and ceramic parts, the S-powder could be a high temperature powder such as magnesia or tungsten powder or any other powder material which has a higher melting point than the base material.
SSS is the only powder-based process that can effectively work in zero gravity condition and as such it is ideal for use in the International Space Station for fabrication of spare parts and tools. In 2016, SSS won an international competition Grand Prize by NASA as the most capable and versatile metallic and ceramic Additive Manufacturing technology for micro-gravity and planetary applications. Followings are the advantages of SSS over current AM approaches:
SSS can process a range of diverse materials.
Any high melting point material may be processes by SSS as long as there is another material with a higher melting point that can be used as separator agent.
SSS can build very fast because it only treats part surfaces, not its core.
The SSS machines can be inexpensive and simple (hence reliable) because there is no reliance on expensive technologies such as laser and electron beam.
SSS can be more accurate than spot-heating processes that use laser and electron beam because in spot-heating processes heat expands through conduction hence the process resolution is not as fine as the beam diameter.
The nozzle opening in SSS may be a tall and thin slot along the length of the nozzle which would allow large-scale parts to be built with layers that could be as thick as bricks thereby allowing rapid construction of large structures with cementitious or other materials.
SSS is the only powder-based AM process that can operate without powder layering by inserting its nozzle deep into the base powder and depositing the separation powder for every part layer profile, each time raising the nozzle to deposit the succeeding layer. Among other advantages, this property of SSS makes it the only powder based approach that can work in micro gravity condition without requiring complex mechanisms (such as those used for creation of centrifugal force) for powder layering.
Metallic (bronze and stainless steel) and ceramic (lunar regolith)
parts made with the SSS process
Bronze part produced without powder layering
A double-layer concrete part with layer height of 1.5cm