Patent Application
20190389005
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The present invention relates generally to a metal additive manufactured part, and more specifically to a process for producing a smooth surface finish on a metal additive manufactured part such as a shrouded impeller.
Rough surface finish on metallic components can be very detrimental for performance, fatigue life, and general appearance. In gas turbine engines, for example, rough surface finish of flow path components can lead to significant efficiency losses. Metal additive manufacturing (AM) is increasingly being considered for use for parts with increasing complexity, strength, and performance requirements. The 3-dimensional layered construction, variations in powder bed heights across the bed, and other factors like the Marangoni effect due to surface tension gradients may cause marked surface roughness, which affects the resulting part performance. Additionally, AM processes allow designers to break free from traditional design constraints and optimize the part topology, leading to parts with less material and greater complexity. The wider adoption of AM may be limited by the surface finish being produced by the various AM techniques and the extent of post-processing required after fabrication. The ability to control the surface finish is a function of the AM technique used, the manufacturing process parameters, material, geometry of the part, direction the part is oriented during the build, and the post-processing techniques utilized.
A process for producing a smooth surface finish on a metal part such as a shrouded impeller that has been produced using a metal additive manufacturing process. The printed metal part is heated up to around its Solution Heat Treat or annealing temperature, The metal part is placed in a fluidized salt bath that has been heated to around the metal part's incipient melt temperature to smooth the relatively rough surfaces, after around 10 seconds the metal part is removed from the fluidized salt bath, the metal part is then rapidly cooled to around 1,000 F in an inert gas using Argon to prevent any change in the grain structure, and the part is removed from the inert gas chamber. For vacuum melt alloys, such as Inconel or titanium, the part is cooled in a protective atmosphere. For air melt alloys, such as stainless steels the metal part can be cooled in air.
The present invention is a process of forming a smooth surface on a metal part formed using the metal additive manufacturing (AM) process. The part can be a shrouded impeller for a gas turbine engine compressor or a pump for a liquid rocket engine. The AM process can be of the metal powder bed type in which the part is built up layer by layer by depositing layers of metal powder and melting the specific areas of the metal powder using a laser or electron beam. Once the metal part has been “printed”, the surface finish will be too rough to use in specific machines such as a shrouded impeller for a compressor or a pump.
The process for producing a metal part from additive manufacturing with a smooth surface is shown in the flow chart of
After the metal part has been removed from the fluidized salt bath, the metal part is rapidly cooled to prevent a change in grain structure. If the metal part is made from a non-air-melted material, the metal part can be rapidly cooled in the chamber using a protective atmosphere, such as Argon gas. Otherwise the part can be processed in air. Similar to heat treat cycles, the metal part should be rapidly cooled to around 1,000 F to prevent adverse grain structure. Once the metal part has cooled to around 1,000 F, the metal part can be removed from the chamber or left in the chamber and cooled to ambient temperature outside of an inert environment.
