Secondary finishing processes in metal Additive Manufacturing
Comparison of AM medical device after shoot peening (top) and after vibratory grinding (bottom)
In order to achieve the necessary specifications or improve properties such as surface quality, geometrical accuracy and mechanical properties, it is often necessary to post-process and finish components produced with Additive Manufacturing techniques.
The usual surface roughness values for selectively laser melted metal parts vary between 15 µm and 40 µm (Rz in X/Y direction). Most physical characteristics can be enhanced by adding well-established fabrication processes at the end of the AM process chain.
The high quality of metal products produced using AM processes enables the use of many metal-machining finishes to meet the requirements of surface quality and geometry.
Following removal of support structures to separate the parts from the build platform, the products can be milled, drilled, polished, etc. Internal surfaces, such as those in internal/tempering channels for example, can be polished using abrasive flow machining.
Heat treatment is often included in the process chain as well as shot peening which is used to improve the mechanical and tactile properties of the surface of AM parts.
Another post process of interest is electro polishing, as this electrochemical treatment significantly improves the surface finish of AM parts. Its first objective is to minimise micro roughness, thus reducing the risk of dirt or product residues adhering and improving the cleanability of surfaces. However, electro polishing can also be used for deburring, brightening and passivating, particularly for surfaces exposed to abrasive media. Since electro polishing involves no mechanical, thermal or chemical impact, small and mechanically fragile parts can also be treated.
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