Mar 25, 2017 | By David

Responding to demand from a number of its end users, LPW Technology has conducted a detailed investigation into the effects of gaseous corruption on 3D printed metal products, the results of which were published today. The study suggests that material properties can be significantly affected by oxygen corruption in particular, and the metal powder used in a 3D printer should be changed as regularly as possible.

LPW supplies metal powders for use in 3D printers. It offers products in Aluminium, Cobalt, Copper, Nickel, as well as other custom alloys. They are optimized for use in 3D printers that use the SLM and SLS techniques, amongst others. In these 3D printing processes a high energy beam, usually a laser, is used to rapidly melt selected portions of a bed of metal powder, gradually building up the desired shape.

The 3D printing usually takes place inside a sealed chamber, as many of the by-products of the process can be harmful or toxic. Furthermore, any reactions between the metal and the atmosphere, particularly Oxygen and Nitrogen gas, must be reduced as much as possible. This is achieved by filling the chamber with an inert gas ‘blanket’, or preferably by creating a vacuum. However, neither technique can completely eliminate interactions with oxygen, and some of the metal powder will fuse with the atmosphere, leading to impurities. As the 3D printer is used again with the same powder bed, subsequent print jobs will see a gradual increase in the amount of impurities there, and this can lead to all sorts of problems.

LPW’s study was carried out using a nickel-based superalloy, a material that was specially designed to have superior mechanical strength, excellent resistance to corrosion and good surface stability, amongst other benefits. The results showed that, as the number of build cycles with the 3D printer increases, the amount of oxygen impurities in the metal powder base increases accordingly. This was generally a linear progression. As the amount of impurities passes a particular limit, the quality of the material properties in the final 3D printed part starts to deteriorate significantly.

Oxygen content in Inconel 718 powder after repeated use in SLM builds

The data shows that when oxygen concentration in the metal powder goes above 200ppm, there are noticeable changes in the final product, which are barely measurable below that level. Tensile strength and ductility were shown to be greatly affected by the presence of impurities from the atmosphere. Alternative impurities could also be caused by Hydrogen or Nitrogen gas, which were less present but detrimental to the build quality even at very small concentrations.

Effect of number of builds on mechanical properties of Inconel 718 tensile specimens produced by SLM

Concluding recommendations from LPW suggested the necessity of maintaining the powder bed regularly, and the study declared that a close relationship with its customers was required to provide the most appropriate powder specification possible. The vacuum atomisation process was indicated as the best method for critical applications. While 3D printed plastics are still mostly used for prototyping, additive manufacturing is now a major solution for building final versions of metal components in the aerospace industry, for example. The highest quality material properties are essential in this sector, amongst others, meaning that 3D printing techniques must continue to be refined and improved through research. This latest study from LPW will be invaluable, as 3D printing technology continues to gain in popularity throughout the manufacturing world.  



Posted in 3D Printing Application



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Anthon wrote at 3/27/2017 6:44:27 AM:

have they tried argon? some welders use argon to prevent oxygen from ruining the welds.

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