The future of 3D printing with metal powder

3D printing techniques are increasingly employed in the manufacture of a variety of goods from spectacles to medical implants. Some components are constructed directly from a computer model without the need for creating a mould.

All this works fine until the need arises for a metal part. This could be a custom part designed for an advanced aircraft or spacecraft and has to be made of a specific metal or a combination of metals. Now the 3D printing process has advanced to produce articles in metals or a combination of alloys.

This has become a crucial development in advanced aerospace engineering where parts are sometimes required that have different chemical or physical properties at either end. For example, one side should be able to sustain a high temperature while the other side should have a low density. Another combination may be for one side to be magnetic while the other is non magnetic.

These types of parts cold be made from separate units that are welded together to create the final article. The downside here is that the weld may not perform well at high stresses and, may become brittle and fail. This is not a desirable attribute for an application in advanced aircraft or spacecraft.

In a technique jointly developed in the United States by space agency NASA’s Jet Propulsion Laboratory, the California Institute of Technology and Pennsylvania University, the 3D printing process deposits molten metal layers on a rotating rod. The metals are melted by lasers in a process called selective laser melting. Earlier 3D printing methods involved sintering beds of metal powder, single layer by single later.

The rotating rod technique allows a part to be made from the inside out with different metals and alloys within one individual part.

This technique will have implications far beyond the aerospace industry and will also affect the ways in which a metal supplier such as Dynamic Metals will have to adapt to meet new customer demand.

Ordinary items such as nuts and bolts will be designed in a combination of metals and alloys while some machine parts will no longer require any bolts, screws or even welding.

However, the laser melting process still has some hurdles to overcome before it consigns other 3D printing techniques to history’s dustbin. Although the metal parts that have been produced with the new technique are certainly impressive, they still lack a good surface finish. This is because, at present, the method of layering metal particles on top of each other produces a rough surface.

In addition, the highly localised heating method that produces these parts will also create residual stresses in the finished item. This in turn can lead to some deformation in the part.

One of the greatest unknowns that is the subject of research is the microstructure of the printed part. The laser melting process creates inconsistencies in this microstructure that in turn also depends on the part’s shape and geometry. All of this will impact on the final mechanical performance of the new part.

At present, it does not seem that 3D metal printing will completely replace CNC machines in making metal parts but the laser melting technique is certainly an exciting new innovation to complement CNC methods.