Aerospace relevant Additive Manufacturing technologies

[AirborneMetals]

In the aerospace industry, currently the following AM technologies are widely used:

Laser based technologies

AM technologies employing a laser as the heat source to fuse particles together are known as SLS (Selective Laser Sintering), SLM (Selective Laser Melting) and DMLS (Direct Metal Laser Sintering).

As the names suggest, SLS achieves sintering (heating of the material to near-melting temperatures to fuse particles by diffusion) while SLM achieves full melting. DMLS is a further development of SLS using a more powerful laser and refers to the process as applied to metal alloys.

SLM essentially does the same as sintering but goes one step further by achieving a full melt, thus obtaining a homogeneous part with fewer or no voids (helping preventing failure). However, the technology is feasible only with single metals powders.

In all cases, a 3D CAD file is used to model the part to be produced. The actual building process is quite time-consuming and therefore, as of now it is primarily suited for smaller series. DMLS is faster due to the more powerful laser. In practice, it might be possible to build multiple parts simultaneously, depending on part size and machine capabilities.

The manufacturing principle is shown below (next page). The powder feedstock is applied to a powder bed that moves upward. Using a roller, the material is then applied to the fabrication powder bed that moves downward as the part builds up. Layer thickness is usually measured in micrometers and excess powder is being retrieved for recycling. The computer-controlled laser beam then fuses the particles together. 

The aerospace industry aside, these technologies are also pioneered in medical orthopedics.



Electron Beam Melting (EBM)

EBM employs an electron beam as the energy source. It is fundamentally different from the laser based technologies. EBM achieves full melting.

In contrast to the laser based technologies, the part is constructed under vacuum. This makes it a suitable technology for titanium, since the metal has a high affinity for oxygen which may lead to unfavorable characteristics of the end product. Moreover, titanium powder is highly combustible (as discussed below) and the inert environment helps to significantly reduce the risk of explosion / fire.

This process typically uses pre-alloyed material. The energy density is higher than with SLS, resulting in a higher build rate.

High quality, dense parts without porosity can be produced. This may eliminate the need for post process sintering.

The working principle of the technology is shown here.