PROCESS DESCRIPTION

3D printing (also called additive manufacturing) of metals has only been developed in the last few years but is already seen as one of the technologies for the future. Many companies and research centres are investing in research and development with the aim of standardising 3D printing in production.

3D printing involves making components by adding layers of material one by one. This method differs from conventional production processes in that the component is produced directly by melting powder or wire feedstock. The process is well developed in the production of plastics and has been used in this segment for some time. 3D printing of metals is quite another matter: the units are fairly expensive by comparison and are used in industry or at research facilities.

In contrast to conventional manufacturing, 3D printing offers advantages in the production of complex components. The addition of layers one by one very effectively facilitates the production of complex structures that would be difficult or impossible to achieve using traditional manufacturing techniques. 3D printing is frequently used for the manufacture of individual items or small batches as it would be too expensive to set up a conventional production facility. Typical examples include hip or dental prostheses in medicine as well as turbine blades or turbochargers.
 

Aspects of the technique

Present-day methods for additive manufacturing with metals can be organised according to the aspects of material feed and energy sources:

Powder bed

The most common techniques nowadays involve a bed of powder. This means layering coats of powder onto the blank and melting the layers onto the existing component. The source of energy for this can be a laser or an electron beam. In the former case, the process is called Laser Powder Bed Fusion (L-PBF), whereas in the latter, it is referred to as Electron Beam Melting (EBM)

Powder spraying 

Spraying powder requires the use of a carrier gas, meaning that electron beams cannot be used for the energy source. Powder spraying by lasers is already used for additive manufacturing and is known by the name laser metal deposition (LMD). Use of a welding arc in the form of a plasma beam has been known by the name plasma-arc welding for many years. Efforts are being made to adapt this method for additive manufacturing.

Wire feed 
Additive manufacturing techniques using a wire feed can in principle be used with any kind of energy source. Use of these techniques is becoming increasingly widespread due to the relatively low cost of the filler material.

Binder 

Metallic powders are mixed with a binder (often polymer). This binder is used to print a component layer by layer. The first step after printing is to burn out the binder. The next step involves sintering the component at a high temperature. Debinding and sintering cause the component to shrink. This shrinkage must be taken into account in the printing process.