Anteral Academy 07: What is metal Additive Manufacturing?

What is Additive Manufacturing?

Additive manufacturing (AM) or 3D printing is an additive technology used to manufacture parts. It is ‘additive’ in that it doesn’t require a block of material or a mold to manufacture physical objects, it simply stacks and fuses layers of material.

The success of these technologies is determined by the true benefit behind them, that is, the free-form fabrication arising from the fact that no machining tools are used during a 3D printing process. AM technologies could therefore allow the designers to develop products that are, in principle, independent of how they are manufactured.

As a matter of fact, high-quality and reliable parts can be obtained only by following design rules and considering limitations that are specific of each AM process. Consequently, 3D printing opens new perspectives, but at same times poses new challenges. Maximum size of microwave components that can be built by 3D printing depends significantly both on the technology and on the building direction.

Metal Additive Manufacturing

Metal AM technology combines the design flexibility of 3D Printing with the mechanical properties of metal. From tooling inserts with cooling channels to lightweight structures for aerospace, any application that involves complex metal parts potentially benefits from Metal 3D Printing.

There are several 3D printing technologies in development currently. Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS) are two metal additive manufacturing processes that belong to the powder bed fusion 3D printing family. These two technologies have a lot of similarities: both use a laser to scan and selectively fuse (or melt) the metal powder particles, bonding them together and building a part layer-by-layer.

The differences between SLM and DMLS come down to the fundamentals of the particle bonding process: SLM uses metal powders with a single melting temperature and fully melts the particles, while in DMLS the powder is composed of materials with variable melting points that fuse on a molecular level at elevated temperatures.

The basic fabrication process of SLM and DMLS are very similar. Unlike polymer powder bed fusion process, the parts are attached to the build platform through support structures. Support in metal 3D printing is built using the same material as the part and is always required to mitigate the warping and distortion that may occur due to the high processing temperatures.

Selective Laser Melting (SLM)

The SLM process begin with the creation of a three-dimensional Computer-Aided Design (CAD) model that is subsequently converted in a STL model (STereoLithography), and the supporting structures are designed for the overhanging areas that correspond to down-facing part surfaces with no material underneath.

Afterwards, cross-sections of a given thickness, called “slices” are generated from the STL model with descriptions of the part and supports. For each sliced layer, a laser-scan path is calculated. It defines both the boundary contour and the filling sequence that often is a raster-pattern.

After pre-processing, the part layers are sequentially built in the SLM system, one on top of the others, as follows:

1. The metal powder is spread uniformly over the building platform by a recoater.
2. A high-power fibre-laser beam selectively scans the building platform and fully melts the pre-deposited powder layer following the cross-section of the part.
3. The melted particles fuse and solidify to form the part layer.
4. The building platform is lowered, and the process is repeated until the entire job is completed.

Once the SLM manufacturing process is completed, the components are cleaned and detached from the building platform. Finally, their surface quality is improved through shot-peening of the inner surfaces and polishing of the flanges.

Metal 3D printing for RF engineering

These technological aspects translate into the following main advantages for RF engineers:

• More efficient development of new components since prototyping activities have reduced time and costs.
• Additional design flexibility, because no mechanical constraints arise from the use of machining tools (freeform fabrication), even if some design restrictions also apply to additive manufacturing (AM) processes.