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3D Metal Printing

Methods of 3D Metal Printing

| Author / Editor: Simone Käfer / Janina Seit

People interested in 3D printing are confronted with a seemingly infinite number of 3-letter terms. Our editor tried to provide an overview of current additive metal printing processes and found out that in fact there are not that many.

Renishaw uses the SLM powder bed process. It is the most common procedure.
( Source: Simone Käfer/MM )
  • Powder bed process: SLM/SLS, DML, LMF and EBM
  • Additive procedures: LMD, DED, DMD, Laser Cladding and MPA

Before taking a look at abbreviations such as SLM, EBM, LMD or MPA, one should first differentiate between powder-bed welding and deposition processes such as laser deposition welding. In powder bed welding, a slider is used to apply a thin layer of metallic material onto the building platform. Then a laser or electron beam cuts out the desired shape. Now the installation space is lowered a little and the next layer of metal powder is pushed over the object. In this way, the component is created layer by layer.

SLM — Selective Laser Melting

This technology includes Selective Laser Melting (SLS), which is also called Direct Metal Laser Sintering (DMLS) or Laser Metal Fusion (LMF). The term SLS is also used in plastic 3D printing, where the "S" at the end stands for "sintering". The average powder size is 20 to 50 µm, but also particles of up to 100 µm can printed. The printing space is preheated to just below the melting temperature of the material, minimizing the energy consumption of the laser and preventing distortion of the component. Also, the atmosphere in the installation space is nitrogenous. The residual powder, in technical jargon called "oversized", can be reused after passing through a sieve. According to Renishaw, this method requires support structures only if the component has overhangs > 45°. Basically, support structures also compensate for stresses. They are produced before the actual construction process with half the energy input of the laser and twice the scanning speed. It is the most widely used process implemented by Renishaw, Trumpf, Matsuura, 3D-Systems, Concept Laser, EOS and SLM Solutions.

EBM - Melting with an Electron Beam

Another powder bedding process is electron beam melting (Electron Beam Melting, EBM). The differences to the SLM process are due to the electron beam. It requires a vacuum, which is why the installation space must be completely sealed. However, it does not need to be preheated because the high scanning speed generates sufficient preheating. This makes the process even faster, but also hotter. Increased speed is also due to the fact that the electron beam can be split up and the powder is melted in several places. This advantage becomes a disadvantage when it comes to fine structures, because the electron beam is wider than that of the laser. EBM printers are manufactured by the Swedish company Arcam.

LMD - Laser Deposition Welding

In additive processes, the powder is applied accurately by a nozzle and solidifies on the spot. Here again two different techniques are distinguished: LMD and MPA. Both methods usually do not require support structures. LMD stands for Laser Metal Deposition. Other terms are: Direct Energy Deposition (DED), Direct Metal Deposition (DMD) or Laser Cladding. The powder is sprayed into the protective gas stream and melted in the melting bath of the laser. In this way, the material can be applied accurately. According to OR Laser, powder particles between 40 and 90 µm as well as a low feed rates are best suited for this application. Small particles and high feed rates would block the laser beams and thus impair the efficiency and quality of powder deposition welding.

This process is a logical further development of conventional deposition welding. It is therefore particularly suitable for repairs, coating work, joining processes or components made of different materials — even on one machine, as it can be supplied by several powder containers. This enables individual alloys to be mixed and sandwich structures to be printed. LMD is also used in hybrid machines that use machining technology in addition to additive processes. For these kinds of applications, DMG Mori is well known.

MPA - Who Needs Lasers?

The metal powder application (MPA) can do without lasers. Its main manufacturer is Hermle Maschinenbau. Powder particles are rapidly accelerated by means of a carrier gas and applied to a substrate or a previously printed layer. Both the powder and the surface are deformed significantly, thus creating an adhesive contact surface. A powder jet comprising several millimeters and build-up rates of more than 200 cm³ per hour qualify the thermal spraying process for a comparatively massive volume build-up on medium to large component surfaces. A combination of several materials is also possible. The manufacturer combines this additive process with a cutting machine.

This article was first published by MaschinenMarkt.

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