Metal Stamping Guide

DMLS & SLM

Master the most popular metal 3D printing processes for high-end applications.

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Metal Stamping Guide

DMLS & SLM

Direct Metal Laser Sintering (DMLS) and Selective Laser Melting (SLM) are the most used metal 3D priting processes today. They are particullarly suitable for high-end applications as they offer great design freedom & advanced material properties.

In the section, we will dive deeper into the manufacturing process, technical charactereistics and benefits and limitations of these two, very simillar processes.

DMLS & SLM for metal stamping

What is DMLS/SLM 3D printing?

A DMLS/SLM metal 3D printer in action
A DMLS/SLM metal 3D printer in action

DMLS (Direct Metal Laser Sintering) or SLM (Selective Laser Melting) are two powder bed fusion metal 3D printing technologies. The practical difference between SLM and DMLS are very slim. For design purposes, the two technologies can be treated as the same.

They both use a high power laser to bond metal powder particles together to form a part layer-by-layer. SLM achieves a full melt, while DMLS causes the metal particles to fuse together on a molecular level due to the very high temperatures. Most metal alloys are compatible with the DMLS process, while only certain (pure) metal materials can be used in SLM.

How does DMLS/SLM work?

Schematic of a typical DMLS/SLM 3D printer
Schematic of a typical DMLS/SLM 3D printer

Here are the basic steps of the DMLS/SLM 3D printing process:

  • The build chamber is first filled with inert gas and then heated to the optimal print temperature.
  • A thin layer of metal powder (typically 50 μm) is spread over the build platform.
  • The laser scans the cross section of the part, selectively bonding the metal particles.
  • When entire area is scanned, the build platform moves down a layer and the process repeats until the whole build is complete.
  • After printing, the build first needs to cool down and then the loose powder is extracted.

The 3D printing step is only the beginning of the DMLS/SLM manufacturing process. After the print is complete, several (compolsory or optional) post-processing steps are required before the parts are ready to use. Compulsory post-processing steps include:

  • Stress relief: Due to the very high processing temperatures during printing, internal stresses develop. These need to be relieved through a thermal cycle before any other operation.
  • Removal of the parts: In DMLS/SLM the parts are essentially welded onto the build platform. A band saw or EDM wire cutting is used here.
  • Removal of the support: Support in DMLS/SLM is always required to mitigate the warping and distortion that occurs during printing. Support is removed manually or CNC machined.

To meet engineering specifications, additional post-processing steps are often required. These may include:

  • CNC machining: When tighter tolerances than the standard ± 0.1 mm are required, machining is employed as a finishing step. Only minimal material is removed this way.
  • Heat treatments: To improve the material properties of the part, heat treatments or Hot Isostatic Pressing (HIP) can be used.
  • Smoothing/Polishing: Certain application require a smoother surface than the standard RA 10 μm of as-printed DMLS/SLM. CNC machining and manual, vibro or chemical polishing are all available solutions.
Metal powders for 3D printing

Metal powders for 3D printing

The raw material used in DMSL/SLM and many other 3D printing processes comes in a powder.

The characteristics of the metal powders are very important for the end results. To ensure good flow and close packing, metal particles need to have a spherical shape and a size between 15 and 45 microns. To achieve these tight requirements, methods such as gas or plasma atomization are commonly used.

The high cost of producing these metal powders is a key contributor to the overall cost of metal 3D printing.

Benefits and limitations of DMLS/SLM

The main strength of DMLS/SLM is its ability to create highly optimized, organic structures from high-performance metal alloys.

Parts manufactured with DMLS/SLM can have a complex, organic shape that is optimized to minimize their weight while maximizing their stiffness. Or they can have internal geometries that cannot be produced with any other method.

The material properties of DMLS/SLM parts are excellent. Parts with almost no internal porosity are manufactured from a wide range of metal alloys, from aluminum and steel to high-strength superalloys.

We saw in a previous section though that the costs connected with DMLS/SLM are high. For this reason, it is only economically viable to use this processes for optimized parts for high-value engineering applications.

From a technical perspective, the main limitation of DMLS and SLM is their need for extensive support structures. These are needed to avoid warping and to anchor the part to the build platform. Also, out of the printer, the surface roughness of the produced parts is relatively high for most engineering applications, so post-processing is necessary.

  Excellent design freedom
  High manufacturing & design cost
  High accuracy & fine details
  Extensive need for support structures
  High-performance materials
  High surface roughness

Technical characteristics of SLM & DMLS

The table below summarizes the basic technical capabilities of a typical DMLS/SLM metal 3D printer today. For additional design guidelines, jump to the design rules.

Property DMLS/SLM
Material selection Large range of materials currently available

Aluminum alloys, titanium, stainless steel, tool steel, cobalt-chrome alloys, nickel superalloys, precious metals etc.
Dimensional accuracy ± 0.1 mm
Typical build size 250 x 150 x 150 mm

(up to up to 500 x 280 x 360 mm)
Common layer thickness 20 – 50 μm
Typical surface roughness RA 8 - 10 μm
Support Always required
Internal porosity Less than 0.2 - 0.5%
Cost per part $$$$$