Direct Metal Laser Sintering: Everything To Know About DMLS 3D Printing

Direct Metal Laser Sintering is the most commonly used metal 3D printing method. Employed by 3D printing companies including 3D Systems, SLM Solutions, Concept Laser, EOS, and more, DMLS is a fast-growing and innovative technology. Therefore, we did our research on the DMLS process, post-processing requirements, compatible materials, and advantages and disadvantages to create this guide to Direct Metal Laser Sintering.

If you found this guide useful, be sure to check out our other 3D printing technologies guides.

Approx reading time: 4 minutes.

Introduction

DMLS is a form of metal powder bed fusion technology, in a similar vein to Electron Beam Melting. This is also similar to Selective Laser Sintering in that powders are used along with a laser to create parts layer-by-layer. SLS however uses plastic powder materials whereas DMLS uses metals.

History of Direct Metal Laser Sintering

Direct Metal Laser Sintering was patented by ERD and EOS back in 1994, before EOS pioneered the technology in their DMLS 3D printers. Though the patent didn’t come about until 1994, preliminary research conducted on what would eventually become DMLS can be traced back to the late 1970s.

direct metal laser sintering
A part created using Direct Metal Laser Sintering.

DMLS vs SLM

Often confused with Selective Laser Melting (SLM), the two are very similar but with some slight differences:

  • DMLS: Does not melt powder but instead heats the metal powder to a point where it fuses together on a molecular level. Known as sintering the powder.
  • SLM: Uses laser to fully melt the metal powder.

This creates differences in materials available for use in these two similar technologies. Direct Metal Laser Sintering can therefore produce parts using metal alloys, whereas SLM can only produce single element metals such as aluminium and titanium.

Preparation before printing with DMLS

Direct Metal Laser Sintering is different to technologies such as Fused Deposition Modeling in that it doesn’t use filament. Instead, a metal powder similar to SLS is used. This metal powder has to be very fine and has a specific geometry to ensure the smoothness of parts printed using DMLS.

Metal 3D printer performance depends on three main factors:

  • Laser spot size (how large the laser is and therefore how precise it is).
  • Geometry of metal powder (finer powders vs less fine powders).
  • Layer height (smaller layers means longer print times but better quality surface finishes and part quality).

Overall, metal 3D printers are usually accurate to around 0.1mm. They are not like desktop FDM printers that are often plug and play however, and often require trained operators to monitor the machines and perform the necessary maintenance tasks.

This video by Stratasys Direct explains in better depth the Direct Metal Laser Sintering process:

Direct Metal Laser Sintering 3D Printing Process

Firstly, the roller within the metal 3D printer spreads out a thin layer of powder in the 3D printer’s empty tank. This powder layer is spread to be the same as the height of one layer (usually 20-100 microns). The print chamber of the 3D printer is then heated up.

The heated print chamber heats the powder until it is not far below its melting point. The 3D printer’s laser then follows the preset shape of the 3D file design to trace the part, sintering the metal. Once the laser has finished sintering the full layer, a new layer of powder is spread again by the roller, and the process repeats. This continues, layer-by-layer, until the finished metal part is created.

direct metal laser sintering

DMLS Post-Processing

Unlike technologies such as Fused Deposition Modeling, you cannot just remove your finished part straight after printing with Direct Metal Laser Sintering. There are a number of compulsory steps to do before the print can be finished. In addition, there a number of optional steps to take for better finish quality.

1. Heat Treatment

Before you can remove the object from the build platform, heat treatments are required with Direct Metal Laser Sintering. This involves heating and cooling the object at regulated temperatures to help the part solidify and become stronger. This also helps increase the porosity of the metal.

2. Support Removal

Supports help with metal part quality in a variety of ways. Firstly, they act as a heat sink, deflecting heat from the part and minimizing distortion due to heat and printing stresses. Unlike with Stereolithography or FDM, removing supports with Direct Metal Laser Sintering is not as easy as just breaking off the plastic supports. With DMLS, the metal supports need to be broken off with machines, which can lead to problems with surface finish on these areas. These areas need to be filed afterwards.

3. Excess Powder Removal

As with Selective Laser Sintering, parts are surrounded with the material powder in the build chamber. Therefore, any excess unsintered powder needs to be removed from the build chamber and either thrown away or reused in future prints.

4. Optional Extras

  • Machining – to improve surface finish.
  • Polishing – shinier surface finish.
  • Metal plating.
direct metal laser sintering
A metal part used to replace a part of missing skull, created with Direct Metal Laser Sintering.

Direct Metal Laser Sintering Materials

Though 3D printer manufacturers are continuously innovating to create new metal powders, there are a number of main metals used in DMLS 3D printing. The main metal powders used include aluminum and titanium, though others such as Cobalt-chrome, Stainless steel and Inconel are also commonly used.

Direct Metal Laser Sintering can also be used with precious metals to create 3D printed jewelry. This process involves metals such as gold, platinum, or silver to create stunning pieces of jewelry with complex geometries that other manufacturing processes just cannot do.

DMLS Companies

Though new 3D printer manufacturers are entering the DMLS market every year, there are a few dominant companies in the sector. These include 3D Systems, who bought French company Phenix Systems to put together their own DMLS 3D printer product line. Also, EOS are another dominant force with their EOSINT range of printers. Recently, GE Additive have made their move to take over the industry, purchasing companies such as Concept Laser and Arcam. Lastly, German company SLM Solutions create a number of industrial DMLS 3D printers.

direct metal laser sintering
Concept Laser are a prominent DMLS 3D printer manufacturer bought out by GE Additive.

Applications

Direct Metal Laser Sintering is heavily used in industries such as the aerospace and automotive sectors. This is because DMLS offers fantastic topology optimization through creating stronger metal parts that weigh less. DMLS is also used in the medical sector, especially dental, creating customized dental implants with very accurate geometries.

Direct Metal Laser Sintering Advantages and Disadvantages

DMLS Advantages

  • Great for creating geometrically complex parts where much customization is required. DMLS is a great alternative when other manufacturing methods simply cannot create parts with certain geometries.
  • Offers significant benefits through topology optimization – reducing weight and increasing strength of rockets, planes, and cars.

DMLS Disadvantages / Limitations

  • DMLS offers a small build size compared to other technologies. Other technologies such as FDM can offer build sizes of over 100cm³ which DMLS cannot compete with.
  • DMLS is a very expensive process. All metal 3D printers are industrial and can cost $250,000+. In addition, metal powders are extremely expensive, with stainless steel 316L powders costing $350-450/kg.

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