3D Metal Printing Direct Metal Laser Sintering (DMLS)

Manufacturing Engineering & Processes

3D Metal Printing Direct Metal Laser Sintering (DMLS)

Direct metal laser sintering (DMLS) is an additive metal fabrication technology, sometimes mistakenly referred to as selective laser sintering (SLS) or selective laser melting (SLM). This process utilizes a 3-dimensional CAD model, creating a file which is then forwarded to the software utilized by the machine. The direct metal laser sintering machine makes use of a powerful fiber optic laser.

Current common materials available include Inconel 625, Inconel 718, Cobalt Chrome, Aluminum and Titanium.

The manufacturing process involves use of a 3D CAD model where a digital file is created and sent to the machine’s software. The technology fuses metal powder into a solid part by melting it locally using the focused laser beam. Parts are built up additively layer by layer, typically using layers 15 to 25 micrometers thick. This process allows for highly complex geometries to be created directly from the 3D CAD data, fully automatically, in hours and without any tooling. DMLS is a net-shape process, producing parts with high accuracy and detail resolution, good surface quality and excellent mechanical properties.

Benefits

DMLS has many benefits over traditional manufacturing techniques. The ability to quickly produce a unique part is the most obvious because no special tooling is required and parts can be built in a matter of hours. Since DMLS can use most metal alloys, prototypes can be functional hardware made out of the same material as production components.

DMLS is also one of the few additive manufacturing technologies being used in production. Since the components are built layer by layer, it is possible to design internal features and passages that could not be cast or otherwise machined. Complex geometries and assemblies with multiple components can be simplified to fewer parts with a more cost effective assembly. DMLS does not require special tooling like castings, so it is convenient for short production runs.

Applications

This technology is used to manufacture direct parts for a variety of industries including aerospace, dental, medical and other industries that have small to medium size, highly complex parts and the tooling industry to make direct tooling inserts. With a current build envelope of 250 x 250 x 185 mm, and the ability to ‘grow’ multiple parts at one time, DMLS is a relatively cost and time effective technology. The technology is used both for rapid prototyping and production components.

Constraints

The size, feature details and surface finish, as well as print through error in the Z axis may be factors that should be considered prior to the use of the technology. However, by planning the build in the machine where most features are built in the x and y axis as the material is laid down, the feature tolerances can be managed well. Surfaces usually have to be polished to achieve mirror or extremely smooth finishes. Engineering material characteristics are not currently documented as industry standards therefore, critical applications must be avoided unless the component are fully tested and qualified for the target application.

For production tooling, material density of a finished part or insert should be addressed prior to use. For example, in injection molding inserts, any surface imperfections will cause imperfections in the plastic part, and the inserts will have to mate with the base of the mold with temperature and surfaces to prevent problems.

In this process metallic support structure removal and post processing of the part generated is a time consuming process and requires use of EDM and/or grinding machines having the same level of accuracy provided by the RP machine.

When using rapid prototyping machines, .stl files, which do not include anything but raw mesh data in binary (generated from Solid Works, CATIA, or other major CAD programs) need further conversion to .cli & .sli files (the format required for non stereolithography machines). Software converts .stl file to .sli files, as with the rest of the process, there can be costs associated with this step.

Mechanical Tolerances

With the tolerances that are achievable and the durability these parts offer, Laser Sintering has become the preferred process of prototyping, and is quickly becoming an acceptable and even conventional method of manufacturing.

Current standard tolerances are +/- 0.005” for the first inch, and +/- 0.003” for each inch thereafter.

Standard tolerances can range from 0.010” to as fine as 0.003”.

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