Laser Melting (LM)

A laser melting machine distributes a layer of metal powder onto a build platform, which is melted by a laser (or multiple lasers). The build platform will then be lowered and the next layer of metal powder will be coated on top. By repeating the process of coating powder and melting where needed, the parts are built up layer by layer in the powder bed.

Laser melting requires support structures, which anchor parts and overhanging structures to the build platform. This enables the heat transfer away where the laser is melting the powder. Therefore it reduces thermal stresses and prevents wrapping. The build envelope can be filled by several parts being built in parallel as long as they are all attached to the build platform.

The technology manufactures parts in standard metals with high density (above 99%) and good mechanical properties (comparable to traditional production technologies). A constantly widening set of standard metals is available. Parts can be further processed as any welding part.

LM is still an expensive and slow process. Tolerances and surface finishes are limited, however they can be improved through post-processing.

Pre-build planning

The production of parts is planned in a build preparation software. One or several parts are placed in the build, using the digital 3D files (typically in the STL file format). Important decision during the set-up phase is the orientation of the part in the build envelope and what support structures are required. This depends on:

• Geometry, overhangs and inclination
• Location of most critical tolerances and surface finishes
• Areas where post-processing is required and potentially additional material needs to be added

Post-processing

• Removal of build envelope: The build envelope is removed from the machine
• Remove powder: Build platform with the parts attached is taken out of the loose powder. Excess loose powder is removed by sand blasting. This is usually straight forward, however might require some extra effort for parts with complex geometric features (e.g. trapped powder)
• Thermal processing: After the build, parts are often thermally processed to release residual stresses and improve part characteristics and metallurgical structure. Which regime is best depends on the application, desired part characteristics, the material used and the part characteristics. Typical processes include vacuum heat treatment, heat treatment under inert gas or hot isostatic pressing (HIP).
• Removal of supports and post-machining: Afterwards, parts are taken off the build platform, typically through wire cutting EDM or machining. Further support structures are mechanically removed. Parts might be partially post-machined in order to fulfil critical tolerances.
• Surface finish: Often parts need to be further processed to improve surface finish – either mechanically (e.g. polishing, grinding, peening) or chemically (e.g. plating, electro polishing).