Laser Melting (LM)

image of Explanation of the technology laser melting (same as direct metal laser sintering, DMLS, selective laser melting) including characteristics, materials, machines, vendors, applications and process chain. image of Explanation of the technology laser melting (same as direct metal laser sintering, DMLS, selective laser melting) including characteristics, materials, machines, vendors, applications and process chain.

Synonyms

Selective Laser Melting, SLM, Direct Metal Laser Sintering, DMLS, Laser Cusing

Process description

A thin layer of metal powder is selectively melted by a laser. The parts are built up layer by layer in the powder bed. Read more

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.

Advantages / disadvantages

Laser melting can manufacture parts in standard metals with high density, which can be further processed as any welding part. However, the technology is rather slow and expensive as well as surface finishes are limited. Read more

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.

Application areas

  • Prototypes are produced in standard metals for form / fit and functional testing by laser melting
  • Support parts (jigs, fixtures, helps) are produced in standard metals
  • Small series parts down to one of a kind are directly produced in standard metals (further post-processing might be required to improve surface or tolerances)
  • Tools for injection molds are produced in hot work steel enabling conformal cooling (complex cooling channels directly beneath the surface

Characteristics / restrictions

  • Maximal build envelope: 600x400x500 mm3
  • Minimum feature size: 0.04-0.2 mm
  • Accuracy: +/- 0.05-0.2 mm (+/- 0.1-0.2%)
  • Minimum layer thickness: 0.03 mm
  • Typical surface finish: 4 – 10 microns RA
  • Density: Up to 99.9%

Characteristics are only indicative, as there are different types of machines available.

Process chain

When planning the build, critical tolerances, surface finishes and overhangs need to be taken into consideration. After the build, parts often need to be thermally processed and the support structures need to be mechanically removed. Laser melting parts can be further post-processed as any welding part. Read more

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).

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