Powder Bed Fusion

Definition

Heat source scan path defines boundary countour and fill sequence to fuse nearby powder kernels together. Usually the energy source; mostly lasers. Powder Bed Fusion has the distinct advantage of needing virtually no supports. This is due to fact that most geometry and density combos can be supported by the powder alone.

The significant limitation of PBF technqieus is they are almost all thermally fused. This means that it has consequential heating gradients as well as significant heating and cooling times. Not properly cooling parts and beds will have measurable thermal stresses which may cause excessive cracking and distortion.

SLS was supposedly first patented by EOS in 1998 (with an expiry for circa 2008).

Source: https://www.sciencedirect.com/topics/engineering/powder-bed-fusion


Source: Thermophysical Phenomena in Metal Additive Manufacturing by Selective Laser Melting: Fundamentals, Modeling, Simulation and Experimentation" - Christoph Meiera, , Ryan W. Pennya , Yu Zoua , Jonathan S. Gibbsa , A. John Harta, Source Link

Science / Technique

Consistent Key Elements

• Energy source (usually laser)
• Powder based material. This powder is generally rolled on, fused, then lowered before another layer of powder is rolled on over it.

Source: "Critical Influences of Particle Size and Adhesion on the Powder layer uniformity in Metal Additive Manufacturing" - Christoph Meier, Reimar Weissbach, Johannes Weinberg, Wolfgang A. Wall, A. John Hart. https://www.sciencedirect.com/science/article/pii/S0924013618304801

• SLS - Selective Laser Sintering

  • Primarily Nylon Powders using a CO2 Laser. Invented by EOS GmbH
  • source: https://www.xometry.com/resources/3d-printing/selective-laser-sintering-sls/
  • EOS has an SLS methodology called FDR (fine detail resolution). However, besides a finer optical laser, the technique seems to be identical.

• DMLS - aka "Direct Metal Laser Sintering" - EOS

  • Direkt Metall Laser Schmelzen (German acronym): meaning Direct Metal Laser Melting often mis-represented as Direct Metal Laser Sintering
  • 50-150 microns
  • Employ 1-12 lasers

• SLM - Selective Laser Melting - SLM Solutions GmbH

  • Generally accepted as the more "common" term of the systems, but may be considered tokenized by SLM Solutions GmbH
• Source: https://www.xometry.com/resources/3d-printing/dmls-vs-slm-3d-printing/#:~:text=DMLS%20and%20SLM%20are%20both,alter%20the%20part's%20detail%20resolution.

• EBM - Electron Beam Melting

  • Sometimes referred to as EBAM - Electronic Beam Additive Manufacturing (coined by Sciaky).
  • Electron particle beam instead of a laser beam. Note the technique is very similar but with a different heat source. Generally 1000C and above temperatures.
  • Associated with convential welding techniques:
    • Plasma Arc Welding (PAW)
    • Gas Tungsten Arc Welding (GTAW)
    • Metal Inert Gas (MiG)
  • https://www.ge.com/additive/ebm#:~:text=compromising%20on%20quality.-,Electron%20Beam%20Melting,a%20clean%20and%20controlled%20environment.
  • https://www.youtube.com/watch?v=CUeDevI6kyE

    Material

• SLS

  • Nylons (PA6/PA11/PA12/PA66)
  • Filled Nylon - glass or carbon fibers
  • Thermoplastic Polyurethane (TPU)
    • Formlabs TPU 90A https://formlabs.com/blog/flexible-sls-3d-printing-material-tpu-90a/
    • Protolabs TPU 70-A https://www.protolabs.com/services/3d-printing/elastomer/tpu/?3d%20printing%20tpu&gad_source=1&gclid=CjwKCAjwkuqvBhAQEiwA65XxQOJTw56Hy0hSgIAb5xDQ2mC34dgg5cmp9qgXZM11KNx0k-GGtt2LzhoCWbQQAvD_BwE&utm_term
  • Castable Polystyrene

• DMLS / SLM

  • Most Metals with "reasonably" attainable melting points
  • Titanium Ti64
  • Stainless Steel 316
  • Nickel Alloys NI718

    Example Companies

• Formlabs
• EOS (SLS/DMLS)
• GE Additive
• SCIAKY - https://www.sciaky.com/

  Limitations

• Does not need supports
  • Enclosed cavities will hold "powder"
• Powder bases are usually unhealthy for human exposure without proper PPE