Perfecting Surface Roughness Secondary Post-Processing in HP Multi Jet Fusion

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Introduction

Surface roughness post-processing in HP Multi Jet Fusion (MJF) 3D printing is a crucial step in achieving the desired surface quality and texture of printed parts. This section of the MJF Secondary Post-Processing Guide focuses on methods to homogenize surface finish and reduce roughness, enhancing both the aesthetic and functional properties of the parts.

Vibratory Finishing:

Vibratory finishing is a popular technique to smooth the surfaces of 3D printed parts. It involves placing parts in a vibratory tumbler with abrasive media, which gently wears down surface peaks to create a more polished finish.

  • Types of Media: Ceramic, plastic, or steel media can be used, each offering different levels of abrasiveness.
  • Wet vs. Dry Process: Wet vibratory finishing typically results in a more polished finish, while dry finishing is more aggressive.
  • Key Factors: The choice of abrasive media, processing time, and the tumbler’s revolutions per minute are crucial for achieving the desired surface roughness.

Chemical Vapor Polishing:

Chemical vapor polishing smooths the surface of thermoplastic polymer parts, including internal cavities, through a physiochemical process.

  • Process Efficiency: It acts on the surface without degrading the part’s mechanical properties and can achieve a surface roughness value of less than 1 µm.
  • Versatility: Suitable for various thermoplastic polymers, including PA 11 & 12, TPE, and TPU.
  • Outcome: Results in matt, gloss, or shiny surfaces without losing fine detail or affecting dimensional accuracy significantly.

Recommendations for Best Results:

  • For Thin Sections: Caution is advised with very thin sections (less than 1 mm) as they are prone to structural deformation with chemical polishing.
  • Impact on Color: The process can affect the color of the parts, for instance, cutting through partially fused outer layers in gray parts to give a piano black finish.
  • Handling Sharp Edges: The process is less efficient with sharp edges and may require additional steps for such geometries.

Achieving the Desired Surface Finish:

The desired level of surface roughness and glossiness can be controlled through the choice of method and its parameters. It’s essential to consider the final application of the part when selecting the most suitable post-processing technique.

Conclusion:

Secondary post-processing techniques like vibratory finishing and chemical vapor polishing play a vital role in refining the surface quality of HP MJF 3D printed parts. By choosing the appropriate method and carefully tuning the process parameters, manufacturers and designers can significantly enhance the appearance and feel of their printed products, making them suitable for a wide range of applications.

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