MJF Secondary Post-Processing Guide
Welcome to the realm of Multi Jet Fusion (MJF), a cutting-edge 3D printing technology that opens up new frontiers in creating intricate and functional parts. The journey, however, doesn't conclude with the printing process. Secondary post-processing steps play a pivotal role in refining these creations, adding visual appeal, improving surface finish, and enhancing physical properties. In this guide, we'll delve into the various techniques of MJF secondary post-processing, offering insights and tips for each step.
Cosmetic Post-Processes:
Dyeing:
Dyeing is a versatile and widely adopted technique to infuse color into MJF-printed parts. Whether done manually or using automatic dyeing solutions, the process involves immersing the part in a hot dye to achieve color uniformity.
Manual Dyeing: A dye mix is prepared in a bath, heated, and parts are immersed for around 8 minutes. Thorough cleaning is crucial for optimal results, and considerations for warpage in thin parts are essential.
Automatic Dyeing: These solutions offer efficiency with specific programs for dye bath mixing, conditioning, dyeing, part rinsing, dye disposal, and bath cleaning. Dyes are available in powder and liquid formats, each with specific concentration and temperature requirements.
Impact of Dyeing: While enhancing visual appeal, dyeing may slightly impact tensile strength and other mechanical properties due to minimal water absorption.
- Painting:
Introducing a layer of pigmented liquid composition, painting not only enhances color uniformity but also provides additional properties such as UV resistance and wear resistance.
Application Methods: Painting can be applied manually or automatically using a spray gun. Thorough cleaning, priming, and sanding are crucial for achieving a uniform surface. The number of layers influences both color and surface smoothness.
Surface Improvement: The application of multiple layers of paint not only enhances color but also contributes to improving the surface roughness of MJF 3D printed parts.
- Graphite Blasting:
Graphite blasting provides a metallic-looking surface by using a mix of glass bead media and graphite to achieve uniform color. This not only enhances aesthetics but also reduces friction between moving parts.
Considerations: Proper settings for air pressure and distance to the part are critical. Graphite blasting is recommended for visual prototypes but may not be suitable for final parts subject to frequent handling due to limited wear resistance.
- Smoothing Blasting:
Similar to bead blasting, smoothing blasting propels abrasive media onto the part's surface at high pressure to achieve a better surface finish. It uses more abrasive media and higher pressure, resulting in a range of finishes from matt to glossy.
Effect on Surface Roughness: Besides providing a better surface finish, smoothing blasting contributes to reducing surface roughness. The combination of abrasive media, pressure, and processing time results in enhanced visual and tactile qualities.
- Electroplating:
Electroplating adds a thin layer of metal to the part's surface, providing both aesthetic and functional benefits such as conductivity and mechanical strengthening.
Electroless Plating: Mechanical etching, chemical etching, and palladium application are part of the electroless plating process. The part's surface is then submerged in an electroless plating solution, coating it with nickel or copper.
Gas Activation Technology: This technique uses ionized gas to make the surface conductive without the need for mechanical or chemical etching. It offers fast and selective metallization but results in a small area of connection without electroplating.
Conductive Coatings: Coating the part is the easiest and most economical way to make the surface conductive. However, it may not provide durability over time due to weak adhesion.
Once the surface has been made conductive by electroless plating, gas activation, or with a conductive coating, the standard procedure for electroplating can be done, deposing a metal coating on the surface of the part. Various metals can be used to plate the surface: notably, nickel, copper, chrome, and precious metals such as gold or silver.
Surface Roughness Post-Processes:
- Vibratory Finishing:
Vibratory finishing, whether wet or dry, smooths the part's surface using ceramic or plastic media. The choice of media, size progression, revolutions per minute, and processing time play a crucial role in achieving the desired surface finish.
Effect on Surface Roughness: The abrasive media used in vibratory tumbling, whether ceramic or plastic, influences the Ra value achieved. The process is not constant over time, being more efficient at the beginning.
- Chemical Polishing:
Chemical polishing, or chemical smoothing, is a physio-chemical process that smooths thermoplastic polymer parts' surfaces, including internal cavities.
Chemical polishing is a controlled process that achieves a surface finish with a roughness value of less than 1 μm. It can result in matt, gloss, or shiny surfaces without compromising mechanical properties.
Surface Impact: The process is non-line-of-sight, preserving fine details without affecting the part's dimensional accuracy significantly. However, there is a risk of structural deformation for very thin sections.
Conclusion:
This guide on MJF secondary post-processing opens up a realm of possibilities, allowing creators to enhance both the aesthetic appeal and functional properties of 3D printed parts. Whether through dyeing, painting, blasting, or electroplating, each technique brings its unique advantages to the table. Understanding these post-processing steps empowers designers and engineers to unleash the full potential of MJF technology, turning their creations into masterpieces.
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