Plastic-based 3D printing technologies are usually classified into three categories: light-curing, FDM hot-melt, and PBF powder bed fusion. Light-curing 3D printing is still mainly used for temporary use of hand prototypes (except Carbon) due to material properties; FDM hot-melt technology is mainly used for functional prototypes, fixtures or very small quantities of special parts manufacturing due to efficiency and surface roughness issues. And PBF nylon powder bed technology has been considered the most likely technology to push 3D printing to mass production due to its advantages of no support, material mechanical properties, good weather resistance, and longitudinal stackable molding.
PBF mainly refers to two technologies, SLS laser sintering and MJF multi-jet melt forming introduced by HP in 2016, of which MJF has significantly improved in productivity compared to the first generation of SLS technology and is now growing rapidly worldwide. (In this paper, PBF refers to Power Bed fusion powder bed fusion technology, including both SLS and MJF. SLS refers to Selective Laser Sintering; MJF refers to Multi Jet Fusion multi jet fusion molding).
.MJF multi-jet melting: the closest 3D technology for medium volume direct manufacturing
The full name of MJF is Multi Jet Fusion, which translates to Multi Jet Melt Molding in Chinese and was introduced to the market by HP in 2016.MJF technology has the following main advantages.
1, high manufacturing efficiency: MJF4200 full bin printing a process for 15.6 hours
2, manufactured parts with good mechanical properties: MJF uses materials such as PA12/PA11/TPU/PP, the mechanical properties of molded parts are similar to those of injection molded parts and have the same environmental weather resistance as injection molded parts.
3. Longitudinal and stacked printing, no support required
Compared to light-curing and FDM hot-melt technologies, which require a distressing support structure, PBF technology does not require support and uses a sandblaster to dispose of the powder on the surface after printing.
PBF nylon technology has been used in many cases of direct manufacturing of industrial parts worldwide, such as BMW's I8 Roadster window rails made with MJF, Nissan's aftermarket automotive parts made with MJF, Daimler's truck parts printed with SLS, and HP's own 3D printers, half of which are made directly through MJF 3D printing. cases prove that nylon-based 3D printing can be used for direct production.
.Shortcomings of BF nylon 3D printing technology
Although the mechanical properties of PBF nylon 3D printed parts are already close to those of injection molding, there are still some shortcomings.
1. How to ensure batch consistency (mechanical properties and dimensional consistency) of the printed parts.
The following two videos show our internal MJF printing in 2018 and the sample parts we got through external service providers in 2021, and we can find that there are significant differences in the performance of the molded parts using the same equipment and the same powder grade (PA12).
We tested the sample strips provided by the main nylon 3D service providers in China, and the mechanical properties of the test strips from different manufacturers vary greatly. The situation exists in both MJF and SLS technologies, and the main reasons for this are the ratio of new to old powder, the number of powder reuse and packing density control. By reducing the proportion of new powder and increasing the number of reuse of old powder, the printing cost can be reduced, but then the mechanical properties of the part will be sacrificed.
Nylon 3D printing can only be used for direct production if it ensures sufficient strength and consistency in continuous manufacturing, otherwise it will remain a short term use as a prototype.
2.The surface of nylon 3D printed parts is rough and cannot be used as appearance parts
.Chemical steam surface treatment: a new idea for nylon 3D printing to improve mechanical properties and surface quality
Since HP released MJF technology in 2016, the manufacturing efficiency of PBF nylon powder bed technology has taken a big step forward, but how to enhance the mechanical properties of nylon technology as well as improve the surface roughness, there is no good means in the industry for a long time in the past. In this regard, PostProcess (USA), AMT (UK) and DyeMansion (Germany) have made many attempts. Earlier this year, the author saw AMT's chemical vapor polishing solution, and really had a bright feeling.
1, the role of chemical fumigation polishing a: to enhance the mechanical properties of PBF nylon parts
Through the actual test can be seen: after the chemical polishing treatment of MJF printed parts, the mechanical properties are significantly improved, please see the following video.
2, chemical fumigation polishing role two: improve the surface quality of PBF printed parts According to the test, the surface roughness of MJF nylon parts after surface treatment is reduced from Ra8 to Ra1.2 on average, while the air/water tightness is significantly improved, which is very helpful for doing some manifold and runner type applications.
MJF technology itself already has the advantages of manufacturing efficiency and material properties, coupled with chemical surface treatment to improve mechanical properties and surface quality, providing new ideas for manufacturing companies to use 3D printing technology for small to medium volume rapid moldless manufacturing. We welcome companies to contact and test with us.