• Assaf Weiss

FDM Vs. MJP - 3D printing technologies

עודכן: 4 בספט׳ 2021

The world of 3D printing is changing in from of our eyes in the last few years, with the introduction of new technologies and the improvement of current available technologies in a fast pace. In this post we will discuss the comparison of two quite established 3D printing technologies - FDM and MJP.

FDM technology

The FDM technology is one of the first 3D technologies that were commercially introduced. This technology was developed by Stratasys in the early 90's. The basic concept of this technology is quite simple, and since the patent stratasys had on this technology expired a few years ago, a lot of new 3D printing companies that utilized this technology were established in the last few years (to list some of the big players - Ultimaker and Makerbot) which manufacture pretty cheap 3D printers (from a few hundreds of dollars and up to a few hundred thousand dollars for the commercial machines).

This technology works by extruding the raw material, the raw material (by the form of filaments mostly) is pushed through a nozzle, and at the same time is being squished onto the printing bed to produce a fine, thin layer (typically between 0.05 mm to a few tenth of a millimeter). The model is built layer by layer until the full model is built. Most of the home use printers make use of the same material for building the model as the material that is being used as a support structure, this makes the removal of the support material quite complex in some cases, and also leaves a rough surface finish where the supports made contact with the model. The more sophisticated machines (both for home use, and for commercial uses) make use of a soluble support material (in water or other chemical solutions), soluble support is more common in commercial printers, but it is slowly making its way into the hobby and home used printers.

Since in this technology uses solid standard raw material, the variety of materials is the largest of all 3D printing technologies, and the limits to the usage of materials is maximum extruder / heated bed working temperature (and of course - the raw material has to be a thermoplastic polymer).

The most popular materials used with this technology are ABS, PLA, PA, ASA, PC, PETG (most of them can be filled with all kinds of fillers, from glass fiber and carbon fiber to metals and glitters...). Some more exotic materials, mostly printed with high end FDM 3D printers are Ultem, PEEK, POM and many more.

Printng resolution in X and Y mostly depends on the nozzle diameter (minimal nozzle size is around 0.1mm). Z resolution is typically up to 0.05 mm and is also dependent on the nozzle diameter.

MJP technology

MJP technology is a proprietary 3D systems' 3D printing technology. This technology makes use of printing heads similar in operation to an ink jet printing head. Using piezo-mechanical elements, the print head inject thousands of small droplets of a photopolymer onto the printing tray thus depositing layer by layer until the final model is built. In between layers a UV light is shined on the layers in order to catalyze the polymerization of the photopolymer. In this technology the materials being used are proprietary to 3D systems which means the variety of materials is much smaller than the FDM technology. Printing resolution is 800x900 DPI in the x and y directions, and 790 DPI in the z direction (32 micron layers). This technology uses a melting support material that is being melted with heat after the print is done, this process leaves a smooth surface finish throughout the print.

Comparing the two technologies

The table above lists the main differences between the two technologies.

Comparison between prints from the two technologies

In order to better understand the differences, we will try and demonstrate them using prints from the two technologies. The two prints are models downloaded from Thingiverse

image 1 : Yoda bust printed using a FDM printer

image 2: Yoda bust printed using a MJP printer

In both images above we took photos of the same model printed in FDM and MJP. Image 1 was printed in FDM and image 2 was printed in MJP. Because of the nature of the FDM printing process, the model reflects much more light (from the layer structure and from the molten plastic which has some shine to it). It can be clearly seen that the MJP model is much more detailed than the FDM model. In addition we can see some defects to the FDM model because lack of appropriate support structures, and resolution issues (the easiest to notice are the holes in the ears which are caused by a very thin wall that the 0.4mm nozzle can't capture).

Image 3: A close up of the Yoda bust printed in FDM

Image 4: a close up of the Yoda bust printed in MJP

Images 3 and 4 are close ups of the Yoda bust in FDM and MJP accordingly. In the MJP print we can see the high resolution of the print around the eyes and nose (wrinkles) the high resolution of the ears, and so on. In the FDM print, the lack of supports caused the chin to droop (we could have tried to fix that by using more supports but then the supports removal process could have caused other defects, since our FDM printer uses the same material for supports as the build material).

image 5: a rook model printed in FDM

image 6: a rook model printed in MJP

In images 5 and 6 we can see a rook model printed in FDM and MJP accordingly. The inner spiral (DNA shape) in the FDM model was not recreated so well because the diameter of the strands was too close to the nozzle diameter, the outer spirals came out pretty good, but the lower one which needed more supports drooped in some locations. These features were printed flawlessly in the MJP print, this mainly demonstrate the issues FDM printers present when printing small delicate features. we could have tried printing this rook on the FDM printer with a 0.1 mm nozzle and a 0.05 mm layer height but this would have caused the print time to multiply by almost an order of magnitude and still will not provide the same print resolution as the MJP.

image 7: rook printed in FDM

image 8: rook printed in MJP

In images 7 and 8 we can see a close up of the text area on the top of the rook model. In the rook printed using MJP technology, the text can be clearly seen and was reproduced flawlessly. In the FDM printed model on the other hand, the text wasn't reproduced at all since it was thinner than the nozzle diameter of 0.4mm. Image 7 also demostrated the stringing phenomena that may occur in FDM prints (this can be reduced by optimizing some printing parameters).

To summarize, we can say that when high resolution, small features, surface finish are not an issue, FDM can be used (and will allow the use of a variety of materials) , but when form and fit, surface finish, resolution and small details are a necessity, FDM is not a good solution, and MJP can do the job.

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