FDM vs PolyJet 3D Printing: Key Differences & Comparative Insights

Fused Deposition Modeling (FDM) is a 3D printing technology that uses a polymer filament to ‘draw’ slices of a 3D file. It bonds the filaments to one another by partially melting them. PolyJet is also a 3D printing technology, but it works by inkjet-printing a ‘picture’ of each slice in modified acrylic resin. This picture is then fully cured using a UV light attached to the print head. 

One big difference between FDM vs. PolyJet is the materials used. FDM uses filaments of common plastics while PolyJet simulates those materials using various resins. This results in a significant price difference between the two. FDM is also limited in resolution by filament diameter. PolyJet, however, is limited only by inkjet resolution, making its minimum feature size 5 to 20 times smaller than FDM. This article will further discuss the similarities and differences between FDM vs. PolyJet and provide alternatives to both.

FDM Definition and Comparison to PolyJet

FDM technology was first created in 1988 by Scott Crump. The process works by melting a plastic filament in the print head. The temperature is controlled so that it delivers plastic in a gel state that has enough energy to fuse, but not enough to flow. The printing head translates in the X-Y plane and extrudes this gel as a continuous strand. The strands fuse together, but even the best printers cannot prevent porosity or make the material homogeneous.

FDM prints successive 2D slices of a model to build a solid 3D representation of the file. The nozzle moves horizontally to pack strands neatly against the layer below. FDM offers two major advantages over PolyJet: material and machine costs. FDM material generally costs 1/10 as much per kilogram as PolyJet resin. The machines are also three to five times cheaper.

To learn more, see our article on the FDM Printing Process.

Attribute

Material costs

FDM

$10/kg to $50/kg

PolyJet

$200/kg to $500/kg

Attribute

Max print resolution

FDM

50 to 500 microns

PolyJet

16 to 45  microns

Attribute

Capital cost

FDM

$50 to $250,000

PolyJet

$19,000 to $700,000

Attribute

Can be easily maintained

FDM

Yes

PolyJet

No

Attribute

Capable of printing fine details

FDM

No

PolyJet

Yes

Attribute

Less wastage of materials

FDM

Yes

PolyJet

No

Table. FDM vs. PolyJet Comparison

FDM vs. PolyJet: Technology Comparison

FDM is a simple process that delivers the general shape of 3D files. PolyJet, on the other hand, is a more intricate technology that delivers dimensionally accurate 3D representations, including fine details. FDM technology is nearing its upper limit of resolution because further improvements to single-point printing drive print times up to impractical levels. PolyJet has not reached its resolution limit and is still developing.

FDM vs. PolyJet: Material Comparison

FDM prints using common polymers. A switch to a different material requires only a quick change in the printer’s settings, and raw material providers needn’t do anything special to it. Typically, FDM materials cost between $10 and $50 per kilogram. PolyJet materials, on the other hand, are complex, specialized resins. These materials may optimize strength, flexibility, transparency, and a range of other properties. PolyJet materials typically cost $200 to $500 per kilogram.

FDM vs. PolyJet: Product Applications Comparison

FDM is the low-cost option that is suited to robust and simple components. Its models cannot be used for fine mechanical assessment, but the prints can be valuable as prototype representations of thicker, simpler parts. PolyJet is more expensive and is suited to engineering and cosmetic uses like: pre-tooling design checks, validation of grips/overmolds, tests of flexure, and assembly features. If hand-finished and painted, PolyJet parts can substitute for cosmetic and functional parts for trial and sales-sample builds.

FDM vs. PolyJet: Print Volume Comparison

The range of build volumes for FDM is impressive. The largest FDM machine (the Terabot) can print up to one cubic meter. The largest PolyJet machine has a 1000 x 800 mm table and a build height of 500 mm.

FDM vs. PolyJet: Surface Finish Comparison

FDM parts show visible layer steps in the Z-direction, each one generally 0.2 to 0.5 mm in height. This makes for a rough surface and is even more apparent on curved surfaces. PolyJet parts also show visible Z steps, but they are between 16 and 45 microns in height, less than 1/10th of FDM’s step size. Hand-finishing operations like sanding and even polishing can produce very smooth surface finishes (up to lens-level transparency).

FDM vs. PolyJet: Cost Comparison

Both the equipment and printing material for FDM are cheaper by far than for PolyJet. The latter’s process also wastes as much as 20-40% of its resin. FDM parts are produced by many competing suppliers, so prices are consistently low. PolyJet parts, meanwhile, are more costly, making it a reasonable choice only when the highest quality or finest detail is necessary.

What are the Similarities Between FDM and PolyJet?

1. FDM and PolyJet share the same principle of Z-axis layering using an orthogonal printer transport mechanism.
2. Both offer a range of material properties that aim to represent those of manufactured parts. Thick FDM parts are strong in the X-Y axes but weaker in the Z direction due to imperfect intra-layer fusing. PolyJet parts are equally strong along all axes because of the nature of the material application.
3. Both systems are office-friendly. The machines require a stable temperature environment and good ventilation.

What are the Other Comparisons for FDM Besides PolyJet?

The following 3D printing technologies are also comparable to FDM:

1. FDM vs. FFF: FFF (fused filament fabrication) is a close analog of FDM in that it uses an extruded, heated filament to build model slices, relying on partial melting to bond the filaments into a whole. The lack of a heated print chamber is the main difference, making FFF models prone to residual stress and warping. To learn more see our full guide on FDM vs. FFF.
2. FDM vs. SLS: SLS (selective laser sintering) uses some of the same common polymers (like nylons) that FDM employs. But SLS material is supplied in powder form. To build the part, a laser selectively melts and fuses the powder. To learn more, see our full guide on SLS vs. FDM.
3. FDM vs. LOM: LOM (laminated object manufacturing) models are of similar resolution to FDM but can be stronger due to low porosity and great intra-layer bonding.

What are the Other Comparisons for PolyJet Besides FDM?

The following 3D printing technology is comparable to PolyJet:

• PolyJet vs. Multijet: Multijet Printing (MJP) employs the same inkjet technology as PolyJet. It uses a print head that deposits materials on subsequent layers. The main differences between the two arise in the post-processing stages. The support removal process of PolyJet parts consists of several steps. This includes the use of a water jet system and dipping the parts into a chemical solution. Multijetting, on the other hand, only requires keeping the parts in an oven to melt the paraffin wax. To learn more, see our full guide on Polyjet vs. Multijet.

Summary

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Dean McClements

Dean McClements is a B.Eng Honors graduate in Mechanical Engineering with over two decades of experience in the manufacturing industry. His professional journey includes significant roles at leading companies such as Caterpillar, Autodesk, Collins Aerospace, and Hyster-Yale, where he developed a deep understanding of engineering processes and innovations.

Read more articles by Dean McClements