PolyJet 3D Printing: How Resin Jetting Actually Works

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  How PolyJet 3D printing builds a part
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  Multi-material builds and what they are good for
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  Where PolyJet stops being the right answer
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  Design rules that keep PolyJet parts usable
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  From CAD file to finished PolyJet part
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  PolyJet compared with other routes

PolyJet 3D printing is a material jetting process. A print head travels across the build platform and deposits thousands of microscopic droplets of liquid photopolymer, one pass at a time. A UV lamp mounted beside the head cures each pass almost immediately, so the resin goes from liquid to solid in seconds rather than minutes.

The head carries separate nozzle arrays for model material and support material. That split matters. Support is jetted where overhangs, undercuts, and internal channels need it, then removed after the build. Because support is jetted rather than printed as the same plastic, it can be dissolved or blasted away without touching the model surface.

Layer thickness typically runs from 14 µm to 32 µm depending on the machine and the resin. Thinner layers buy you smoother curved surfaces and finer vertical detail, at the cost of build time. A 16 µm layer on a 50 mm tall part takes roughly twice as long as a 32 µm layer on the same geometry.

The build platform indexes down by one layer height after each pass, then the head sweeps again. There is no melting, no powder bed, and no laser. That is why PolyJet parts come out with a smooth as-built surface and why the process tolerates thin walls and small features that powder-based systems struggle to clear.

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  Droplet sizePicoliter-scale droplets from multiple nozzle arrays
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  Cure sourceUV lamp trailing the print head, cure within the same pass
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  SupportJetted separately, removed by water jet or manual tools
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  Layer range14–32 µm, chosen per job against build time

The strongest reason to choose PolyJet 3D printing over other resin processes is material mixing inside one build. A single job can place a rigid opaque shell next to a soft 30 Shore A gasket and a clear window, with the digital model defining where each one lands. No assembly, no adhesive, no secondary bonding step.

Digital materials are the mechanism. The printer blends two base resins at the nozzle level in set ratios to produce intermediate properties. That gives you a continuous range rather than a fixed catalogue. You can dial a durometer between two endpoints, or shift a color, without changing feedstock.

Clear resins are worth calling out. They print transparent and can be polished or dipped to improve clarity, which is useful for light pipes, fluid visualization manifolds, and lens housings in early fit checks. They are not optically clear at the level of a ground glass optic, and they yellow under sustained UV exposure.

Where this helps most: overmold studies, grip and seal prototypes, multi-durometer parts, and any assembly where you want to test the interface between two materials before committing to tooling. Where it does not help: parts that see sustained load, heat above roughly 60–80 °C, or long-term outdoor exposure.

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  Rigid opaqueSimulates ABS-like housings and brackets
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  FlexibleElastomer-like resins for seals, grips, and living hinges
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  TransparentLight pipes and fluid paths; yellows under UV
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  Digital blendsIntermediate durometer and color, set by the model

PolyJet parts are photopolymers. They are not engineering thermoplastics, and they do not behave like them. Tensile and impact values drop as the resin absorbs moisture and sees UV, and a part left on a windowsill for a year will not measure the same as the day it was built. Treat PolyJet output as a dimensional and ergonomic model, not a service part.

Heat is the other hard limit. Most PolyJet resins soften well below the range where a machined aluminum or PEEK part keeps working. If your prototype sits near a motor, an exhaust path, or a soldering operation, the resin will creep or sag. That is a material property, not a print setting you can tune out.

Threads and press fits are a common trap. Printed threads under M6 are fragile and strip easily. Better to print a pilot hole and cut the thread with a tap, or design in a heat-set insert boss with enough wall thickness. Press fits need a printed slip allowance and a real pin, not a printed pin.

When the part has to carry load, seal against pressure, or hold ±0.005 mm across a mating face, the answer is usually machining. We run 127 high-precision CNC machines across 3 wholly-owned plants, including 16 simultaneous 5-axis centers, and the tolerance we hold is ±0.005 mm (±0.0002 in) with finishes down to Ra 0.2–0.8 μm. That is a different class of part from a jetted resin model.

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  HeatResins soften far below metal or PEEK service temperatures
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  UV and moistureProperties drift over months, not years
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  Printed threadsFragile under M6; tap or use heat-set inserts
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  Load pathsMove to machined metal when the part carries real stress

Design for support removal from the start. Any internal channel needs a path for the support to exit, either through an open end or a drain hole. A closed cavity traps support and you will not get it out without cutting the part. Aim for a minimum channel of about 1 mm and give it two openings where geometry allows.

Wall thickness below roughly 0.5 mm gets unpredictable. Thin walls print, but they curl and they are hard to measure. If a wall is structural in your design intent, keep it at 1 mm or above. If it is a membrane or a living hinge, print a test strip first and flex it before you commit the whole geometry.

Orientation drives both surface finish and build time. The top face of a build is the smoothest because it is the last layer. Vertical faces carry the layer stair-step. If one face has to look good, rotate the model so that face points up, then accept the finish elsewhere.

Shrinkage is small but real, and it varies by resin and geometry. For parts that must mate with a machined counterpart, print a test coupon with the same wall section and measure it before you release the full model. A 0.1 mm error on a printed boss is normal. The same error on a machined bore is not.

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  Support escapeGive every internal channel a drain path
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  Minimum wall0.5 mm floor, 1 mm for anything structural
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  OrientationPoint the critical cosmetic face upward
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  ShrinkagePrint a coupon before releasing mating geometry