Designing for LSPc

 

Lubricant Sublayer Photo-curing (LSPc) is a type of vat polymerization printing which cures liquid resin with a light source. The physics of the polymerization process will have an impact on print success, and a model that is not optimized for LSPc can create inconsistent results. Use the guidelines below to design models for printability on the XiP.

 

Designing Walls

 

Recommended

Acceptable

Minimum wall thickness

>1 mm

>0.3 mm (reinforced)

>0.5 mm (free)

Maximum wall thickness

<5 mm

< 25 mm

Wall span between ribs

< 25x thickness

<50x thickness

Walls between 1-5 mm will form reliably at all orientations and withstand peel forces generated by the membrane separation and support removal. Walls as thin as 0.3 mm are possible with limited span, and vertical orientation.

Walls thinner than 0.8 mm may saturate during washing. If you're printing thinner walls, limit wash times to avoid saturating the material. If you're using supports, touch points should be sized at least half of the wall thickness or smaller.

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Reinforced Wall

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Freestanding Wall

Walls thicker than 5mm may require additional heating during post-cure or longer post cure times.

Ribs should be used for for stability on large spans and to prevent warping issues during washing and curing.

 

Designing Holes

 

Recommended

Acceptable

Vertical holes

> 0.8mm

>0.3mm

Non-vertical holes

>1mm (opaque)

>2mm (clear)

>0.6mm

Blind hole depth

< 3x diameter

< 8x diameter

Thru-hole length

<8x diameter

<25x diameter

 

Holes1.png Holes2.png

Holes smaller than 1.0mm in diameter may close during printing. Larger holes may be required for clear resins. Smaller holes are possible when oriented vertically, but cleaning small or deep holes may be a challenge.

Avoid blind holes and holes with large aspect ratios, if possible. Blind hole depth is limited for holes with a smaller diameter than 3 mm, since the surface tension of the liquid resin prevents it from draining properly.

Washing with a pressurized jet (with a syringe, for example) allows for deeper holes, as you'll be able to clean uncured resin out of the holes after printing. Be sure to add vents to bottom of blind holes when possible.

 

Overhangs and Spans

 

Recommended

Acceptable

Horizontal Overhang

<2mm

<4mm

Horizontal Spans

<5mm

<20mm

Angled Overhang

>30°

>5°

Horizontal overhangs beyond 2mm should be supported.

Bridging

Horizontal surfaces bridged between supports may span twice the distance as overhangs. This applies also to support influence radius. Spans as large as 20 mm are printable with a loss of dimensional accuracy.

Angled overhang

Allow a 30° minimum angle in order to build self-supported with typical wall thickness (up to about 25:1 span to thickness). Shallower angles are possible with shorter spans or ribs.

 

Engraving and Embossing

 

Recommended

Acceptable

Character Height

> 4mm

>2.5mm

Emboss Height / Engrave Depth

>0.5mm, or equal to line width

>0.25mm

Line Width

>0.4mm

>0.25mm

 

emboss1.png

 

Text may be embossed or engraved onto the part surface. Chose a sans-serif font and character height > 4mm for best results. Use an emboss height / engrave depth equal to line width for best readability. Avoid calligraphic or serif fonts with narrow line width.

If using engraved text on the down-skin surface (facing the build plate), stay within the recommended size range, and use rounded or beveled edges. Islands (like the center of letter O or P) require support or should be filled in.

 

Cupping

 

Recommended

Hole Area

>5% of surface or > a diameter of 3mm

If a cup-shaped feature is printing open to the vat, the resin will be pulled up by vacuum when the Z-axis lifts to separate, and the resin will pressurize when the axis returns to the platform.

To avoid defects, place a vent hole at the base of the feature. Nexa X allows adding tapered holes and matching plugs so the hole can be patched after printing. The hole should be sized appropriately for the size of the trapped volume – a diameter of 10% of the span is usually sufficient.

Cupping.png

Enclosed Volumes also require holes to avoid cupping. The holes also are used to allow washing. Place holes at the extremes of the volume to allow for complete draining.

 

Slenderness

 

Recommended

Max Slenderness

12:1 – High strength material

8:1 – tough material

3:1 - elastomers

When the design of the supported part is slender, it is likely to sway during printing. Dimensions may come out large as you move away from the build plate due to sway between layer exposure.

- Orient for short build height.

- Widen support base and verify no bend point in the scaffold

- Add supports to steep surfaces

The best option is to reorient your part in the build to limit the height of the build. If the feature in question cannot be reoriented, then build the feature perpendicular to the build platform to prevent drag forces from deflecting the feature.

Elastic materials are most sensitive to high aspect ratios. Target a ratio less than 3:1 when working with these materials.

For exceptional parts, reduce the aspect ratio by printing parts back-to-back or attached to a support mast.

 

Mesh Preparation

 

Recommended

Acceptable

Deviation Tol.

0.05 mm

0.20 mm

Angle Tol.

10°

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CAD Mesh

HiResMesh.png

Hi-Res Mesh

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Low Poly

The size of .stl mesh may impact part appearance, with coarse meshes resulting in visible faceting.  

Meshes must be closed volumes (manifold) and joined (boolean addition) to process reliably, however Nexa X is robust to many mesh quality issues.

NexaX 2.0 file preparation software provides insight on the printing time and material usage. Use the build slider to verify the sliced images appear as expected.

If you have any questions on design and file preparation, please feel free to open up a support case with our Services team or reach out to support@nexa3d.com

Updated

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