LSPc Basics

What is LSPc?

LSPc (Lubricant Sublayer Photocuring) is the print process utilized by Nexa3D's XiP and NX series printers. LSPc is a subset of stereolithography (commonly referred to as SLA); to troubleshoot the LSPc process one needs to understand how stereolithography works. 

Stereolithography

Stereolithography is a type vat polymerization, a method of 3D printing that uses a light source to cure liquid resin photopolymer into a solid part.

In first generation stereolithography (SLA), a UV laser and a set of moving mirrors raster each layer of a print. Similarly, Digital Light Processing (DLP) uses a projector to cure the photopolymer.

Masked Stereolithography

Nexa3D's XiP and NX series printers specifically use Masked Stereolithography (mSLA) to print parts quicker than ever. During each print cycle, the LCD screen underneath the membrane of the resin vat masks the light of the LED array to cure the liquid material into shape.

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Masked Stereolithography (mSLA)

1. Build Plate, 2. Uncured material/Resin Vat, 3. Everlast Membrane, 4. LCD Mask, 5. Collimating Lens, 6. LED Array

Now that we understand the basics of stereolithography, we can take a closer look at the LSPc print process.

LSPc Print Process

The LSPc print cycle happens in three stages: Squish, Cure, and Peel. The cycle repeats until every layer is cured, completing the printed part.

Each stage of the cycle has a unique set of complex physics concepts, but a basic understanding of the stages can help users categorize and determine root causes when troubleshooting failures.

Stage 1: Squish

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The first stage of a print cycle is when the build plate lowers into the resin vat to squish the liquid material to the appropriate layer height (variable depending on material and settings, but the most common height is 100 microns).

This prepares the material to be cured during the second stage of the process.

Stage 2: Cure

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In this stage, the printer cures the squished material trapped beneath the build plate. The monochromatic LCD displays an image of the sliced layer to mask the light that fires from the LED array located beneath. This cures the material into the shape of the sliced layer, and the layer should adhere to the build plate and membrane.

Since the entire layer is printed at once, the exothermic reaction that occurs during polymerization is more intense in LSPc printing than in other SLA methods. This is automatically mitigated by way of material profile settings for validated resins, but it is important to note when using custom materials.

Shrinkage rates are different for each resin, but typically within the 0.5 to 3% range for most materials.

The exposure time will vary depending on the material and settings used to set up the print file. To continue the cycle, the printer then needs to peel the cured material from the membrane.

Stage 3: Peel

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In this last stage of the cycle, the printer peels the cured layer from the membrane by lifting the build plate up and away from the resin vat. The proprietary membrane allows the cured layer to peel away and release. There is always an amount of force applied to the part during this stage, which is referred to as Peel Force.

Peel force can increase or decrease depending on the physical properties of a part, and excessive peel force can cause print failures. We recommend taking a look at our Designing for LSPc guide as well as our Support and Orientation Tips article for more specifics on how to mitigate it.

While there are many complex fluidic physics happening during this stage, there are a few basic points to keep in mind:

  • Peel force will increase as the membrane ages
  • The process takes time, which means that dense builds may need extra time to peel safely
  • Peeling tends to be faster when more resin is in the vat due to hydrostatic pressure
  • Enclosed volumes and cupping features need to be oriented they allow liquid resin to escape during the print process; well placed drainage holes can help avoid blowouts with hollow parts, and proper orientation can help reduce peel force on parts with cupping features

After the cured layer releases from the membrane, the build plate moves back down into the resin vat to squish the next layer and continue the cycle.

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