The future of stereolithography, seen through innovations by Axtra 3D, Formlabs and 3D Systems

Stereolithography has been the defining resin-based 3D printing technology for four decades, but in recent years, a cluster of new light-engine approaches has pushed well past the laser-traces-a-vat model that Chuck Hull patented in 1984. Three systems — 3D Systems’ PSLA 270, Formlabs’ Form 4 series, and Axtra3D’s Lumia X1 — illustrate where photopolymer 3D printing is going and why the older SLA/DLP distinction no longer captures the full picture.

The SLA and DLP baseline

In classic SLA, a UV laser traces each layer’s cross-section point-by-point across the resin surface, hardening material along one path at a time. This results in very high precision, excellent surface quality and large build volumes, but because the laser must trace every feature individually, throughput scales poorly with part complexity or build density.

DLP stereolithography addressed the speed problem by replacing the laser with a projector that flashes an entire layer at once as a pixel image. That simultaneous exposure means layer time is largely independent of cross-sectional area, making DLP substantially faster than laser SLA. The trade-off is resolution and surface quality: the pixel grid of a DLP projector produces harder edges and blockier surfaces at lower resolutions, and the inverted build orientation (printing upside-down against a transparent membrane) introduces peel forces that can distort or damage bulkier cross-sections.

LCD-based systems (often called mSLA in consumer contexts) operate on a principle similar to DLP — masking a backlight with a liquid crystal screen — but use less expensive hardware at the cost of lower optical power, shorter screen lifespans, and less even light distribution.

Enter 3D Systems PSLA 270

Feeling pressure from increasing competition, 3D Systems took a significant step away from traditional SLA by introducing the PSLA technology. Unlike most resin 3D printers that project from the bottom, the PSLA 270 projects downward from the top, building parts in the conventional SLA orientation—the platform descends into a vat of resin, with no peeling against a membrane. Dual HD projector-based SLA offers up to 5x faster curing layer times compared to laser-based technology, with 7-watt projectors delivering first-article success at 90 µm pixel resolution. Because it retains the top-down, open-vat geometry of classical SLA rather than the inverted-membrane geometry of DLP/LCD, there is no contact and no gravity-based distortion—the end result is precision, consistency, and part quality irrespective of geometry, with a fraction of the support structure required by other solutions.

The system addresses the pixel-edge problem common to projection systems through proprietary image processing: 3D Systems’ software automatically adjusts pixel edges using gray-scaling techniques, resulting in high-quality, production-grade plastic parts with excellent surface quality. The PSLA 270 also uses 3D Systems’ Figure 4 materials portfolio, giving it access to rigid, flexible, high-temp, flame-retardant, and biocompatible resins — the same library used in the company’s Figure 4 production platform.

In short, the PSLA 270 is a DLP-speed machine with classical SLA geometry: it drops the laser without adopting the inverted membrane architecture that limits most projector-based systems to larger cross sections.

Formlabs Form 4, the masked superhero

Formlabs’ Form 4 series changed the game in a different way. The Form 4 is not a traditional SLA or LCD printer—it is a new category of masked SLA printer (mSLA) with a Low Force Display print engine invented by Formlabs. The system is inverted and builds upward from a membrane-bottom resin tank. But Formlabs has substantially reworked the peel mechanics that make this geometry problematic at scale.

At the core of the LFD print engine is the Backlight Unit, an ultra-high-power light source using 60 LEDs, integrated cooling, and collimating lenses, with an optical power intensity of 16 mW/cm². From here, light passes through the light-processing unit, where it is shaped to match the printed layer using a series of polarizers, optical coatings, and a custom liquid-crystal display. The 50 µm pixel size of the high-resolution LCD and pre-tuned anti-aliasing delivers sharp details, smooth surface finishes, and accurate tolerances.

The key engineering achievement is in the release system. Peel forces are minimized using a new Release Texture and redesigned Flexible Film Resin Tank. The Release Texture is a proprietary, microtextured optical film that introduces airflow to prevent the resin tank from suctioning to the LPU. The result is that the Form 4 achieves the speed of a masked system while substantially reducing the print failures, support requirements, and part distortion that typically accompany inverted LCD printing. Most prints, using an 80th-percentile print height of 53mm and a 100-micron layer height, can be completed in less than 2 hours.

The Form 4 is positioned primarily at professional prototyping, dental, and engineering markets—not large-format industrial production. The Form 4L scales the same engine to a 353 × 196 × 350 mm build volume using 145 LEDs and prints 2–4x faster than its predecessor, the Form 3L.

Axtra3D Lumia X1 doubling up

Axtra3D’s Hybrid PhotoSynthesis (HPS) takes a fundamentally different approach: rather than choosing between a laser and a projector, it runs both simultaneously. In this coaxial system, both light sources operate simultaneously, curing resin at the same wavelength and in the same image plane. In the HPS process, the light projector cures most of the layer, while the laser simultaneously cures the layer’s contours with high precision.

The logic leverages DLP projection for fast but soft, pixelated edges and a laser for precision. The image generator covers the bulk of the cross-section—”flash hatching”—enabling the speed of DLP, while the laser creates the border contours for better surface quality and accuracy at 50-micron resolution. The two light sources share the same wavelength and focal plane, so they cure cooperatively in a single pass rather than sequentially.

Axtra3D pairs HPS with its TruLayer Technology, which uses multiple sensors beneath the printer’s membrane to ensure rapid detachment of the print layer from the vat, minimizing pauses between layers and speeding up the printing process. The combination targets continuous, high-throughput production of parts that need both speed and surface finish — applications where conventional DLP would sacrifice one for the other. The company was founded in 2021 by AM veteran Gianni Zitelli (one of the co-founders of Nexa3D) and Praveen Tummala, who previously served as Director of Technology at XponentialWorks, and is headquartered in Charlotte, North Carolina, with R&D in Vicenza, Italy.

How the three compare

All three systems address the same core problem — the speed-quality trade-off of laser SLA — but from different engineering directions. The PSLA 270 retains the open-vat, top-down geometry of classical SLA and replaces the laser with dual projectors, thereby increasing speed while avoiding membrane-related distortion. The Form 4 keeps the inverted membrane geometry of mSLA/LCD but rebuilds the peel and optical systems from scratch to eliminate the reliability and quality losses that membrane printing typically causes. Axtra3D’s HPS rejects the either/or choice entirely and runs both a projector and a laser simultaneously, using each source for what it does best within a single layer.

Compared to traditional SLA, all three are faster. Compared to traditional DLP, all three deliver better surface quality and edge definition. The PSLA 270 scales to mid-frame industrial production, the Form 4 targets professional prototyping through light production, and the Lumia X1 positions itself for high-throughput production of complex parts where neither pure DLP speed nor pure SLA quality is sufficient on its own.