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What is an mSLA 3D printer and how does it work?

By <a href="" target="_self">Sophie Jin</a>

By Sophie Jin

Posted on June 13, 2024

In resin 3D printing, SLA printers have long been favored for their precision and surface quality. But in the quest for accessibility, speed, and cost-effectiveness, manufacturers have been exploring different types of SLA printing, including inverted SLA and the more recent buzz, mSLA. But what exactly is an mSLA 3D printer, and how does it work?

What is SLA printing?

Stereolithography (SLA) is an additive manufacturing process using a laser to selectively harden liquid photopolymer resin. The resin is contained in a vat, and the laser precisely draws the desired shape on the surface of the resin. As the laser moves, the resin solidifies, forming one layer of the 3D object at a time.

SLA stands out for its ability to produce complex geometries with exceptional precision and surface quality. Compared to traditional manufacturing methods, SLA 3D printing offers the advantage of quickly producing complex parts or prototypes, facilitating faster design iterations and market entry.

Additionally, SLA technology allows for the formulation of resins with diverse mechanical, optical, and thermal properties, mimicking those of thermoplastics like ABS or polycarbonate. Consequently, SLA-printed parts can exhibit similar characteristics to traditionally manufactured parts, including strength, durability, and flexibility, making SLA a viable option for producing functional prototypes or end-use parts with specific material requirements.

What is SLA and how does it work?

What is SLA and how does it work?

If you are interested to know more about how SLA 3D printing works, we’ve given an in-depth stereolithography guide here.

Democratize SLA printers with inverted SLA

Traditional SLA printers are top-down, with the light source positioned above the resin tank and the build platform moving downward as the object is printed layer by layer. However, these printers typically require large resin tank and complex infrastructure, making them expensive and less accessible to smaller companies.

To make SLA printing more accessible, inverted SLA printing technology was introduced by Formlabs’ co-founders Max Lobovsky, David Cranor, and Natan Linder in 2011 with the Form 1 printer. In inverted SLA printing, the light source is positioned below the transparent-bottomed resin tank, and the object is printed upside-down, with each layer pulled upward. Unlike traditional SLA printers which require large vats filled with liquid resin, inverted SLA printing enables the dispensing of only the necessary amount of resin – just a thin layer. This capability enables the creation of resin parts using significantly smaller printers that can fit on a desktop.

Over the years, several iterations have been made to enhance the reliability of inverted SLA printers. In 2019, Formlabs introduced the Form 3 SLA 3D printer featuring a flexible-bottomed resin tank.

In inverted 3D printing, large builds are challenging to print due to the high peel forces exerted on cured parts. This light-touch structure of the Form 3 and Form 3L enables peeling parts away from the bottom of the tank with ease, largely reduce the peel forces during the print process and ultimately enable larger build volume.

Speed up 3D printing with mSLA

In addition to build volume, another aspect to be improved for inverted SLA printing is speed.

For the inverted SLA printing that Formlabs has used for years, the laser only cures resin that is within the beam diameter of the laser. This means that the printer must move the laser beam around using mirrors at a high rate of speed to cure all the areas of the model in any given slice of the build file. This limits the print speed, particularly when it comes to medium to large parts printing.

What is mSLA, or LCD 3D printing?

In contrast to SLA including inverted SLA that cure the resin with a laser, mSLA (Masked Stereolithography) cures the entire cross-section of the build platform at once, significantly enhancing the print speed.

mSLA printing refer to all the masked resin 3D printing technologies, no matter what types of light source and masking techniques are used. However, mSLA printing is now often used interchangeably with LCD 3D printing, as the later uses the mainstream LCD screens to mask the light and cure with LED light.

This approach, driven by its speed enhancement and cost-effectiveness compared to SLA, has gained traction among manufacturers.

However, the transition to mSLA comes with a trade-off in accuracy, as the diffusers and lenses in LCD printing may lead to lower light intensity compared to the point-like laser beam used in SLA printers.

How does Form 4 work as the next generation mSLA 3D printer?

In the latest generation of Formlabs’ flagship SLA printer line, the Form 4, the company has transitioned from its legacy inverted SLA printing to advanced mSLA printing. The new printer combines the structure of inverted SLA with LCD printing with its newly developed Low Force Display (LFD) print engine to address accuracy concerns associated with traditional mSLA printing.

Graphic Representation of Formlabs' advanced mSLA 3D printing

Graphic Representation of Formlabs’ advanced mSLA 3D printing

To balance print quality and speed, this engine employs an array of ultra-high-powered LED lights with strong optical power intensity and uniformity, along with a custom LCD screen featuring a 50 μm pixel size and high light transmission.

As previously discussed, inverted resin printers typically face challenges related to peel force, which arises as the cured part is lifted from the resin tank, and squish force, which occurs when the cured part descends into the resin tank.

To minimize these excessive forces, manufactures usually use a flexible film resin tank that provide a surface for liquid resin to cure again and facilitate gentle separation from cured layers. However, these films have limited lifespan and may adhere to the LCD screen, leading to increased peel forces.

To further mitigate these issues, Formlabs has redesigned two key features in the Form 4 printer. Firstly, it re-engineered a flexible dual-layer film resin tank that supports over 75,000 layers of printing, with an average lifespan of 1-2 years. This tank can also gently separate from cured layers. Additionally, the Form 4 printer incorporates a proprietary optical film that enables air to pass underneath the tank, allowing for smooth lifting without the risk of suctioning onto the LCD screen, as shown in the following video:

Another challenge that is often associated with mSLA is higher long-term operational wear. LCD screens, exposed to constant light and heat, are consumable components that require frequent replacement to maintain print quality. Formlabs addresses this issue by engineering the LCD screens to withstand 600,000 to 1,900,000 layers of printing. Additionally, they integrated a temperature sensor to control the heat level, ensuring prolonged screen durability and consistent print quality.


As the demand for rapid prototyping and end-use production continues to increase, manufacturers are exploring the next generation of 3D printing. With advancements like the Formlabs Form 4 3D printer integrating the fast speed of mSLA and meticulous engineering to address accuracy and durability concerns, we can expect to see more accessible and reliable options emerging.

If you are interested to know more about SLA and mSLA printing, please contact TriMech for a consultation

<h4>Written by <a href="" target="_self">Sophie Jin</a></h4>

Written by Sophie Jin

Sophie Jin is a Marketing Coordinator, Intern. Prior to joining TriMech, Sophie worked as a business journalist both in Canada and China, covering various industries, particularly tech companies.