Are consumer MSLA resin 3D printers good for prototyping enclosures?

By Cameron Coward   |   May 3, 2022   |   Provided By Avnet

Follow a few basic steps to improve the chances of success with a MSLA resin 3D printer.

Here at Avnet, we cater to the electrical engineering crowd. But more engineers today take on interdisciplinary tasks, which means you might be designing enclosures for your boards — or 3D printing prototype enclosures designed by others in or outside of your organization.

Fused deposition modeling (FDM), also known as fused filament fabrication (FFF), is the most common 3D printing process in both the consumer and professional worlds. It is popular because it is affordable and versatile, but there are other 3D printing processes that offer better quality.

Stereolithography (SLA), which was the first patented 3D printing process, is known for producing parts with smooth surface finishes. Until a few years ago, SLA printing was too expensive for the consumer space. But the recent proliferation of affordable masked stereolithography (MSLA) consumer 3D printers is changing that.

Those MSLA printers are now at price points that are competitive with budget FFF printers. They are popular for models, miniatures and figurines because they almost eliminate the layer lines that FFF printers are infamous for leaving on parts. The smooth surface finish seems perfect for mechanical parts, too, which raises the question: Are consumer MSLA resin 3D printers good for prototyping enclosures?

The difference between FFF and MSLA 3D printing

FFF 3D printers use spools of thermoplastic to feed an extruder. The extruder then pushes the filament through a hot end, which melts the thermoplastic and deposits it onto the bed in layers to form a three-dimensional part. While modern FFF 3D printers have high-resolution movement, the diameter of the hot end nozzle, along with other real-world factors, limits effective surface quality. Furthermore, the size of each layer determines the overall print time.

MSLA 3D printers work using UV-sensitive liquid resin, which cures and hardens when exposed to UV light. The resin sits in a vat, under which is an array of UV LEDs. Between the LEDs and the resin vat is a transparent LCD screen. When curing each slice of a print, pixels on the LCD screen turn on to mask the areas that shouldn’t cure.

The pros of MSLA 3D printing

• Surface quality: This offers three distinct advantages. First, resolution of the LCD panel determines the XY resolution of the print. That, along with layer thickness, determines the overall surface quality of the print. Most of today’s MSLA printers utilize monochrome LCD screens, which further allows for grayscale pixels along edges. That provides basic antialiasing capability, which results in even smoother finishes.
• Print time: The second major advantage is that MSLA printers cure the entire layer at once—no matter how large or small that layer happens to be. That means that given equal height and layer thicknesses, print time will remain the same whether your bed is full of several parts (or one very large part) or a single part. Typical cure time is around two to four seconds per layer, which is faster than the time FFF printers will spend on most parts.
• Fewer moving parts: Finally, MSLA printers have few moving parts. Except for models that have tilting beds to reduce peeling forces, MSLA printers only move in the Z axis. That means fewer points of potential failure and often a lower cost. It also removes the need for a stable surface for the printer because users don’t need to worry about inertia like they do with FFF printers.

The downsides of MSLA 3D printing

MSLA 3D printing should sound pretty enticing right about now, but there are some practical downsides for you to consider.

• The mess: The most common frustration users have with MSLA printing is that it is messy. Resin is toxic, so you must handle it and uncured parts with care while wearing gloves. Ventilation is also important and printed parts require washing in alcohol. After washing, they must sit in strong UV light for 5-15 minutes to fully cure.
• Strength and material selection: Because MSLA printers only work with UV-cured resin, material selection is limited. FFF printers have a wide variety of thermoplastic materials to work with and many of those are also popular for injection molding. But basic resin is weak and brittle—fine for decorative models, but a poor choice for prototypes that need to hold up to handling.
• There are engineering resins available, including some that claim to mimic the properties of popular plastics like ABS. Some, like Siraya Tech’s Blu resin, are quite strong. You can mix resins to attain the right properties for your applications, but the material and color selection is still much smaller than what you’d find for filament.
• Operating costs: Operating costs are also a concern, as resin (especially engineering resin) is more expensive kilogram for kilogram than all the common filament materials. Add in the cost of replacement vat film and replacement LCD panels, which are considered consumable and have a limited number of working hours, and resin printing becomes more expensive than printing with filament.
• Build volume: Another major drawback is build volume. MSLA printers tend to be smaller than their FFF cousins and surface quality is inversely proportional to size, given the same LCD panel resolution. A 6-inch 4K monochrome LCD panel will yield better results than an 8.9-inch 4K monochrome LCD panel, but will give you less room in the X and Y axes to work with.

For example, the Anycubic Photon Mono X 6K has a 9.25-inch 6K monochrome LCD panel. That results in an XY resolution of 34µm and an XYZ build volume of 197 x 122 x 245 mm (7.8 x 4.8 x 9.6 inches). For comparison, the Anycubic Chiron costs much less and has an XYZ build volume of 400 x 400 x 450 mm (15.5 x 15.5 x 17.72 inches). The upcoming ELEGOO Jupiter, which will be one of the largest consumer MSLA printers on the market, will have a build volume of 278 x 156 x 300 mm (10.94 x 6.14 x 11.81 inches).

Does MSLA printing produce better parts?

The primary draw of MSLA resin 3D printing is that it produces very fine detail, smooth surfaces and nearly invisible layer lines. That makes it perfect for artistic models that prioritize visual fidelity over mechanical properties. One would assume that those qualities would also make MSLA printing ideal for prototype enclosures, but is that correct?

The appeal is obvious. Imagine presenting your prototype with an enclosure that looks like it was injection molded, but without needing to invest in tooling first. FFF-printed parts are immediately identifiable as such. That isn’t always a problem, but the result is something that looks like a prototype and not a polished production-ready sample.

The prototype design

To find out if MSLA printing can make that a reality for you, I decided to test the idea. I started by designing a simple enclosure for a Nucleo-64 STM32 development board. It has only the basics: mounting points for the board with openings for the two buttons and the USB port.

But I did design this enclosure as if it were a real-world prototype, meaning I took manufacturability into mind. The walls have heavy draft angles to make the two halves of the enclosure easy to release from injection molds.

I designed it this way to mimic what you, the enterprising engineer, would do in real world. You’d take your CAD files and print them to assemble a prototype before production.

The testing process

I printed this model on both FFF 3D printers and MSLA resin 3D printers to compare the results. The FFF 3D printers were a BIBO and Voron Trident. The MSLA printers were an Anycubic Photon Mono X 6K, an ELEGOO Mars 3, a Phrozen Sonic Mini 8K, and an Anycubic Photon M3.

For the FFF tests, I used Polymaker PolyLite ASA filament and generic PLA filament. For the MSLA tests, I used Anycubic Basic, ELEGOO Standard resin, Siraya Tech Blu and Siraya Tech Build resins. I ran the FFF tests at layer heights from 0.1 to 0.2 mm and the MSLA tests at 0.02 to 0.05 mm. All other settings I selected to best suit the specific machine and material for each test.

A word about orientation

Part orientation is important for a successful, high-quality 3D print. With FFF 3D printing, orientation is straightforward. For this enclosure design, which lacks tricky overhangs, I laid the flat face of each part directly onto the bed and printed without rafts or brims. The textured PEI bed did impart a texture onto that face, but that was uniform and pleasing to the eye.

Orientation is a more complex topic for resin printing. The standard advice is to tilt models at an angle relative to the platform, rather than laying it flat. The reason for this is to reduce peelings forces—the forces acting on the part as the cured resin pulls away from the vat film. By angling the part, you avoid having layers with large surface areas and thereby minimize the peeling forces that cause layer separation.

But that axiom doesn’t consider the geometry of the part. If, for instance, your part has a 45-degree slope, then tilting it by 45 degrees would be counterproductive. Instead of blindly tilting your part to an arbitrary angle, you should orient the part in whatever manner minimizes the cross section throughout the printing process.

As a result of that orientation, most parts printed on MSLA machines will require supports. Most slicing software for resin printers will produce a truss-like support structure. In my tests, I utilized both automatically generated supports and manually positioned supports. My goal in both cases was to keep the number of support interface points to a minimum and to make those points as small as possible to keep the surface quality as good as was practical.

The results

The FFF-printed enclosures turned out as expected. They look great from a few feet away, but up close you can see faint layer lines and other minor imperfections, such as the Z seam. Anyone examining them closely would see that they’re prototypes and not injection-molded parts.

An FFF-printed enclosure with minor surface imperfections

Those that printed at lower layer heights and in PLA were smoother, while those that printed with ASA were stronger. Dimensional accuracy was acceptable for 3D-printed parts, but that can’t compare to injection-molded or CNC-milled parts. Tolerances fell within +/- 0.2 mm, which was enough to verify fit for a prototype.

The resin enclosures were a different story. Some portions of the enclosures looked fantastic. Those areas were smooth, with a pleasant surface finish similar to “soft touch” plastics. To the naked eye, those portions would be almost indistinguishable from an injection-molded part.

Unfortunately, not one of the dozens of resin test parts printed without failure. Some parts had noticeably warped surfaces. Others had gaps, holes and cracks. All the parts had noticeable flaws where the support structures contacted the part surfaces.

A resin-printed enclosure with significant warping and layer delamination

A resin-printed enclosure with support interface imperfections and failed geometry

You could sand the parts to remove the support artifacts, but that is true of FFF-printed part layer lines as well. The best solution is to orient the parts in such a way that the supports only touch surfaces that will be hidden after assembly.

Dimensional accuracy was good, particularly with the engineering resins. Those have predictable shrinkage rates, which is easy to compensate for within the slicing software. Warping aside, tolerances fell within +/- 0.05 mm. Most dimensional inaccuracy is explained by inconsistent shrinkage, exposure settings and grayscale/antialiasing settings.

The causes of flaws and their solutions

What causes the flaws mentioned above and are they solvable? If artistic models print well, why don’t mechanical models?

The answers come down to two factors: peelings forces and the nature of mechanical part geometry. These test enclosures have large, flat surfaces that make warping obvious and that result in excessive peelings forces if they lay flat relative to the build platform.

If a figurine warps by a small amount, most won’t notice. But if a part that should be flat or straight warps, it is hard to miss. You could model your parts to avoid such surfaces and favor organic shapes, but then you would be designing the part for 3D printing suitability instead of the chosen aesthetic. Manufacturability is always a concern, but you shouldn’t need to alter your industrial design for the sake of a prototype.

Some steps you can take to improve your chances of success when using an MSLA resin 3D printer for prototype enclosure include these.

1. Use high-quality engineering resin.
2. Heat the resin before use, which reduces warping caused by the resin warming during the printing process.
3. Orient parts to minimize supports and position support contact points where they won’t be seen.
4. Avoid large cross-sectional areas.
5. Keep vat film clean to reduce peeling forces.
6. Rub a thin layer of PTFE lubricant on the vat film to further reduce peeling forces.
7. Calibrate your printer’s exposure settings for the resin you use.

Conclusions

While consumer MSLA resin 3D printers seem like they’d be ideal for printing high-quality prototype enclosures, the practical realities of the technology make success difficult to achieve. Most engineering teams would be better off sticking to FFF 3D printing for their prototypes.

If the surface finish of FFF-printed parts is unacceptable to you, then a commercial laser SLA 3D printer will produce good results and will be more reliable than MSLA. If such printers exceed your budget, then an inexpensive consumer MSLA printer could be worth trying if you take the lessons from this article into account so that you have appropriate expectations.

About Author

Cameron Coward, Senior Technology Writer at Avnet

Cameron Coward is a senior technology writer at Avnet. Before transitioning to a writing career, he ...

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