Resin 3D Printers

There are many options when it comes to obtaining parts to build robots. The best option for beginner roboticists is to use kits, which come with the majority of components to build the physical structure, and then you can add on to it. However, this is quite limiting compared to the usage of 3D printers to augment your robot component procurement capabilities.

Mk I robot built by Robots.software, based on an OSEPP robot chassis kit

Having a 3D printer unlocks the ability to download 3D files (usually in the .STL file format) from the internet, where the options for robots to build are vast. Websites like Thingiverse.com contain literally thousands of files you can download for free and 3D print complete robots.

Within the world of 3D printing, there are a couple different options that use radically different technology to accomplish the same goal of generating physical objects from 3D files.

The most common printers you will find use FFF (forced filament fabrication). This is when a spool of filament made of plastic and sometimes other additives is forced into an extruder, which heats up to melt the plastic. The machine then draws the pattern for each layer with the molten plastic, where it solidifies to create the needed structures. While this is a great method, the degree of accuracy of this technology is no match to the resin printers, which will be the focus of this post.

Robots.software's Monoprice Voxel FFF 3D Printer printing an InMoov robot part.

Background

Process

For our Robotics Lab, Robots.software procured the AnyCubic Photon Mono 2 as well as the AnyCubic Wash and Cure 2.0 washing and curing station.

Resin printers work very differently than FFF printers. There is no spool of filament that serves as the raw material. Instead, there is a central pool of resin in liquid form which is sensitive and hardens when exposed to ultraviolet light.

WARNING:

The resin is highly toxic and must be handled in accordance with the Safety Data Sheet for safe handling and disposal instructions. Each resin is different and cannot be treated the same.

The main downside of resin printers is that the resin is toxic until it is fully cured by ultraviolet light. The fumes are toxic and use must be done in a well ventilated area with proper personal protection equipment to include safety goggles, respirator mask to filter out the fumes and gloves. The resin is toxic to the touch and the environment must be meticulously cleaned of resin residue or you will spread toxic chemicals. Each resin is different and you must adhere to the handling instructions for that particular resin.

For the initial testing of resin printer use for robot parts, Robots.software used a water washable resin from Sunloo. This is in contrast to most resins, which must be washed in nearly pure (>=95% isopropyl alcohol) to remove the resin.

Resin printers use UV radiation (light) to cure each layer of the object, layer by layer. A central build plate moves the printed piece up one layer at a time, as each layer is cured to the next via the UV radiation.

This allows a great deal of precision, typically a much higher resolution than can normally be achieved with FFF type 3D printing. They are much quieter than the FFF type as well.

Step 1: File Processing

The first step is to download the files and load them into the slicer software for your resin printer. Robots.software is using Chitubox, which is a great free open source option that has profiles ready to use for many of the most common resin 3D printers.

You can use the slicer to save the file to the USB stick, and load it into the side of the Photon Mono 2. This particular model is not equipped with wireless or bluetooth, so the files must be loaded in this manner.

Step 2: The Print

Using the touchscreen display on the printer, the file can be selected and printed. The time remaining is displayed on the screen, typical of 3D printers. This is perhaps the easiest part of the process for us, as the machine does all the work, curing the print layer by layer.

The robot part emerges from the soup of toxic resin, a semi-solid object in need of washing and curing.

Step 3: Washing

During this step, we submerge the printed pieces removed from the build plate (wearing PPE) into a vat of water, since we are using water washable resin. This water is also considered toxic, but can be rendered disposable by allowing it to fully cure in sunlight (best to use a sealed container with a clear lid) where the resin particulate can then be filtered out after curing.

The parts are removed from the water and submerged in a vat of isopropyl alcohol, which has a basket for holding the parts in it. The vat is then placed on the washing station. A magnetically driven fan inside the vat swirls around the alcohol, cleaning the parts. The fumes from the alcohol are highly flammable, so special care must be taken in order to not blow up. Do not perform this near open flame or sparks of any sort.

Step 4: Curing

After the alcohol bath, the parts are removed from the vat and left to dry for about 10 minutes. They are then placed onto the rotating table and placed into the Washa and Cure machine. The yellow UV protective cover goes over the top, and the parts are slowly rotated around while bathed in UV light. The resin "cures" and hardens.

Overexposure has been seen to lead to brittleness, which is one of the downsides of robot parts printed with resin printers. Trial and error is required to dial in the settings and fine tune for your specific printer and resin combination.

Conclusion

Resin printers offer an extreme degree of precision for robotic component fabrication. However, the environment must be set up and care must be maintained when working with resin to be able to reap the benefits of this technology while minimizing the risk.

Robots.software's AnyCubic Photon Mono 2

Jaw pistons bathing in isopropyl alcohol in the lab.