Perhaps the most critical step in the 3D printing process is the post-processing system. This involves washing your completed print, allowing it to dry, then curing it to completion. If you are getting acquainted with 3D printing and would like to test a smaller scale, inexpensive wash and dry system, a DIY wash will be perfect for your purposes.
The importance of a wash system
Resin 3D printing, whether it be SLA, DLP, or LCD, yield freshly printed models covered in uncured, liquid resin that drips off of the dental model on the build platform. Most resins, though not toxic, are classified as sensitizers that can cause irritation upon contact. For dental 3D printing purposes, our goal is to create aligners, occlusal guards, and other appliances to deliver to patients using 3D printing technology. Any uncured resin remaining on the 3D model must be completely washed off. The model then must be dried then cured. A high-quality cure box is imperative to producing a model that will be safe to use to fabricate aligners and other dental appliances.
Shortcuts for an established workflow
This three-step process could be done in one using the following wash and dry products.
- Sprintray Pro Wash/Dry by SprintRay yields washed and dried models within 9 minutes and has a goal of recycling isopropyl alcohol.
- Form Wash by Formlabs uses an automated wash system to produce clean prints with the goal of eliminating glove use during the post-printing process. The Form 3 Workflow washes models in approximately 5 minutes.
- Curing and Washing Machine by Prusa warms resin for the pre-print, then washes, dries, and cures completed models.
Making a DIY wash and cure system is not only inexpensive but also uses accessible materials that can be easily purchased. A DIY wash system is perfect to start with and will help you and your team understand the necessary components to 3D printing.
A clean 3D print requires two washes
Arguably, the most satisfying moment of truth of the 3D printing process is viewing the final print as the build plate rises from the vat. Excess resin drips off of the model as you unlatch the build plate. All that resin needs to be washed off before you can properly cure the print. To do this, we use isopropyl alcohol (IPA) as the solvent in two batches.
A DIY wash will comprise of two washes. The first wash is considered the “dirty wash” because it becomes the most saturated from the fresh print. The purpose of this wash is to rid of as much excess IPA as possible. A very effective method to wash the model is to use a stirring rod and a magnetic plate to agitate the solvent. This first wash IPA will be the first to be poured out into a designated IPA waste bottle to be properly disposed of.
The second wash is considered the “clean wash” because it washes a significantly cleaner resin-covered model. This wash ensures that the model is completely cleaned of any liquid resin. Using the stir rod and magnetic plate again will move the IPA without disturbing any uncured parts of the model. At this stage, the model is only partially cured. Any dents and scratches will be present in the final cure.
Download a post-printing process checklist to nail the 6 steps
Disposing of the IPA
Once the first wash becomes too saturated with resin, you will notice it become translucent and cloudy. Dump out the IPA into a sealable bottle or jug that is properly labeled and only designated for contaminated IPA. The second, less-saturated wash will now become the first wash. The empty container will then be filled with fresh IPA and used as the clean wash.
Do NOT flush the resin-saturated IPA down the drain as it should be treated as hazardous waste. To dispose of the used IPA, there are three options.
- Distillation: a process that requires investment in equipment and time. This is not an efficient or effective method for small quantities of IPA. Formlabs user, Walt Gillespie, shares his method here.
- Evaporation and decanting: for small batches of used IPA, pour the used solvent into a container and set it in the sun until the IPA evaporates. You will be left with a slab of resin that can be cured and tossed.
- Hazardous waste disposal: perhaps the safest and most efficient method is to contact a local waste disposal facility and inquire about their IPA disposal protocol.
Safety precautions
As previously addressed, liquid resin is an irritant that should not be ingested or contacted with skin. Isopropyl alcohol is also an irritant that can cause rash, itching, and dryness and can be especially dangerous if contacted with the eyes. To avoid any risk, take caution to wear eye protection, gloves, masks, and the proper clothing when handling resin and IPA. IPA is flammable and should be stored in a safe place.
Assembling a DIY wash station
The following materials should be adjusted towards your specific printer, your print quantity, and lab accordingly. The beauty of making a DIY wash station is having the ability to create a customizable station that will fit your needs. The materials listed will help you get started on your 3D wash station.
- 2 glass containers – serves as the wash containers
- purchase extra lids if you have the option.
- Magnetic mixer – to agitate the resin from the models
- Magnetic stir bars – to use with the magnetic mixer
- Isopropyl alcohol (99%) – to use as the solvent for our wash
- Pressurized air hose – to dry models before the cure
- Cure box – to finish our models using UV light
- Flush cutters and a metal scraper – to remove the models from the build plate
- Silicone ice tray – to hold prints in the cure box and prevent resin from sticking to the cure box
Download a comprehensive list of materials
Purchase glass containers and lids that will be able to fit the width and depth of your build plate. The idea is to be able to place your build plate with the finished models into the wash. To do this, you can cut a hole out of the lid that will fit the build plate and allow it to hover in the IPA. TIP: cut a hole out of one lid and use that for both washes. Purchase one extra lid if possible to cover the IPA and prevent it from evaporating.
Another option is to design and 3D print a lid to hold the build plate in place.
Fill the containers with IPA, enough to cover the models when inserted. Add a magnetic stir bar, insert your build plate, then place the containers on the magnetic mixer and turn it on. Allow the stir bar to mix around for 2-3 minutes. Then, transfer the lid and build plate to the clean wash and repeat.
Use flush cutters and a scraper to remove the models from the build plate. Use an air hose to dry the models then place them in the cure box to finish. Depending on your printer and the type of resin you use, you will need to use a specific amount of time for specific resin companies. For example. SprintRay requires 15 minutes to cure their Die and Model resin.
Removing models from the build plate
Once you have washed your models in IPA, they are ready to be removed from the build plate. A pair of flush cutters will allow you to pry the model off of the build plate without damaging the sides and will reduce the possibility of breaking models. A tried and true method is to use the cutters and align them parallel to the build plate, pinch one of the corners of the models and lift upward to release one of the edges of the model. Once there is a separation, use a metal scraper to get underneath the model and glide it along the build plate to release the model. This will take some practice and getting used to the grip and the angle of the cutters.
TIP #1: If you find that the cutters will not release an edge of the model no matter how much you lift and chip away at it, this could be an indication that your build plate needs sanding. A smooth build plate will ensure that your models will not stick in the grooves, making in a stuck model. If you find that you are seeing shadows of model arches after removal, sand the build plate, wipe it down, and use IPA as a final wipe.
TIP #2: When nesting models, make an effort to envision the angle at which you will release the models. Build plates that can print six nested models will be tight, so utilize as much space as you can to adjust and angle the models to allow as much access to the corners as possible.
Click to watch a quick video on how to remove models with flush cutters and a scraper!