3D Print finishing

Guide to Post-Processing and Finishing SLA Resin 3D Prints

Scott Gabdullin

Updated on November 15, 2023

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Stereolithography (SLA) 3D printouts are a go-to way of modeling products for many people like business owners or chemists because its many advantages provide them with lifelike prototypes or miniatures.

These isotropic designs can give life to what was originally an idea while making them waterproof and smooth. However, they will need some finishing touches before they can be considered an accurate representation.

A designer will often need to spend considerable time working out the kinks of their raw SLA prints. Overall, there are five unique processes that someone will have to complete before they can use their 3D print, namely:

Washing
Curing
Sanding
Painting
Electroplating

This guide will detail what each post-processing step entails and give some helpful tips on how to do them. By the end, the reader should have a firm understanding of how to take their raw SLA prints and turn them into usable models for numerous applications.

Tools And Procedures

Starting this guide with a recap of the best tools to use when finishing 3D printouts is best. Unlike Fused Filament Fabrication 3D prints (FFF), SLA post-processing needs certain materials to ensure a better finish.

The core items someone needs to finish SLA prints are:

Sheets of plastic
Gloves(nitrile or neoprene)
Alcohol (Isopropyl/IPA)
Ultrasonic cleaner
Turntable
Drying towels
Ultra-violet(UV) lighting
Flush plier cutters
Sand Paper
Paint (Acrylic)
Spatula
Print removal tool

This kit is a good starter for anyone, as it features essential items someone would need to finish their print. Unless an unforeseen circumstance happens, like a change of preference, there is no need for anything more than these components.

It is okay not to use all these tools when trying to remove and finish your SLA print successfully, but this list of gadgets will aid most post-print jobs reasonably well. This is by no means a fully detailed catalogue of items, as some people may want to do other specific things with their printouts.

Removing SLA Prints

Removing SLA print requires quite a bit of care because of how vulnerable they are fresh out of the machine. A method that will promise consistent success is doing the following:

Place paper towels or plastic sheets down to catch any falling debris after taking it out.
Wear gloves before handling to avoid smudging or damaging the prototype or the user’s hands.
Gently remove the plate from the 3D printer, ensuring not to hit the design against any walls or overhangs.
Using the spatula, lift the edge of the 3D print.
Slide a print removal tool under the raised edge and hoist off of the printing apparatus

Supports

Supports are a vital part of any SLA print because of how fragile the resulting product will be after coming out of the printer. This section will be a brief explanation of their makeup and how to care for them properly.

Three constituents constitute a support structure:

The raft
Connector points
Scaffolding

The raft connects the support structure to the printer build surface. Scaffolding holds the print itself in place, so it does not fall to one side during construction. The connector points are where the framing and the design meet.

Not every model needs our support, but those with minute details or are larger than a basic shape will acquire something to ensure it doesn’t fall over and break.

Some of the more vulnerable features that need support are overhangs, protruding edges, or minor elements. Naturally, the exact specification of the necessary supports depends on the design itself.

There are inherent dangers of not using proper support for a new model. Other than falling off and possibly breaking, a design could suffer from:

Loose, floating resin particulates
Warped features
A flat model
Incorrectly positioned layers

Cleaning the Supports

It is up to personal preference whether someone wants to clean the supports before or after their SLA print cures. However, the cleaning process is still the same whether a designer does it pre or post-curing. However, cleaning the supports might require more care post-curing.

After deciding when to clean them, the first thing to do is to use the flush plier cutters to snip off each attached support beam. Take care not to shatter the support structure so future projects can utilize them.

Ensure the pliers are flush against the SLA print’s frame, so there aren’t any protruding poles or sticks. Admittedly, removing the supports from the printout shouldn’t take too much time or effort, as it only takes patience and a steady hand.

Washing SLA Prints

Washing an SLA print is a crucial part of the post-processing routine because it removes any sticky resin on the front. Without this step, the model will not respond well to the additional steps of curing and sanding.

The most professional way to clean an SLA print is to use the ultrasonic cleaner. This jewelry store staple allows users to clean their print quickly and easily without using their own hands, preventing any mishaps due to human error.

However, depending on the circumstance, someone may wash and soak them by hand because ultrasonic cleaners can be expensive. If that is the case, submerging them in the cleaning solution with gloved hands is the best action.

Most chemicals used to make and clean resin prints are considered skin irritants, so it is best to avoid direct contact at all times. It is after they have fully cured that the 3D printout is safe to touch.

Helpful Washing Tips

When cleaning the design, one valuable tip is cleaning it in IPA solution. Many experts have concluded this solution leaves the most effective results. The only caveat is isopropyl alcohol is usually sold in large amounts, so it’s best to stock up.

If the design includes small crevices, soaking the overall structure may not properly clean it. In that case, syringes are best to clear out any hiding resin deposits. This careful approach will prevent any resin from obstructing those small channels.

It wouldn’t hurt to clean a particular part more than once, ensuring it washes and rinses properly. It is up to the user’s best judgment and personal preference to determine whether or not something is properly clean.

Curing SLA Prints

Curing an SLA print involves placing it under UV light rays so the polymerization chemical reactions can adequately harden. This procedure is necessary because the resin will need more time to form fully, and if left uncured, it may lead to a spotty result.

Although UV light can harm humans, it works wonders for SLA printouts when used in a controlled environment. The short waves of light impart significant energy into the sticky substance, encouraging it to settle.

This simple combination of warmth and UVs gives so much more structure to the design without having to do anything extra. Plus, it makes them more manageable when sanding and smoothing out the finer details.

Helpful Curing Tips

Common resins may not need a curing process to thicken fully. However, the materials used to make particular 3D prints will typically need some form of post-curing to ensure optimization.

While curing, it is best to give each part a set time limit under the light so that it sets correctly. Turning the model as it cures might be the best way to achieve proper resin coagulation.

Curing machines make this process much more straightforward because they thicken the design independently. This convenience gives the user time to set up the materials necessary for sanding it down and smoothing it out.

However, simple sunlight can cure a green state 3D print if the designer does not have the money to invest in a curing apparatus. Of course, weather conditions determine how effective the sun is at post-curing a model.

Sanding SLA Prints

Although there are other methods users can do to polish their model, sanding the parts of an SLA 3D print remains one of the preferred methods for creating a smooth, blemish-free product. Sanding can remove any support marks left over after a not-so-clean cut with the flush cutters.

It would be wise to ensure your model can handle a tough sanding session by filling it if it is hollow. Filling a project will give it stability and structure, preventing it from denting or warping during a sand job.

Depending on the size of the printout, it may be best to use sanding materials because it allows the user to get into the more intimate spots on the design. Sandpaper is an excellent tool to use in this regard, as long as the person sanding is careful.

On the other hand, if a design is much bulkier, it will be much harder to handle, making a sanding machine necessary or small-head power tools. It is challenging to smooth out intricate objects with deep holes and inner supports.

Sanding the deeper parts of a 3D model Is recommended for those trying to use their 3D model in a professional setting because it gives a smoother texture to the build. Generally, product designers often want a model that they could potentially sell to a customer.

Helpful Sanding Tips

Sanding can be tedious and slow, but it is one of the requirements for many SLA prints, primarily when someone will use it professionally. The best paper to start with for sanding printed parts is low grit sandpaper.

The low grit paper is excellent for removing some of the more prominent spots on the 3D printout, like support marks or odd protrusions. Once the user determines that the big pieces have been sanded smooth, it will be time to switch to finer grit sandpaper.

Leveling up the sandpaper to 3000 grit will result in a smooth and glossy finish on most SLA designs. Designers are encouraged to continually increase the right level until they are satisfied with smoothness and sleek finish.

The level of grit varies drastically as some sandpaper grits are as fine as 12000. This sanding level may be overkill and can even damage some models, so increase the grittiness with caution.

Wetting the sandpaper may allow it to catch on the more rigid parts of the printout. Moistening the paper is a great trick for those having trouble getting their design to its desired smoothness. Fortunately, SLA parts take considerably less sanding compared to FFF prints to smooth them.

Once the user finishes sanding, they can use a soft cloth to wipe down their SLA print. Wiping it with a gentle fabric will take care of any remaining minor stains leftover from the sanding job.

Coloring SLA Prints

After sanding the print out to the desired smoothness, it is time to color the 3D design giving it a much more lifelike appearance. There are numerous methods for coloring 3D prints, including:

Painting with acrylic
Using dyed resin during printing
Dyeing the resin after printing
Spray Painting
Color Using Pre-Dyed Resin

If someone opts to use dyed resin coloring SLA print, it will require alcohol ink, the most commonly used ink. Once complete, place the pigment inside the SLA printing machine so it can thicken and set onto the separate parts of the model.

Alcohol inks are the best choice because they dissolve into clear resin, giving designers consistent colors throughout the print. One caveat to using dyed resin is the washing process will need more care because the IPA solution might melt the colored wax.

One of the better practices for mistake-free dyeing is to label every single wash solution used in the process so modelers can separate them, which will help avoid accidents. For example, it would be easy to mistakenly dye part of the print that should remain white if labels do not come into play.

Helpful Pre-Dyeing Tips

If done correctly, coloring the 3D print with dyed resin can be an easy experience. Using syringes to apply the alcohol ink is best because they allow for exact measurements. Shaking the container filled with components is recommended to promote proper mixing.

After thoroughly mixing the dye, the remaining process is relatively straightforward. Place the mixed paint into the printer’s tank and print normally. Make sure not to add anything new after loading the dye, as that may lead to a printer malfunction.

Color Using Post-Dyed Resin

Coloring The 3D project using pre-dyed resin is a suitable method, but dyeing afterward is also an option if there needs to be a quick change. This process usually involves submerging whatever part of the piece needs coloring into a dye solution.

This method won’t take too long but is not as definite as dyeing the resin beforehand. Some resin materials, like transparent or elastic, adhere to dye solutions better than others.

One of the benefits of dyeing post-print is a more considerable margin of error regarding coloring prints. Unfortunately, pre-dyeing requires the user to commit an entire vat of resin to a specific color. While doing it in the post period allows them to dye separate parts of the print in different colors.

Furthermore, it’ll be easier to clean after the design comes out of the printer because they won’t need a specific IPA to cleanse or maintain the undissolved resin.

In short, post-dyeing a print provides a much more customizable experience and does not marry the user to a specific color.

Acrylic Painting to Color

If dyeing the 3D works is not a strong suit, painting with acrylic is always a fine choice. With painting, the user can utilize the artistic side of their brain and make it look beautiful with just a paintbrush and a vision.

Of course, this does take a lot more time than pre or post-dyeing 3D print, but it gives a person maximum control over how the model looks. They will be able to paint every nook and cranny of a complex piece so it fits their desired appearance.

Moreover, it removes the pain of having separate watching stations for dyed pieces because every piece can be washed and cured as usual since designers will paint them once dry.

Plus, even if someone does not have the best painting skills, the resin is not very expensive, so redoing it’s not a significant investment. The largest investment was purchasing the 3D printer.

Basically, if time is not a factor or a large team is working on painting each model, then using acrylic paint to color the SLA prototype is a good choice.

Coloring With Spray Paint

While acrylic may be a good choice, spray-painting is another acceptable way to add some lively shades to the 3D design. In fact, A true spray painting artisan will potentially color an SLA print much better than the pre or post-dyed methods.

Additionally, spray painting takes less time than acrylic paint because it is primarily pointing and spraying, albeit carefully pointing and spraying. An excellent way to ensure the best result is to use multiple different colors and try to complete the paint job in one prolonged sitting.

Another helpful hint would be to start using a thinner coat before graduating to a thicker layer on the finalized piece.

A quick tidbit about spray coating SLA parts; the user may get away with not curing a specific feature that will be spray coated two or three times. Curing clear resin pieces with a coat of paint might produce unsightly blemish spots on the finished product.

Skipping the curing process is recommended if the piece is used solely as a visible representation of something and does not need to demonstrate specific features. Pieces that will be spray-painted will only need a thorough sanding before applying the first thin coat.

Electroplating SLA Prints

The final step to completing SLA prints is to electroplate them so they can be more resistant to wear and tear corrosion and harmful rays. This procedure includes depositing metal ions on the piece’s surface via an electrochemical process.

Unlike the almost-equivalent process of filament 3D printing, SLA parts are often less durable after coming out of the printing machine.

This reason makes the electroplating step crucial if someone desires to use their creativity for something other than aesthetics.

Electroplating makes the final product more usable as a prototype, and it is much cheaper to electroplate the design than printing with metal materials.

Electroplating Process

Cleaning: It is always good practice to thoroughly clean the print before trying to electroplate it. That means getting rid of any fingerprints, dust, or dirt particles it may have picked up during the process.

Cleaning the piece is quickly done with an alkaline solution, or if wetting is necessary, the user may need to implement a chromic-acid mixture.

Pre-Dipping: Pre-dipping the design before it gets etched will eliminate parts that are not molded or extremely stressed. On top of that, it makes the difficult parts to etch more accessible to the chemical by swelling it up.

Etching: Now comes the etching process, with which sulfuric acid or potentially a mixture of chromium trioxide will complete the job fast. This process is necessary because the etched areas better suit the piece’s surface for absorbing and bonding with the settled metals.

Conditioner: This step is optional, but a conditioner is a great way to encourage the piece to absorb uniformly.

Neutralization: Neutralizing the piece after etching will ensure no additional etch lines. Note that designers must rinse each part as much as humanely possible before applying the neutralizing agent.

Pre-Activating: Another optional step would be pre-activating the design to promote absorption. Although if the modeler already used the conditioner, this step is unnecessary.

Activation: The SLA printout will be bombarded with a low amount of precious metals during the activation process. These metals are the chemical catalyst that will aid in electroplating, making the surface more conducive.

Accelerators: Dousing the print in an accelerant to remove extra covalent bonds that might skew the electroplating process. On top of making the activator better at its job, it will also prevent skip-plating incidents.

Bathing: Once all the plastic is rinsed and dry, it will be introduced to an electroless bath, where the solution’s thick liquid will apply a thin metallic coat. Usually, people opt to use nickel for this process, but copper is an acceptable alternative.