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Post-processing of 3D printed parts (PLA, ABS, SBS, PETG)

Table of Contents

• Remove Supports
• Removing Soluble Supports
• Sanding
• Cold welding
• Filling voids
• Polishing
• Priming and painting
• Pair smoothing
• Epoxy coating
• Metallization

Introduction

FDM technology is best suited for fast, low-budget prototyping. Layer lines are usually visible in FDM prints, so post-processing is essential if a smooth surface is to be achieved. Some post-processing techniques can also make a print more durable by changing the degree of its elastic properties, density, structural and textural features.

In this article, we will discuss the most common post-processing techniques in FDM.

Post-processed FDM prints (left to right): cold welded, void filled, raw, sanded, polished, painted and epoxy coated. Photo 3dhubs.com

Removing Supports

Removing supports is usually the first step in post-processing for any 3D printing technology that uses them. In general, props can be divided into two categories: standard and soluble. Unlike other post-processing methods discussed in this article, the removal of props is mandatory and does not result in improved surface quality.

Initial printout with props, poor prop removal, good prop removal. photo 3dhubs. com

Removal of standard props

Tools

• Wire cutters, needle nose pliers, tongs
• Toothbrush, brush

Process

Normally, backups come off the printout without problems, and hard-to-reach places (such as holes or cavities) can be cleaned of backup material with an old toothbrush. Proper placement of support structures and correct print orientation can significantly reduce the negative impact of supports on how the final printout will look.

Pluses

• Does not change the overall geometry of the part.
• The process is very fast.

Cons

• Does not remove layer lines, scratches or other surface defects.
• If excess material or marks remain from the support structure, print accuracy and appearance suffer.

Soluble Support Removal

Instrumentation

• Solvent resistant container
• Thinner
• Ultrasonic cleaner (optional)

Process

Soluble support standard materials are removed from the printout by immersing it in a reservoir of the appropriate solvent. Supports are usually printed:

• HIPS (usually with ABS)
• PVA (usually with PLA)

A glass container like a preservation jar is fine. Any non-porous vessel is suitable for water treatment. To quickly remove props from HIPS/ABS printouts, you will need a solution of equal parts D-limonene and isopropyl alcohol. Many other support structure materials such as PVA (with PLA) dissolve in normal water.

Pro Tips

Use an ultrasonic cleaner to shorten the solution time and change the solvent as it becomes saturated. A warm (not hot) solution works faster - heating is useful if there is no cleaner.

Pluses

• Complex geometry is allowed for which the standard method of removing supports is not possible.
• Smooth surface at the support points.

Cons

• Improper dissolution of the props can cause discoloration and skewed printouts.
• Does not remove layer lines, scratches or other surface imperfections.
• May cause small holes or holes if soluble material seeps into the object during printing.

Skok

SHIKS SHIP SHIP ABS ABS ABS PROBECTION

Instrumentation

• E END1 with grain
  on 150, 220, 400, 1000, 1000 and 2000
• Cleaning cloth
• Toothbrush
• Soap
• Face mask

Process

After the props have been removed or dissolved, sanding can be done to smooth the part and remove any obvious defects such as blots or marks from the props. Which sandpaper to start with depends on the thickness of the layer and the quality of the print: for layers of 200 microns or less, or for prints without blotches, you can start with sandpaper at P150. If there are blobs visible to the naked eye, or the object is printed with a layer thickness of 300 microns or more, stripping should begin with P100.

The process can be continued up to P2000 grit (one approach is to go to 220, then 400, 600, 1000 and finally 2000). Wet sanding is recommended from the very beginning to the very end - this will avoid excessive friction, which can lead to an increase in temperature and damage the object, as well as contaminate the sandpaper itself. Between sanding, the printout should be cleaned with a toothbrush and washed with soapy water, then wiped with a cloth to remove dust and prevent it from sticking together. Even P5000 can be sanded to achieve a smooth, shiny FDM part.

Pro Tricks

Always sand in small circular motions - evenly over the entire surface of the part. It may be tempting to sand perpendicular to the layers, or even parallel, but this can lead to gouges. If the part is discolored or has a lot of scratches after sanding, it can be heated a little to soften the surface and allow some defects to smooth out.

Pros

• An exceptionally smooth surface is obtained.
• Further post-processing (painting, polishing, smoothing and epoxy coating) is greatly facilitated.

Cons

• Not recommended for double or single shell parts as sanding may damage the printout.
• The process is difficult in the case of sophisticated surfaces and the presence of small details in the object.
• If the grinding is done too aggressively and too much material is removed, the appearance of the part can be affected.
Acetone for ABS. Dichloromethane for PLA, ABS
• Sponge Applicator

Process

If the size of the object exceeds the capacity of the printer, the object is printed in parts and then assembled. In the case of PLA and some other materials, assembly can be done with Dichloromethane or a suitable adhesive (the choice of adhesive depends on the plastic). In the case of ABS, it is possible to "weld" with acetone. The mating surfaces should be slightly moistened with acetone and squeezed tightly or clamped and held until most of the acetone has evaporated. So the parts will be held together by chemical bonds.

Pro Tricks

Increasing the surface area of ​​the acetone contact increases bond strength. Tongue-and-groove to help.

Pros

• Acetone does not change surface color as much as most adhesives.
• After drying, the compound acquires the properties of ABS, which makes further processing easier and more uniform.

Cons

• The bonding of ABS parts by cold "welding" with acetone is not as strong as if the part were printed as a whole.
• Excessive use of acetone can dissolve the part and affect final appearance and tolerances.

Void Fill

Black ABS Print, Filled and Sanded

Tool Kit

• Epoxy (for small voids only)
• Automotive body filler (for large voids and joints)
• ABS filament and acetone (only for small voids in ABS printouts)

Process

Unusual voids may come out after the part has been ground or the soluble props have been dissolved. These voids are formed during printing when the layers are incomplete due to any restrictions on the trajectory of the print head, which is often inevitable. Small gaps and voids can be easily filled with epoxy and no additional treatment is required in this case. Larger gaps or voids left by assembling a multi-part object can be filled with automotive bodywork filler, but the printout will then need to be re-sanded. Putty works great, is easy to process with sandpaper and can be painted. Moreover, the parts connected by such a filler, or voids filled with it, turn out to be stronger than the original plastic.

Cracks in ABS printouts can also be filled with ABS thinned with acetone, which reacts chemically with the ABS object and seeps into existing voids. It is recommended to make such a putty from 1 part ABS and 2 parts acetone, then it will not spoil the surface if used correctly.

Dichloromethane works on all plastics: ABS, PLA, HIPS, SBS, etc.

Epoxy is also useful if you want to make your 3D printed part more durable

Pros

• Epoxy filler is easy to sand and prime, resulting in an excellent surface for painting.
• An ABS solution of the same filament will give the same color so nothing will be visible on the surface.

Cons

• Auto body filler or other polyester epoxy adhesive is opaque when dry and will leave discolored areas on the printout.
• Additional processing required to achieve a uniform surface.
• If the grinding is done too aggressively and too much material is removed, the appearance of the part can be affected.

Polished

PLA model, polished. Photo rigid.ink

Tools

• Plastic Polishing Compound
• Sandpaper for P2000
• Cleaning cloth
• Toothbrush
• Polishing pad or microfibre cloth

Process

Once the part has been sanded, a plastic polish can be applied to the part to give a standard ABS or PLA object a mirror finish. After the part has been sanded for 2000, it is necessary to remove dust from the printout with a cloth and rinse the printout under warm water using a toothbrush. When the object is completely dry, buff it on a buffing pad or microfiber cloth, adding a polishing compound as you go, such as polishing jewelry. They are designed specifically for plastics and synthetics and give a long-lasting shine. Other plastic polishes, such as those used to polish car headlights, also work well, but some of them contain chemicals that can damage the printout.

Pro Tricks

To polish small parts, place the polishing wheel on your Dremel (or other rotary tool such as a power drill). For larger and stronger parts, you can use a grinder, just make sure that the part does not stay in one place for too long, otherwise the plastic may melt from friction.

Pros

• The part is polished without solvents that can warp it or change its tolerances.
• When properly ground and polished, a mirror-smooth surface is obtained, very similar to cast.
• Polishing and deburring plastics is extremely economical, making this a very cost-effective method of achieving a quality finish.

Cons

• If you want to achieve a mirror-smooth surface, the part must be carefully ground before polishing, which may affect tolerances.
• After polishing, the primer or paint no longer sticks.

Primer and paint

Gray PLA FDM print spray painted black. 3dhubs.com

Tools

• Cleaning cloth
• Toothbrush
• 150, 220, 400 and 600 grit sandpaper
• Aerosol primer for plastics
• Finish paint
• Polishing sticks
• Polishing paper
• Masking tape (only if multiple colors are expected)
• Nitrile gloves and matching face mask

Process

After the printout has been properly sanded (it is sufficient to reach P600 when painting), it can be primed. Aerosol plastic primer should be applied in two coats. This primer is intended for subsequent painting of models, provides an even coating and at the same time thin enough not to hide small elements. Thick primer, which is sold in hardware stores, can clump, and then you have to seriously work with sandpaper. Apply the first spray coat with short pressures from a distance of 15-20 cm from the object, trying to do it evenly. Let the primer dry and smooth out the unevenness with 600 grit sandpaper. Apply a second coat of spray with light, quick pressures, also very gently and evenly.

When the priming is completed, you can start painting. You can paint with artistic acrylic paints and brushes, but a spray gun will provide a smoother surface. Hardware store spray paints are thick and viscous and difficult to control, so use paints that are designed specifically for modeling. The primed surface must be sanded and polished (sanding and polishing sticks, which are used in nail salons, can be purchased online, they are great for our task), and then wiped with a cloth. The paint should be applied to the model in very thin layers, the first layers should be transparent. When the paint finish becomes opaque (usually 2-4 coats), let the model rest for 30 minutes to allow the paint to dry completely. Carefully polish the paint layer with manicure sticks, repeat the procedure for each of the colors (between each applied paint).

Separate parts of the model can be covered with masking tape so that the colors, if there are several, do not mix. When painting is complete, remove the masking tape and polish the object with polishing paper. Polishing paper, such as 3M or Zona, comes in a variety of grits and is a relatively new product. It is sold in packs in various online stores, and after processing with this paper, the ink layer or topcoat will literally shine - and nothing else can achieve this effect. Apply 1-2 coats of top coat to protect the paint and let it dry completely. The top coat is selected in accordance with the recommendations of the paint manufacturer. If the topcoat and paint are incompatible, it can render your entire painting job meaningless, so compatibility is very important here.

Pro Tips

Don't shake the can when spraying! It is important not to mix the pigment or primer with the propellant (propellant gas), which will cause bubbles to form in the spray. Instead, the can must be rotated for 2-3 minutes so that the mixing ball rolls like a pearl, and does not strum.

Pros

• Excellent result, if you take into account all the nuances of the process and practice.
• With the final appearance of the object, you can do anything, no matter what material it is printed on.

Cons

• Primer and paint increase the volume of the model, which affects tolerances and can be a problem when it comes to a part of a larger object.
• High quality spray paint or spray gun increases costs.

Vapor smoothed

Vapor smoothed black ABS printed hemisphere

Tools

• Cleaning cloth
• Solvent resistant sealed container
• Thinner
• Paper towels
• Aluminum foil (or other solvent resistant material)
• Face mask and chemical resistant gloves

Process

Line the bottom of the container with paper towels, if possible along the sides. It is critical that the vapors cannot damage the container and that the container itself is sealed. It is recommended to use a glass or metal container. Apply enough thinner to the paper towels so that they are wet but not soaked - this will also help them adhere better to the walls. Acetone is famous for its ability to smooth out ABS. PLA can be smoothed with a variety of other solvents (dichloromethane works well), but this plastic tends to be much harder to smooth than ABS. When working with any solvents, please follow the safety precautions for handling chemicals and always take appropriate precautions. Place a small "raft" of aluminum foil or other solvent-resistant material in the center of the paper towel-lined container. Place the printout on the "raft" (either side of your choice) and close the lid of the container. Steam polishing can take varying amounts of time, so check your printout periodically. To increase the speed of polishing, the container can be heated, but this must be done carefully so as not to cause an explosion.

When removing the printout from the container, try not to touch it in any way, leave it on the “raft”, take them out together. In all those places where the printout has come into contact with something, there will be defects, since the outer layer will be under-dissolved. Before working with it, let the printout completely “breathe” so that all solvent vapors have evaporated.

Many aerosols and/or solvent sprays are flammable or explosive and their vapors can be harmful to humans. Be extremely careful when heating solvents, always handle them and store them in a well ventilated area.

Pluses

• Many small blotches, as well as many layer lines, are smoothed out without additional processing.
• The print surface becomes extremely smooth.
• The procedure is very fast and can be performed using widely available materials.

Cons

• Doesn't "heal" gaps, doesn't completely hide layer lines.
• During the smoothing process, the outer layer of the printout dissolves, which greatly affects the tolerances.
• Negatively affects the strength of the printout due to changes in the properties of its material.

Immersion

PLA model immersed in dichloromethane. Photo 3dpt.ru

Tools

• Solvent resistant container
• Thinner
• Eye hook or cog
• Heavy wire for sculpture or landscaping
• Dryer or drying frame
• Face mask and chemical resistant gloves

Process

Make sure the container you are using is wide and deep enough to completely submerge the printout in the solution. Fill the container with the appropriate amount of solvent - be careful not to splash. As with vapor smoothing, ABS dip smoothing can be done with acetone, which is easy to find in the store, and for PLA, dichloromethane can also work well with ABS, HIPS, SBS, PETG, and many other materials. PLA is quite resistant to solvent smoothing, so it may take several passes to achieve the desired result. Prepare the printout for dipping by screwing a hook or eye screw into it in an inconspicuous place. Pass the wire through the eyelet or wrap the wire around the screw so that the printout can be immersed in the solvent. If the wire is too thin, it will not be able to withstand the buoyant force on the printout, and it will be difficult to sink the object.

Once the printout is ready, use a wire to completely immerse it in the solvent for a few seconds. Remove the printout and hang it by the wire in a dryer or on a drying frame to allow the solvent to completely evaporate from the surface. After ejection, the printout can be gently shaken to facilitate the drying process and ensure that no solvent has accumulated in the depressions.

Pro Tricks

If an opaque whitish coating appears on the print after drying, this can be corrected by holding the object over a solvent bath for a while so that its vapor slightly dissolves the surface. This restores the original color of the printout and achieves a shiny outer layer.

Pros

• The surface of the print is smoothed much faster than steam polishing.
• Significantly less fumes are generated than other solvent polishing methods, so this method is less hazardous.

Cons

• The surface is smoothed very aggressively, so you can forget about tolerances.
• Too long immersion can lead to complete deformation of the object and a significant change in material properties.

Epoxy

Black ABS printout, half epoxy coated, half uncoated

Toolbox

• two-component epoxy resin05
• Sponge Applicator
• Mixing container
• Sandpaper P1000 or finer

Process

After the printout has been cleaned (preliminary cleaning gives the best end result), wipe it thoroughly with a cloth. Mix the resin and hardener in the proportion indicated in the instructions, accurately measuring all volumes. The curing process of epoxy resin is exothermic, so glass containers and containers made of materials with a low melting point should be avoided. It is recommended to use containers that are specifically designed for mixing epoxy resins. Incorrect ratio of resin and hardener can result in longer curing time or no curing at all and result in a permanently sticky substance. Mix the resin and thinner as directed in the instructions - carefully, in smooth movements to minimize the amount of air bubbles remaining inside the mixture. Very little epoxy is needed, and most of these resins only work for 10-15 minutes, so plan accordingly.

Apply the first coat of epoxy with sponge applicator, being careful not to build up in crevices and small parts. When the printout is sufficiently coated, allow the resin to fully cure - as described in the instructions that came with it. One coat may be sufficient, but for optimum results it is best to lightly sand the printout with fine sandpaper (on P1000 and above) to eliminate any imperfections. Wipe off the dust with a cloth and, in the same way as before, apply a second layer of epoxy.

Pros

• A very thin layer of epoxy won't affect tolerance too much (unless the printout has been sanded too hard beforehand).
• A protective shell is formed around the object.

Cons

• The layer lines will remain visible, they will only be covered by a smooth shell.
• If too much epoxy is used, it can flood parts and edges, and the surface can appear greasy.

Plating

FDM-printed structural element nickel plated with Repliform using RepliKote technology

Tools (for home work)

3

• Electroplating solution can be obtained by mixing metal salt, acid and water, but if the proportions are inaccurate and the substances are of insufficient quality, you cannot count on a professional result. If you buy a ready-made solution (as in Midas kits), you can be sure that the problems with plating are not caused by the solution.
  • Sacrificial anode. The anode material must match the metal of the solution: for example, if copper sulfate is used in the solution (with water it is copper sulfate), then the anode must also be copper. Any object made of the appropriate metal will do (for example, copper wire for copper plating), or you can buy special strips of metal for galvanization.
  • Conductive paint or acetone with graphite. Electroplating requires the surface of the printout to be electrically conductive, and this can be achieved with a conductive ink or a solution of equal parts graphite and acetone. Conductive paint will work with any material, but acetone with graphite will only work with ABS.
  • Power rectifier. A simple battery can be used as this element, only it will not be as effective and will not give a fast enough result than the rectifier itself (household current). The rectifier is safer in the sense that it can simply be turned off and thus cut off the current during the galvanization process.
  • Conductive screw or eye hook
  • Non-conductive container
  • Contacts
  • Non-conductive gloves and goggles. Galvanizing solutions are acidic and can cause injury if splashed into the eyes, so wearing goggles is very important. Solutions also irritate the skin and conduct electricity, so insulating gloves are needed.

  Finishing	★ ★ ★ ★ ☆
  Approvals	★ ★ ★ ☆ ☆
  Speed ​​	★ ★ ★ ★ ☆
  Suitable for	all thermoplastics FDM

  Process

  Electroplating can be carried out at home or in a professional workshop. To do everything right, you need to be well versed in the materials, in what is actually happening - and at home these opportunities are usually limited. In order to achieve excellent surface quality and to have more plating options, including chrome plating, it is best to use the services of professional workshops. The copper galvanization process will be described below as an example.

  At home, you can galvanize with copper or nickel, and this coating will then serve as the basis for galvanizing with other metals. It is critically important that the printout surface be as smooth as possible before it is galvanized. Any bumps and lines in the layers will be enhanced as a result of the process. Prepare the sanded and cleaned object for plating by coating the plastic with a thin coat of high quality conductive paint, or with a graphite and acetone solution for ABS printouts. Allow the conductive coating to dry completely, sand if necessary to ensure a smooth surface. At this stage, it is extremely important not to touch the printout with bare hands or to wear gloves, because sweat marks on the object will certainly affect the quality of the galvanization.

  Insert a screw or eyelet in an inconspicuous place on the printout and connect it to the negative terminal of the rectifier. This will be the cathode. Connect the copper anode to the positive contact of the rectifier. Fill the container with enough copper plating solution so that the printout is completely covered with it. Immerse the anode in the container and turn on the power. After the rectifier is turned on, immerse the printout in the container, making sure that it does not touch the anode anywhere. Beware! When the object is already in the bath, the galvanization system is active, and contact with the solution, cathode or anode can be traumatic. Set the voltage on the rectifier to 1-3 Volts, and the process will go to full metallization. To speed things up, the voltage can be increased, but not more than 5 volts. When enough metal has deposited on the printout, simply turn off the power and dry the object with microfiber towels. When it's dry, varnish the object to protect it from corrosion.

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