Practical 3D Printing: Surface Finishing

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Surface Finishing

10.06

00:00	Depending on the application, some prints will be ready to use straight from the printer, but for some cases we might want to use some post-processors to achieve a particular finish for the part.
00:11	This is mostly done for aesthetic purposes, as although there are many techniques, like those we've discussed around build orientation, to achieve the best possible surface finishes, the nature of FDM 3D printed parts will always result in a tell-tale surface finish, with some layer lines to some degree.
00:30	For some parts this just might not be acceptable, and we'll be wanting to achieve a smoother or more consistent finish.
00:36	This also goes for 3D printed moulds or patterns for composite parts, as the surface finish of these is transferred to the final product.
00:44	In most cases we want the mould surface to be as smooth as possible, as this also serves the purpose of helping with mould release.
00:53	There are also some coatings that we'll discuss that can help seal and protect our 3D printed parts, keeping them waterproof and helping them last longer.
01:02	With the reasoning out of the way, let's dive into the options we have for finishing 3D printed parts, and the practical skills required to achieve them.
01:10	At the end of the previous module that focused on the printing process, we briefly discussed removing support material from the part.
01:18	Let's quickly look back at this in a bit more detail.
01:21	In many cases the supports will be easy to break off by hand, but for some stubborn or harder to reach areas we can use tools like pliers, screwdrivers or razors to help.
01:32	If we look at our 3D printed brake disc cap for example, we can use a flat head screwdriver to gently pry the supports from the nut pockets.
01:40	The support around the filleted edge of the mounting surface can mostly be broken off by hand, but as the curve tapers away, the last bits of the support are quite stubborn.
01:50	This is where a razor comes in, but the resulting surface still has a small lip on it.
01:55	If we want to make sure that this support is in place, we can use a flat head screwdriver to remove the lip from the support.
01:57	If we have a prototype part like this where the main purpose is just checking fitness, we can move straight to the sanding phase.
02:03	Starting with something around an 80 or 100 grit wrapped around a sanding block, we can carefully remove the lip and then move to a finer 240 or 400 grit to create a smoother surface finish.
02:15	To finish up, we'll use a rag and a small amount of isopropyl alcohol to clean off the dust.
02:21	Again, for a part like this, there's no need to do anything more than remove the remains of the support material, but that's not always going to be the case.
02:30	If we're looking for an even better finish, we'd usually turn to some form of coating.
02:35	This could be as simple as body filler.
02:37	For clarity, we'd still likely sand the part beforehand to remove any unwanted irregularities and start with as smooth of a surface as possible.
02:46	This will reduce the amount of filler required and help keep the weight down as much as possible.
02:51	There are a lot of options for the actual filler itself, but mostly what we'd use on a car is suitable.
02:57	In the past, we've used 3M lightweight body filler with success on 3D printed moulds for composite parts.
03:03	After initial sanding of the part, we follow the supplier's instructions for mixing the two part filler, essentially adding the hardener and then mixing thoroughly.
03:12	A side note here, single part fillers like glazing or spot putties can be used on parts that are already relatively smooth, but for rough parts, a regular body filler will work.
03:22	With the filler mixed and ready, we can then apply it to the surface of the 3D printed part using a spreader, scraper or applicator to spread the filler into a very thin layer over the surface.
03:34	After allowing the filler to cure as per the supplier's instructions, we can sand the part like we did before, starting with something around 80 to 100 grit and then moving on and finishing up with something like 400 grit.
03:47	The result should be a nice smooth finish, free of any layer lines, but it will still have a matte finish and a patchy appearance, so we'll likely want to apply some more coatings depending on the application.
03:58	For an end use, acidic part, we'll next use a spray on primer, something like Rustoleum's products that also bond to plastic, and following this, more sanding with 400 grit or finer to finish.
04:11	Then we can finish up by painting the parts with typical spray paints, or again, Rustoleum's paint and primer works well.
04:18	For 3D printed moulds for composite parts, the process is slightly different.
04:23	After sanding the body filler, we'll next use a polyester primer.
04:27	This is sprayed on and designed specifically as a surface coat for composite tooling.
04:32	Following this, we can sand again with a very fine sandpaper, before cleaning and applying release agents and so on, which are out of the scope of this course along with the composite construction.
04:43	It should be mentioned that in some cases, high build primers can fill in the surface of the part well enough that a body filler is redundant.
04:51	Another example of a commonly used coating for 3D printed parts is a product called XTC3D.
04:57	This is a protective coating for smoothing and finishing 3D printed parts for all thermoplastics and also thermosets, which we'll discuss in the next section of the course, focused on SLA or Resin 3D printing.
05:10	This consists of two liquids, A and B, that are mixed together in two parts A to one part B.
05:17	Then it's just a matter of applying it in a thin layer over the surface of the part, the coating will then self-level and wet out uniformly without leaving any brush strokes.
05:27	After a few hours, the XTC3D cures and the result is a hard and impact-resistant coating that's relatively smooth and glossy.
05:36	However, we'll still usually finish it with sanding and follow with priming and painting or applying a release agent for molds.
05:43	Although it can appear this way, this coating doesn't melt the plastic.
05:47	This is actually how the acetone vapor smoothing process works.
05:50	This is a very simple process, but it's a very simple process.
05:51	Essentially dissolving the outer layer of the part exposed to acetone, leaving a smooth and glossy finish.
05:58	This works on any material that can be dissolved by acetone, including ABS and ASA, but it doesn't include PLA, PETG, nylon, or TPU.
06:08	The process here starts with some sanding, like most smoothing processes.
06:12	Then we need to prepare a container that isn't affected by acetone.
06:16	Glass is usually a good option here.
06:19	There's a few different ways to generate acetone vapors.
06:22	Put simply, acetone evaporates in air.
06:25	So, partially filling the container with acetone and then covering but not sealing the container will result in acetone vapors filling the container before escaping.
06:35	It can help to soak paper towels in acetone and position them around the container for a more consistent atmosphere.
06:42	And some people will also use small fans on the lid of the container to promote flow of the vapors.
06:48	We then need to support the part in the container keeping it out of contact with the acetone liquid and the paper.
06:55	It's important that whatever we use to support the part won't dissolve in the acetone.
06:59	Metal is usually a good option here.
07:02	It's also ideal to support the part in a way that all surfaces will be exposed and subject to the smoothing at once.
07:09	At least those that we want smoothed anyway.
07:11	There's also no set time frame on the process so we need to constantly monitor the parts, which is why a clear container is ideal.
07:20	We want to get to the point where the outer layer of the part will be just dissolved and the surface will self level, resulting in a smooth and consistent finish with no layer lines.
07:30	Finally, we can remove the parts from the container, ideally by holding the supports and not the tacky surface finish of the part.
07:38	Then we place the parts in a well ventilated area so the rest of the acetone will evaporate and the part will return to its hard original state.
07:46	This can take anywhere from a few hours up to a couple of days.
07:50	Naturally this smoothing process is ideal for complex geometries that would be difficult to smooth by hand.
07:56	But it also helps even out the isotropic nature of the mechanical properties of an FDM printed part as the outer layers are essentially melted together.
08:05	The final technique worth discussing in this module is flocking.
08:09	This is the process of spraying small fiber particles onto a surface that has been pre-coated with an adhesive.
08:16	The result is a soft grassy texture, similar to velvet.
08:20	This is primarily used on interior components like dashboards to add a nice aesthetic touch and reduce the glare or reflections on the windscreen.
08:29	We've used it on the 3D printed center console to match the dash in the HPA SR86.
08:35	This process is actually very simple and requires no real preparation of the printed part other than cleaning and then applying the adhesive with a brush in a thin even coating.
08:45	Next, the gun is prepared by connecting the tank of fibers to the material.
08:49	This can then be sprayed onto the surface evenly until it's completely covered and left for the adhesive to dry.
08:56	Following this, any excess of fibers can be shaken or brushed off.
09:00	We've covered a lot in this module, so let's summarize before moving on.
09:04	After removing the part from the printer and any support material, we may wish to add some finishing processes to achieve better surface finish or a specific aesthetic.
09:15	This usually begins with sanding the printed part directly starting with something around 100 grit sandpaper and working up to at least 400.
09:24	For a smoother finish, we'll often use body fillers or specific coatings like XTC3D followed by more sanding in preparation for priming and painting.
09:34	3D printed composite tooling is usually sprayed with a polyester primer before applying release agents.
09:40	Acetone vapor smoothing is another option but only suitable for certain plastics like ABS and ASA where the outer surface will be covered with a thin layer of sandpaper.
09:48	This is usually sprayed with a thin layer of sandpaper before applying release agents.
09:50	Finally, flocking is an easy way to achieve a professional level finish with very little preparation for 3D printed parts and can be a good way to match the item with other parts in the vehicles interior.