Selecting the right 3D printing technology can be difficult, especially when you consider all the different key drivers in the decision-making process. Are you looking for a smooth surface finish? Maybe you’re looking for strong mechanical properties with a common, easy to use plastic such as ABS or ASA? Now, what if I told you that you didn’t always need to compromise here? With minimal amounts of post-processing techniques, you can achieve a smooth injection molded finish using FDM technology. Sure, parts are fully functional right off the print tray, but utilizing an additional post-processing step can help elevate your part to the next level, and really catch the end user’s eye. Like the flexibility that 3D printing provides, users have many different solutions for their post-processing needs, so let’s dive in!
3D Printing With ABS and ASA
Acrylonitrile butadiene styrene (ABS), is a common thermoplastic polymer, most well known for its toughness and impact resistance. Acrylonitrile styrene acrylate (ASA) is a far less known thermoplastic but shares many mechanical properties as they are structurally very similar. In addition to the properties they share, ASA boasts increased weather and UV resistance, making it an ideal solution for automotive and outdoor applications.
Options for Post-Processing FDM 3D Printed Parts
Suspended Rotational Force
One method to post-process FDM 3D printed parts is tumbling, which is an effective and very popular method to reduce the appearance of layer lines. The greatest upside to tumbling as a post-processing technique is that it allows the operator to batch multiple parts at once, which results in a time and cost savings to the user. Its only downside is this process can be damaging to small thin-walled parts. Traditionally, “automated” surface finishing solutions were limited to rotary and vibratory tumblers that were initially designed for metal parts.
Today, there are other options that hardware, software and chemistry to optimize 3D printed surface finishing such as Suspended Rotational Force (SRF). This technology provided by PostProcess Technologies creates optimized energy with vertical motion combined with additive formulated consumables to achieve the required surface finish. This combination allows users to precisely control cycle variables such as temperature, duration, frequency and lubricity to develop a customized and unique recipe to perfectly surface finish parts, time and time again. With the PostProcess RADOR, you can achieve the desired Roughness Average (Ra) for your FDM 3D printed part.
Before (Ra)= 688.88 µ in
After 4hr Post Process in RADOR (Ra)= 239.27 µ in
In the images above, it is important to note that the roughness value was decreased drastically using the Post Process RADOR, while preserving the integrity of the fine and fragile details of this print. With the ability to batch up to thirty of these per cycle, that results in an average of about eight minutes per part. This value would be significantly higher if left to the traditional post processing methods.
Media blasting is yet another means of achieving a clean, smooth finish for 3D printed parts, without the diligent manual labor of hand sanding. This process can be carried out with various types of media such as glass beads, aluminum oxide or even steel shot. Media selection is based on material hardness, working speed and abrasive properties. Counter top blasting stations for low throughput operations can be purchased at a relatively low price point and larger industrial solutions are available for larger part volumes, and increased throughput.
Image source: Machinedesign.com
Click to enlarge
Vapor smoothing is a unique method of post-processing but lends itself to be very limited in material applications as it only applies to ABS and ASA filaments. Most are familiar with the childhood science experiment of applying acetone to Styrofoam and watching it “dissolve.” This is because acetone reacts with polystyrene, a polymerized version of styrene present in ABS and ASA. Acetone, when applied directly to the surface of ABS and ASA, can have aggressive and adverse effects, such as melting and warping. However, when the materials are in indirect contact with acetone, such as when it’s in a vapor form in a sealed container, it tends to produce a glossy porcelain finish. For infrequent users a DIY vapor smoothing apparatus can be assembled for relatively cheap, but for more regular or high-volume users, a commercially available smoothing chamber may be a more practical solution. Now, of course it is important to note that with increased surface finish, users may experience a decrease in surface detail and dimensional accuracy, so maintaining the original design intent is critical when selecting a post-processing technique.
NOTE: Acetone is highly flammable and can produce noxious fumes that are harmful if ingested. Exercise extreme and proper precautions when handling acetone and any other dangerous chemicals.
Hand sanding, be it wet or dry, is another common method of post-processing but lends itself to be very time consuming as it puts one operator in front of one part at time. Hand sanding can also be challenging when it comes to complex geometries and fine details. This technique is traditionally followed by either priming and painting or clear coating. Primer and paint help reduce the appearance of layer lines, resulting in a crisp, uniform appearance, while clear coating can produce a shiny, porcelain like appearance.
From Left to Right: Raw FDM, Vapor Smoothed, 4 hr Post Process Cycle, 8 hr Post Process Cycle
Click to enlarge
To learn more about post-processing FDM parts, watch our on-demand webinar, Overcoming FDM Support Removal Bottlenecks.