Monday, November 17, 2014

Getting Started With 3D Printing - PLA vs. ABS

There are two main types of plastic used in most FDM printers, polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS). ABS is the same plastic Legos are made from and PLA is a bioplastic typically derived from corn starch. I will not go into a lot of the technical differences, but will instead focus on the practical issues related to each type of plastic.

Each plastic has its own advantages and disadvantages. Most of the newest low cost printers available today will only print with PLA. In order to complete a successful print, the plastic must stick well to the print bed. Sometimes it may be beneficial to heat the print bed to 40-50°C for PLA. However, it is often not necessary and many commercially available printers designed to print with PLA do not have the ability to heat the print bed at all. ABS requires a heated print bed for parts to stick. It is necessary to heat the print bed to 110-130°C when printing with ABS. This is quite hot, remember water boils at 100°C.

There are other practical concerns related to both plastics to consider. ABS shrinks substantially more than PLA while cooling. This can often cause parts to warp. When a part warps the edges or corners lift off the platform. This can lead to a part becoming completely unstuck from the platform or even if it stays in place may be completely unusable. ABS also gives off some fumes while printing. They are not overwhelming, but they are noticeable. One of my colleagues has sever allergies and asthma and reacts to just about any type of smell or fumes in the air. She never had a problem with the ABS fumes in the room.

Since PLA doesn't shrink as much as it cools it is much less prone to warping and the finished parts are much closer to the intended dimensions. This difference often doesn't mean much. However, if you are printing something like a phone case it is much easier to design one that fits just right if you print with PLA rather than ABS.

Given the minimal shrinkage, lack of fumes, and no need for a heated bed you might be wondering why I'm even presenting a choice between ABS and PLA. PLA seems to be far superior in almost all respects. One factor to note, however, is it is far more finicky to print with. With PLA, if things are not perfect the printhead can become clogged. This is not a problem I've ever had with ABS.

I was so fed up with problems related to ABS that I've been printing exclusively with PLA for the last couple of years. For the 9 months, with my first generation Replicator, I have not been able to print something that takes more than an hour and a half before the print head jams. Often it jams much sooner. Newer printers may be more reliable, but I don't have experience to speak to that. Yesterday I switched back to ABS and was able to do a two hour print of a comet and a five hour print of a fossil skull with no problems. For my printer I may switch over to mostly ABS and just print in PLA when I need something that fits precisely.

While I'm talking about Plastic I should mention that both types should be stored in sealed containers. Over time they will both absorb moisture and this could cause problems while printing. I use a container designed for long term storage of food and I toss in some silica gel to absorb moister. The container I use was less than $15 on Amazon and will hold two spools of plastic. The other bonus with using containers for storage is it will keep your plastic relatively dust free. If dust accumulates on the filament it can cause the print head to become clogged.

Go Back to earlier parts in the series: Part 1Part 4

No comments: