In 3D Printing, It's all About Quality

The openness of 3D printing technology has enabled many more people to contribute to the design and development of 3D printing over the last 10 years than would have ever had the chance to do so otherwise.

Many have found it tempting to define print quality by a single metric. In the past that metric was the technical specification of Layer Height, the thickness of each layer printed, usually measured in fractions of millimeters, or more recently microns. The Series 1 and Series 1 Pro can easily achieve resolutions as fine as 50 microns. But what what does that really tell you about print quality?

It certainly does make a difference if  the smoothness and vertically oriented feature size of your prints are a concern to you, but it doesn’t speak fully to the precision or accuracy of the machine itself.Another measure of print quality is motor resolution. Each of our stepper motors, thanks to digitally interpolated microstepping, gets over 50,000 steps per revolution.

After several mathematical calculations involving pulley size, number of revolutions over the 12” build length of both the X and Y axes of the Series 1 and Series 1 Pro, and the aforementioned microstepping jargon, we can calculate that each axis is capable of over 400,000 positions in every direction.

You can think of these steps, or positions, as physical pixels over the 12” build length of each machine we make. And if you do some more math, you find that the distance between each position (the size of each pixel) is about 0.76 microns, or about one ninth the length of an X chromosome.

So we could say that the machine can position itself in almost sub-microscopic intervals. But this too would not be a fair measurement of print quality. After all, it doesn’t mean you can make items this small, seeing as the nozzle diameter of our machine is 400 microns.

When people want “a good quality print” they are looking for as faithful a representation in their hands, as what they expected to get in their minds. This is a perfectly valid requirement, and the industry has spent years trying to quantify it.

There are some limitations that are inherent to all 3D printing, that will keep perfect prints from being created, no matter the quality of the machine. For instance, the quality of your print may be limited if the digital resolution of the input file is poor.

The 27-year-old STL file type, which remains the current industry standard for 3D prints, has limitations that are being addressed. Computational limitations have also played roles in print quality, and are only now starting to be lifted as computer power increases to match the rising quality standards of 3D printers.

One popular way to define a good quality print is one that does not contain any extra-geometric artifacts. This brings up the valid concept of ‘manufacturing artifacts.’

Every method of manufacturing produces what engineers call ‘artifacts.’ Artifacts are patterns or markings, however small, that appear on a manufactured object as a result of the specific manufacturing process used. We’ve all seen such artifacts, even on finished products, and many of us may not have even noticed them.

Laser cut plywood parts tend to have burn marks on them, and the edges of the parts are completely charred. The charring comes from the laser, and is an unavoidable feature of the process. Injection molded parts tend to have a line on them, where two pieces of their mold met and a tiny amount of molten plastic seeps through. Metal machining such as turning or milling produces artifacts that resemble the tool that was used to machine them. Weld points tend to have extra material surrounding the entire area of the welding operation. And lastly, cast parts take on a textured surface - the same surface texture of their mold, usually made out of plaster or sand.

Even selective laser sintering (SLS), considered to be a very high end form of 3D printing, exhibits artifacts on machines that cost upwards of $800,000. These artifacts come in the form of very visible layering on organic geometries, and a rough textured finish as a result of the powder sintering process.

Artifacts are accepted as part of the manufacturing process, but many steps can be taken to reduce their final visibility. Deburring is a common process for metal and injection molded parts. Sanding and grinding are used on cast and welded parts respectively. In addition, manufacturing equipment designers try to create machines that leave as few artifacts as possible.

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In FFF 3D printing, where filament is used and deposited on to a build platform layer by layer, as with the Series 1 and Series 1 Pro, the artifacts that appear are wave-like as a result of a number of factors including the natural frequency of the machine’s frame, the limitations of the STL file type, computational limitations in the machine’s computer, the nature of stepper drivers, the inertial effects on the toolhead by the motion of the axes, and the flowrate of the extruder among other factors.

3D Printing artifacts have been extensively studied by many people and organizations in the industry, and there are dozens, if not hundreds of pages of discussion on the subject of how to mitigate these effects. Looking at all FFF machines, it appears as though these artifacts are universal; it’s simply an effect of the process. You can visit the websites of our competitors and find the exact same artifacts on the prints that they show.

We’re still looking at ways to reduce the incidents of these artifacts and we’ve made significant progress in this regard. When upgraded to our latest stepper drivers, (the ones that do all of the ‘digital interpolation’ mentioned above) the amplitude of the patterns is reduced dramatically. They are much less visible, meaning that the latest machines have fewer artifacts than any other 3D printer we’ve seen. Our work will continue until our machines can produce perfection down to the atom, but it may be possible that no manufacturing process will ever be completely free of artifacts.The advantages of FFF have always been speed, cost per part, and specifically for our products, return on investment, reliability and quality. If your need for dimensional accuracy trumps any other concern be it cost, economic risk, or turnaround time, consider using injection molding in your prototyping phase.

In the mean time, we are happy to be known for having among the best print quality of any FFF machine, and certainly the best value dollar for dollar of any 3D printer on the market.

Here are some of the high-quality prints that we've made on the new Series 1 Pros and Series 1s!

 

Brandon Toomey