The Dark Side of 3D Printing

Like a large portion of the product design and manufacturing world, I have a lot of enthusiasm for the potential of 3D printing. I have also experienced the reality of 3D printing – most of it positive, but not all by any means. In other words, 3D printing has come a long way, but it’s still got a long way to go on three fronts: hardware, software, and materials.

When I learned about and made a move to experimenting with 3D printing and other additive technologies a few years ago, I thought by now I would have had no use for subtractive technologies, such as milling and drilling. However, experience (and some hard knocks) have taught me that additive technologies cannot be used exclusively as my only tools. They are actually complementary in what I’ve come to realize is a hybrid approach that employs both additive and subtractive technologies.

Like many others who have been relatively early adopters of 3D printing, problems have been encountered – some of which can be resolved, while others continue to frustrate. Although the video below discusses problems with a specific 3D printer, they are somewhat typical for so-called “low-end” 3D printers using PLA or ABS materials (these are the only materials I currently use).

3D Printing Problems

We’re not making these problems up. Last week at Autodesk University, we talked with a number of 3D printer users who expressed some disillusionment and frustration with the problems they encountered. Autodesk itself said during a presentation on its Spark/Ember programs that although they estimate that some 200,000 3D printers have been sold since the technology’s inception, they say they have data that supports part failure rates of 25-75%. They made no mention of exactly what this failure range means, but could be due to a number of factors, including material, design, setup, etc.

I’ll admit I’ve been guilty of contributing to some of the problems I’ve personally encountered with 3D printing, and based on my experience, I can classify them in the following general categories:

Bad Design. This goes without saying. I’ve never seen a comprehensive list of good design practices specifically for 3D printing plastics, but very generally, design guidelines for injection molding apply for 3D printing.

That said, though, based on my experience, special attention should be given to the following issues to minimize problems:

• Minimum wall thickness (to eliminate brittleness and deformation (warp))
• Maximum part size
• Minimum feature size (largely a function of part orientation and resolution)
• Undercuts
• Minimum fillet radius
• Overhanging non-supported structures
• Tolerances to allow for part shrinkage

Of course, there are other design considerations for increasing successful part production, but I feel these are most of the main ones for ensuring relative success.

As I’ve said in the past, just because you can design and produce a part with 3D printing does not guarantee it’s a good design. Enough said.

STL Limitations.

STL (STereoLithography) is the file format native to the stereolithography CAD software originally developed by 3D Systems. STL is also known as Standard Tessellation Language. This file format is supported by many other software packages, and is widely used for additive manufacturing and CAM. On the down side, STL files describe only the surface geometry of three-dimensional objects without any representation of color, texture, or other common CAD solid model attributes.

The STL file format is simple and is relatively easy to output. Consequently, many CAD systems can output the STL file format. Although the output is relatively simple to produce, some connectivity information is discarded, and this can cause problems in the 3D printer.

3D printers build volume shape as a series of slices. Ultimately these machines require a series of closed 2D contours that are filled in with solidified material as the layers are fused together. A natural file format for such a machine would be a series of closed polygons corresponding to different Z-values. However, since it’s possible to vary the layer thicknesses for a faster though less precise build, it was easier to define the model to be built as a closed polyhedron that can be sliced at the necessary horizontal levels.

The STL file format is capable of defining a polyhedron with any polygonal facet, but in practice it’s only used for triangles. Not exactly universally versatile.

Some newer, more capable, file formats for 3D include the Additive Manufacturing Format (AMF), an emerging standard with native support for color, multiple materials, and constellations; and the PLY file format, an alternative file format offering more flexibility than most stereolithography applications.

Keep an eye on these, especially AMF, because even with its limitations, STL won’t be going away anytime soon.

Materials and Process. I regard the problems I’ve had with materials and process to be the biggest of the three I’ve described. The materials (specifically PLA and ABS) are not as innocuous, clean, and free of waste as we’re led to believe. The machine and secondary operations also require careful attention because of hot beds, hot extruders and material, and material can become airborne when machined.

For a number of reasons I usually print a first article using PLA and ABS for a final 3D print. I like PLA because it is relatively odorless, setup is quick, and the nozzle/melt temperature are relatively low. ABS usually requires more setup, employs higher temperature, can smell weird, but produces parts with better physical/mechanical characteristics.

With PLA, though, I’ve noticed that when machining a part out of the 3D printer, shards of the material penetrate ungloved fingers with a feeling similar to handling fiberglass. I guess the moral here is to avoid machining PLA, or at least wear hand and breathing protection, as I don’t seem to have the same issues with ABS.

Looking ahead, I foresee a time down the road where the spools of plastic material commonly used today with 3D printers will eventually be superseded by many of the same powder and liquid materials currently used in higher-end commercial additive machines. What these new materials might cost is anybody’s guess, but processing them should be more efficient and the results more predictable.

So, as things continue to improve on the 3D printing front, I’ll employ a hybrid fabrication approach that includes both additive and subtractive technologies, because together they add up to a greater probability of successful design execution. I’ll just be more judicious about the materials and techniques I use.

Despite the problems I’ve encountered, 3D printing is an amazing and quickly evolving set of technologies that involve hardware, software, and materials that I’m certain will continue to reach heights we can’t yet imagine.

Tags: 3D printing, ABS, PLA, stereolithography, STL

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