How sustainable is 3D printing as a manufacturing process?

With additive manufacturing (AM), novel parts can be designed and built with optimized topologies, eliminating the need for machining individual pieces and then assembling them. Many are hopeful that this technology will benefit the environment through a decrease in the amounts of energy and raw materials required to make components in all sorts of industries.

The Additive Report discussed 3D printing and its place in sustainable manufacturing with MIT Professor Timothy Gutowski, head of the university’s Environmentally Benign Manufacturing (EBM) research group. EBM focuses on examining the environmental effects associated with manufacturing products.

Additive Report: Can you provide an overview of the benefits of 3D printing in terms of sustainability?

Tim Gutowski: Any benefits depend a lot on the details. For lifecycle analysis claims, you’re setting up some version of additive manufacturing versus some version of a conventional manufacturing process. And one problem is that we have a better idea of the waste numbers for conventional manufacturing processes than we do for additive, because the latter is still a work in progress.

A textbook I use for my classes—Manufacturing Engineering & Technology, 7th Edition—lists certain waste values for conventional manufacturing processes. Many of those processes have a very low scrap rate and are not all that wasteful, such as powdered metal and some sheet metal operations. Machining, in general, can be efficient with relatively low waste. So it depends on what you’re setting the example up against.

AR: How do you make a fair comparison between technologies?

Gutowski: One way to compare two processes is using a “buy-to-fly ratio,” where you divide the total material consumed by the amount of material that ends up in the product. In the case of an airplane, the buy-to-fly compares the raw material you buy with the material that ends up in a part that flies on the plane. (Editor’s note: The lower the ratio, the lower the waste; a ratio of 1 is the ideal because it means zero waste.)

I do think there are some clear examples where waste reduction with 3D printing is a legitimate claim. Companies like Siemens and GE are now using additive to make optimized fuel nozzles and other engine parts with complex internal passages that in the past had to be cut from very hard materials, which meant you couldn’t easily machine them, so they had to be made in many separate pieces and then assembled.

The buy-to-fly ratios for machining those type of parts can be enormous—up to 8 or 10—so that’s an easy target for making a claim about waste reduction with 3D printing. But for other applications, the buy-to-fly ratio is smaller.

AR: Because 3D printing is an additive technology, shouldn’t there be zero material waste?

Professor Tim Gutowski, head of MIT’s Environmentally Benign Manufacturing research group.

Gutowski: Even with additive, there is some loss and some waste. There’s the issue of separating the part from the support plate, plus the need to obtain a good surface finish, which usually means some machining and waste. Then there’s the material for support structures and overhangs, all of which increase the amount of waste.

AR: Can metal powder recycling minimize waste production?

Gutowski: The people who make powdered metal systems all claim that they re-use the powder at very high rates for certification, and I think they’re doing that. At the same time, there’s another interesting dynamic going on: These powders are extremely expensive, so there’s every incentive to recycle them. But in a future world where people are pushing for commodity powders and they become cheaper, a different dynamic may occur.

AR: What have you found in your research on energy use for additive versus conventional manufacturing?

Gutowski: Additive processes tend to be more energy intensive, measured in joules of energy per kilogram of material processed, because they’re slower. They use a lot of energy to produce the same amount of product.

In fact, most 3D printing processes are something like seven orders of magnitude more energy intensive than high-volume conventional manufacturing processes such as machining, casting, and injection molding.

AR: Are there any bright spots in the energy-use data for additive?

Gutowski: One exception was the Big-Area Additive Manufacturing (BAAM) machine, which had very high production rates, with an energy-intensity level comparable to other conventional processes. I would consider that a bit of a breakthrough. (Editor’s note: BAAM is 3D printer from Cincinnati Incorporated that builds durable tooling, prototypes, and production parts from fiber-reinforced plastic. It can print parts the size of a car at rates up to 80 pounds per hour.)

But the BAAM creates a product with a crude surface finish. After printing an entire car body, they have to either hand-finish it or put it on a big 5-axis machine tool to get a smooth, glassy finish—so we’re back to machining.

That’s the fundamental trade-off in additive manufacturing: If you want to go fast, you’re going to lay down a lot of material at once, but If you lay down a lot of material at once, it’s going to have a coarse finish.

To determine whether 3D printing is more energy efficient in a particular case, you’d have to also look at the material itself and how much is wasted, because there’s a lot of energy embodied in sourcing the materials.

AR: Do you have any conclusions about the sustainability of 3D printing?

Gutowski: The sustainability discussion requires much wider boundaries for investigation than a constructed scenario where you substitute a certain manufacturing process for a different process.

In the big picture, we’re not sure to what extent additive manufacturing is a substitute and to what extent it’s a complement to conventional processes. Together, they enable you to do more things.

For dramatically optimized engine parts that cannot be made easily by conventional processes, 3D printing would be a substitute process. But I certainly would not make a general claim that additive is less wasteful of energy and materials than other processes. It depends on the details and what other process you’re comparing it with.

We know that if people want to do something and you make it easier for them, they’re going to do a lot more of it—and the ultimate effect might be to use more material, not less. To monitor this at a large scale, you could ask the question, “As the fraction of products manufactured by additive manufacturing increases, do we see an overall reduction in the raw materials we use?”

I think there’s a lot of enthusiasm, and people would like to do the right thing. But I think you have to be a little bit humble about what sort of benefits it’s going to bring to society.

Ultimately, additive manufacturing is a tool, like a wrench or a screwdriver, though it’s much more sophisticated. This tool could be used in constructive ways, toward sustainability, or it could be used in destructive ways to make life less sustainable.