Is 3D printing a green technology?

25 November 2014

3D printing is a green technology, right? Here Jeremy Pullin reveals that not all processes are as environmentally friendly as they claim to be when compared to conventional manufacturing

Discussion forums such as LinkedIn are awash with people arguing the merits of 3D printing / additive manufacturing (AM) over conventional manufacturing.

One of the areas in which great benefits are claimed for AM is the promoted perception that it is a more environmentally friendly way of making things. This claim, however, is not as straightforward as it appears.

Take for example what happens to waste or excess materials, which basically involves all of the raw material that doesn’t make up the final part. I have read and heard dozens of times that 3D printing is green because it only uses the material it needs to make the part and unlike subtractive techniques there is no waste.

There are many different 3D printing technology groups but this claim (with, perhaps, a couple of exceptions) is not true.

For liquid resin processes, metal powder bed and Fused Deposition Modelling (FDM) there are sacrificial scaffolds. Depending on the part geometry these scaffolds can be anything from a very small proportion of the total material consumed to the majority of what is actually used.

Once solidified, this material cannot be simply chucked back into the machine for the next build; it’s a waste product. In the case of metals, the powders have to be passed through a sieve before they can re-enter the machine, incurring further losses.

Methods that do not require scaffolds have waste issues of their own. For jetting and Smooth Curvature Printing (SCP), the name used by Solidscape for its printing process, there are sacrificial support materials that cannot be reused. Much of the post build support removal involves the use of further materials in the form of cleaning / dissolving agents that further add to the waste stream.

In the case of SCP, the support material is melted away in a hot oil bath after building.

For paper Selective Deposition Lamination (SDL), Laminated Object Manufacturing (LOM), Selective Laser Sintering (SLS) and other non-metal powder bed technologies there is also waste.

In SDL, the excess paper is cut up during the process and, although recyclable, is not reusable. For SLS, the unfused powder is altered by heating in the build chamber, which means that some materials cannot be reused at all but others can be mixed with virgin powders (mixing ratios vary per material) before being fed back into the machine.

An exception is found in the rather excellent BluePrinter. In the thermal head printing process the chamber is not heated to the high temperatures found in SLS. The powder is therefore not degraded in the same way and so, what doesn’t end up in the vacuum cleaner, can be thrown back into the machine.

In August 2012, the US department of energy issued a report in which it stated “Building objects up layer by layer, instead of traditional machining processes that cut away material can reduce material needs and costs by up to 90 per cent”. This claim was based on a misrepresented figure from an article in the Economist magazine.

Extensive research by myself (ten minutes with Google on a lunch break) found the origin for the 90 per cent figure to be a single metal part produced as a trial by the European Aeronautic Defence and Space (EADS) centre in Bristol.

It failed to mention that the part had actually been redesigned for AM by the very capable Andy Hawkins and team at EADS. It also didn’t mention that the comparison was based on machining from a solid billet rather than a net shape casting or that the
figure didn’t include any sacrificial material consumed in the AM process.

This is a classic example showing how a single case should never be used as the basis for a claim concerning an entire technology.

So, if you are going to consume more material than appears in the final part then you may wish to use materials that claim to be environmentally friendly in their own right. The best known of these is polylactic acid (PLA), a plastic made from corn starch used as FDM filament.

It can decompose into water and carbon dioxide in 47 to 90 days, but this is only the case when it is treated at high temperatures in commercial composting facilities. When buried in landfill PLA can remain intact for the same time as oil/gas based plastics.

If you do want to concentrate on environmental considerations you may also question the wisdom of using corn starch for the production of plastics rather than the production of food. Even if you ignore the growing need for food production to keep pace with an ever exploding world population, the US has shown how food prices have been driven up as arable resources have been diverted into the production of biofuels.

What is said above only attempts to look at one particular claim concerning the amount of material used in 3D printing and should not be considered in isolation. There are, of course, environmental gain areas such as lightweight aerospace parts that can be realised due the geometry capabilities of additive techniques, geometries which cannot be achieved by conventional means. These weight savings lead to aircraft using less fuel during their lifetimes.

There are also efforts being made to try to make 3D printing a bit more environmentally friendly such as the Ekocycle from 3D systems in conjunction with the Coca-Cola Company. This printer uses material cartridges containing 25 per cent post consumer recycled plastic.

If you want to see something greener though, check out the Ethical Filament Foundation and its work in conjunction with Ultimaker and Autodesk, or Protoprint Fair Trade Filament — a social enterprise that produces filament from materials sourced by local waste pickers in India.

In the words of the philosopher Kermit — it’s not easy being green.

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