Image: AMGTA

The Additive Manufacturer Green Trade Association (“AMGTA”), recently revealed the preliminary results of a life-cycle analysis study titled “Comparative Life-Cycle Assessment: Comparison of Casting vs Binder Jetting for an Industrial Part.” As a reminder, the study was commissioned in 2021 by the AMGTA to better understand the potential for binder jetting to replace traditional sand casting.

It was conducted by the Yale School of the Environment (YSE) in partnership with AM company Desktop Metal, and Trane Technologies, a company that brings sustainable solutions to buildings, homes, and transportation through an environmentally responsible portfolio of products and services.

The team working on this project analyzed a steel scroll chiller in an HVAC system from Trane to determine the comparative manufacturing impact of binder jet 3D printing versus traditional metal casting. The preliminary results confirmed a dramatic 38% reduction in greenhouse gas (GHG) emissions through the binder jetting process primarily driven by reduced energy demand during the production phase.

In addition to this reduction of GHG, other key takeaways from the study highlight the importance of energy mix, negligible value of redesign for lightweighting, material production impacts as well as the ability of binder jetting to produce a more sustainable part.

Evaluation and reservations

The study evaluated a traditional casting process followed by machining, plating, and finishing steps in Mexico. The same scroll set design was evaluated through an additive binder jetting process of 3D printing, curing, and sintering followed by the same plating and finishing steps in the same location in Mexico. As a matter of fact, for this study, both the traditionally manufactured part set, and the additively manufactured part set, were evaluated at the same location with the same energy mix.

According to AMGTA, due to the nature of the binder jetting, YSE’s researchers concluded that a redesign for lightweighting via a lattice-type structure may not necessarily lead to additional reductions in GHG emissions, primarily because the majority of electricity consumed related to printing, curing and sintering steps would not be impacted by lattice-type structures. The analysis suggests a 10% mass reduction in the scroll set would lead to a 1% reduction in GHG emissions.

Researchers also evaluated additional potential production locations and their corresponding energy mixes. The findings indicate that such sensitivity to the grid “cleanness” needs to be considered when comparing AM with traditional processes to ensure a valid conclusion. While production in a more sustainable energy location provides environmental benefits for both production processes, the difference in environmental impacts between the methods diminishes as the energy mix becomes more “green.” Production volumes also play a significant role in GHG emissions of additive manufacturing especially for less efficient use of build volumes and small batch operations.

Industry reservations come from the fact that since scroll sets are normally made of gray iron because it has dampening properties and the proper cast iron microstructures don’t form when one makes powder, the boundary conditions are crucial and LCA is not necessarily the ideal assessment method because there are so many variables within a single entry.

In a conversation started by Sarah Jordan online, John Barnes explained for instance that “the emissions of atomization vary greatly depending on which type of atomizing technology is used, never mind getting into which gas, where the electricity comes from. I’m not really sure how one can conclude “binder jetting” is better or worse than “casting”. It has to be a lot more specific than that.”

And Sarah Jordan to add that a few variables from the foundry industry may also be interesting to explore: “what type of furnace, what model, what size, where does the power come from, how far does the raw material come from, is it primary or secondary, how much returns and how are those accounted for since part of the metal gets remelted infinitely, what is the yield, what binders are used for the sand (a huge source of emissions), if you are using resins in the sand are you reclaiming the sand (aka burning off the resin to reuse the sand) or are you sending it to the landfill? These are just some of the questions off the top of my hand.”

While the conversation might easily got a little off topic, Jordan kicked off a discussion that I am willing to continue. Being able to identify the most extensive variables to compare technologies is crucial, and we got to admit that maybe LCA, the most-widely used assessment method in this industry, is not always the way to go.

That being said, I would like to remind that these are only the preliminary results. I strongly encourage you to be cautious and to wait for the publication of the final report before drawing your own conclusions.

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