How Sustainable is Metal 3D Printing? AMGTA’s First Report Says “It Depends”

Two months after commissioning the first research project on the environmental sustainability of metal 3D printing, the Additive Manufacturer Green Trade Association (AMGTA), a global trade group created to foster and promote the environmental benefits of additive manufacturing (AM), published a literature-based systematic review. The paper, titled, “State of Knowledge on the Environmental Impacts of Metal Additive Manufacturing” synthesizes existing academic literature comparing the environmental impacts of metal AM with conventional manufacturing methods.

According to the study’s co-authors Jeremy Faludi, Assistant Professor of Design for Sustainability at Delft University of Technology (TU Delft) in the Netherlands, and Corrie Van Sice, Manufacturing Sustainability Research Engineer also at TU Delft, metal AM would not be a more environmentally sustainable choice for many industrial applications, based on existing literature. But there are several applications where AM is a more sustainable choice, and these appear to be the industries where it is currently being used most, namely aerospace.

A 3D printed component of the GE Catalyst engine used in Cessna Denali aircraft that was reduced from 855 parts to just twelve. Image courtesy of Nick Hurm/GE Additive

Savings per kilogram of aircraft mass could, in turn, save between 134 and 200 gigajoules of fuel energy over a typical 30-year commercial aircraft lifespan. Based on researched literature, the study considered that replacing 9% to 17% of fleet-wide aircraft mass with lightweight AM parts made from aluminum-, nickel-, titanium-, and steel-alloys could offer cumulative emissions savings estimated at between 92 to 215 million metric tons of carbon dioxide through the year 2050 because of a 6.4% fuel reduction.

The paper states that “it is an environmental benefit when resource-intensive materials such as titanium are greatly reduced, or when lightweight designs enabled by AM result in significant energy savings in the use phase. However, because it is unclear where these benefits will be strong enough to overcome the increased processing energy, much more research is required to enable modeling and prediction to support decision-making.”

Grade 23 titanium spine, hip, and knee sample implants by Tangible Solutions via SLM and CellCoreGmbh nichrome alloy rocket engine thrust chamber via SLM. Image courtesy of SLM Solutions

The AMGTA was launched in November 2019 as a non-commercial, unaffiliated organization open to any AM or industry stakeholder that meets certain criteria on production or process sustainability. Leaning upon founding members Sintavia, LLC, a metal AM service provider; Taiyo Nippon Sanso Corporation, supplier of stable industrial gases, and QC Laboratories, a material testing laboratory, AMGTA is trying to shed light on a sector that needs to learn more about its eco-footprint and what it will need to focus on in the future to become more sustainable.

The importance of publishing sustainability reports for the industry is rising as 3D printing companies become increasingly more worried about assessing and quantifying their progress toward zero emissions, reducing carbon footprint, and other goals. The AMGTA’s objective is to serve as a key resource to educate the public and industry about the known positive environmental benefits of the technology, but also to help develop industry best practices, and to promote the adoption of AM as an alternative to traditional manufacturing. But for that to happen, it is focusing on consistent reporting methodologies about the true sustainable nature of 3D printing.

The AMGTA’s inaugural sustainability report identified areas where information is sparse, unclear, and needed while summarizing current knowledge. According to the information presented, while AM generally has much higher carbon footprints per kilogram of material processed than conventional manufacturing, when considering the direct manufacturing process itself, impacts depend greatly on part geometry. For example, a solid cube will be a much lower impact to produce by machining, while a hollow shell or lattice can be a lower impact to produce by AM.

An Inconel 718 aircraft engine bracket redesigned and optimized for AM, cutting jet fuel usage dramatically. Image courtesy of Sintavia

Literature found by the authors corroborates this, especially that the electrical energy intensity of AM generally (not only metal) was between one and two orders of magnitude higher than conventional machining and injection molding, and processing speeds were three orders of magnitude smaller. Suggesting that AM is usually a less sustainable choice than casting, extrusion, rolling, forging, or wire drawing. To beneficially replace those processes, the report suggests that there should be situations where AM greatly reduces part mass, combines multiple conventional machining processes, or avoids tooling for short production runs.

The report further recognizes the need for additional life cycle assessment (LCA) studies to quantify environmental impacts, especially direct comparisons of AM to machining, and especially for technologies such as binder jetting and directed energy deposition (DED). These LCAs should ideally also include more of the product life cycle, described the authors.

“No one should expect metal AM to be a more sustainable way to manufacture basic metal parts given the focused energy inherent in laser melting, but AM should present a more sustainable course for manufacturing finished precision components,” indicated the AMGTA’s Executive Director Sherry Handel. “These findings validate the AMGTA’s plans to provide the industry with rigorous, independent, and ongoing research. The AMGTA will continue to commission studies and publish research findings in an effort to update the industry and other key stakeholders on what our eco-footprint is now and what we will need to focus on in the future to be more sustainable.”

As for a possible solution to reducing the environmental impacts of metal AM, the authors found that replacing the metals that require melting with new materials that bond chemically at ambient temperature could help. However, “such replacements would require great advances in material development to match metal’s functionality.” For now, it is clear from the report that AM is environmentally beneficial where tooling is avoided for low part quantities, high-embodied-impact materials (like titanium) are saved, design optimization improves performance in the use phase and that use phase dominates lifetime impacts, and remanufacturing extends the life of high-value components

Additionally, the AMGTA addressed the health hazard of using metal AM powders, as some of them pose serious toxicity risks. The authors found that most metal powders studied have the potential for causing allergic skin reactions, damage to organs after prolonged exposure, cancer, and are harmful to aquatic life. “Nanoscale particles can be generated, and while general dust inhalation hazard seems to be low given machine enclosures and ventilation, smaller particles may pose toxicity risks to workers because of their ability to pass biological barriers.” Here, The authors suggested that workers exposed to nanoscale metals should do regular biological monitoring, such as urine analysis, to watch for toxic exposure and that more research is still required on the workplace health hazard of metal AM powders.