Over the past few years I have been to a few presentations by HP on their Jet Fusion technology. By most metrics, Jet Fusion is the most-efficient and highest quality additive manufacturing technology. However, the current systems cost over 100k USD. This means for small-run and distributed manufacturing, FDM additive manufacturing is probably the best option. I’ve recently been interested studying the economics of small-scale and localized 3D Printing.
This first post is a study of the ecology of 3D printing, primarily focusing on FDM and net CO2 emissions. In a second post I will discuss the engineering and bottom-line efficiency of different 3D printing technologies.
FDM and the Environment
The RepRap project, aside from being an interesting project in the application of open source hardware and distributed manufacturing, has its roots in environmentalism. The team saw local production as a mechanism for reducing dependence of supply chains and industrial manufacturing. Early in the project the team evaluated several different materials for 3D printing such as ABS, Polypropylene (PP), Polycaprolactone, and Poly Lactic Acid (PLA). It was discovered by the RepRap project that PLA was an ideal material for printing dimensionally accurate objects and met the environmental objectives of the project as well. In particular, PLA is synthesized from food starch and without the use of any fossil fuels. This allowed the team to explore local synthesis PLA from locally-sourced agricultural by-products, furthering the objective of distributed production. Similarly, it has been discovered in 2009 by a team at the Korean Advanced Institute of Science and Technology that PLA can be synthesized using genetically engineered bacteria, further reducing the dependence on industrial manufacturing processes. In 2016 it was announced that the French company CARBIOS is bringing this process to commercial production to address the 15% annual increase in demand for PLA. In the graph below, we can see that the carbon emissions associated with PLA are roughly 1/3 to 1/10 of the comparable emissions of traditional plastics. For all bioplastics the demand has grown from 0.9 million tons in 2009 to 5.3 million tons in 2019.
Complexity and 3D Printing Efficiency
A 2013 study by Michigan Technical University by Pearce, et. al. showed the environmental lifecycle of 3D printing at the small scale. In this study they compared injection molding with a sub $1000 RepRap 3D printer. In this study the team evaluated a baseline solid block, waterspout, and fruit juicer for overall energy demands of production and transportation in the case of injection molding over 3000 miles. The team showed that for low-complexity components, the RepRap 3D printer was an inferior manufacturing method regarding emissions, unless the fill density of the component was reduced. However, for a high complexity component, such as the waterspout, the emissions from 3D printing were a fraction of those found in conventional manufacturing. In this way, complexity in 3D printing is low-cost and allows for efficient manufacturing. The team also noted that localized manufacturing allows for the control of energy sources, and it is much easier to run a local 3D printing operation off a solar panel than it is to run an industrial scale injection molding facility and supporting logistics system off green energy. In the case of using 3D printing with photovoltaics, the emissions were roughly 29% less in the case of the block and 84% less in the waterspout. In the figure below we can see the varying fill rates of the block. In the chart, the energy demands of the block and waterspout, respectively, are compared to injection molding with varied infill rates and energy sources.
Recycling with 3D Printing
Recycling is a critical are where 3D printing can help mitigate greenhouse gas emissions. Traditionally, recycled plastic is difficult to sort at large volumes. This leads to most of the plastic collected by municipalities for the purpose of recycling being sent to landfills and incinerators. A study at the University of Georgia estimated that only 9% of global plastic production is recycled, 14% incinerated, and 79% landfilled or littered. In the same study, this problem is attributed to the relatively short service life of plastic goods used from things such as disposable cutlery, packaging, and electronics. However, one of the benefits of thermoplastic, is that it may be reformed several times. Similarly, plastic production is growing rapidly. Despite this tremendous growth, the Royal Society of London estimates that only 4% of global petroleum demand is used for the production of plastics. A study of greenhouse gas emissions in the production of plastic drain covers showed that the emissions are 36% lower when using recycled material.
One of the most common concerns of recycled plastic is that it no longer retains its material properties. Since plastic is a polymer, it is made of long chains of monomers which are attached together. Over several thermal cycles these polymer chains begin to break apart and degrade. Several studies have shown that successive thermal cycles of plastic can degrade the tensile strength roughly 5–30%. This variation in recycled plastic properties makes it difficult to account for the final mechanical strength of a component. However, for bespoke manufacturing where the mechanical properties can be tested, this make recycling somewhat simpler. Recycling provides somewhat marginal benefits in the overall greenhouse gas emissions associated with production and consumption. The most immediate concerns are more directly related to the pollution of the goods themselves, rather than the energy consumption of their production. However, 3D printing can provide a mechanism for alleviating some of the above by shortening supply chains and allocating materials by their required mechanical properties.