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Any new technology, however promising, must be assessed for its environmental sustainability. This applies to 3D printing, also called additive manufacturing (AM), which is being developed as an alternative manufacturing technology in many fields of production. Clean technology is defined in terms of the lifecycle, greenhouse gas emissions, air pollution, toxic materials, and the use of non-renewable resources.
At present most 3D printing is carried out on a small scale. However, it is expanding quickly as tools and materials become more affordable, process quality improves, and innovative techniques emerge.
Comparison of the Sustainability of Some 3D Printing Processes
Thermoplastic extrusion
This application uses a wide range of energy, but through proper designs it can produce self-supporting part designs with low waste. It uses easily recycled plastics like polyethylene terephthalate (PET), poorly recycled plastics like acrylonitrile butadiene styrene (ABS), and polylactic acid (PLA), which is biodegradable but requires special composting.
Inkjet
This technique uses materials like ceramics, plaster, sawdust, concrete, starch, salt and sugar. While it saves a lot of energy on batch printing and reduces waste, the large-scale printing of consumer goods is unviable.
Photopolymer
This process is capable of using multiple liquid polymers, with batch printing associated with high energy-efficiency. It uses more toxic raw materials (but with higher reusability value), often produces less waste, and requires minimal support material. The solidified polymer cannot be recycled.
Laser Sintering
This uses a lot of energy except when batch printing. It is adapted to a wide range of materials including metals, ceramics, thermoplastics, and glass, though slightly less with batch printing. Residual powder can be reused, and support metals recycled, though the support plastic goes to landfill.
Issues with 3D printing
3D printing cannot typically be used to print a whole working object with multiple materials simultaneously. Instead, it produces simple components, to be assembled with other parts. However, experimental multi-material printers are already in existence, and if commercialized, could greatly increase the reach of 3D printing.
The downside is that the use of unlike materials in the same print cycle reduces recyclable potential. A potential green solution is to use more complex parts, avoiding the need for assembly and disassembly, as well as using one or a very few tunable materials to create a whole object.
A third option is using only biodegradable materials, including compostable wiring and incinerable plastics. The environmental impact depends on the consumption of energy and material, which varies with technology, material and frequency of use.
Sustainable 3D printing demands optimization of the period of operation and part geometry. In general, 3D printing is probably better for the environment compared to machining technologies, but injection molding production processes are superior at the same scale. A printer used for only a few hours each week will leave a larger footprint than when used continuously. 3D printing of hollow-core parts is cleaner than solid-block parts, but with machining, the reverse is true.
Another concern is worker exposure to toxic materials with 3D printing, whether at home or in offices, largely due to the absence of safety measures that are routine in industrial situations.
The cleanest processes sometimes produce the lowest quality, however, and green materials for 3D printing like wood, sawdust and salt are often unavailable or unviable.
Resource utilization is practically the same with 3D printing or injection molding. Transportation costs may be only marginally reduced, even with on-site printing, since feedstock shipping is still required. If a single producer were to offer multiple types of 3D printed parts of a single material on demand, only warehousing and shipping costs apply. Even so, this impacts manufacturing costs only slightly.
Clean Advantages of 3D printing
Lean production is a huge advantage of 3D printing, since it eliminates warehousing and work-in-progress costs, and reduces any financial incentive to overproduce, unlike injection molding.
Optimal printer design, with minimal support material, could also reduce waste generation markedly with certain technologies, but not all. For instance, inkjet and fused deposition modelling (FDM) are very low-waste processes.
3D printing is ideal for legacy repair of single components of outdated machines like washing machines or bike parts. This keeps perfectly good machines in continued use, avoiding needless discards or replacement.
3D printed parts may also impart higher use-phase energy efficiency, such as by lessening the component weight in aerospace and transportation applications. Regenerative cooling and fuel efficiency could be optimized by designing complex engine parts for printing like combustion chamber walls containing fluid channels.
Conclusion
At present, injection molding is the most efficient production method for large runs covering hundreds of thousands of parts. Inkjet printing is the 3D printing method with the lowest operating costs due to its use of inexpensive open-source recipes, requiring only operator expertise.
Greenhouse gas emissions are likely to drop steadily if 3D printing replaces injection molding technology globally. However, with current technology, whether 3D printing could replace injection molding technology globally remains a question.
Sources and Further Reading
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