Environmental Sustainability in Manufacturing
By: Justin Hollenbeck
Impact of Traditional Manufacturing
For decades, traditional manufacturing (TM) methods have grown towards higher production rates, higher precision capabilities, and abilities to produce parts of greater geometric complexity and wider material selection. Despite these improvements, the environmental sustainability burden of TM has been exacerbated.
Two predominant categories of monolithic TM exist: subtractive manufacturing (SM) and bulk-forming. SM transforms a solid block of raw material into an end-use part by removing material. During the transformation process, waste products are produced, which creates extra costs and does not generate value for the process. Material waste accumulates through removed chips/expended cutting tools, fluid wastes accumulate through inefficient cutting fluid management, and energy waste accumulate through heat loss and vibration. Higher volume, higher complexity parts are correlated to higher waste products, and, importantly, any part modifications generate as much waste and costs as the original part creation.
Bulk-forming, as used in this article, refers to a process that produces a 3D part by solidification of molten material (plastic, metal, etc.). Bulk-forming (plastic injection-molding, casting, etc.) often requires an initial SM tooling step and incurs the same SM waste products listed above. These waste products and the energy waste of the entire forming process, together, balloon the waste products of one forming production run; yet bulk-forming methods, when employed for high-volume manufacturing projects, can leverage the economies of scale to reduce per-part energy consumption. And though this may appear to be more sustainable, there is often significant waste associated with overproduction (due to high minimum order quantities). Moreover, most TM (SM and bulk-forming) processes require significant up-front capital so are consolidated at one centralized location, often located abroad. This creates significant energy/material expenditures in transport from the subtractive manufacturer to the distributor.
TM waste minimization approaches have been implemented, including reduction/elimination of waste at the source (e.g. within the process itself), improving recycling processes, and improving waste quality. Yet these efforts are largely insignificant and impose additional burdens on the environment. A critical examination of manufacturing methods, in general, is required to effectively strategize towards a more sustainable future.
Impact of Additive Manufacturing
Additive manufacturing (AM) methods have recently emerged as viable alternatives to SM methods in the production of end-use parts. AM uses a variety of methods to create end-use parts by strategically depositing layers of material. Currently, AM alone is unable to achieve the high precision and quality finish of an SM-produced part or the high production rates of forming. However, AM production rates have closed the gap with SM production times, and AM is arguably better positioned than both SM and forming counterparts to satisfy modern geometric complexity and material selection requirements.
Critically, AM is the environmentally sustainable manufacturing solution of the future, as it holds four distinct advantages over SM technology: Material efficiency, resource efficiency, production flexibility, and part flexibility. AM produces little (if any) material waste per part and does not require expendable tooling or cutting fluid processes. Per part, AM technologies impose a significantly less energy demand than the SM counterparts, despite the additional energy requirements for post-production finishing of most AM processes. Material/energy usage is not dependent on part complexity, and, unlike SM processes, any additional design modifications do not inherently impose a significant material or energy burden. The ability to make on-demand products reduces inventory needs and other associated wastes, an advantage over forming methods. Moreover, AM machines are generally smaller than TM machines, and the average cost of AM machines is dropping, enabling manufacturers and designers alike to have AM capabilities in house. This reduces the energy and material required to transport the end-use part to the distributor.
A Sustainable Solution for Traditional Manufacturing
How can TM become more environmentally competitive? The answer lies in the adoption of a more hybrid approach. Hybrid manufacturing (HM) methods combine AM and SM in the one process, enabling subtractive manufacturers to maintain their part quality advantages, bulk-forming manufacturers to maintain their production advantages, and both methods to achieve environmental sustainability initiatives. In making a part, HM machines can deposit material as needed and remove material as needed, leveraging the four key sustainability advantages of AM (listed above) with the key part quality of SM.
With HM capability, a subtractive manufacturer can deposit material using AM methods, minimizing energy and material waste, then machine the resulting part down to precision tolerance and desired surface finish with minimal energy/material waste. A bulk-forming manufacturer can use hybrid manufacturing for tool building, which reduce tooling costs, enable tighter MOQ optimization, and minimize overproduction. Any design modifications can be quickly carried out at minimal cost, and complex part designs that are energy and material expensive with TM methods alone, like a multi-material, monolithic part, can be produced. Further, modern HM technology is priced competitively to AM technologies, easily integrates with existing SM machinery, and has a fast learning curve. It is no surprise that HM technology is growing quickly in the manufacturing industry.
What’s on the Horizon?
In terms of environmental sustainability, AM technologies available on the market today are not all sunshine and roses. A significant amount of metal powder is often wasted in metal powder bed AM methods. Energy systems employed to create the metal powders and wire are still inefficient in material and energy usage. And, while not related directly to environmental sustainability, operator safety standards have only recently been established and need to be examined thoroughly before any long-term health effects of AM emerge.
Despite these obstacles, the manufacturing industry is striving for a more sustainable future. Led by advancements in AM technology, manufacturing is proving to be an agile sector, increasingly able to supply products with minimal material and energy waste. Recent advancements in HM technology have opened the door for subtractive and bulk-forming manufacturers alike to expand their (and their clients’) design freedom and step into a brighter, more environmentally sustainable future.