Читать книгу Metal Additive Manufacturing - Ehsan Toyserkani - Страница 27

Beyond the undisputable process flexibility of AM technologies, it also offers several major environmental benefits if the process chain and designs are properly developed. According to Diaz et al., manufacturing activities are responsible for 19% of the world's greenhouse gas emissions and 31% of the US total energy usage [33]. AM technologies are usually greener than conventional methods because there is less material wasted, and there may be up to 50% energy savings during part production [34]. However, it is only true if a full cycle assessment is conducted on the AM‐made part to ensure its design is fully optimized for AM. Moreover, metal‐based AM technologies virtually eliminate machining and the subsequent need for toxic cutting fluids; costly pollutants that presently are challenging to dispose of and have a negative environmental impact [33]. Besides, AM parts can bring about weight reductions in the range of 50–100 kg per aircraft. This will result in a significant reduction in fuel costs, based on the fact that for every kilogram removed from every aircraft in a fleet of 400 commercial jet‐liners (Ex: Air Canada), annually reduces consumption by 60 000 liters.

Figure 1.19 MX3D smart bridge (a) main structure (b) side wall.

Source: Courtesy of MX3D [32].

Across the globe, manufacturing sustainability has become a crucial factor for the supply chain on all fronts. Companies are seriously working on the waste reduction, efficiency improvement of operations through the integration of AM and digitization to comply with their environmental and social obligations.

AM companies are commuting to be a major part of this adventure. Metal AM manufacturers are announcing their commitments to promote sustainability and safety through the minimization of waste, enhancement of material chemistries for safety, utilization of less energy, usage of less labor, and reduction of consumables.

AM is widely used in the repair sector to improve environmental footprint due to time and material‐intensive traditional methods. Local manufacturing that is possible by AM is promoting firms' efforts to come closer to the circular/localized economy concept, an idea that fosters the optimum use of resources to avoid waste while minimizing gas emissions and energy demands.

Many companies are developing blueprints highlighting their commitments for the goals mentioned earlier. For example, the Global transit manufacturer Wabtec recently released its 2020 Sustainability Report [35]. When the report highlights several activities being undertaken by the company to improve its global environmental performance, it pinpoints the integration of AM processes such as binder jetting for sustainability by producing lightweight transportation components.

In all front of these commitments, a thorough analysis must be done to ensure metal AM is sustainable for making specific parts. Metal AM is not usually sustainable for making conventional parts that are not optimized for AM. It is recently reported by the Additive Manufacturer Green Trade Association (AMGTA) that metal AM has a higher carbon footprint per kilogram of the material used in the process compared with its counterparts processed by conventional methods while considering direct manufacturing processes exclusively [36]. This report is based on nonoptimized geometry when conventionally designed parts are directly printed without any geometrical and process optimization. However, as known, the design features have a major impact on the CO₂ footprint. When machining a block of material for simple geometries would be preferable, AM will be much appealing for making parts with hollow shells, lattices, features with complex curvatures and internal conformal channels. Thus, the sustainability of the use of AM has a direct correlation with the complexity of geometry. A simple but effective study was carried in [37], shedding light on the sustainability of AM and its CO₂ footprint when three different geometries made from Ti‐6Al‐4V by electron beam AM and machining were analyzed as shown in Figure 1.20. The surface finish was also a part of this analysis when the analysis considered the CO₂ footprint for gas atomization of powders required for AM as well as ingots required for processes. As seen in the figure, the energy demand and CO₂ emission for AM are higher than of the machining if the geometry tagged as ID1 is produced. It is evidence that metal AM at its current form is not a sustainable solution for simple geometries without any internal features.

Figure 1.20 (a) Three different geometries made of Ti‐6Al‐4V by different processes, (b) primary energy demand, (c) CO₂ emissions. Transportation cost is neglected.

Source: Republished based on CC BY 4.0 open access [37].

In contrast, for the geometry tagged as ID3 that features some complexity in the internal channel, metal AM offers a substantial improvement in terms of CO₂ emission and also energy demand compared with its counterpart produced by machining. The geometry tagged as ID2 that features simple internal channels, metal AM and machining both have more and less identical energy demand and CO₂ footprint.

In summary, it is extremely important to do a thorough analysis of the sustainability of metal AM upfront to understand the benefit of the process for specific geometry. In addition, life cycle assessment studies are needed to quantify the impact more precisely. The full product life cycle from production to overhaul must be included in the analysis.