## 4 Results and Discussion
### Quantitative Analysis of the Impact of AM, Lean and Green Manufacturing  
[PERSON] et al. [67], in their work on the environmental impact of additive manufacturing processes, found environmental and energy improvements between 36 and 75%. [PERSON] et al. [101], while investigating the remanufacturing of turbine blades by laser direct deposition, found reductions in the carbon footprint and energy savings by approximately 45% and 36%, respectively, compared to the replacement of the turbine blades with a new component. Existing studies that considered the cradle to gate indicated that the weight of a product manufactured via AM can hypothetically be reduced to approximately half via topology optimization, thereby resulting in a 25-58% reduction in the energy consumed and 60% reduction in climate-change-related impact during manufacturing [73; 131; 132]. For automotive and aerospace parts manufactured via AM, existing studies indicate the feasibility of energy savings during the use stage, resulting in a reduction in the environmental impact by 11-20% over the life cycle [70; 133]. [PERSON] et al. [134] found a 12-47% reduction in the environmental impact for different part geometries produced using wire arc additive manufacturing (WAAM) due to its suitability for manufacturing complex part geometries when compared to CNC milling. Similarly, [PERSON] et al. [135] achieved an average reduction of 20% in the environmental impact by reducing the assembly operations for the design of a train floor attachment through binder jetting. [PERSON] et al. [136] conducted a life cycle and environmental performance analysis of directed energy deposition and welding operation for the repair of a casting die. The outcome of the study shows a 12% reduction in CO\({}_{2}\) emissions when using AM, compared to the traditional welding operation. [PERSON] et al. [137] investigated the energy and carbon-saving potential of wire arc additive manufacturing for the repair of mold inserts and found that energy consumption and CO\({}_{2}\) emissions could potentially be decreased by 26% and 32%, respectively. Secondly, AM allows the recycling of polymer-based products [44]. However, the recyclability potential of various AM materials differs [138]. [PERSON] et al. [139] stated that some unused metallic powder during the AM process can be used for the same application up to eight times after sieving, though with lower quality each time. However, [PERSON] et al. [140] indicated that the repeated recovery and reuse of AM materials is not applicable to all materials, for instance, titanium and aluminum alloys, due to reactivity with environment conditions. This may result in a loss of approximately 20% to 25% of the recycled metal powder in the process. [PERSON] et al. [141] conducted a comparative analysis of the lifecycle of the industrial repair process of gas turbine burners using traditional machining and additive manufacturing, specifically selective laser melting (SLM), with an emphasis on the energy, resource and recycling analyses. The results show a potential for reduction in the depletion of abiotic resources by 50% for the SLM and 83% for traditional machining during recycling. The authors further indicated that it is difficult to achieve a reduction in costs and material losses in metal powder production. Thus, the metal powder production process is less cost effective both in installation and operation as frequent waste treatment is required before disposal. On the contrary, with wire-based metal additive manufacturing, a higher feedstock efficiency within the range of 93-98% could be achieved with the potential of reducing the overall waste generated during AM by approximately 30% [142; 143]. Recycling helps to reduce the quantity of polymer waste in landfills and marine habitats [103]. Some of the polymer materials used are biodegradable; hence, they do not degrade the environment at their end-of-life state [100]. Thirdly, AM can be used to make products on demand.