## 3 Measuring the benefits and costs of applying the technology:
#### 3.3.2 Environmental Impacts of AM  
Various research on the environmental influence of these processes was performed 10 years after the first generation of AM machines. Although AM has many benefits, such as freedom of design, flexibility, and sustainable advantages, it also has a minor environmental impact on industrial development [142]. Therefore, the environmental investigation is an essential issue in the AM industry based on regulations leading manufacturing productions and end-of-life disposal of products and growing demand for environmental certification requirements (ISO 14000) worldwide. Numerous studies indicate that AM has a great potential to considerably decrease environmental impact and energy per unit of Gross Domestic Product (GDP) [143; 144; 145]. In fact, AM carries the potential to diminish the carbon footprint by optimizing designs and the decrease in the waste flow [30]. By 2025, carbon dioxide (CO\({}_{2}\)) emissions are estimated to be 130.5-525.5 million tons (Mt). In this respect, lightweight components, which is produced by AM, play an important role to reduce the energy consumption of the AM process [135]. As reported by [PERSON] et al. [146], an optimal design would save the material usage up to 40%. This fact is more important when we know that a 100 Kg reduction in the weight of a long-range airplane leads to 2.5 million dollars in saving in fuel consumption and 1.3 Mt CO\({}_{2}\) savings during the aircraft's lifetime [30]. The environmental impact of AM can be investigated mainly in three features [117] (see Figure 9) as follows:  
* **Resource consumption:** In AM, material and energy consumption represents the principle resource consumption. Conventional manufacturing compared to AM consumes more materials but the energy consumption would be relatively higher due to the lower production size of products [147; 148; 149], especially for AM processes that include its processing at high-temperature [117]. * **Waste management:** subtractive manufacturing processes produce a large quantity of waste in order to produce a product, which may be reduced by 90% while using AM [150]. This means that AM generates less waste. * **Pollution control:** compared to subtractive manufacturing processes, AM eliminates the use of harmful chemicals, e.g., casting release compounds, cutting fluids, and forging lubricants. [PERSON] et al. [151] studied different environmental impacts in AM, e.g., energy consumption, material preparation, recycling, material toxicity, and landfilling. Numerous studies also show that a comprehensive study on AM helps not only in identifying and preventing negative environmental effects but also in enhancing the satisfactoriness of AM technology. Nevertheless, studying an interdisciplinary technological area, understanding the environmental impact and energy of AM according to the life cycle outlook is really challenging. A variety of approaches were considered to evaluate environmental impacts, such as environmental impact scoring systems (EISS), life cycle analysis (LCA), and design for environment (DFE) [30]. LCA,established in the 1990s and developed by the Society of Environmental Toxicology and Chemistry (SETAC), is an internationally recognized technique to systematically evaluate the environmental impacts of different industrial products, processes, and activities [152; 153]. The LCA method, compared to other approaches of environmental impact assessment such as Design for Environment or Carbon Assessment [154], has a capability to quantify precisely and with diverse criteria, the environmental effect of a global system. This method has been normalized by SETAC and UNEP (United Nations Environment Program) under the standard ISO 14,044 [155]. According to ISO 14,040 [156], LCA consists of four steps. These steps will be performed in a framework, as shown in Figure 10. In the primary step, the goal and scope of the study and the restrictions have to be specified.