# A Knowledge Graph Framework to Support Life Cycle Assessment for Sustainable Decision-Making
## 4 Case Study: 3D Printing
### Domain Expertise of 3 DP  
In the first step of the methodological framework, a basic understanding of the 3 DP process of a product should be established. In this case, the understanding was archived mainly through a literature review. In our earlier publication [56], we presented a preliminary examination of the 3 DP process. This current study builds upon that by adding further details to each stage of the product life cycle and by including more information and further studies. The **engineering phase** marks the commencement of the process, encompassing both the design formulation and the choice of materials. During the preliminary phase of 3 DP,the design is developed, often utilizing advanced software to design and fine-tune complex geometrical structures [57]. Engineers utilizing a 3D design software, known as computerized design (CAD) software, or a 3D scanner, have developed this design, serving as the foundation for production. The final output needs to be a closed-volume model with specified dimensions of height, depth, and width [58]. Instead of conventionally using CAD software, it can be beneficial to combine 3D laser scanning with rapid prototyping, highlighting improvements in costs, speed, and accuracy over conventional methods [59]. Furthermore, integrated 3D scanning with reverse engineering can be effective for quality control in the manufacturing of rapid-response products [60]. To make certain the design is feasible, both designers and engineers need to evaluate the capabilities and limitations of 3 DP technology. For instance, in multi-material 3D printing, they contribute to the production of functional materials that possess complex microstructural characteristics [61]. In addition, the printing technique must be selected during the creation procedure [58]. Furthermore, the engineer must give careful thought to the integration of various additives, the selection of appropriate post-processing techniques, and the formulation of an effective design strategy. Following the creation of the design, suitable materials are chosen, based on specific application requirements, taking into account mechanical properties, printing speed, and resolution [62]. Materials scientists and engineers play a crucial role in the selection of appropriate materials that meet the requirements [63]. The materials could differ between metal, paper, and plastic [58]. The following activities are part of **pre-processing**. The 3D-CAD-model has to be exported as a net consisting of triangles. The common file formats are STL for daily use and IGES or STEP for use in industry. After that, the new model has to be checked for printability, focusing on the units of dimensions and the orientation of the net's normal vectors. These steps could be performed using software. For production, this file has to be transferred to computer-aided manufacturing (CAM) software, called Slicer; through multiple steps, this program creates a CNC code that could be executed via a machine [64]. During the slicing stage, there is the possibility to fine-tune a multitude of parameters within the software for an enhanced outcome. Fundamental configurations are adjustable, such as the height of the individual layers, the density of the infill pattern, the velocity at which printing occurs, and the thickness of the walls. Furthermore, the software provides advanced configurations that allow for an optimized process [58; 65]. The majority of 3 DP methodologies necessitate the inclusion of support structures, which are systematically integrated into the workflow using the slicer as part of the pre-processing phase [58]. The **printing process** involves layer-by-layer material deposition to produce the physical object. This process uses a range of printing technologies, each chosen based on the material used and the complexity of the design [66].