## 2 Materials and Methods
### Design Considerations in D/MA of AM Parts  
Contrasting from the subtractive manufacturing method (retronym for machining processes that sculpts a form by removing material from the initial block material), AM, in general, does not suffer from the sculpting of hollowed-out shapes and undercut issues usually reserved by subtractive manufacturing methods [6; 14]. Also, those 3D-printing technologies that do not require support structures on printing parts, such as PBF (power bed fusion) and BJ (binder jet) allow parts stacking on a single build volume for added productivity both on time and costs [15].  
In AM, measures are taken to maximize the packing density within the job box (i.e., the space within the 3D printer where the actual printing process occurs) to enhance productivity. Packing density is affected by various factors, such as the shape and size of the objects. From a design perspective, protruding parts and unnecessary details are the main factors that decrease the packing density, which should be considered in the design stage. Also, unlike subtractive manufacturing, the anisotropic property of additive manufacturing requires printing orientations to be considered [3; 16], especially when structural performance matters [17]. The PBF 3D-printing process generates a lot of heat, and parts may undergo thermal deformation [18] in the printing and cooling process, depending on the shape of the parts. For instance, parts with uneven thicknesses are more susceptible to heat deformation due to uneven shrinkage in the cooling stage [19]. The productivity of additive manufacturing is influenced more by the size and amount of material used rather than the complexity of the shape. Therefore, methods such as topology optimization to minimize material can be effective on 3D-printed parts [20].  
Additive manufacturing has superior aspects in terms of formability compared to the subtractive machining process. While the formability of CNC is affected by the freedom of the axis, which makes it hard to carve out undercuts and hollow shapes, additive manufacturing is relatively free from such constraints [21]. Additionally, unlike subtractive machining, where material consumption and processing time are heavily affected by the complexity of the shape, additive manufacturing allows efficient shaping without being constrained by the shape. Parts that would need to be made separately using subtractive machining can be designed as uni-body shapes, enabling proactive consideration of DfMA (design for manufacturing and assembly) [22].  
While CNC can handle almost any solid material that can be machined, the material choice in additive manufacturing is relatively limited. The spectrum of material choice becomes even narrower depending on the choices of 3D-printing technology. Anisotropic properties due to defective layer adhesion problems [3; 16] and the reluctant choice of low melting point materials in the case of FDM (fused deposition modeling) to ensure an adequate flow during the extrusion and sintering efficiency in the SLS (selective laser sintering) process pose performance issues of the parts made via the AM method. However, adaptation of high-performance polymers such as PA12 (Polyamide-12) and metal-reinforced polymer composite materials can secure higher structural performance [23], and 3D-printing technologies that can print parts with characteristics close to isotropic are being developed to mitigate material performance issues in the additive manufacturing process [17].