## 1 Introduction
Energy consumption and environmental impact were measured and compared for both FDM and plastic injection molding (PIM) processes using standard dog bone specimens (ASTM D638 Type IV) made of polylactic acid (PLA), using an in-house Ultimaker S3 FDM 3D printer and a Morgan Press G-125T electric injection molding machine. It was found that approximately 99% of the total energy in FDM was consumed during the printing phase, while injection molding consumed about 38.2% less energy and produced lower carbon emissions compared with FDM [18]. The mechanical and thermal properties of recycled thermoplastics and composites have also been investigated using FDM-based 3D printing methods. Recycled plastic materials, including PLA, ABS, and PET, were processed into filaments using different types of extruders, followed by mechanical tests, including tensile strength evaluations. It was shown that the mechanical performance of recycled materials can be improved by optimizing additives and processing parameters, demonstrating that sustainable plastic recycling can be achieved through the judicious use of FDM technology [19]. Extensive research has been conducted comparing parts produced by injection molding and FDM, particularly regarding their mechanical properties. A study evaluating ABS, nylon 12, and polystyrene materials using both rapid prototyping and injection molding methods assessed properties such as dimensional accuracy, tensile strength, water absorption rate, Shore hardness, and microscopic structure. The findings revealed significant discrepancies between the two manufacturing methods [20]. Moreover, investigations into complex part geometries, such as integrated hinges in polyamide (PA) injection-moldedcomponents, demonstrated that weight distribution and mechanical properties are highly dependent on part geometry, sometimes leading to unexpected results [21]. Further comparisons of PLA, ABS, and nylon 6 components produced via FDM and injection molding confirmed that FDM-produced samples generally exhibit lower mechanical properties but higher crystallinity for PLA and nylon 6 [22]. In contrast, studies assessing PLA parts with varying infill densities produced by FDM suggested that 3D-printed samples may, in some cases, surpass injection-molded counterparts in terms of mechanical and thermal properties [23]. Mechanical properties of ABS thermoplastic components produced by Fused Deposition Modeling (FDM) and injection molding have also been comparatively studied. Tensile strength tests were performed on standardized dog-bone-shaped samples with varying cross-sections, printing orientations, layer thicknesses, contour layers, and infill densities [24]. Similarly, the mechanical properties of short carbon fiber-reinforced polyamide 6 (PA6) manufactured by Fused Deposition Modeling (FDM) and Polymer Injection Molding (PIM) were investigated. Tensile, compressive, and flexural tests were performed to evaluate the effects of manufacturing processes on fiber length, microstructure, and mechanical behavior [25]. As 3D printing technology continues to evolve, its influence on manufacturing practices and material properties remains a focal point of research. While additive manufacturing enables greater design flexibility and customization, challenges related to mechanical performance, process optimization, and environmental considerations must be addressed to fully harness its potential in industrial applications. In recent years, the toy industry has increasingly adopted desktop 3D printers for prototyping, customization, and small-batch production. However, most toys are not purely decorative; they are routinely handled, dropped, and subjected to mechanical stress during play. Therefore, it is crucial to evaluate not only the aesthetic aspects of 3D-printed parts but also their mechanical performance, dimensional accuracy, and surface characteristics.