Experimental evaluation of the mechanical, dimensional, and surface properties of polycarbonate parts fabricated by injection molding and stereolithography

The choice of process, material and quality of a mechanical parts needs to be strongly investigated because there several parameters, with different effects, to take into account. In this, polycarbonate samples were produced using Stereolithography (SLA) and Injection Molding (IM) to compare their mechanical behavior, dimensional accuracy, and surface quality, supported by Taguchi-based process analysis. Tensile testing revealed that SLA samples exhibited uniform mechanical behavior in all three directions but showed lower elongation at break (8.32%) compared to IM samples, which reached 12.68%. The elastic modulus and maximum stress remained comparable between the two fabrication methods. For the IM process, the holding pressure demonstrated the highest influence on the breaking load with a Delta value of 0.46, while injection pressure was the dominant factor affecting elongation at break, with a Delta value of 4.36. Indeed, dimensional accuracy was evaluated for four geometric characteristics. SLA parts showed lower standard deviations and smaller deviations from nominal dimensions, confirming it as the more precise technique. One-way ANOVA indicated significant differences between the produced dimensions, with extremely low p-values such as 4.2399E-29 for the L3 dimension, demonstrating strong repeatability and consistency in SLA manufacturing. Thus, it is evident that surface roughness measurements performed using a 3D laser microscope indicated that IM parts had considerably smoother surfaces, with roughness values more than 63% lower than those of SLA prints. The measurements showed a shrinkage of the length, while a small positive gap was observed. While IM ensures superior surface finish due to the nature of polymer flow and mold contact, SLA provides higher geometrical fidelity due to its layer-by-layer photopolymerization process. In fact, these findings highlight that an essential trade-off must be considered between SLA offers better dimensional precision, and IM ensures better surface quality. Therefore, the selection between SLA and IM depends on the final component requirements as precision or surface topology and material elasticity behavior are prioritized.