This study proposes a human-in-the-loop framework that integrates operator observations into a large language model (LLM) to control process parameters for defect handling in fused deposition modeling (FDM) 3D printing. Fully autonomous LLM-based control handles ambiguous sensor data poorly and cannot detect abnormal conditions that lie beyond the installed sensors. Operator observations may compensate for these limitations, but their actual impact on LLM decision-making has not been sufficiently validated. We therefore implemented the proposed framework and defined experimental scenarios involving erroneous parameter injection and environmental disturbances. The framework was evaluated in terms of LLM response quality and print quality. The LLM achieved over 80% response quality on the defined evaluation metrics and generated appropriate parameter adjustments, improving print quality by more than 55% on average. Comparative experiments further revealed that, without operator observations, the LLM sometimes failed to recognize defects. These findings demonstrate the effectiveness of human–LLM collaboration and provide a practical foundation for intelligent FDM process control.

The additive manufacturing (AM) process is known to have a major influence on environmental impact. To find out AM process with lower environmental impact in the product manufacturing process, this study compares material extrusion (Fused Deposition Modeling, FDM), powder bed fusion (Laser Sintering, LS) and material jetting processes (Poly-Jet, PJ) for 200 NIST test artifacts, using data from the specification and software of three 3D printers (J750, P770 and uPrint SE Plus), the findings from various literature and Ecoinvent of SimaPro 8.4 database. The results showed that the effects of materials on the environment were the severest for LS (20.45 Pts) and the least for FDM (10.38 Pts) although the effects of power consumption on the environment were severest for FDM (126.91 Pts) and least for LS (20.18 Pts). To reduce the emission to environment in PJ and FDM, it is recommended to improve their printing speed and reduce power consumptions of waterjet and auxiliary equipment for support removal.