| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 106 === Among many 3D printing technologies, Fused Deposition Modeling (FDM) is more popular than other types of 3D printers, due to its low cost and small size. Recent studies have shown that fused deposition modeling (FDM) type 3D printers have high emission rates of the ultrafine particles (UFP) and volatile organic compounds (VOCs) in the printing process, which can cause indoor air pollution and health risks. The thermal decomposition of commonly used thermoplastic filament materials, such as ABS and PLA, due to the operating temperatures of nozzle at 230°C and the bottom plate at 110°C is the main source of the emission. Many existing studies are focusing on the pollutants emitted to the external environment but ignored the problem of particle distribution inside the printer. In this study, the flow inside a FDM printer is investigated by flow visualization and numerical simulation. For flow visualization, a 1:1 transparent acrylic printer model is used with exactly the same components such as the heater plate, extruder module installed in real printer models. Using oil mist as tracer particles and illuminating with laser sheet, the internal flow field can be observed in order to understand the distribution of the ultrafine particles during the printing process. ANSYS FLUENT is used for the CFD numerical simulation. The nozzle and heater plate were set to 230°C and 110°C and the flow from of the cooling fan of the extruder module is set by the fan P-Q curve for simulation. The experimental results from flow visualization are compared with the simulations. The results show that the extra aluminum block at the center of the two-step motor reduces the backward recirculating region compare to the previous study. Because the main particle emission is near the nozzle while the fan is cooling the extruder module, the downward jet caused by the gap below the extruder module spreads out the particles. The lateral jets created by the fins also bring the particles to both sides and speed up the overall internal air circulation. These results suggest that it is helpful to separate the cooling fan area from the printing area and collect the pollutants from the printing area, because it can effectively avoid pollutant spreading by forced convection. Lastly, results from changing the heater plate position show that at the upper heater plate position (Y=190mm), the spread of the particles is stronger due to the downward flow impinges on the heater plate which creates faster side flows than the lower heater plate position (Y=30mm).
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