Infrared thermography of welding zones produced by polymer extrusion additive manufacturing

Abstract

In common thermoplastic additive manufacturing (AM) processes, a solid polymer filament is melted, extruded though a rastering nozzle, welded onto neighboring layers and solidified. The temperature of the polymer at each of these stages is the key parameter governing these non-equilibrium processes, but due to its strong spatial and temporal variations, it is difficult to measure accurately. Here we utilize infrared (IR) imaging - in conjunction with necessary reflection corrections and calibration procedures - to measure these temperature profiles of a model polymer during 3D printing. From the temperature profiles of the printed layer (road) and sublayers, the temporal profile of the crucially important weld temperatures can be obtained. Under typical printing conditions, the weld temperature decreases at a rate of approximately 100 °C/s and remains above the glass transition temperature for approximately 1 s. These measurement methods are a first step in the development of strategies to control and model the printing processes and in the ability to develop models that correlate critical part strength with material and processing parameters.

Weld formation during material extrusion additive manufacturing

“…Overall the temperature profiles match those from our earlier work 46 , other modeling 23 , and thermocouple based measurements 49 , typically resulting in cooling rates on the order of 100 °C/s. Note, we do not measure significant reheating of sublayers as subsequent ones are added; this is attributed to the geometry of our sample lacking neighboring layers and long times between printing subsequent layers.…”

“…Similar to our recent work where we describe those techniques, here we print a vertical sheet that is 16 layers high, one extruder width wide (≈0.4 mm), and 200 mm long. 46 We printed over a range of temperatures (from 210 °C to 270 °C) and a range of print speeds (from 3 mm/s to 100 mm/s), where the print speed is defined as the velocity of the extruder assembly along the x-axis. The linear feed rate of the filament into the extruder is directly related to the print speed as is the apparent shear rate.…”

“…IR thermography was recently shown to be an effective means to measure two-dimensional temperature profiles in ME 46 . In this methodology, the temperature of weld zone (W i ) is not measured directly, but is obtained from the average of the layer that is actively being printed (L i+1 ) and the first sub-layer (L i ) or W i = ( L i +1 + L i )/2.…”

“…A detailed description of this process was recently published. 46 We did need to modify the previously published IR thermography protocol for the regime when print speed is below 10 mm/s, which was not previously investigated, see Supporting Information. Data sets for all the temperature profiles used in this work are included in the electronic supplemental information (ESI).…”

Integration of physically-based and data-driven approaches for thermal field prediction in additive manufacturing

“…Seppala and Migler were interested in the cooling rate near newly extruded region and investigated the weld zone properties through side view IR thermography [92]. As summarized in [93], one of the key advantages in applying pyrometry is to collect temperature without physical contact, which makes it possible to monitor surfaces of any geometry.…”