# Process-Dependent Influences on Adhesion in Multi-Material Extrusion
## 3 Specimen Manufacturing and Experimental Setup
### Fluctuations in Nozzle Placement of Tool-Changing Printers  
In order to determine the effect of tool switching on relative placement of the extrusion nozzle in z-direction, the following two different printer architectures were investigated: an E3D Toolchanger (E3D, Oxford, UK) with four Hemera direct extruder tools and a customary Ultimaker 3. The former has an independent tool head with a coupling mechanism that can pick up each tool with a dedicated tool plate, which is centered on the tool head by three guides on the head side and three corresponding balls on the tool side. Other printers with similar architecture exist on the market; however, the manufacturers typically give no concrete numbers on the repeatability of such systems, which makes experimental investigation necessary. The goal of such an investigation is to determine the magnitude of fluctuation and eliminate it as best as possible in order to repeatably manufacture multi-material specimens with the exact properties. On the other hand, the Ultimaker 3 printer uses two print cores, one of which can be mechanically switched between an idle and an active position. While in the idle position, the nozzle sits higher than the other currently active nozzle in order to avoid collision with the printed part. In the active position, the nozzle is lowered to sit underneath the inactive nozzle, and the distance is compensated by lowering the print bed by the appropriate amount. Once again, similar architectures exist, yet no discrete number on the deviation of the switching mechanism is usually given, which makes experimental testing necessary. While multi-material printer architectures with a single nozzle exist and eliminate the possible problem of inaccurate tool switching, they might have other problems like contamination inside the nozzle and are not part of this investigation. In order to determine the fluctuations in nozzle height after a tool change, each extrusion tool was carefully calibrated beforehand in the z-direction using a thickness gauge. While this or a similar process is typically used in calibration of MEX machines, the precision of this process is quite low. Subsequently, rectangular single-layered structures were manufactured on both machine architectures and their thicknesses were determined using a Mitutoyo ID-B1005 (Neuss, Germany) linear gauge (repeatability of 0.01 mm (MPE) and maximum permissible error of 0.02 mm (MPE) over a range of 5 mm). Using the gauge, the difference in distance between the center of the structure and the build plate right beside the structure was determined. With perfect calibration, this measurement would ideally be equivalent to the initial layer height chosen in the slicer. In reality, it deviated by the amount of miscalibration plus any possible deviations of the switching mechanism. Since the miscalibration should stay constant as long as homing is not performed, repeating the measurement should make distinguishing of these two influences possible. Hence, the experiment was conducted 10 times on each tool of the E3D Toolchanger, as well as the switching nozzle of the utilized Ultimaker 3, and each singular measurement was repeated 10 times. The tool switching mechanism was activated ten times after each test and the structure was removed before the next shape was fabricated at the exact same location. No homing was initiated in between the measurements. The results showed that while the accuracy of the measurements was at least 0.01 mm, the position of each Toolchanger (E3D) tool randomly fluctuated by \(\pm\)0.02 mm. On the other hand, the position of the Ultimaker nozzle slowly moved further away from the print bed between each measurement, adding up to a total of 0.04 mm over the 10 data points, while two consecutive measurements never differed by more than 0.01 mm. This suggests a non-constant miscalibration with low fluctuation. The precision of calibration was determined to be around \(\pm\)0.03 mm at most.