Over the past few weeks, we have made numerous attempts at printing the flexible NinjaFlex material on the FDM printers in the lab. The two printers that we have tried to print on are the Wanhao and FlashForge machines, since they are the only ones capable of extruding the 1.75 mm filament that we have. The results of various printer settings during tests are summarized below:
1. Initially, we tried printing with an extruder temperature of 230 C and bed temperature of 50 C and extruder head speed of 10 mm/s. The printer was depositing droplets of material instead of a constant smooth bead, so the print ended up not being flat.
2. We initially thought the issues in the first test print were with the extruder temperature being too high. For our second test, we dropped the temperature to 220 C. When the print failed again, we opened up the Bowden extruder head and found that the TPE material had buckled inside and wrapped itself around the gears on the inside (see image below). The material was unwrapped from the gears so that the print would work next time. Pictures of the failed prints are shown below as well.
We realized that we needed to keep tension in the material to prevent it from getting jammed in the extruder head. The image below shows how the material sags due to its flexibility as the print progresses. To counteract this sagging and keep tension in the material, we added a counterweight (heavy clip) to the spool so that it would stay taut with each motion of the extruder head as seen in the image on the right.
3. Once we had figured out how to prevent the buckling of the material, we readjusted the extruder head temperature to 240 C based on some recommended settings that we found online (https://talpadk.wordpress.com/2013/10/10/3d-printing-using-ninja-flex-filament/). With these settings of print speed of 10 mm/s, extruder head temperature of 220-240 C, and bed temperature of 50 C, the print began to progress much better with continuous beads and consistent quality. The printer disconnected from the Repetier software numerous times, causing us to have to restart the print on more than one occasion, but we feel confident in the settings to make printing with the flexible material possible. The disconnection was most likely due to a gcode error. Another step was taken to copy the gcode onto a micro SD card to directly input it into the Wanhao, This was left to print over night and the next day the machine dragged the filament off the print bed and gobs of layered TPE filament was solidified to the extruder nozzle, as seen below.
To resolve this issue, the hot end and extruder nozzle were removed from the drive block. The whole assembly, including the fan and heat sink, had to be disassembled. The NinjaFlex was scraped off, although an acetone bath would provide a thorough removal of the plastic. After reconstructing of the FDM extruder, the software produced an error stating that the temperature readout was out of range. After taking the device apart again, it was clear that the thermistor was torn at the ends (below). Unfortunately, this component needs to be replaced for the machine to be operational again.
4. The last attempt to print the NinjaFlex was a flat insole on the FlashForge to remove any support material that may have been giving us print errors. After the STL file was sliced with Cura and the extruder nozzle and print bed reached desired temperatures (235 C and 65 C, respectively), the extruder nozzle path rotated the actual first layer by 90 degrees, which resulted in an unbounded y-direction tool path. The gear continued to force polymer through the nozzle as the filament poured over the print bed. This was attempted three times after changing the flat orientation of the STL file in Replicator G.