3D Printing TPU (thermoplastic urethane) and other flexible materials is notoriously difficult. Flexible materials are difficult for an extruder to push through the hotend. In order to be successful, you need the right extruder setup and the right print settings.
Proper Extruder Setup
A fully constrained filament path from the extruder drive gear to the hotend is essential when printing flexible filaments. If there are any air gaps in the path the filament travels to the hotend, it will bend out of the way.
The extruder setup on the Powerbelt3D Zero uses a short teflon tube to the hotend. It is important to make sure that the teflon tube is cut so that it can be positioned as close to the extruder drive gear as possible.
Flexible Filament Print Settings
Flexible filaments generally need to be 3D printed slower than rigid filaments. By printing slower, the filament is able to be pushed and melted in the hotend successfully. We chose 30mm/s.
If the print settings are set to be too fast, the flexible filament can compress in the cold side of the hotend. This causes the extruder motor to “skip” and a clicking noise can be heard. The plastic will not extrude out of the nozzle where it is supposed to, and the built up pressure in the hotend can cause it to ooze out in the infill of the part, or during travel moves.
No (Minimal) Retraction
Flexible filaments like TPU are more sensitive to extruder movements. We would recommend no retraction, or minimal retraction (~0.1mm). Using no retraction avoids rapid small extruder movements that could cause small gaps in 3D printed layers. Printed parts with too much retraction are weak, and can have wispy strings of plastic where they aren’t supposed to be.
3D printing flexible filaments like TPU can be challenging. With but the right print settings and proper extruder hardware, it can be painless.