Working with flexible filament, such as TPU, is challenging.
One of the main challenges of working with TPU filament is its high elasticity and low rigidity. This means that TPU filament can stretch and bend easily, which can cause problems with extrusion, retraction, and feeding. It can be similar to trying to push rope. It is advisable to reduce the retraction distance and speed, as well as the print speed, to prevent stringing and oozing.
Another challenge of working with TPU filament is its sensitivity to temperature and humidity. TPU filament can absorb moisture from the air, which can affect its print quality and performance. Moisture can cause bubbles, cracks, and warping in the printed objects, as well as increase the risk of nozzle clogging. To prevent these problems, it is essential to store TPU filament in a dry and cool place, preferably in a sealed bag with desiccants. Moreover, it is recommended to use a heated bed and an enclosed print chamber to maintain a stable temperature and avoid drafts.
A third challenge of working with TPU filament is its adhesion to the print surface. TPU filament can stick very well to some surfaces, such as glass or PEI, but not so well to others, such as blue tape or BuildTak. This can result in either poor bed adhesion or difficulty in removing the printed objects. To solve this dilemma, it is helpful to use a thin layer of glue stick or hairspray on the print surface to improve the adhesion. Alternatively, it is possible to use a flexible or magnetic build plate that can be easily detached and bent to release the printed objects.
One final challenge that I’ve experienced is that some TPU (or filaments with TPU in them) tend to expand when heated up. I normally like to warm up my machine for a few minutes before beginning a print. This allows for any expansion and movement to happen while the machine is sitting idle, rather than while the machine is printing. However, I’ve found that some TPU based filaments will burn and end up leaving burnt pieces in the nozzle, which end up clogging it. For TPU based filaments, I prefer to retract the filament approximately 100mm, then warm up the nozzle, and include a line of code in the beginning of my file that feeds the filament back into the nozzle. For this same reason, I also like to do a cold pull after each part that I print with TPU based filament. I just cut off the last 25mm or so of the filament. I have far fewer issues that way.
These are some of the challenges of working with TPU filament that I have encountered and how I have overcome them. I hope this information was useful for you. If you have any questions or comments, please feel free to leave them below. Happy printing!