The demand for various materials for 3D printing is increasing every day as more and more people use 3D printing for their work or hobbies. In the early years of 3D printing material development, there were only hard thermoplastics because they are easy to extrude.
What is TPU in 3D printing?
Flexible filament material is one of the most popular materials for 3D printers because it can be bent and curved and does not break easily. The elasticity of the material was measured on the Shore hardness scale according to the ASTM-D2240-00 standard system. There are two common scales for measuring Shore hardness, namely Shore A and Shore D. Flexible filament is usually measured in the Shore A system, which is classified as medium hardness.
TPU or thermoplastic polyurethane filament is an elastomeric material: a plastic polymer is combined with an additive so that it becomes a slightly elastic material. This material is very popular in industry, especially in the textile and fashion sectors.
TPU flex properties have a Shore A hardness scale between 70-95, so it is similar to tire rubber (70-75), shoe soles (85), and shopping cart wheels (95-97).
TPU filaments have a melting zone of 210-240 °C and a relatively low glass transition temperature of about 65-70 °C. The material is also considered non-toxic and does not produce fumes during the printing process.
3D printing with TPU filament is possible, but only under certain conditions. Due to its flexible properties, 3D printing with TPU filament requires special handling.
Checklist for 3D printing TPU:
- Direct extruder head required
TPU is a flexible material, although it is not considered a high-temperature material (not to be confused with silicone), and it requires a very short distance between the extruder drive and the melt chamber of the heating element to be extruded precisely. This is where a direct extruder comes in. Some users can use a combination of a Bowden extruder and precise Capricorn PTFE tubing, but it is still difficult to set the print correctly. A dual-gear extruder is another component that can improve the success rate when printing TPU filament.
- Print slowly
Printing TPU must be done as slowly as possible, as TPU has high viscosity and is constantly sticky in the molten state. Slowing down the print also helps ensure that gravity plays a role in advancing the filament. With a maximum printing speed of TPU usually around 15-25 mm/s, printing TPU at this speed will result in a good bond between the layers.
- Low or no retraction
Retraction involves pulling the filament mechanism back in small amounts to reduce stringing - this is very effective for obtaining a nice, smooth extrusion for 3D printing. However, TPU filament is a flexible wire and the push-pull mechanism can cause a jam, as the material can get stuck on the extruder's feed gear. With this setting, the print must be slowed down and only a little bit of retraction used. There are some users who can print well without retraction.
- Always dry the filament
TPU is considered a highly hygroscopic material, which means that TPU absorbs a large amount of water particles in a short time. Due to these properties, TPU must be stored properly in tight storage spaces, and printing TPU with active filament dryer units like the SUNLU S2 or SUNLU S4 drastically improves surface quality. Undried TPU material leads to many uneven drips and likely a clogged nozzle. Another bad outcome is very poor stringing. So if the user notices too much stringing, the probability is high that the TPU filament is moist.
- Bed platform type
Printing TPU filament directly on carborundum-coated glass, PEI, or BuildTak beds must be avoided, as the material adheres strongly to these materials. A thin layer of PVA glue must be applied to this surface so that it can be easily removed after printing. Plain glass or mirrors are well-suited for printing TPU material without any additional coating.
- Neatly wound filament
TPU 3D printing filament is a stretchable wire material. Improperly wound wire can immediately lead to print jams because the diameter changes due to the stretching of the filament, causing the feed gear to lose its grip. Neatly wound spools like SUNLU filament products avoid this problem significantly. Furthermore, it is better to place the spool position on top of the extruder head (facing down) so that the extruder gear pulls the filament with the lowest possible torque. The filament spool must move freely with only minimal force.
- Minimize print support as much as possible
TPU filament is bad at bridging or overhang printing, even though it is still possible to add support, the surface result is not nice. Try to avoid support, long bridging, or steep overhangs when preparing a 3D model for printing TPU.
- Post-processing
3D printed objects made with TPU material cannot be sanded like other solid, hard materials. The only process that can be performed is using heat tools like a heated cutter or an oven. Also, for painting TPU, only special paints like rubber paint can be used.
As a flexible and soft material, TPU is now widely used in 3D printing, from toys, fashion, and industrial spare parts to souvenir items. However, due to the limited glass transition temperature of TPU, it cannot be compared to silicone.
Uses for TPU filaments
You should only use TPU filament for objects that require flexible shapes, such as custom-fit bumper phone cases, flexible flip-flops, anti-vibration bumpers, wristbands, or watch straps. TPU can be somewhat hard when printed with high infill. So if you want to print a very flexible model, use either softer specification material like filament with 85A Shore or reduce the wall/infill parameter. However, be aware that reducing wall thickness can easily lead to layer cracks.
Through the use of multi-head, dual-head, or multi-material 3D printing, a unique combination of hard materials like PLA/PETG can be combined with TPU. With creative ideas—the possibilities of 3D printing are endless.
——————————————————
