A comphrensive guide to TPU 3D printing

James Madison
2023-11-10T15:58:55+08:00

Demand for 3D Printing different materials grows every single day as more people use 3D Printing for their work or hobbies. In the early years development of 3D Printing material was only available in hard thermoplastic because it’s easy to extrude.

What is TPU in 3D printing

Flexible filament material is one of the popular materials among 3D Printer users since it is capable of flexing, bending and is not easily broken. The elasticity of the material was measured on Shore hardness scale based on ASTM-D2240-00 standard system. There are two popular scales in Shore Hardness measurement which are Shore -A and Shore-D. Flexible Filament is usually measured in Shore-A system which is put into position as medium hardness.

TPU or Thermoplastic Polyurethane Filament is an elastomer material: plastic polymer combines with some additive so it becomes slightly elastic material. This material is quite popular in industries, especially in textile/fashion sector.

TPU flex properties have a hardness scale Shore-A between 70-95 so it is similar from tire rubber (70-75), shoe outsole (85) and shopping cart wheels (95-97).

TPU Filament has a melt zone from 210-240C and has a fairly glass transition temp of around 65-70C. The material is also considered non-toxic and does not produce fumes during the print process.

3D Printing with TPU Filament is possible but with certain conditions. Due to its flexible properties - 3D Printing TPU Filament needs specific process handling.

Checking List for 3D Printing TPU:

1. Direct Extruder Head Required

TPU is a Flexible material although is not considered high temperature (don’t mix up with silicone material) and it needs a very short distance between extruder drive and hotend melt chamber to extrude precisely. A direct extruder comes into play for this. Some users can use a combination of Bowden extruder and precise Capricorn PTFE Tube, but it is still difficult to set print properly. Dual/Double gear extruder is another part that can improve the success rate of printing TPU Filament.

2. Printing slow

Printing TPU needs to be as slow as possible the properties of TPU are high viscosity and continuous sticky during a melted state. Slowing down the print also helps gravity to take a role in pushing the filament. At a maximum print speed of TPU in general about 15-25mm/s and this with speed TPU print will have good bonding between layers.

3. Low or No retraction

Retraction is pulling out the Filament mechanism in small amounts to reduce the stringing effect - this is quite effective in getting a nice smooth extrusion for 3D printing. However, TPU Filament is a flex wire and the mechanism push-pull gear can cause jam since the material can stick to extruder feed gear. Slowing and just a small amount of retraction must be applied in this setup. There are some users able to do printing nicely without retraction at all.

4. Always dry the Filament

TPU is considered a highly hygroscopic material which means TPU absorbs a high amount of water particles in a short time. Due to these characteristics, TPU must be stored properly in tight storage, and printing TPU with active filament dryer units like SUNLU S2 or SUNLU S4 will drastically improve surface quality. Non-dried TPU material will cause a lot of uneven blobs and likely jammed nozzle. The other bad result that comes out is very bad stringing, so if the user finds too much string - high possibility the TPU Filament is moist.

5. Bed Platform Type

Printing TPU Filament on Carborundum coated glass, PEI or Build-Tak bed directly must be avoided as the material will stick strongly on those materials. A thin layer of PVA glue must be applied to that surface for easy release after printing. Plain glass or mirror is good for printing TPU material without any additional coating.

6. Neat Winding Filament

TPU 3D Printing Filament is stretchy wire material. Improper spooled wire can cause jammed printing immediately as the filament stretch changes the diameter size causing the feed gear to lose the grip. Neat winding spools like SUNLU Filament products avoid this problem significantly. The spool position is also better to put on top of the extruder head (downward) so the extruder gear pulls the filament with as low torque as possible. The filament spool needs to move freely with just a small amount of force.

7. Minimize the print support as possible

TPU Filament is bad in bridging or overhang print even still possible can add support but the surface result is not nice. Try to avoid support, long bridging, or steep overhang when preparing 3D model for Printing TPU.

8. Post-processing

The print 3D Printed objects with TPU material cannot be sanded like other solid hard materials. The only process that can be done is using heat tools like a heated cutter or oven. As for Painting TPU also can only use special paint like rubber paint.

As a flexible and soft material - TPU is now widely used in 3D Printing from toys, fashion, and industry spare parts to souvenir goodies. But still, it cannot be compared with silicone due to the limitation TPU glass transition temperature.

TPU Filament usage

You only use TPU filament for objects that require flex shapes like custom bumper phone cases, flexy flip flops, anti-vibration bumpers, bracelets, or watches-strap. TPU can be a bit hard if printed in high infill so if you want to print a very flexible model either you use softer specification material like Filament with Shore 85A or reduce parameter wall/infill. Just be careful that reducing wall parameter thickness can easily create layer cracks.

Using multi or dual-head or multi-material 3d printing can produce a unique combination of hard materials like PLA/PETG with TPU combined. With creative ideas - The possibilities of 3D Printing are endless.

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WRITTEN BY: James Madison