Have you ever thought about 3D printing flexible parts?

If so, Thermoplastic Polyurethane, or TPU as it is commonly known, is definitely a material to add to your list. TPU 3D printing offers unique possibilities that cannot be achieved with other 3D printing materials such as ABS, PLA or nylon. By combining the properties of plastic and rubber, TPU can produce elastic, highly resilient parts that can be easily bent or compressed. In today's tutorial, we'll explore the benefits and applications of TPU, the technologies that support the material, and some tips to help you make 3D printing with TPU as easy and efficient as possible.

What is TPU?

Thermoplastic polyurethane (TPU) belongs to the family of thermoplastic elastomers and rubber bands that combine the best properties of thermoplastics and rubbers (thermosets). You may be familiar with the term TPE - or ThermoPlastic Elastomer. Formerly known as a material for flexible 3D printing, TPE is a very soft, rubbery plastic that can be bent or stretched without deformation. However, due to its softness, TPE is a very demanding material for machine extruders for 3D printing. TPU, on the other hand, can be seen as the newer version of TPE. TPU has rubber-like elasticity, high tear and abrasion resistance, high elongation at break and thermal stability. In addition, TPU is resistant to oils, greases and a variety of solvents. As it is stronger than TPE, TPU is therefore also much easier to print.

Applications

TPU has a wide range of applications in all industries. For example, it is a good option for 3D printing flexible functional prototypes or end-use applications that need to be bent and compressed.

Consumer goods

For consumer goods, TPU is ideal for the production of accessories such as phone cases and shoe components. In 2015, New Balance developed running shoes with TPU 3D-printed midsoles. By using this material in conjunction with generative design, the footwear giant has achieved a high degree of flexibility and strength in addition to optimal weight and durability.

Medical

Another interesting application of TPU is medicine. For example, the material can be used to create orthopaedic models. In 2016, the US company Graphene 3D Lab presented a conductive TPU filament that is suitable for the production of flexible electronics, including wearable medical devices such as bracelets.

Automobile

With its high chemical resistance to oils and greases, TPU is ideal for automotive applications such as seals, plugs, pipes and protective applications. One example is a 3D-printed electric car from Chinese start-up XEV Limited. The car consists of around 100 parts, many of which were 3D-printed with TPU alongside PLA and nylon.

3D printing with TPU: the technologies

If you want to explore 3D printing with this flexible material, there are two main technologies to choose from: Selective Laser Sintering (SLS) and Fused Deposition Modeling (FDM). Let's dive into the possibilities of each.

Selective laser sintering

Selective laser sintering (SLS) is a powder bed fusion 3D printing technology that uses a laser beam to selectively melt and fuse powdered material. SLS offers many advantages for industrial manufacturing, as the technology is able to produce functional parts with great mechanical properties. In addition, SLS does not require support structures, so free-form parts without removal marks are possible. However, parts do require some post-processing to achieve a better surface finish.
Initially, the technology was used with different types of nylon, but with recent advances in materials research, it is now possible to sinter TPU powder. There are currently several manufacturers on the market offering TPU powders with different Shore hardness grades:

• 3D Systems offers its own DuraForm TPU elastomer that is compatible with its Pro 60 HD-HS 3D printer.
• The French AM specialist Prodways has TPU-70A in its material portfolio with an elongation at break of more than 300%. The Shore hardness of TPU-70A can be adjusted based on the energy input.

Design tips for the use of TPU powders

Minimum wall thickness

1.5 mm is the minimum wall thickness when using TPU powder. 3D printed parts with a wall thickness of 1.5 mm are very flexible, but you can also make your part stiffer by increasing the wall thickness to 3 mm.

Minimum size of the features

When designing details for your TPU part, make sure that they are at least 0.5 mm in size. For the visibility of embossed and engraved details, their height and width should not be less than 1.5 mm.

Complex designs

As a powder bed technology, SLS can create enclosed and interlocking parts (e.g. a chain), eliminating the need to assemble individual printed components. For this to work, the distance between the parts must be at least 1 mm. For large objects, the distance should be increased.

Outlet holes

Hollowing out your part can be useful as it reduces printing time and saves material. However, don't forget to spark your design holes with a diameter of at least 1.5 mm to remove the powder in your part after the printing process.

Fused Deposition Modeling

FDM can also be used with TPU filaments.

There are two main advantages of using FDM instead of SLS in the production of TPU parts: First, FDM is less expensive, and second, it is typically faster to produce TPU parts with filaments than with powders. On the other hand, 3D printing with TPU filaments using FDM results in a less dimensionally accurate part with visible print layers that cannot be smoothed. Since TPU is a soft material, especially when compared to ABS and PLA thermoplastics, TPU filaments can bend in the extruder mechanism, causing the filament to unravel and clog an extruder. However, the softness of the material makes the layer adhesion in TPU prints strong and durable.

5 tips for 3D printing with TPU filaments

Basic printer requirements:

Extruder temperature: 225-250 ° C
Type of extruder: Direct drive extruder is recommended
Heated print bed: 50 ± 10 ° C
Cooling: Partial fan is recommended (medium or high setting)
Closed build chamber: not necessary
Build platformKapton tape (PEI)

Pressure temperature

The recommended extrusion temperature range is between 225-250°C, depending on the type of 3D printer and TPU filament you have. Note, however, that when printing at higher temperatures, the filament can melt faster and flow more easily from a nozzle.

Speed

TPU normally prints best at slower speeds. It is recommended to set half the average speed (15 mm / s - 20 mm / s) to ensure high quality prints.

Extrusion multiplier

Extrusion multiplier is the 3D printer setting that allows you to control how much filament comes out of the nozzle or simply the extrusion rate. Since TPU filaments cannot extrude properly during the printing process, this leads to improper bonding of layers and perimeters. One way to deal with this problem is to increase the extrusion factor slightly.

Withdrawal

Retraction is the mechanism in a 3D printer that pulls the filament backwards into the extruder to prevent the molten filament from escaping. This feature is very useful with rigid filaments such as PLA and ABS, but with TPU filaments, retraction can be a challenge and lead to clogging. Therefore, it is highly advisable to disable retraction to prevent stretching and compression of the flexible filament in the nozzle.

Rafts and skirts

A raft is a disposable horizontal surface on which a part is printed and is used to prevent warping. As TPU parts do not normally warp, rafts are not recommended when 3D printing with TPU, not least because they can cause additional printing problems due to high printing speeds. In contrast, it would be advisable to print a skirt - a few loops around the print to check the flow of the filament and ensure the success of the first few layers.

Conclusion

TPU is a very useful material that offers unique properties and a wide range of possible applications. However, 3D printing with TPU can be difficult at first due to the unique properties of the material, which is why it is important to understand the possibilities and limitations of TPU before printing. We hope that with this tutorial, you will be well on your way to successfully producing your 3D printed TPU parts.