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 bend or compress easily. In today's tutorial, we will examine the advantages and applications of TPU, the technologies that support this material, as well as some tips to help you make 3D printing with TPU as simple and efficient as possible.

Thermoplastic polyurethane (TPU) belongs to the family of thermoplastic elastomers and rubber bands that combine the best properties of thermoplastics and rubbers (duroplastics). You may be familiar with the term TPE - or Thermoplastic Elastomer. Previously known as a material for flexible 3D printing, TPE is a very soft, rubber-like plastic that can be bent or stretched without deformation. However, due to its softness, TPE is a very demanding material for machine extruders in 3D printing. TPU, in turn, can be regarded as the newer version of TPE. TPU possesses rubber-like elasticity, high tear and abrasion resistance, high elongation at break, and thermal stability. Furthermore, TPU is resistant to oils, fats, and a variety of solvents. Since it is firmer than TPE, TPU is therefore much easier to print.

TPU has a wide range of applications across 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.

For consumer goods, TPU is ideal for manufacturing 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 combination with generative design, the shoe giant achieved optimal weight and durability alongside a high degree of flexibility and strength.

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

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

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

Selective Laser Sintering (SLS) is a powder bed fusion additive manufacturing technology that uses a laser beam to selectively melt and fuse powdered material. SLS offers many advantages for industrial manufacturing, as the technology is capable of producing functional parts with superior mechanical properties. Furthermore, SLS requires no support structures, making freeform parts possible without removal marks. However, parts do require some post-processing to achieve better surface quality. Initially, the technology was used with various nylon types, but with recent advances in materials research, it is now possible to sinter TPU powder. Currently, there are several manufacturers on the market offering TPU powder with various Shore hardness grades:

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

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

As a powder bed technology, SLS can produce 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.

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

There are two major advantages of using FDM instead of SLS in the manufacture of TPU parts: firstly, FDM is less expensive and secondly, 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, particularly when compared with ABS and PLA thermoplastics, TPU filaments can bend in the extruder mechanism, which leads to filament wrapping and clogging of an extruder. However, the softness of the material makes layer adhesion in TPU prints strong and durable.

Extruder temperature: 225-250 ° C Type of extruder: Direct Drive Extruder is recommended Heated build platform: 50 ± 10 ° C Cooling: Part fan is recommended (medium or high setting) Enclosed build chamber: not necessary Build platform: Kapton tape (PEI)

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

TPU typically 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 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 an inadequate bonding of layers and perimeters. One way to handle this problem is to increase the extrusion factor somewhat.

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

A raft is a disposable horizontal surface on which a part is printed, and serves to prevent warping. Since TPU parts typically do not warp, rafts are not recommended when 3D printing with TPU, not least because they can cause additional printing problems due to high print 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.

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