These days, 3D printing is more accesssible than ever. Chances are that, if you’re reading this article, you’ve been using a 3D printer for a while and might be wondering what else you can print.
Besides the practically infinite number of 3D models you could print, there’s another dimension that can broaden your 3D printing experience: 3D printing filament – from simple, more printing-friendly materials like PETG and modified versions of PLA, such as PLA+ and Tough PLA, all the way up to stronger, trickier-to-print filaments like carbon fiber-reinforced nylon. Having so many options, you may wonder which should be part of your next adventure.
In this article, we’ll tell you about a particular category of 3D printing materials: flexible filaments, specifically thermoplastic polyurethane – better known as TPU. Read on to discover this material’s properties, its main applications, the pros and cons of TPU-printed parts, as well as ideal 3D models to print with it.
We’ll also cover the main problems you may face when printing with TPU and how to solve them. Although TPU filament can be printed using different technologies (like SLS), this article will focus on printing TPU using fused deposition modeling (FDM) printers.
What Is TPU?
TPU is one of the most common 3D printing materials for FDM printers. As a flexible material, it’s known for being elastic, shock-absorbing, and resistant to heat and chemicals. Additionally, it’s one of the most durable materials and offers greater layer adhesion than rigid materials like PLA and PETG. These unique properties make it a perfect fit for a wide spectrum of applications.
TPU and other flexible filaments are typically defined by a measure of their resistance to deformation – in other words, their Shore hardness. The Shore hardness scale ranges from 0 to 100. The greater the number, the harder the material and, hence, the less flexible.
TPU usually scores between 85A and 95A, being one of the most rigid of the flexible filaments. The letter next to the number refers to the type of plastic. The Shore A scale is used for soft rubber, elastomers, and natural rubber.
Many companies have expanded their filament assortment by including TPU and other flexible filaments. Some popular brands like NinjaTek and Overture are known for providing good quality TPU filaments, but there are many more options.
Another aspect to keep in mind when dealing with TPU is its hygroscopic nature, which means it absorbs a lot of moisture from the environment. To overcome this problem, you can use a filament dryer, which heats up the filament to dehumidify it and get it ready for printing.
Applications
As you can expect, TPU-printed parts tend to be elastic, flexible, and resilient. Depending on the application, these characteristics can become an advantage or a drawback. The parts most appropriate for TPU are those that should withstand rough environments or that are expected to be exposed to constant pressing or stretching conditions.
For example, a TPU-printed gauge – a positioning tool that helps while performing a manufacturing task – can benefit from the elasticity of TPU. By modifying the infill density, you can vary the stiffness of the piece, becoming a sort of dynamic tool. Nissan took advantage of this attribute and implemented a windshield centering gauge fixture that they use to ensure the correct distance between one of the pillars of the car and the windshield.
However, TPU’s elasticity is not desirable for all use cases. For example, Nissan also uses a lower drill positioning tool during the manufacturing process, and it indicates the drill placement to the operator. This tool requires a rigid material to avoid misplacement due to flexion or torsion of the printed part.
The Trouble with TPU
Printing with TPU is definitely trickier than printing with PLA. While warping isn’t a typical issue related to TPU, there are other complications that may (and will) arise when you start printing with this material, including clogging, stringing, and under-extrusion, among others (we’ll cover these in more detail below). Some of these issues are related to the printer physical configuration, with the extruder and hot end being the main components responsible for these problems.
Additionally, the print settings for TPU are quite particular, and these must be modified in the slicing software in order to successfully print with this material. Some of these settings are more obvious than others, like Printing Temperature and Print Speed, while others are less common, like Retraction Distance and Retraction Speed. In fact, this might be the first time you hear about them.
Hardware Recommendations
Most of the problems you’ll face when working with TPU are related to the extrusion system. While most of the new FDM printers come with a direct extruder, it’s still possible to find some printers with Bowden extruders. In the latter case, due to the long distance between the feeder and the hot end, as well as the stretching property of the TPU, the extruder struggles to deliver the filament to the hot end efficiently.
Ideally, you should be able to solve this problem by simply modifying some values of the print settings in the slicer. However, it’s highly probable that you may have to make some upgrades as well. The simplest upgrade would be the Bowden tube. A better-quality Bowden tube, like the Capricorn Bowden tube, should do the job.
But if you really want to take your printer to the next level, we recommend upgrading to a direct extruder. By doing so, the distance between the feeder and the hot end will be drastically reduced, improving the filament feeding process and, hence, the printing quality. Or you might want to get even more creative and check out projects like Proper Printing’s, pictured above.
Another part of your printer you may think of is the nozzle. Gentle filaments like PLA and PETG won’t wear the nozzle as much as abrasive filaments like those reinforced with carbon or glass fibers. In the case of TPU, it lies more on the non-abrasive filaments side, along with PLA and PETG. However, you might expect a little bit more wear than when using PLA. So, if you ask yourself which type of nozzle you should use, the short answer is that brass nozzles are more than enough to work with TPU, but using a stainless steel or a hardened steel nozzle won’t do any harm.
Build Plate
The final hardware item we want to discuss is the build plate. TPU is a more, let’s say, melty material than PLA and PETG. So, you shouldn’t face any warping problems – unless you print big contact areas in the first layer. If the bed is properly leveled, the TPU should adhere to the build plate without trouble.
On the other hand, removing a TPU printed part can represent a real challenge. If you’re using a rigid glass plate, a scraper is mandatory to help remove the printed part. Depending on the stiffness or flexibility of your printed part, a flexible PEI sheet could be another option. If you opt for this alternative, we recommend using a smooth one, since a textured flexible sheet may cause extreme adhesion of the part to the build plate. Of course, there are quite a few options to look into.
Another important observation is that – ironically – when working with TPU, it’s not common to use glue stick or blue (painter’s) tape to ensure bed adhesion. Part removal goes much easier by taking steps to avoid strong adhesion between the part and the build plate.
Software Recommendations
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