Despite the impressive variety of thermoplastics that can be printed on consumer-level desktop 3D printers, the most commonly used filament is polylactic acid (PLA). That’s because it’s not only the cheapest material available, but also the easiest to work with. PLA can be extruded at temperatures as low as 180 °C, and it’s possible to get good results even without a heated bed. The downside is that objects printed in PLA tend to be somewhat brittle and have a low heat tolerance. It’s a fine plastic for prototyping and light duty projects, but it won’t take long for many users to outgrow its capabilities.
The next step up is usually polyethylene terephthalate glycol (PETG). This material isn’t much more difficult to work with than PLA, but is more durable, can handle higher temperatures, and in general is better suited for mechanical parts. If you need greater durability or higher heat tolerance than PETG offers, you could move on to something like acrylonitrile butadiene styrene (ABS), polycarbonate (PC), or nylon. But this is where things start to get tricky. Not only are the extrusion temperatures of these materials greater than 250 °C, but an enclosed print chamber is generally recommended for best results. That puts them on the upper end of what the hobbyist community is generally capable of working with.
But high-end industrial 3D printers can use even stronger plastics such as polyetherimide (PEI) or members of the polyaryletherketone family (PAEK, PEEK, PEKK). Parts made from these materials are especially desirable for aerospace applications, as they can replace metal components while being substantially lighter.
These plastics must be extruded at temperatures approaching 400 °C, and a sealed build chamber kept at >100 °C for the duration of the print is an absolute necessity. The purchase price for a commercial printer with these capabilities is in the tens of thousands even on the low end, with some models priced well into the six figure range.
Of course there was a time, not quite so long ago, where the same could have been said of 3D printers in general. Machines that were once the sole domain of exceptionally well funded R&D labs now sit on the workbenches of hackers and makers all over the world. While it’s hard to say if we’ll see the same race to the bottom for high temperature 3D printers, the first steps towards democratizing the technology are already being made.
Engineering Challenges
Put simply, a machine that supports these so-called engineering plastics needs to be an amalgamation of a traditional 3D printer and an oven. But of course, therein lies the problem. The printer itself, especially of the type and quality that we’ve become accustomed to at the desktop level, wouldn’t survive in such an environment. For a consumer 3D printer to successfully produce parts in PEI and PEEK, it would need to be extensively modified; which is exactly what NASA did with a LulzBot TAZ 4 back in 2016.
The first step was building an insulated enclosure that could fit around the TAZ 4, and installing an array of 35 watt infrared heating lamps inside of it. Naturally the machine’s exposed electronics would overheat in such an environment, so they had to be relocated to the outside of the box.
The stepper motors would overheat as well, but rather than trying to move them, the team at Langley Research Center opted to design cooling jackets to fit over each motor through which pressurized air could be circulated.
Like other desktop 3D printers, the TAZ 4 also utilized a number of printed parts in its construction. Printed in ABS , these parts would have quickly failed inside the heated chamber meant to support PEEK. The parts were reprinted in PC, but even this material wasn’t resilient enough for permanent use. So in classic RepRap tradition, the team printed the third and final set of parts on the modified printer itself in a form of PEI known commercially as Ultem.
Somewhat surprisingly, the team had little trouble upgrading the TAZ 4 with a hotend and nozzle that could extrude plastics at up to 400 °C. The popular E3D-v6 hotend costs less than $100 USD and was found to be capable of reaching these temperatures, though the team did need to replace its thermistor with a higher-rated model and make some adjustments to the printer’s Marlin firmware to allow it to reach temperatures that under normal circumstances would trigger a thermal shutdown.
Ultimately, the NASA report concluded that the modifications to the LulzBot TAZ 4 were a complete success. They noted that attempting to print PEI with the IR heating lamps off lead to serious print issues such as warping and delamination, though this was to be expected. No final dollar figure is given for the cost of the modifications, but considering the base price of a TAZ 4 was approximately $2,200 USD at the time, the entire project was likely 1/10th the cost of comparable commercial offerings.
Starting from Scratch
NASA’s experiment showed that it was possible to modify an existing open source desktop 3D printer to print high temperature engineering plastics, and they even showed it could be done relatively economically. But nobody would say that bootstrapping this way was an ideal solution. There was too much duplicated effort involved in the conversion, as the engineers had to specifically undo design choices originally made by LulzBot. Even so, the experiment did create a valuable baseline for other projects that want to start from scratch.
Just last month, a team from the Michigan Technological University unveiled Cerberus, an open source high temperature 3D printer capable of producing parts in PEI and PEKK that can be built for just $1,000 USD. Rather than attempting to adapt an existing design, the team started from the ground up with high temperature printing in mind. All of the sensitive electronic components are mounted well away from the sealed build chamber, which uses a mains-powered 1 kW space heater core to rapidly bring it up to operating temperature.
Crucially, all of the stepper motors have also been moved outside of the build chamber. While this does make the kinematics somewhat more complex than what you’d see in a traditional desktop 3D printer, it means the Cerberus doesn’t need a dedicated motor cooling system like NASA’s modified TAZ did.
A simplified design combined with the use of off-the-shelf control electronics including the Arduino Mega 2560 and RAMPS 1.4 board, and the same E3D-v6 hotend used on the modified TAZ 4, puts the Cerberus well within the means of the motivated hobbyist. Especially since the team has provided clear and detailed assembly instructions for their printer, something notably missing from NASA’s report.
Expanding Possibilities
Between NASA’s TAZ 4 retrofit and all-new designs such as the Cerberus, it’s clear that the technical capability to print PEI and PEEK objects in the home workshop is there for anyone who wants it badly enough. It’s not quite as easy as buying a $200 3D printer on Amazon yet, but if the demand is there, more low-cost machines based on these core principles will certainly start hitting the market. It’s really not much different than the current wave of affordable laser cutters that have been taking over makerspaces these last few years.
So, is there a demand for them? This time last year, the answer might have been different. But with the world still combating the COVID-19 pandemic, there’s a new demand for rapidly produced personal protective equipment (PPE) that nobody could have anticipated.
As explained in the documentation for Cerberus, the team at Michigan Technological University was inspired to look into developing an affordable high temperature 3D printer specifically because it could be used to create PPE that would survive heat sterilization. Rather than being disposable, the team believes items such as face masks printed in PEKK could be used over the long term.
Printed parts that can be repeatedly sterilized would obviously have other potential medical applications. A portable low-cost machine that can produce these components could potentially save lives in remote areas of the world were rapid access to traditional supplies and equipment may be unavailable.
Critics of 3D printing have often said that the core failing of the machines is that the parts they print are rarely robust enough to be used as anything more than a rough prototype. But when a $1,000 printer can produce parts in aerospace-grade materials, it seems like we’re closer to a manufacturing revolution than ever before.
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