Source: MiniFactory

Looking for 3D printing with a stronger-than-metal polymer - PEEK? Our guide covers everything you need to know about PEEK.

PEEK (polyetheretherketone) is one of the most popular thermoplastics in manufacturing, and for good reason. PEEK can produce parts stronger and lighter than stainless steel and aluminum with extremely high thermal, chemical and wear resistance. Parts made from this engineered material can be found in almost every industry.

PEEK is valuable for delivering better-than-metal medical implants and aerospace components because of its high strength-to-weight ratio. In fact, 3D-printed PEEK parts (printed by Orion AM) will touch down on the Moon in April 2023 as part of a study of how different materials perform in the harsh lunar environment. PEEK was chosen because it is strong enough to replace metal parts in some circumstances and is known to be resistant to space environments.

It is also ideal for electrical parts due to its electrical insulating properties and is widely used in applications requiring long-term resistance to pressure and wear, such as in the oil and gas industry.

Combine the qualities of this plastic with the capabilities of 3D printing and you have the ability to make almost any custom shape and complexity of parts out of a material that can withstand the harshest conditions. It's no wonder we're seeing more 3D-printed PEEK parts replacing metal in spacecraft, orthopedic implants, and even engine parts in high-performance auto racing.

Parts 3D printed in PEEK from Roboze, Stratasys, Indmatec and material spool from Evonik.

At the same time, demand for 3D printers that can work with this material is growing, prompting manufacturers to produce increasingly affordable, larger and easier-to-use PEEK printers for companies looking to implement in-house manufacturing and prototyping .

Although PEEK is still among the most expensive polymers for additive manufacturing (still cheaper than most metals) and not the easiest to work with, today it is much more accessible than ever. If you are not familiar with PEEK (and other polymers in the PEAK family), skip to the end to learn more about this sought-after and functional material.

Now let's take a look at how to choose the best PEEK 3D printer for you, from office-friendly desktop versions to high-volume production machines.

This lattice-filled part is actually made of a PEKK material from the same family as PEEK from Stratasys (Source: Stratasys)

Not all printers can print PEEK.

A spool of PEEK filament may look like any other 3D printing plastic, but put it in a consumer machine and you'll quickly realize that this material needs something more; specifically more heat.

Not only do you have to extrude the PEEK with a super heated die (300+ ºC) but you also have to keep it hot with a heated layer and chamber. Several 3D printers go beyond the heated bed and camera with technology that heats the PEEK part itself. Localized heating of the part, as well as a heated chamber to control crystallization, improves interlayer adhesion, according to Brian Alexander, polymer scientist and PEEK 3D printing expert at Solvay Specialty Polymers. The heat must be constant and controllable, as how quickly you let the last layer cool also matters.

Infinam PEEK 9359 from Evonik (Source: Evonik)

Alexander and his team recently tested the Orion 3D printer and found that its thermal radiation heating, which heats the material (not air) to 320°C, produced better quality PEEK prints than injection molding, even along the Z axis.

Print speed and layer height are important factors for successful PEEK printing. Fortunately, better PEEK printers will automate many of these settings for a more hassle-free experience.

Although most PEEK is 3D printed using FDM filament roll printing, PEEK has recently advanced in a more economical pellet form and as a powder for selective laser sintering (SLS).

PEEK printers can print more than PEEK

If they can print PEEK, these 3D printers can handle other high-performance polymers with similar print perimeters and high heat needs, such as PEAK, PEKK, PEI/Ultem, PPSU, and others. Of course they can handle plain ABS and even PLA if you can turn the heat down low enough.

3D printed PEEK is ideal for replacement parts (Source: Zortrax )

What to look for in a PEEK printer

Of course, not all PEEK printers are the same, and you'll need to balance your budget with the features you need in a printer and those you could live without. If you only need PEEK parts occasionally, or you're not sure you need PEEK at all, try ordering your PEEK parts from an on-demand 3D printing service desk.

Below are some of the best features of PEEK printers in our opinion.

  • HEPA filter to capture harmful fumes and particles
  • Insulated chamber so heat doesn't heat up your workshop or leak heat from the machine
  • Quick heat up camera so you don't wait an hour or more to start printing
  • Dual extruders so you can print support material in something other than PEEK, such as soluble material, for cost savings and easier removal
  • Integrated filament dryer so your PEEK material is always ready to go
  • Controlled cooling to prevent warping
  • Fast print speed
  • Built-in camera for continuous print monitoring
  • Power failure protection that resumes printing from where you left off
  • Sensors to detect if you have enough thread to complete the job
  • Sensors for detecting stuck thread.

What is PEEK?

Complex part 3D printed in PEEK by Apium (Source: Apium)

UK-based company Imperial Chemical Industries (now known as Victrex) introduced polyetheretherketone (PEEK) in the 1980s. In its basic form, this material is a high-purity semi-crystalline polymer comprising repeating monomers of two ether groups and a ketone group.

PEEK belongs to the polyaryletherketone (PAEK) polymer family, which also includes PEKK (Polyetherketoneketone), but outshines the others because it can operate at higher temperatures and retain its excellent mechanical properties at continuous service temperatures up to 240 °C (464 °F), allowing it to replace metal in harsh end-use environments.

PEEK is one of the few plastics compatible with ultra-high vacuum applications, making it suitable for the aerospace, automotive and chemical industries.

Not all commercial PEEK products provide the same level of performance. You'll find PEEK filament and powder from a wide range of manufacturers, but be sure to check the technical specifications and data sheets to make sure you're getting all the PEEK qualities you need. Talk to your supplier about density and strength.

Specialty polymer manufacturers such as Solvay and Evonik make PEEK specifically for additive manufacturing and can advise you on the best ways to print their specific materials.

Do you even need PEEK?

PEEK comes in more than its "natural" beige color, like this blue PEEK and black PEEK filled with carbon fibers from Apium (Source: Apium Additive Technologies)

PEEK has many compelling features, especially when it comes to producing functional prototypes and parts for regulated industries, but it is expensive and difficult to work with, so you may be asking yourself: Do I really need to print with PEEK?

Let's look at the pros and cons:

 PROFESSIONALS

  • Highly resistant to extreme temperatures up to 260°C (480°F) as well as corrosive liquids, gases and high pressure
  • Insoluble in common solvents, which protects it from hydrolysis and allows it to be used without degradation by high-pressure water or steam
  • Remedy: PEEK has an inherently low specific gravity of 1.3 g / cm 3 , less than half that of aluminum and one-sixth that of steel
  • High self-lubricating ability and low friction
  • Exceptional slip resistance
  • Very little wear
  • Good dimensional stability
  • Low flammability and low smoke on combustion
  • Exceptional insulating properties
  • Excellent resistance to sterilization at high temperatures
  • Completely biocompatible
  • Safe for food and resistant to oils and animal fats

AGAINST

  • It must be processed at very high and constant temperatures
  • More expensive than most other threads
  • Low resistance to chlorine/bromide, concentrated sulfur and nitric acid, as well as to ketones and nitrobenzene. PEEK is also attacked by halogen and sodium, which limits its use in certain areas of industry
  • Low resistance to UV light
  • PEEK filament is highly hygroscopic and must be stored carefully and dried before use
  • PEEK is prone to warping and dimensional changes during printing if the heat is not precisely controlled

Some of the distortion, shrinkage, and printing difficulties with PEEK can be alleviated by combining PEEK with composite materials such as glass fibers, graphite, or carbon fiber reinforcements. Annealing after printing can also improve the qualities of your parts. The low UV resistance of PEEK can be circumvented by adding a layer of pigment that consists of special particles. Carbon filled grades provide improved UV stability and can be used in certain applications that require greater UV resistance.

Source: MiniFactory

Alternatives

If your part doesn't require all the qualities of PEEK, consider these alternatives, which are easier to print and lower in cost.

PEKK is also part of the same family as PEEK, but requires a lower processing temperature and has a wider processing window, making it easier to print. PEKK is slightly more elastic than PEEK with good shock absorption.

Last it offers similar properties to PEEK but at a much lower cost and is also easier to process at lower temperatures. Ultem has poorer friction and wear properties than PEEK. Ultem is the trade name for polyetherimide (PEI).

Carbon fiber reinforced polyamide doesn't offer nearly the strength or chemical resistance of PEEK, but is still an extremely tough material commonly used for fixtures, tools, and a host of other industrial applications.

What is PEEK annealing and why you might need it

Annealing or heating PEEK can dramatically change its mechanical properties (Source: Intamsys)

Annealing is a heat treatment and a common post-processing method for PEEK that can improve the material density of the printed part. However, Materials Scientists disagree as to whether it is essential to each part and whether it contributes to the mechanical properties of the part at all. This is not a process unique to additive manufacturing, as it is also used in injection molded PEEK.

PEEK, as mentioned, needs high heat to process, but it also needs heat to change its very mechanical nature. How much heat and for how long your particular part needs is also not easy to calculate. Check with your printer manufacturer for print profiles and guidelines, but you're sure to expect some experimentation in any case. Some printer manufacturers say that their machines reach high enough temperatures during printing that they change the chemical nature of PEEK so that annealing as a post-processing step is simply not necessary.

Annealing also has a downside, according to Solvay's Alexander. “If you anneal, you're shrinking the part as it crystallizes, so you'll either get deformation or voids, which can lead to delamination. All polymers shrink during crystallization, but the difference between AM and injection molding is that you apply back pressure in injection molding, which eliminates voids and you can design for the shrinkage.” Alexander notes that there are some tricks and tips to work around. of deformation and voids and in additive manufacturing, but he does not recommend annealing.

A true understanding of PEEK requires knowledge. Just know that your printer may include an annealing setting or a list of annealing options you can follow, such as letting the component cool exactly 10°C per hour to 140°C or leaving the component at 200° C for one hour for each millimeter of wall thickness.

3D printing tips for PEEK

Printed Parts PEEK (Source: MiniFactory)

Now that you have a thorough overview of PEEK, you might want to start printing with it yourself. Here are some basic tips and tricks to keep in mind when 3D printing with PEEK:

CONSTANT TEMPERATURE

PEEK does not react well to fluctuating or unstable temperatures. Therefore, a heated chamber printer is highly recommended, if not required. To get the best results when 3D printing PEEK, keep the 3D printer in an environment that experiences minimal temperature changes, away from solar radiation and high traffic areas.

BEWARE OF STAIN

Sometimes you may notice black spots when printing with PEEK. While this can have a number of different causes, the most common explanation is that the print material used is dirty, or that the 3D printer is having trouble handling the required temperatures.

KEEP NOZZLE CLEAN

You should always clean the nozzle after finishing the printing process. All residual material must be removed from the nozzle, otherwise it can become clogged and eventually lead to staining (mentioned above).

BEWARE OF FAILED CRYSTALLIZATION

Improper crystallization can sometimes occur when printing with PEEK materials. If parts of the print differ in color, such as a brownish discoloration as opposed to the standard beige color, this may indicate improper crystallization. It may be caused by temperature fluctuation during the printing process.

STORE THREAD IN A DRY PLACE

When not printing 3D with PEEK, you should store the material in a cool, dry, dark place until you use it again. In this way you will preserve the quality of the material and will ensure that you will achieve optimal results.


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