Have you ever stopped to think about the materials used in the most demanding jobs on the planet? Think about the parts found inside a jet engine, life-saving medical implants, or deep down in the ocean’s abyss. In those extreme environments, you can’t just pick any old piece of plastic or metal.
You’ll need something extraordinary and exceptionally durable under the conditions present. That’s the superstar material, PEEK!
PEEK is a high-performance thermoplastic that is changing the way we think about products across multiple industries, including aerospace, automotive, and medical technology. PEEK is a little bit of a beast, but to create precise components from PEEK, you need a rather specialized skill set: PEEK CNC machining.
In this guide, we will take a closer look at this amazing material. We will determine exactly what PEEK is and its characteristics in comparison to other engineering plastics.
Then we will look at some of the unbelievable benefits of CNC machining PEEK.
We’ll also be honest about its challenges and finish by looking at the incredible applications where PEEK parts are making a real difference. Let’s get started!
What is PEEK (polyether ether ketone)?
So, what is this strange stuff with the strange name? PEEK stands for Polyether Ether Ketone. It belongs to a family of plastics known as high-performance thermoplastics. Think of it this way: it is plays in the plastics major leagues.
PEEK is a semi-crystalline thermoplastic, which means its molecular structure is very stable and organized. The secret to its remarkable mechanical strength and toughness lies in this structure.
PEEK is one of the only plastics that can successfully replace metal components in many industrial applications where the components will see excessive stress.
The material properties of PEEK are completely bonkers. It has a high melting point and high heat resistance, which allows PEEK to function flawlessly at high temperatures, whereas most plastics would just melt or deform.
It also exhibits extremely high chemical resistance, which means it can withstand substantial amounts of harsh and corrosive chemicals. But not all PEEK is created equal. There are numerous PEEK grades to choose from, as PEEK is designed for specific applications. It contains unfilled PEEK (also known as virgin PEEK), which is the purest form and is extremely tough.
There are filled grades of PEEK, such as glass-filled PEEK (also known as glass-reinforced PEEK), that incorporate additional glass fiber to impart exceptional rigidity and dimensional stability. There are also carbon fiber-filled grades for even more strength and wear resistance.
For medical applications, there are also specialized biocompatible grades specifically designed for safe use within the human body. The various PEEK grades make PEEK material great for manufacturing strong, high-quality PEEK components.
What are the Advantages of machining PEEK?
When you decide to use PEEK plastic for your project, you are not only getting a strong material, but also a wide range of useful properties. PEEK is a modern material that can be machined into complex shapes with precise tolerances using a CNC machining process.
Excellent chemical resistance
PEEK is superior when it comes to resisting chemicals. It is chemically resistant, meaning it can survive exposure to a variety of organic and inorganic liquids, including jet fuel and strong acids.
Its superior chemical resistance makes it ideal for components used in chemical processing plants or in the oil and gas industry, where parts are constantly exposed to chemicals.
Most parts made from metals corrode when exposed to harsh substances, but PEEK maintains its integrity under non-oxidizing environments. Resulting into long enduring components.
Very low moisture absorption
Have you observed a plastic part swelling or changing shape when exposed to a humid environment? PEEK won’t do that. It absorbs very little moisture when submerged, even during extended periods. This is a significant factor, as low moisture absorption results in excellent dimensional stability.
Parts won’t shrink or grow in size to change in shape, which is critical in complex assemblies where every millimeter counts and performance is paramount. This is particularly important in the beverage industry or for medical devices used in sterilization.
Wear and abrasion resistance
PEEK is a highly abrasion-resistant thermoplastic material. It can take a remarkable amount of friction/rubbing before wearing out. This makes it ideal for dynamic parts, such as bearings and seals, which consist of mating surfaces that rotate and move.
PEEK carbon-filled grade offers a level of wear resistance and lower friction for applications where even heavier or more extreme wear is present. As a result, carbon-filled grade PEEK will extend the wear life of parts and enable them to operate efficiently under higher static loads.
Unaffected by continuous hot water/steam exposure
Most engineering plastics will degrade over time from repeated hot water or steam applications. The process is known as hydrolysis. PEEK is extremely water- and steam-resistant, making it the perfect fit for any application that requires frequent steam sterilization.
This is why you’ll find components made from PEEK plastic parts in medical devices and autoclaves, or food processing equipment. It can withstand multiple methods of sterilization without compromising its mechanical properties.
Some grades biocompatible
This is one of the greatest strengths of PEEK. Some grades, such as medical-grade PEEK, fall under PEEK’s biocompatibility category. This means they can be inserted inside the human body with no reaction.
You will find PEEK and USP Class VI PEEK, used to create next-generation medical implants (e.g, spinal fusion cages, joint reconstruction) and orthopedic devices. Its strength and compatibility with medical imaging (MRI, CT) make PEEK an industry leader in modern medical solutions.
Resistant to biodegradation
When creating a component for a critical application, you want it to be reliable and durable. PEEK is not subject to biodegradation, meaning it is resistant to environmental degradation.
For parts used in industrial applications that are exposed to extreme environments, or for parts used as medical implants that remain in the body with an expectation of over a lifetime, long-term resistance to chemical stability and durability is critical. PEEK components can be trusted for decades.
What are the Limitations of PEEK machining?
PEEK is a premium material that requires careful attention to its production and deliverables. The same characteristics that give it such incredible tensile strength could also fight against you during machining.
Special handling is needed to reduce internal stresses and avoid heat cracks
In machining, the PEEK material may be susceptible to internal stresses when injected. You must consider those stresses in the PEEK machining processes. The stresses could create microscopic cracks in the finished part’s surface, compromising its tensile strength.
This is a very real concern for machinists; special methods, tooling, and techniques must be utilized to avoid jeopardizing the structural integrity of the part.
Annealing required
As mentioned above, it may be necessary to anneal the material in PEEK machining processes.
Annealing is the controlled heating and cooling process to relieve the internal stresses in PEEK, as it will help “relax” the chemical structure of the material and move any underlying stresses developed from a machining process.
This may be the most important step regarding tolerances for dimensional stability of the finished component, and to minimize the likelihood of developing a crack or warping later. While this is an additional step, it is very advantageous for consistent and reliable PEEK parts.
Poor heat transfer
PEEK is very poor at transferring heat. In CNC machining processes, the machining tool generates considerable heat due to the friction involved between the cutting tool and the workpiece. I
It’s also due to the PEEK’s resistance to thermal transfer that the heat often remains trapped in the cutting zone, resulting in considerable heat buildup.
It is very easily possible to attain melting of the plastic, which would certainly affect surface finishes, aesthetics, and dimensional accuracy. Managing this temperature using a traditional liquid coolant and the appropriate cutting parameters is one of the foremost difficulties of machining PEEK.
Can crack when drilled deep
In terms of a problem when drilling deep holes in PEEK, the overall scenario engendered by
internal stress and lack of heat dissipation forms a unique situation, based on the fact that if you drill
the hole deeply in one step, the heat and stress will build, and can push the material to crack. Consequently, to mitigate this action, machinists use what is termed peck drilling, which means drilling a
little, pulling the drill out to clear the chips and allow the area to cool, and repeating until the total depth of the hole has been accomplished.
What Are the Applications of PEEK Machining?
PEEK machining is being selected as the material of choice for some very complex applications in many industries, due to the unique combination of properties PEEK has demonstrated and the ability to perform when other materials would not.
1. Aerospace Components
In the aerospace sector, weight is everything. Compared to aluminum and steel, PEEK is extremely light but has exceptional strength and stiffness. It is used for brackets, seals, electrical insulators, and other aerospace parts. PEEK is temperature resistant, can withstand aggressive aviation fluids, and is the ideal product for the severe environment found inside an aircraft.
2. Medical Implants and Devices
As stated above, medical-grade PEEK plastic is a superstar in the medical markets. Because of its biocompatibility, strength, and radiolucency (it doesn’t block X-rays), PEEK is perfectly suited for spinal implants, suture anchors, and dental healing caps.
As a result of PEEK plastics’ application in medical technology, patients have better outcomes, and new surgical procedures have been developed.
3. Oil and Gas Industry
Subsurface components are subjected to great pressure, temperature, and corrosive chemicals. Industrial-grade PEEK plastic is used to manufacture seals, valve seats, and electrical connectors for downhole equipment.
PEEK plastics’ high resistance to deleterious chemicals and extreme conditions means that these important components will not fail and incur unexpected downtime, and maintain safety.
4. Semiconductor Manufacturing
The process of manufacturing computer chips requires extreme purity and precision. PEEK is used to manufacture components for wafer handling. It’s also useful in chemical processing equipment because PEEK does not off-gas impurities that would contaminate the sensitive silicon wafers. Consistent chemical stability and dimension stability are important in this high-tech environment.
5. Automotive and High-Performance Vehicles
In the automotive industry, especially in high-performance vehicles and electric vehicles, PEEK is used to make parts that require high strength and very low coefficients of friction.
Some good examples are thrust washers in transmissions, seal rings, and bearings. Additionally, by not adding weight to the vehicle, it can help achieve efficiency while also providing reliable performance and being capable of handling residual heat in wear situations.
Tips for PEEK CNC Machining
Successfully machining PEEK requires skill and the right approach. The key tips to consider include:
Use the right tools
PEEK can obviously be very abrasive, especially the filled grades such as glass-reinforced PEEK, and it can quickly dull standard steel tools. It’s best to use sharp carbide tools. For the most advanced applications and the best finish, diamond tools (PCD) are highly recommended.
Keep it cool
Keeping temperatures under control is everything. A reasonably liberal flow of standard liquid coolant will help keep the PEEK material from melting. In addition, the coolant will help wash away the chips and keep the cutting edge temperature under control.
Control your speed and feed
It may seem counterintuitive, but you generally want to run slightly slower cutting speeds and a higher feed rate. This allows you to create larger chips that help dissipate heat from the part. It will take some finesse to find the right balance, but it is key to keeping the heat buildup under control.
Anneal for stability
Always consider annealing the PEEK stock before machining and the finished part after machining. This process will alleviate internal stress and is the most effective way to ensure the long-term dimensional stability of the part, thereby preventing future cracking or warping.
Don't get stuck in a hole
In general, when drilling, and especially deep holes, always use the peck drilling technique. Drill a part of the report depth, pull the drill back to clean the hole, repeat. This simple task will reduce chip packing, minimize heat, and is the best way to avoid cracks in the material.
Clamp the part down firmly
PEEK is a rigid material, but it will vibrate, or chatter, if the workpiece is not held firmly during the machining process. Ensure the workpiece is securely clamped to provide the best surface finish and maintain tight tolerances.
Final Thoughts
PEEK is in a class by itself when it comes to advanced engineering plastics. It is more than just a strong plastic; it is a way to solve problems that seemed impossible to solve before. PEEK is pushing the limits in aerospace, medicine, and other high-tech fields because it can withstand extremely high temperatures, corrosive chemicals and has excellent mechanical properties.
PEEK CNC machining has its own challenges, such as managing internal stress and heat, but these can be mitigated with the right tools and knowledge.
The result is perfectly made PEEK parts that work better and last longer than any other parts in the most extreme conditions. Engineers and designers are utilizing machined PEEK to create a better future. For example, they can make a car lighter or an implant safer for a patient.