Machining PEEK: Tips, advantages & applications

PEEK is a popular thermoplastic polymer found in objects as diverse as medical implants and electrical cable insulation.

The plastic has excellent mechanical properties and a high level of resistance to corrosive substances, making it highly desirable for manufacturers across the world. Despite being regularly used for injection molding and 3D printing, PEEK has a high melting point, which would indicate its suitability for subtractive processes like CNC machining — although PEEK machining comes with its own set of challenges.

This article goes over the fundamentals of machining PEEK: the material properties of PEEK, the advantages of machining PEEK, common applications of machining PEEK, and tips for how to get the most out of machined PEEK parts.

What is PEEK (polyether ether ketone)?

PEEK, or polyether ether ketone, is a high-performance engineering thermoplastic and part of the PAEK family of materials. The semi-crystalline material is used for a wide range of industrial parts and components, exhibiting excellent strength, wear resistance, and abrasion resistance, and retaining its properties even at high temperatures.

PEEK grades offer chemical and water resistance similar to PPS. But with a melting point of 343°C, PEEK can operate at higher temperatures: it can be used continuously to 250°C and in hot water or steam without permanent loss in physical properties.

The high-performance PEEK plastic is available in granular form, in filament for 3D printing, and in bar / rod form for CNC machining. It is typically classified as either industrial-grade or medical-grade.

What are the Advantages of machining PEEK?

There are numerous advantages to PEEK machining, and these can be broken down into two categories: the inherent material advantages of PEEK, and the specific process advantages of using a CNC machine for machining PEEK material.

Material advantages of machining PEEK include:

• Excellent chemical resistance
• Very low moisture absorption
• Wear and abrasion resistance
• Unaffected by continuous hot water / steam exposure
• Some grades biocompatible
• Resistant to biodegradation

Process advantages of machining PEEK include:

• High accuracy
• High repeatability
• Tight tolerances
• Relatively high melting point permits faster feeds and speeds

What are the Limitations of PEEK machining?

Although many machinists use PEEK plastic as a reliable alternative to some metals, there are several limitations to machining the thermoplastic polymer. These include:

• Special handling required to minimize internal stress and heat-related cracks
• Annealing required
• Doesn’t dissipate heat well
• Can crack if drilled deeply

What are the Applications of PEEK machining?

PEEK is a material with a surprisingly diverse range of applications, some of which are best served by CNC machining over other manufacturing techniques. Industrial-grade PEEK plastic is used in the aerospace, automotive, chemical, electronics, and energy industries, while medical-grade PEEK plastic is used in healthcare and dentistry.

These common machined PEEK parts are here categorized by whether they use industrial-grade or medical-grade PEEK:

PEEK machining tips

PEEK is a machinable thermoplastic, but critical steps must be taken before, during, and after machining to deliver the best end product.

• Annealing: Annealing is a process performed on PEEK rods to relieve stress and reduce the chances of stresses and surface cracks in the PEEK material during machining. Annealed PEEK is also less likely to deform. Multiple annealing stages may be required depending on the time required for machining.
• Cutting tools: In most circumstances, PEEK can be machined using silicon carbide cutting tools. If the PEEK is reinforced with carbon fiber, or if exceptionally tight tolerances are required, diamond tools should be used. Furthermore, contamination can be avoided if the cutting tools used are not also used on metals.
• Wet or dry: Because PEEK doesn’t dissipate heat, it needs to be cooled during machining to prevent deformation or breakage. Standard liquid coolant can be used, unless e.g. medical parts are being machined, in which case the PEEK material needs to be cooled by pressurized air. This is because liquid coolant can affect the biocompatibility of PEEK.
• Drilling: Deep hole drilling can cause cracks, since PEEK has a lower elongation than other plastics.

PEEK machining, PEEK 3D printing, or PEEK injection molding?

PEEK material is not limited to CNC machining. It can also be processed via additive manufacturing or injection molding. Choosing between the processes depends on the desired end product, as well as time and budget constraints.

For 3D printing PEEK, both FFF filaments and SLS powders are available. However, the availability of PEEK for CNC machining and injection molding still far outweighs the options for additive manufacturing. 3D printing is becoming increasingly popular for the printing of biocompatible medical implants, since complex (and partially hollow) geometries can be easily realized.

Injection molded PEEK resin is widely used for medical and aerospace applications and beyond. However, its melting point is at the upper end of many injection molding machine’s capabilities, and it may therefore be considered a specialty material. Learn more from our guide on Plastic CNC machining and how to choose the best type for your project.

Customers may also consider other high-temperature plastics besides PEEK, such as PEKK or Ultem.

3ERP in an experienced provider of PEEK machining, in addition to many other prototyping and plastic CNC Machining services and parts. Request a free quote for your next project.