Machining PEEK: Tips, advantages & applications

Machining PEEK: Tips, advantages & applications

PEEK is a widely-used thermoplastic polymer found in various products, ranging from medical implants to electrical cable insulation.

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Known for its excellent mechanical properties and high resistance to corrosive substances, PEEK is highly prized by manufacturers worldwide. Despite its frequent use in injection molding and 3D printing, its high melting point suggests its suitability for subtractive techniques like CNC machining, although machining PEEK has its challenges.

This article explores the essentials of machining PEEK, including its material properties, the advantages of machining it, common applications, and tips for optimizing machined PEEK components.

Understanding PEEK

PEEK, or polyether ether ketone, is a high-performance engineering thermoplastic belonging to the PAEK family. This semi-crystalline material is utilized in various industrial applications due to its strength, wear resistance, and ability to retain these properties at high temperatures.

Offering chemical and water resistance similar to PPS, PEEK can withstand continuous use at temperatures up to 250°C and can be immersed in hot water or steam without permanently losing its physical properties. This high-performance plastic is available in granular form, 3D printing filament, and bar or rod form for CNC machining. It is typically categorized into industrial-grade or medical-grade.

Benefits of Machining PEEK

Material Advantages

• Exceptional chemical resistance
• Minimal moisture absorption
• High wear and abrasion resistance
• Unaffected by continuous hot water or steam exposure
• Biocompatible grades available
• Resistant to biodegradation

Process Advantages

• High precision
• Consistency and repeatability
• Tight tolerances
• The high melting point allows for faster feeds and speeds

Limitations of Machining PEEK

Despite its many advantages, machining PEEK comes with some limitations:

• Special handling required to minimize internal stress and heat-induced cracks
• Annealing is necessary
• Poor heat dissipation
• Deep drilling can lead to cracking

Applications of PEEK Machining

PEEK finds applications in various industries, often best suited to CNC machining over other manufacturing techniques. Industrial-grade PEEK is prevalent in the aerospace, automotive, chemical, electronics, and energy industries. In contrast, medical-grade PEEK is used in healthcare and dentistry.

Common applications of machined PEEK parts include:

Industrial-grade:

• Rollers and wheels
• Bearings
• Washers, seals, and manifolds
• Cable insulation
• Blocks
• Bushings
• Rings

Medical-grade:

• Implants
• Spinal fusion devices
• Trauma fraction devices
• Orthopedic devices
• Dental healing caps
• Drug delivery systems

Tips for Machining PEEK

PEEK is a machinable thermoplastic, but certain steps must be taken to ensure the best results.

• Annealing: This process relieves stress and reduces surface cracks during machining. Multiple annealing stages may be needed based on the machining time.
• Cutting Tools: Silicon carbide cutting tools are generally used, but diamond tools may be required for carbon fiber-reinforced PEEK or tight tolerances. Avoid tool contamination by not using the same tools on metals.
• Wet or Dry: PEEK requires cooling during machining to prevent deformation or breakage. Standard liquid coolant is usually sufficient, though pressurized air is recommended for medical parts to maintain biocompatibility.
• Drilling: Deep hole drilling can cause cracks due to PEEK's lower elongation compared to other plastics.

PEEK Machining vs. 3D Printing and Injection Molding

Apart from CNC machining, PEEK can be processed via additive manufacturing or injection molding. The choice of method depends on the desired end product, as well as budget and time constraints.

While 3D printing with PEEK is growing in popularity for creating biocompatible medical implants thanks to the ease of producing complex geometries, CNC machining and injection molding remain more widely used. For example, PEEK filaments for FDM printing and powders for SLS printing are available, but the range of PEEK for these processes is still limited compared to CNC machining.

Injection molding with PEEK is common in medical and aerospace applications, though the material's high melting point makes it a specialty for many machines. Learn more from our guide on Plastic CNC machining and how to choose the best type for your project. Consider other high-temperature plastics like PEKK or Ultem if PEEK is not suitable.

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