CNC Machining PEEK: Tooling, Feeds, and Heat Management

 

PEEK CNC machining allows manufacturers to turn a high-performance engineering plastic into tight-tolerance parts for demanding industries such as aerospace, medical, and semiconductor applications. When done correctly, it delivers metal-like precision with lower weight, excellent chemical resistance, and long-term dimensional stability.

What is PEEK CNC machining?

PEEK (polyetheretherketone) is a semi-crystalline, high-temperature thermoplastic known for high strength, chemical resistance, and very low creep, even at elevated temperatures. PEEK CNC machining uses turning, milling, drilling, and other subtractive processes to shape extruded or molded PEEK stock into finished components with tight tolerances and excellent surface finishes.

Compared with metals, PEEK plastic machining can often achieve similar precision while reducing part weight, improving corrosion resistance, and simplifying assemblies by replacing multi piece metal designs with a single machined plastic component. These advantages make PEEK CNC machining a preferred solution where reliability and long service life are critical.

Advantages of PEEK CNC machining

PEEK's stiffness, dimensional stability, and low thermal expansion help machined parts maintain tolerances under fluctuating load and temperature, making it ideal for precision components. The material's mechanical strength and fatigue resistance allow it to replace metals in many structural applications, while retaining performance in hot, chemically aggressive environments.

From a manufacturing perspective, PEEK plastic machining supports complex geometries, thin walls, and fine features that can be difficult to mold, especially for low to medium volume production. CNC machining also reduces tooling cost and lead time compared with injection molding, which is important for prototypes, custom parts, and high-mix production.

General best practices in PEEK plastic machining

PEEK has relatively low thermal conductivity, so heat tends to concentrate in the cutting zone; using sharp carbide or diamond-coated tools, controlled cutting parameters, and appropriate cooling is critical to avoid thermal damage. High cutting speeds combined with moderate to low feed rates can promote clean shearing, minimize burrs, and improve surface finish, provided that tool sharpness and heat management are maintained.

Optimized tool geometry with positive rake and relief angles helps reduce cutting forces, limit heat buildup, and achieve smoother surfaces in PEEK CNC machining. For drilling and deep pockets, coolant or air blast is important to evacuate chips and reduce localized heating, preventing softening, smearing, or micro cracking of the PEEK surface.

Annealing and stress relief for PEEK machining

Annealing PEEK before machining relieves internal stresses from extrusion or molding, reduces the risk of warping and cracking, and improves dimensional stability during and after machining. The annealing process increases crystallinity and slightly softens the material, which enhances machinability, lowers tool wear, and improves surface quality.

If annealing is skipped, semi-finished stock may distort as material is removed, leading to out of tolerance parts or surface defects, especially in complex or thick-section components. Many guidelines also recommend a secondary annealing step after rough machining or between roughing and finishing to relax newly introduced stresses and stabilize dimensions before final cuts.

Machining pure (unfilled) PEEK

Unfilled PEEK is relatively easier to machine and produces continuous, ductile chips, but heat control remains essential due to its low thermal conductivity. Sharp carbide tools with positive rake, high spindle speeds, and light to moderate depths of cut help generate clean surfaces without smearing or excessive burr formation.

Because pure PEEK is less abrasive than filled grades, tool life is generally longer and standard carbide tools are usually sufficient for most CNC machining operations. Nonetheless, it is good practice to anneal highprecision unfilled PEEK blanks, especially for thick parts or tighttolerance features that are sensitive to creep and residual stresses.

Machining CF30 PEEK (30% carbon fiber)

CF30 PEEK is reinforced with about 30% carbon fiber by weight, significantly increasing stiffness, strength, and wear resistance compared with unfilled grades. This reinforcement also makes the material more abrasive, so tool wear is higher and tool selection becomes more critical in PEEK plastic machining.

Carbide tools with wear-resistant coatings or diamond tools are commonly recommended to maintain edge sharpness and dimensional accuracy when machining CF30 PEEK. Cutting parameters often need to be more conservative than for unfilled PEEK, with controlled feeds, speeds, and depths of cut to balance productivity, surface finish, and tool life.

For CF30 PEEK, annealing is particularly useful for thick or complex parts to reduce internal stress and prevent micro-cracking along fiber rich regions, especially in highly loaded components. Post-machining stress relief may also be beneficial when tolerance stability over time and temperature is critical, such as in aerospace or precision mechanical assemblies.

Machining GF30 PEEK (30% glass fiber)

GF30 PEEK contains approximately 30% glass fiber, which boosts stiffness, dimensional stability, and creep resistance but introduces very high abrasiveness during machining. This grade can achieve excellent dimensional control and reduced thermal expansion, but it demands robust tooling and careful process planning.

Diamond-coated or high quality carbide tools with optimized geometry are strongly recommended for GF30 PEEK to reduce flank wear and maintain edge integrity. Lower cutting speeds, controlled feeds, and frequent tool inspection are important to prevent chatter, delamination at edges, and inconsistent surface quality as tools dull.

Because of the high fiber content, GF30 PEEK benefits greatly from pre-machining annealing to minimize internal stress and improve crack resistance under mechanical or thermal loading. For precision parts, an additional anneal after roughing can further stabilize the material before final finishing operations in PEEK CNC machining.

Machining MOD PEEK (modified grades)

MOD PEEK generally refers to modified PEEK formulations, which may be filled or compounded with lubricants, pigments, or other additives to tailor properties such as friction, electrical behavior, or processing performance. Typical modifications seek improved wear resistance, lower friction, or easier machining while preserving the core mechanical strength and temperature resistance of standard PEEK.

Machining parameters for MOD PEEK depend heavily on the specific formulation: self-lubricating grades may machine more smoothly, while heavily filled variants may behave closer to CF30 or GF30 PEEK in terms of abrasiveness and chip formation. Tool selection should follow material specific guidance from the supplier, but in general it is safe to start with carbide or diamond tools, conservative feeds and speeds, and then optimize based on achieved surface finish and tool wear.

Because some modified PEEKs are designed for improved dimensional stability, they may be slightly less sensitive to residual stress, yet annealing is still recommended for critical tolerance parts or thick sections. Always confirm the recommended annealing temperature profile and time with the material data sheet, as additives can alter the optimal thermal cycle.

Practical machining tips and cautions

Use sharp tools and positive rake geometries to reduce cutting forces, avoid smearing, and achieve high-quality surfaces in PEEK plastic machining. 

Control heat with appropriate cutting speeds, moderate feeds, minimal depths of cut, and effective coolant or air blast to prevent thermal degradation and distortion.

Rough machine leaving a small stock allowance, allow the part to rest or anneal, then finish machine to final dimensions for best stability in PEEK CNC machining.

For CF30, GF30, and abrasive MOD PEEK grades, plan for higher tool wear, shorter tool change intervals, and more frequent inspection of critical dimensions.