Promoting chip breakage in biomedical-grade PEEK machining through tool texturing and cryogenic cooling

Polyetheretherketone (PEEK) is an advanced thermoplastic polymer with excellent mechanical and chemical properties, making it ideal for various applications. Its elastic modulus, closely matching that of human bone, and its biocompatibility make PEEK suitable for orthopedic prostheses. Machining PEEK poses challenges, especially in biomedical applications, as traditional coolants—which leave oily residues—cannot be used, making dry machining preferable. However, dry machining produces long, continuous chips, reducing productivity and surface quality. Thus, alternative approaches are needed to improve the performance of the PEEK machining process. One promising method is tool surface texturing, which involves creating patterns on the tool surface to modify the chip-rake face contact area. In this context, the present study investigates the effect of tool texturing under different cooling conditions on the chip formation of a biomedical-grade PEEK. To this end, turning trials were conducted on a PEEK bar under dry and cryogenic conditions using laser-textured inserts with different groove depths and geometries: parallel and orthogonal to the cutting edge. Chip morphology was analyzed in detail for each cutting condition, focusing on its overall average length, thickness, and morphology. Chip-tool contact length was also measured under dry conditions. Cutting forces and temperatures were recorded to support the findings. The results indicate that both tool texturing and cooling conditions significantly impact chip formation. Chip breakage was consistently achieved under cryogenic cooling, with texturing further promoting chip-breaking into shorter segments. Conversely, long continuous chips were formed under dry conditions, although tool texturing still influenced the chip characteristics.