Influence of Infill Structures and Process Parameters on the Tensile Strength of 3D-printed PEEK Parts

Polyetheretherketone (PEEK) is a high performance semi crystalline polymer used in technical applications as well as for medical purposes. Its mechanical properties and its temperature resistance often allow its use instead of metal for lightweight applications. In the medical field, its biocompatibility and the modulus of elasticity similar to this of bones make it a good choice for implants. For this purpose, additive manufacturing is a technology that allows the economic production of patient-specific implants. Until now, only few 3D- printers for PEEK are available on the market and only few process knowledge is available so far. In this paper, PEEK parts are fabricated using a 3D-printer based on the Fused Layer Manufacturing (FLM) technology. The influence of different process parameters on the mechanical properties of the specimens is investigated. For this, printing speed, local part cooling, filling degree and infill geometry are varied and the tensile strength of the corresponding specimens is investigated. Fracture surfaces are analyzed using optical microscopy and scanning electron microscopy. Results show a slightly increase of tensile strength at lower printing speed. Filling degree as expected has great influence on the mechanical properties. Optical investigation often shows insufficient adhesion between the single layers. Also a filament with carbon fiber reinforcement is used and compared to the standard material. This material shows a significant increase in tensile strength and stiffness.