Polyimide (PI) and polyetheretherketone (PEEK) are superior high‐performance thermoplastics being extensively used in the fields of fiber‐reinforced polymer composites. However, there is very limited literature addressing the machining behavior of the PI and PEEK composites. The present paper aims to conduct a comparative study into the machining characteristics of these two representative high‐performance thermoplastic matrix composites under varying cutting conditions. Machinability aspects of the carbon/PI and carbon/PEEK thermoplastic composites were evaluated in terms of drilling forces, machining temperatures, delamination damage, surface morphologies, hole dimensional accuracy and tool wear. The results indicate that the carbon/PEEK composites generally show a much poorer machinability than the carbon/PI composites in terms of higher drilling forces, higher cutting temperatures, larger delamination extents and excessive tool wear. Since the carbon/PEEK composites exhibit certain ductility leading to the continuous chip formation, the cut hole surface morphologies and dimensional accuracy are much better than those gained in the carbon/PI composites. Both the cutting speed and the feed rate affect significantly the drilling forces and the resulting delamination damage. The fundamental wear mechanisms of drilling carbon/PI composites are abrasion wear in the form of edge rounding and slight chip adhesion, while for the carbon/PEEK composites, they are abrasion, serious chip adhesion because of the high drilling temperatures promoted at the drill‐work interface and catastrophic failures of coating peeling and edge fracture.
Machining of high-strength carbon fiber reinforced polymers (CFRPs) has faced great challenges in quality control and tool wear management due to their inherent heterogeneity and high abrasiveness leading to serious workpiece damage and rapid tool wear. The present paper contributes to an experimental investigation of evaluating the machinability of one type of high-strength T800/X850 CFRPs representative of aircraft components. The novelty of this work lies in identifying the effects of different specialized drills on the drilling process of the high-strength CFRPs by covering a variety of aspects involving the drilling forces, hole morphologies, workpiece damage, hole dimensional accuracy, and tool wear. Both the in-situ and post-process measuring results were correlated with the input process parameters and the used drill bits. A particular focus was placed on the inspections of the resulting tool morphologies and wear mechanisms governing the drilling of the high-strength CFRPs. The results highlight the importance of using functionally designed drills and optimum cutting conditions in realizing the damage-free drilling of T800/X850 composites.
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