# Study on Burr Formation and Tool Wear in Drilling CFRP and Its Hybrid Composites
###### Abstract
Delamination is one of the most serious defects in the processing of FRP materials, which is an inter-laminar or inter-ply failure phenomenon. Delamination directly affects the mechanical properties of FPR materials and shortens their fatigue lives, hence limiting their further applications [10]. [PERSON] et al. [26] have investigated the effects of three tool types (uncoated, TiN coated and DLC coated) on tool wear, delamination and spalling during drilling of carbon fiber-reinforced epoxy, which cause the rise in thrust force and torque with increasing tool wear. The coatings were not found to be helpful in reducing tool wear or damage to composites. [PERSON] et al. [27] reported that adequate tool selection can minimize the delamination of CFRP and GFRP composite materials during drilling operations, and a low feed rate can reduce axial thrust force and is more suitable for laminated drilling. They also pointed out that the geometry and type of the tool have an impact on feed rate, thrust force and delamination around the hole. [PERSON] and [PERSON] [28] investigated the influence of cutting parameters, such as cutting velocity and feed rate, on power, specific cutting pressure and delamination in the drilling of CFRP materials. The authors concluded that the feed rate has a greater influence on power and specific cutting pressure, so the delamination increases with the feed. By changing the action point and cutting direction, [PERSON] et al. [29] found that upward cutting can cut fibers better than cutting from the machined side to the drill exit in cutting CFRP, and the novel intermittent-sawtooth drill structure effectively reduces burrs and delamination. [PERSON] et al. [8] also reviewed the formation mechanism of delamination drilling FPR materials and reported that the drilling-induced delamination usually occurs at the hole entry and hole exit of the drilled hole periphery. The hole entry delamination (peel-up delamination) is mainly related to the flute shape, helical angle, drilling torque and drill vibration, while the hole exit delamination (push-out delamination) is mainly related to the thrust force, interface quality of the laminates and process conditions. Many other researchers have also studied delamination during drilling FPR materials [30; 31; 32]. By reviewing the above literature, it is found that most of the studies mainly focus on delamination during drilling FPR materials, but the research on uncut fibers and tool wear is still not clear, and there is a deficit in the existing knowledge of the wear mechanisms, including factors that determine the wear resistance of the tool, especially research on hybrid FPR materials, which is still in the exploratory stage. At present, among the three common FRP materials, CFRP is widely used in high-class cars, due to its excellent \"weight-loss benefit\". However, due to its low energy absorption and long production cycle time, CFRP cannot be widely used in ordinary vehicles. [PERSON] et al. [33] found that the use of hybrid CFRP materials can improve the above shortcomings. [PERSON] et al. [34] also reported that carbon/aramid hybrid composites had better stab resistance performances compared to the CFRP, especially the [C8/A8] hybrid composite, which had the best stab resistance without penetration. To further investigate the drillability of hybrid FPR materials, the carbon/aramid hybrid composites (CFRP/AFRP) were successfully synthesized in this study. In addition, the burr formation and tool wear were also comparatively analyzed in drilling CFRP and hybrid CFRP/AFRP (C-AFRP) composites.