This paper focuses on the effect of the drill geometry on the drilling of woven Carbon Fiber Reinforced Polymer composite (CFRPs). Although different geometrical effects can be considered in drilling CFRPs, the present work focuses on the influence of point angle and wear because they are the important factors influencing hole quality and machining forces. Surface quality was evaluated in terms of delamination and superficial defects. Three different point angles were tested representative of the geometries commonly used in the industry. Two wear modes were considered, being representative of the wear patterns commonly observed when drilling CFRPs: flank wear and honed cutting edge. It was found that the crossed influence of the point angle and wear were significant to the thrust force. Delamination at the hole entry and exit showed opposite trends with the change of geometry. Also, cutting parameters were checked showing the feed’s dominant influence on surface damage.

CFRPs Drilling Delamination ModelingDelamination is one of the undesired effects of machining using non appropriate cutting parameters or worn drill. Finite element modeling of drilling of Carbon Fiber Reinforced Polymer (CFRP) composites is an interesting tool for damage prediction. Recently, complete modeling of the process including the rotatory movement of the drill, penetration in the composite plate and element erosion has been developed in the scientific literature. Computational cost of these complex models is a great disadvantage when comparing them with simplified models that consider the drill acting like a punch that pierces the laminate. In this paper both complete and simplified models were developed and compared in terms of delamination prediction. The simplified model, presenting reduced computational cost, slightly overestimates the delamination factor when compared with the complex model. The influence on delamination of thrust force, clamping area at the bottom surface of the laminate and the stacking sequence is studied using the simplified model.

This paper focuses on the influence of the step drill bit geometry on the damage induced during drilling Carbon Fiber Reinforced Polymer materials (CFRPs).Step geometry designed with the aim of avoiding composite damage in CFRPs drilling, is compared to conventional twist configuration. Despite the reduction of thrust force and torque observed when using the step drill, the delamination was only reduced at low feed rates. A numerical model developed for the step geometry was validated with experimental data demonstrating its ability to predict thrust force and delamination for different values of feed rate and cutting speed. Numerical model allowed the development of a parametrical study. Finally, using a response surface methodology a mechanistic model and surface diagrams have been presented in order to help in the selection of optimum variables minimizing drilling induced damage.

CFRPs drilling is a common process in the aerospace industry carried out prior to components assembly. Machining induced damage leads to significant percentage of component rejection. Damage extension strongly depends on drilling geometry and cutting parameters. Fresh drill geometry changes with cutting time due to the wear progression and the risk for hole quality is enhanced as cutting progresses. The influence of wear on hole quality has been analyzed in the literature using mainly an experimental approach.Simulation of drilling process is an effective method that can be used to optimize drill geometry and process parameters in order to control hole quality and analyze the drill wear evolution. In this paper a finite element model for drilling woven CFRPs, reproducing both fresh and worn tools, is presented. Two different point angles considering fresh and honned edge were modeled. A progressive intralaminar failure model based on the Chang and Chang model is considered. Cohesive elements allowed the analysis of inter-laminar damage (delamination). The model demonstrated its ability to predict thrust force and delamination for different values of feed rate and cutting speed. Model predictions show the influence of tool geometry (including variations induced due to wear) on delamination.

Drilling is one of the most frequent machining operations for carbon fiber-reinforced polymer composites, carried out prior to assembly between structural components using mechanical joining. Delamination is the main damage mechanism involved during carbon fiber-reinforced polymer composite drilling causing an elevated percentage of workpiece rejection. Tool geometry strongly influences drilling performance. In this paper, an original work dealing with the comparison between three recently developed configurations (Brad center, Step drill and Reamer drills) in terms of drilling forces and delamination both for woven and tape carbon fiber-reinforced polymers is presented. Reamer drill showed the best results concerning productivity and delamination. Strong differences were found when hole quality obtained in tape and woven composite was compared: multidirectional composite presented poorer hole quality than woven composite under the same cutting conditions. The analysis of variance was developed in order to analyze the influence of each parameter showing the importance of feed rate on surface damage.