Hole Delamination Research Articles

Effect of Drilling Parameters and Tool Geometry on the Thrust Force and Surface Roughness of Aerospace Grade Laminate Composites.

Carbon fiber-reinforced plastics (CFRPs) have been specially developed to enhance the performance of commercial and military aircraft because of their strength, high stiffness-to-density ratios, and superior physical properties. On the other hand, fasteners and joints of CFRP materials may be weak due to occurring surface roughness and delamination problems during drilling operations. This study's aim is to investigate the drilling characterization of CFRPs with different drilling parameters and cutting tools. Drilling tests were performed with the Taguchi orthogonal array design (L18: 2^1 3^3). Tests were conducted with three levels of cutting speed (15, 30, 45 m/min), three levels of feed rate (0.05, 0.1, 0.2 mm/rev), two levels of drill diameter (3 and 5 mm), and three different types of drills (two twist drills with a point angle of 138° and 120° and one brad drill). Thrust forces were recorded during drilling tests, and afterwards surface roughness and hole delamination were measured. Obtained results were analyzed with Taguchi and two-way ANOVA. The general tendency was that low cutting speed, high feed rate, and small diameter drill caused an increase in thrust force. Surface roughness decreases with increasing tool diameter, decreasing feed, and cutting speed. Delamination factors of the samples dropped depending on decreasing thrust force levels. Remarkably, it is possible to control the delamination factor values via better surface quality. The brad drill and larger point angle have a negative effect on the drilling quality of CFRPs. According to all results, the cutting speed of 45 m/min and feed rate of 0.05 mm/rev using a type II drill having a 120° point angle and 5 mm diameter (12th trial) and the cutting speed of 30 m/min and feed rate of 0.05 mm/rev using a type II drill having a 120° point angle and 3 mm diameter (2nd trial) were determined as optimum drilling conditions.

Analysis of Tool Wear and Hole Delamination for Large-Diameter Drilling of CFRP Aircraft Fuselage Components: Identifying Performance Improvement Drivers and Optimization Opportunities

This study provides a comprehensive analysis of the one-shot drilling (CFRP) strategy for machining CFRP materials in the assembly of aircraft components, focusing on key factors such as tool wear, hole delamination, and the evolution of machining forces. The research uses adapted parts of the tail-cone structure of a commercial aircraft as workpieces and employs large-diameter cutting tools to perform drilling operations, with results that can be readily applied to the industry. The study selects cutting conditions by analyzing the effect of cutting parameters on tool life in drilled holes and accumulated cutting time, with the end-of-life criterion based on the extension of the wear suffered by the main cutting edge of the first step. The results show that all tested cutting conditions achieve a similar value of tool life expressed in terms of holes drilled, with differences smaller than 7%. However, one of the cutting conditions analyzed completes the same number of holes within 40% less time. Therefore, considering productivity criteria, it will be interesting to evaluate the use of high values for the cutting parameters. Overall, this research provides valuable insights for improving the efficiency and effectiveness of CFRP machining in aircraft manufacturing.

Optimization of CO2 laser drilling process parameters of GFRP/Al2O3/perlite composites

Glass Fiber Reinforced Polymer (GFRP) composites have excellent mechanical characteristics and are extensively used in aerospace and marine applications. Drilling GFRP composite through conventional methods leads to delamination and taperness, causing quality loss and imprecision. CO2 laser drilling, an unconventional method to drill GFRP composites, is adopted in this study to reduce the delamination and taperness. This work aims at optimizing the process parameters of CO2 laser drilling. Hybrid S-glass/Al2O3/Perlite powder composite is used in this study. Laser drilling parameters: laser power (P), cutting speed (N), focal length (L), and hole diameter(d) were studied to reduce the hole delamination and hole taperness. These results were achieved through mathematical modelling and optimization using Response Surface Methodology (RSM) and Multi-Objective Genetic Algorithm (MOGA). The optimum process parameters were found by minimizing the objective function upon considering the drilled holes economic features, deposition efficiency, geometric features, and hole diameter at larger and smaller sides. The most critical output factors, delamination and taper responses, had a deviation from the objective by less than 3%. The optimum process parameters laser power, cutting speed, and focal length is found to be 80.795 W, 7.9089 mm/sec, and − 1.9641 m respectively. From the experimental confirmation study, the optimum process parameters effectively reduced the hole delamination and taperness.

Optimization of process variables in drilling of carbon fiber reinforced plastics using various multi criteria decision making approaches

AbstractCarbon fiber‐reinforced polymers are one of the lightweight materials used in structural design due to their exceptional mechanical performances. The drilling operation is indispensable as it facilitates the assembling of various manufactured components. However, drilling of fibrous laminates is deemed difficult in comparison to the traditional metals because of the anisotropic and non‐homogeneous nature. The present work addresses the parametric effect on the drilled hole delamination and further reduces it with an optimal combination of parameters for multi‐objectives using different multi‐criterion decision‐making techniques. Initially, the response surface‐based regression model of delamination as a function of three static inputs has been developed, further revised with induced thrust as well as mean torque for the improvisation of the prediction capability. Finally, for the overall improvement, a decision‐making model has been used that includes grey relation analysis, technique for order performance by similarity to ideal solution, and VIšekriterijumsko Kompromisno Rangiranje method. The delamination was found to be minimum at a low drill point angle (100°), high spindle rotation (2150 min−1 ), and low feed rate (0.025 mm/rev) due to reduced thrust force. The mean absolute prediction error was significantly improved considering root mean square torque rather than axial thrust with process variables.

Drilling carbon fiber reinforced plastics with pre-cooling treatment by cryogenic fluid

The high technological properties of carbon fiber reinforced plastics (CFRPs) have led to their ever-increasing use in recent decades for industrial applications, especially in the aerospace and automotive sectors, where the demand for lightweight structures is high. The panels of composite, to be assembled with other materials, may require repeated realization of holes, making the final quality of the union highly dependent on the drilling process. However, the heterogeneity of the composite material may lead to several inconveniencies, such as rapid tool wear and hole delamination, as during machining the drill bit encounters fiber and matrix alternatively, which have different properties. These damages could be reduced through cryogenic drilling, as demonstrated in the related literature, mainly because the machining behavior of composite changes at low temperatures. Starting from this evidence, the present paper proposes an experimental study conducted on CFRP panels using a new methodology of cryogenic drilling, based on the pre-cooling of the composite before starting the machining process, in order to create a uniformly refrigerated material. The analysis is aimed at comparing the hole quality obtained under dry and pre-cooled cryogenic conditions in terms of delamination, surface roughness and dimensional accuracy and at evaluating thrust force, tool wear and the influence of feed rate.

BPNN-ACO application on minimization of hole delamination during GFRP drilling process

Delamination defects during the drilling process on the glass fiber reinforced polymer (GFRP) have a great contribution to the component failure. Hence, it is necessary to properly choose the combination of machining variables to minimize hole entry delamination (EnDel) and hole exit delamination (ExDel) during drilling process simultaneously. This study underlines the modelling and minimizing the EnDel and hole ExDel during GFRP drilling process by combining a backpropagation neural network (BPNN) method and ant colony optimization (ACO). The varied drilling parameters were type of drill point angle, feeding speed, and cutting speed. The optimum BPNN architecture could be obtained by using 3-4-2-5-8-2 network architecture with tansig activation function. The optimum GFRP drilling parameters that can minimize EnDel and ExDel simultaneously were 116° of drill point angle, 51.3 mm min−1 of feeding speed and 4975 rpm of spindle speed.

Influence of cryogenic cooling on milling hole exit of QFRP based on thermal–mechanical coupling

Quartz fiber–reinforced polyimide composites (QFRP) had heterogeneous and anisotropic properties. Because of the gradient change of cutting force at hole exit, some fibers could not be effectively chipping breaking and the defect of delamination burr was often inevitable. In this paper, a cutting force model of fiber fracture stripping considering thermal–mechanical coupling was constructed based on the mechanism of cutting force and thermal action. A series of milling hole tests at different temperatures (from 290 to 80 K) was carried out using liquid nitrogen inner-cooling equipment. Similarly, the hole exit morphology, milling force, and cutting temperature were investigated and the delamination factors were calculated in detail. The results show that the model can explain the reason of hole exit defect, which is attributed to the lack of tangential cutting force and the large gradient change of axial force considering the high cutting temperature. Meanwhile, cryogenic cooling can reduce the effect of cutting temperature for hole exit defect. Although the cutting force is increased, the gradient degree of axial force can be reduced, and the delamination factor can be decreased from 1.08 at low-speed dry cutting to 1.01 of high-speed cryogenic one. At the same time, the increase of tangential force and the decrease of fiber ductility improve the chip breaking ability and the processing efficiency. Conclusion: the spiral hole milling process with cryogenic medium intervention can inhibit the milling hole delamination defects.

The Investigation of Hole Delamination in Drilling Kevlar Composite Panel Using HSS Drill Tool

The drilling process has been mostly used in composite panel machining to be a final product. It becomes a critical process when the composite product requires a high hole precision for the purpose of assembly and quality standard. Machining Kevlar composite is a difficult task due its hardness, fiber layer bounding and fiber orientation. The cutting condition needs to be controlled carefully to minimize the vibration, cutting temperature and hole delamination. This paper discusses the investigation of hole delamination in drilling Kevlar composite panel. The twist drill type of High-Speed Steel (HSS) drilling tool with 12 mm diameter was used to drill a 4 mm thick Kevlar composite panel. Three levels of spindle speed (1000 rpm, 1400 rpm and 2000 rpm) and three levels of feed rate (130 mm/min, 160 mm/min and 180 mm/min) were selected as the configuration of cutting condition. The hole diameter was measured and was compared to the drill tool diameter. The result of the experiment shows that the cutting condition gave significant effect to the drill hole delamination factor. The highest delamination factor was 1.36 and achieved by drilling condition with spindle speed of 1000 rpm and feed rate of 160 mm/min. The lowest delamination factor was 1.161 and achieved by drilling condition with spindle speed of 2000 rpm and feed rate of 130 mm/min.

An Investigation of the Effect of Parameters and Chip Slenderness Ratio on Drilling Process Quality of AISI 1050 Steel

The chip slenderness ratio is a vital parameter in theoretical and applicable machining operations. In predrilled drilling operations of AISI 1050 steel alloy, HSS drills were employed, and the effect of the selected parameters on the chip slenderness ratio and also the effect of the chip slenderness ratio on the thrust force, surface roughness, drilled hole delamination, tool wear, and chip morphology were investigated. The major parameters, influential on the chip slenderness ratio, were feed rate and point angle, while spindle speed was too small to be negligible. With increasing the chip slenderness ratio, the thrust force and the tool wear decreased, which resulted in appropriate chip morphology, but there were increases in surface roughness. However, the chip slenderness ratio had no effect on the drilled hole delamination.

Effect of Tool Wear on Hole Quality in Drilling of Carbon Fiber Reinforced Plastic–Titanium Alloy Stacks Using Tungsten Carbide and Polycrystalline Diamond Tools

This paper reviews the nature of hole defects and postulates the cause of hole defects resulting from the drilling process of carbon fiber reinforced plastic–titanium alloy stacked panels (CFRP–Ti stacks) using tungsten carbide (WC) and polycrystalline diamond (PCD) twist drills. The parameters that describe the hole quality of the CFRP–Ti stacks include CFRP entry hole delamination, hole diameter and roundness, inner hole surface roughness, CFRP hole profile, CFRP–Ti interplate damage, and Ti exit burr. They are caused by heat generation during drilling as well as hot Ti chips and adhesion, Ti burr formation, tool instability, and tool geometry change due to tool wear. For the WC drills, large flank wear and margin wear occurred at the high spindle speed condition, resulting in a reduction of the hole size and an increase of the hole roundness and CFRP–Ti interface damage. At the low spindle speed condition, tool geometry was changed due to the large edge rounding. This resulted in large fiber pull-out at the CFRP hole surface. Ti entry burrs caused damage associated with fiber removal and matrix discoloring at the bottom of the CFRP panel and this interplate damage was observed to increase with tool wear. When compared with the WC tool at the same speed condition, the PCD drill maintained relatively small hole defects under all parameters.

Research on Helical Milling Specialized Tool Based on Chip-Splitting Mechanism

Compared with conventional push drilling, helical milling (orbital drilling) shows great advantages in aeronautical hard-machining materials hole making. However, helical milling of titanium alloy and carbon fiber reinforced plastic (CFRP) under dry cut condition still faces challenges such as burr of titanium alloy hole exit and CFRP hole delamination. In order to solve these problems, an innovative helical milling tool with distributed multi-point front cutting edge is designed based on the chip-splitting mechanism and tool movement feature. The description of cutting edge movement track and simulation of chip shape is used to analyze different functions of front and peripheral cutting edges, the chip-splitting result and the specialized tool's service life. The helical milling experiments are aimed to test the performance of the specialized tool compared with that of traditional end mill. Results show that the specialized tool can machine titanium hole free of burr and CFRP hole without delamination under dry cut condition. The specialized tool has a longer service life with its machining capacity amounting to 80 titanium holes and 65 CFRP holes..

An iterative approach for the evaluation of delamination stresses in laminated composites

AbstractA computational strategy for the evaluation of delamination stresses in multilayered fibre‐reinforced composites is presented. The approach uses special inter‐laminar shear elements and an iterative procedure in the calculation of out‐of‐plane stresses. Both regular and singular elements for the free edge are presented. The solutions are carried on by switching between direct matrix solution methods of small systems of equations and an iterative conjugate gradient method. The proposed discretization avoids ill‐conditioning problems, modelling difficulties and large computational cost associated with three‐dimensional analysis of delamination of holes, cut‐outs, joints and areas of complex stress states.