Drilling Of Composite Materials Research Articles

Influence of drill geometry on thrust force in drilling GFRP composites

In this article, influence of drill geometry on thrust force in drilling GFRP composites is analyzed. Glass fiber-reinforced composite materials are finding increased application in different fields such as automobile, ship building, sport goods, etc., due to their excellent properties. Drilling is indispensable process and it cannot be avoided for joining composite structures. In this study, drilling experiments are conducted on these composite materials using CNC drilling machine. Three different drill bits are used for the experimentation. The response analyzed is thrust force. The influence of drill geometry on thrust force in drilling of composite materials is carried out using three different drill bits, namely, ‘Brad and Spur’ drill, ‘multifaceted’ drill, and ‘step’ drill. The analyses of the results are carried out using effect graphs and three-dimensional graphs. The results indicated that the step drills are performing better than the other drills considered.

Modeling and Analysis of Surface Roughness Parameters in Drilling GFRP Composites Using Fuzzy Logic

Glass fiber–reinforced composite materials are finding numerous applications in many engineering and domestic fields due to their excellent mechanical properties and corrosion resistance. Among the machining processes used, drilling is one of the most important processes and is mainly used in joining of composite structures. Maintaining of proper surface roughness in drilled holes is very important and is to be controlled. In the present work prediction of surface roughness in drilling of composite materials is carried out using fuzzy logic. In recent years, fuzzy logic in artificial intelligence has been used in manufacturing engineering for modeling and monitoring. An L27 orthogonal array is used for experimentation. A fuzzy rule–based model is developed to predict the surface roughness in drilling of glass fiber–reinforced plastic (GFRP) composites. Good agreement is observed between the model results and experimental values. The analysis of experimental results is carried out using Pareto analysis of variance (Pareto-ANOVA) and ANOVA and presented in detail.

Analytical models of composite material drilling

Drilling of composite material structures is widely used for aeronautical assemblies. When drilling, damage to the composite laminate is directly related to the cutter geometry and the cutting conditions. Delamination of the composite materials at the hole exit as directly related to the axial force (F Z) of the cutter is considered to be the major such defect. To address this issue, an orthotropic analytical model is developed in order to calculate the critical force of delamination during drilling and a number of hypotheses for loading are proposed. This critical axial load is related to the delamination conditions (propagation of cracks in the last layers) and the mechanical characteristics of the composite material machined. A numerical model is also drawn up to allow for numerical validation of the analytical approach. A comparison between these analytical and numerical modellings and experimental results from quasi-static punch tests led to the choice of the loading hypothesis closest to the experimental conditions. The selection of corresponding load permits to model the drilling critical thrust force on delamination and then to optimise the cutting conditions. The dimensions and geometrical shape of the cutter are of considerable importance when it comes to choosing this load. The present article focuses on the case of the twist drill, which is commonly used to drill thick plates. However, this work can be adapted to different cutter geometries.

Study of drilling of composite material and aluminium stack

Abstract Drilling of CFRP/Al or CFRP/Ti, or Al/CFRP/Ti is a challenge to manufacturing engineers. Drilling of CFRP is manageable but the minute drill hits the Al or Ti, those hot and continuous chips destroy the hole. Few studies are carried out in this aspect; CFRP/Al is not reported till date. It is important to select right process parameters when drilling multimaterial stack since each material in the stack requires a different set of machining parameters. Hence, Drilling trials have been carried out in carbon-fibre reinforced plastics (CFRP)/aluminium (Grade 2024) stack without coolant, with plain carbide (K20) drills of various diameters to choose optimum process parameters. The parametric influences on thrust force, torque as well as surface finish were experimentally evaluated. The experimental results show that the quality of holes can be improved by proper selection of cutting parameters. This is substantiated by monitoring thrust force, torque, surface finish, circularity and hole diameter. For the CFRP, the circularity is found to be around 6 μm at low feed rates, when the feed is increased the circularity increases to 25 μm. The wear tests carried out show that, during first 30 holes, thrust force in CFRP undergoes a more important increase (90%) than thrust force of aluminium (6%).

Analysis of Thrust Force in Drilling Glass Fiber-Reinforced Plastic Composites Using Fuzzy Logic

Glass fiber-reinforced plastic (GFRP) composite materials are finding increased application in many engineering fields. Machining of these materials cannot be avoided to get accuracy and precision fits. Among the various machining processes used, drilling is one of the most important processes and is mainly used in joining of composite structures. A major problem which encountered in drilling of GFRP composite laminate is damage or delamination. The damage due to thrust force is the important concern in drilling, and it leads to poor machinability. In the present work, prediction of thrust force in drilling of composite materials is carried out using fuzzy logic. Fuzzy rule-based model is developed to predict the thrust force in drilling of GFRP composites. The effectiveness of the fuzzy model was compared with the response surface model. Good agreement is observed between the predictive model values and experimental values. The analysis of machining parameters on drilling is carried out using Pareto analysis of variance (Pareto–ANOVA) and analysis of variance (ANOVA).

Analysis of fracture mechanisms and surface quality in drilling of composite materials

The aim of this work is to clarify the interaction mechanisms between the drilling tool and material. Drilling tests were carried out on glass/polyester and carbon/epoxy composites using different twist drills. The cutting tools and machined surfaces were examined by optical microscopy, scanning microscopy and surface profilometry to study composite damage and tool wear. Among the defects caused by drilling, delamination appears to be the most critical and may occurs at both the entrance and exit planes. A prediction model of thrust force for drilling without delamination is proposed.

The geometrical effect between stages in step drilling of composite materials

The delamination-induced of step drill with step angle, stage ratio, feed rate and spindle speed in drilling Carbon Fibre Reinforced Plastic (CFRP) laminate was experimentally investigated in this study. Delamination can be minimised by changing the drill geometry of step drill. A 0.6 stage ratio of step drill with a larger step angle of 120? produced a smaller thrust force than the one with an 80? step angle during exit of the step drill. However, the effect of stage ratio on the delamination is more critical when the step angle is small.

Investigation into the effects of drilling parameters on delamination by various step-core drills

Geometry and material of drill and drilling parameters have an essential influence on induced-delamination in drilling composite materials. Owing to the chips clogged inside the core drill, three step-core drills in drilling composite materials have been investigated in this study. The Taguchi method with orthogonal array of L 18 (2 × 3 7) was selected to realize the effects of the drilling parameters (diameter ratio, feed rate and spindle speed) on induced-delamination for various step-core drill. The experimental results indicated that the diameter ratio, feed rate and spindle speed have significant influence on delamination and the best combinations found to be A 2B 1C 3 (diameter ratio = 0.74 mm/mm, feed rate = 8 mm/min and spindle speed = 1200 rpm) for all step-core drills within the tested range. Besides, the effect of inside drill diameter and geometry for the step-core drill must be concerned on induced-delamination while first cycle drilling of composite materials.

Evaluation of thrust force and surface roughness in drilling composite material using Taguchi analysis and neural network

This paper presents the prediction and evaluation of thrust force and surface roughness in drilling of composite material using candle stick drill. The approach is based on Taguchi method and the artificial neural network. The experimental results indicate that the feed rate and the drill diameter are the most significant factors affecting the thrust force, while the feed rate and spindle speed contribute the most to the surface roughness. In this study, the objective was to establish a correlation between the feed rate, spindle speed and drill diameter with the induced thrust force and surface roughness in drilling composite laminate. The correlations were obtained by multi-variable regression analysis and radial basis function network (RBFN) and compared with the experimental results. The results indicate the RBFN is more effective than multi-variable regression analysis.

Computerized Tomography and C-Scan for Measuring Drilling-Induced Delamination in Composite Material Using Twist Drill and Core Drill

Delamination is one of the most concern defects in drilling of composite material. Delamination depends on the factors such as feed rate, tool geometry and wear. The mechanics of drilling composite materials has been examined along with the quality of the hole and the effect of tool design parameters. The capacity of computerized tomography (CT) showing sample cross-section in a nondestructive way made it successful in measuring the drilling-induced delamination. In the experiment, the correlation between thrust force and the measured delamination extent in use of twist drill and core drill is illustrated and compared with the known ultrasonic C-scan. It is compared with the ultrasonic technique and is demonstrated a feasible and an effective tool for the evaluation of drilling-induced delamination.

Drilling of uni-directional glass fiber reinforced plastics: Experimental and finite element study

The use of Fiber Reinforced Plastics (FRP) has increased manifold over the last few years. Generally developed for aerospace and other high-end applications, composites are now making inroads into the automotive and general engineering market. Thus good quality and cost-effective manufacturing of FRP composites becomes imperative. Drilling of holes is an important machining operation to ascertain the assembly operations in intricate composite parts. The research endeavors in the field of drilling of composite materials have focused on optimization of the operating variables, tool geometry and theoretical modeling of the critical thrust force. The work done in the Finite Element (FE) modeling of the drilling of FRP composite materials is limited. The present initiative is an attempt to investigate statistically the relative significance of the drilling parameters on the thrust force and torque. The results of analysis of variance (ANOVA) are then used to make assumptions for developing a Finite Element model for predicting drilling induced damage. The FE results are found in good agreement with the experimental results.

Effect of tool wear on delamination in drilling composite materials

Among all machining operations, drilling using twist drill is the most frequently applied for secondary machining of composite materials owing to the need for structure joining. Delamination is mostly considered as the principal failure model in drilling of composite materials. Drill wear is a serious concern in hole-making industry, as it is necessary to prevent damage of cutting tools, machine tools and workpieces. The industrial experience shows the worn drill causes more delamination. This paper presents a comprehensive analysis of delamination caused by the drill wear for twist drill in drilling carbon fiber-reinforced composite materials. The critical thrust force at the onset of delamination for worn drill is predicted and compared with that of ideal drill. The experimental results demonstrate that though the critical thrust force is higher with increasing wear ratio, the delamination becomes more liable to occur because the actual thrust force increases to larger extent, as the thrust factor ( Z) illustrates. Compared to sharp drill, the worn twist drill allows for lower feed rate below which the delamination damage can be avoided.

Prediction of thrust force of step drill in drilling composite material by Taguchi method and radial basis function network

Among material secondary machining, drilling is the most frequently applied factor to composites needing structure joining. Drill geometry is considered the most important factor that affects drill performance. A major concern in drilling of composite materials is the delamination that occurs in the exit as well as in the entrance planes. The delamination damage caused by the tool thrust is known as one of the major concerns during the drilling process. The thrust force of step drill with drilling parameters (step angle, stage ratio, feedrate and spindle speed) in drilling carbon fiber reinforced plastics (CFRP) laminates were experimentally investigated in this study. The experimental results indicate that the step angle, stage ratio, and feedrate are the most significant factors affecting the overall performance. The optimal combinations, such as A2B2C1D3 (i.e., step angle = 100 ° stage ratio = 0.4 mm/mm, feedrate = 0.01 mm/rev and spindle speed = 1,200 rpm), were used under the adopted drilling condition. An experimental approach to the prediction of thrust force produced by step drill using linear regression analysis of experiments and radial basis function network (RBFN) were proposed in this study. In the confirmation tests, RBFN (errors within 0.3%) has been shown to be a better predictive model than multi-variable linear regression analysis (errors within 28%) for quantitative prediction of drilling-induced thrust force in drilling of composite material.

Taguchi analysis of drilling quality associated with core drill in drilling of composite material

The thrust force and surface roughness of core drill with drill parameters (grit size of diamond, thickness, feed rate and spindle speed) in drilling carbon fiber reinforced plastic (CFRP) laminate was experimentally investigated in this study. A L27 (313) orthogonal array and signal-to-noise (S/N) were employed to analyze the effect of drill parameters. Using Taguchi method for design of a robust experiment, the interactions among factors are also investigated. The experimental results indicate that thickness and feed rate are recognized to make the most significant contribution to the overall performance. For thrust force, the drilling conditions were A1B1C1D2, (i.e., grit size of diamond=#60, thickness=1.0 mm, feed rate=0.012 mm/rev, and spindle speed=950 rpm). For surface roughness, the drilling conditions were A1B1C1D3, (i.e., grit size of diamond=#60, thickness=1.0 mm, feed rate=0.012 mm/rev, and spindle speed=1150 rpm). The correlation was obtained by multi-variable nonlinear regression and compared with the experimental results. The confirmation tests demonstrated a feasible and an effective method for the evaluation of drilling-induced thrust force and surface roughness (errors within 10%) in drilling of composite material.

Prevention from Delamination of Composite Material during Drilling Using Ultrasonic Vibration

Composite materials are used for many structures because of its high strong-to-weight ratio and easy formation. Secondary machining processes such as drilling and sawing are required to assemble and join composite materials to other structures. When composite materials are machined, delamination occurs at adhesive layer between laminated layers. It is well known that it is possible to cut hard metals and to improve precision of machined surface by using ultrasonic vibration. This method is applied to machining composite materials in this paper. Drilling of composite materials is focused on. First, this method is examined experimentally. Next, experimental results are examined by analytical method. Using condition of experiment, prevention of delamination can be demonstrated from the proposed analytical method.

The path towards delamination-free drilling of composite materials

The fiber-reinforced composite materials possess advantage for structural purpose in various industries. Delamination is considered the major concern in manufacturing the parts and assembly. Drilling is frequently applied in production cycle while the anisotropy and non-homogeneity of composite materials affect the chip deformation and machining behavior during drilling. Traditional and non-traditional drilling processes are feasible for making fine holes for composite materials by carefully selected tool, method and operating conditions. In this article, the path towards the delamination-free drilling of composite material is reviewed. The major scenes are illustrated including the aspects of the analytical approach, the practical use of special drill bits, pilot hole and back-up plate, and the employment of non-traditional machining method.

Computerized tomography and C-Scan for measuring delamination in the drilling of composite materials using various drills

Whilst drilling is the most frequently employed operation of secondary machining for structure joining, delamination is a very serious defect during drilling of fiber-reinforced composite materials,. The evaluation of the delamination damage in the material is important but rather difficult, particularly for carbon fiber-based composites, because their colour makes visual inspection difficult. A special technique using medical equipment for computerized tomography is presented in this paper. It is compared to techniques using ultrasonic and is demonstrated as a feasible and an effective tool for the evaluation of drilling-induced delamination.

A torque and thrust prediction model for drilling of composite materials

A torque and thrust prediction model for drilling of composite materials

Effect of eccentricity of twist drill and candle stick drill on delamination in drilling composite materials

Drilling is the most frequently employed operation of secondary machining for fiber-reinforced materials owing to the need for structure joining. Delamination is one of the serious concerns during drilling. Practical experience shows that an eccentric twist drill or an eccentric candle stick drill can degrade the quality of the fiber reinforced material. Comprehensive delamination models for the delamination induced by an eccentric twist drill and an eccentric candle stick drill in the drilling of composite materials have been constructed in the present study. For an eccentric twist drill and an eccentric candle stick drill, the critical thrust force that will produce delamination decreases with increasing point eccentricity ξ. The results agree with industrial experience. The need for control of drill eccentricity during drill regrinding has been proved analytically by the proposed models.

Taguchi analysis of delamination associated with various drill bits in drilling of composite material

This paper presents a prediction and evaluation of delamination factor in use of twist drill, candle stick drill and saw drill. The approach is based on Taguchi’s method and the analysis of variance (ANOVA). An ultrasonic C-Scan to examine the delamination of carbon fiber-reinforced plastic (CFRP) laminate is used in this paper. The experiments were conducted to study the delamination factor under various cutting conditions. The experimental results indicate that the feed rate and the drill diameter are recognized to make the most significant contribution to the overall performance. The objective was to establish a correlation between feed rate, spindle speed and drill diameter with the induced delamination in a CFRP laminate. The correlation was obtained by multi-variable linear regression and compared with the experimental results.