Drilling Of Composite Laminates Research Articles

Predicting thrust force during drilling of composite laminates with step drills through the Gaussian process regression

PurposeHere, the authors use step angles, stage ratios, feed rates and spindle speeds as predictors to develop a Gaussian process regression for predicting thrust force during composite laminates drilling with step drills.Design/methodology/approachUse of machine learning methods could benefit machining process optimizations. Accurate, stable and robust performance is one of major criteria in choosing among different models. For industrial applications, it is also important to consider model applicability, ease of implementations and cost effectiveness.FindingsThis model turns out to be simple, accurate and stable, which helps fast estimates of thrust force. Through combining the Taguchi method's optimization results and the Gaussian process regression, more data could be expected to be extracted through fewer experiments.Originality/valueThrough combining the Taguchi method's optimization results and the Gaussian process regression, more data could be expected to be extracted through fewer experiments.

Experimental and numerical investigations on push-out delamination in drilling of composite laminates

This study conducts experimental and numerical studies on the progressive damage occurring during the drilling of composite laminates. In particular, this work focuses on push-out delamination, which occurs at the interface around the drill-exit and is the most critical damage suffered during the drilling process. To investigate the damage progression mechanisms, penetration and interruption drilling tests are performed on composite laminate consisting of quasi-isotropic CFRP plies and fabric GFRP ply (bottom side). After drilling tests, the damage evolution is evaluated using X-ray computed tomography and optical microscopy. Based on the experimental results, a simplified simulation model is established, and damage progression simulation is performed using an explicit dynamic finite element method. The results show that the bending deformation in the bottom two plies triggers the propagation of push-out delamination. Therefore, the extent of delamination is significantly affected by the thickness and the material properties of the bottom plies.

Effect of backup plate in drilling of composite laminates, analytical and experimental approaches

Delamination is the most severe damage in drilling of composite laminates. Using the backup plate is an appropriate method to control drilling induced delamination. In this paper, an analytical model is applied to determine the critical thrust force and the feed rate for drilling of composite laminates with backup plate. To achieve this aim, the classical laminate plate theory (CLPT), the linear elastic fracture mechanic (LEFM) and the oblique cutting model are used. In analytical models, two separate distributed loads have been exerted by cutting and chisel edges. Based on the model results, the effect of the drill diameter, the chisel edge size, and the backup plate size, on the critical thrust force and the feed rate are investigated. Experimental tests are carried out to prove the analytical model.

Optimisation of drilling parameters for minimum circularity error in FRP composite

In composite materials, the damage is characterised by the delamination and circularity error of drilled holes. The amount of delamination and circularity error depends on different machining parameters such as spindle speed, feed Rate, and plate thickness. The present paper attempts to investigate an optimal combination of process parameters for drilling of composite laminates. The work is carried out on industrial grade FRP composite laminates with varying process parameters. The experiments are designed using a 'Box-Behnken design', grounded in the response surface methodology. Circularity error is considered as the output response as it is prominent in the drilling of composite laminates. ANOVA test is carried out to find the significance of the input parameters and test the empirical model. The effect of input parameters on the amount of circularity error is also investigated. Genetic algorithm (GA) and particle swarm optimisation (PSO) is used to predict the optimal settings of input machining parameters.

Investigation on delamination and flexural properties in drilling of carbon nanotube/polymer composites

The drilling of composite laminates is difficult to control and often leads to delamination that significantly affects the strength of the structure. Of the mechanical properties of composite materials affected by drilling-induced damage, flexural strength has received very little attention. In the present paper, experiments were conducted to analyze the thrust force, delamination factor and residual flexural strength in the drilling of woven E-glass fiber-epoxy composites reinforced with functionalized multi-walled carbon nanotubes. The process parameters considered for the experiments are the feed rate, spindle speed, drill diameter, and the weight percentage of carbon nanotubes present in nanocomposite laminates. Drilling experiments were conducted based on Taguchi design of experiment and three-point bending tests were then done to assess the residual flexural strength of drilled specimens. Analysis of variance and Taguchi S/N ratio analysis were performed to investigate the influence of input parameters on each individual drilling characteristics. In addition, the orthogonal array with grey relational analysis was employed to simultaneously optimize the multiple performance characteristics of the drilling process. According to the results, the feed rate is the factor which has the greatest influence on the thrust force and delamination factor, followed by spindle speed. Residual flexural strength, however, is mostly influenced by nano content, followed by feed rate.

Critical thrust and feed prediction models in drilling of composite laminates

Drilling induced delamination has been recognized as a major problem during drilling of composite materials. The size of the delamination zone has been shown to be related to the thrust force. However, thrust force strongly depends on drilling parameters and it is not possible to control it directly. Thrust force can be correlated with feed rate, the most important parameter affecting thrust force. This paper presents analytical models to predict critical thrust force and feed rate at the onset of delamination. The model proposed is based on elastic fracture mechanics, classical plate bending theory and the mechanics of oblique cutting. An advantage of this model over other proposed models is that to avoid delamination via thrust monitoring, the thrust force will need to be sensed and used in adaptive control, while optimal feed rate can be used directly in CNC command generation to maximize productivity.

Prediction of forces during drilling of composite laminates using artificial neural network: A new approach

Drilling of fiber-reinforced plastics (FRP's) is an inevitable machining operation, because it facilitates assembly of several components by means of mechanical fastening. But, drilling of FRP leads to delamination which results in reduced life and efficiency of the FRP part. The delamination that induced during drilling is directly affected by the thrust force and torque. In the present research endeavour, four different types of drill point geometries have been used for making of holes in two different types of composite laminates. The drilling of composite laminate has been conducted at three different levels of spindle speed and feed rate. A new artificial neural network (ANN) approach has been proposed to predict the drilling-induced thrust force and torque. The values of thrust force and torque predicted by the proposed ANN models are in close agreement with the experimental values.

Drilling of composite laminates with solid and hollow drill point geometries

Drilling is one of the most important method for hole making in composite materials. Drilling of polymer matrix composites causes substantial damage around the drilled hole. Damage free holes can be made using modified drill geometry. The present research investigation focuses on the drill geometry as candidate parameter that influence drilling forces and drilling-induced damage. The four different drill geometries (solid and hollow in shape) are used for drilling in composite materials. The cutting mechanism of these drill geometries is substantially different, and therefore influences the drilling-induced damage. The experimental results suggest a strong relationship between the drill point geometry and the drilling-induced damage.

Effects Of Cutting Parameters On Acoustic Emission Signal Response During Drilling Of Laminated Composites Using Factorial Design Method

Factorial design has been used to study the effect of cutting parameters on acoustic emission signal response during the drilling of composite laminates. Experimental design is a strategy of planning, conducting, analyzing and interpreting experiments so that sound and valid conclusion can be drawn efficiently, and economically. In this study, effects of cutting speed, feed rate and tool diameter on the acoustic emission signal response are investigated using acoustic emission\'s energy, amplitude, root mean square and frequency responses and 23 factorial design for drilling operation. Cutting tests were performed under dry conditions. Calculated effects, standard errors at 95% confidence level, and models governing the acoustic emission response to the cutting conditions have been generated from the acoustic emission signal responses. The results revealed that, acoustic energy response has significant effects due to the cutting parameters. Hence a model can be established to relate the acoustic emission\'s energy response and the cutting parameters, and as a result monitor and control the area of delamination during the drilling process.Journal of Science & Technology (Ghana) Vol. 27 (2) 2007: pp. 98-106

Effects of Feedrate and Chisel Edge on Delamination in Composites Drilling

Delamination accompanied with the drilling of composite laminates has been recognized as a major problem. An analytical model is established to predict critical thrust force and critical feedrate at which the delamination crack begins to propagate. For unidirectional composites, the delamination zone is modeled as an elliptical plate, with clamped edges and subjected to a central load. Based on fracture mechanics, laminated plate theory and cutting mechanics, expressions are developed for critical thrusts and critical feedrates at which delamination is initiated at different ply locations. This model has been verified by experiments. A variable feedrate strategy is formulated based on this model, which avoids delamination while drilling in a time-optimal fashion. In addition, the need to modify tool geometry to avoid delamination is highlighted. Chisel edge width has been identified as an important factor contributing to the thrust force and hence delamination.

Delamination During Drilling in Composite Laminates

Delamination is the major concern during drilling of composite laminates. Delamination, in addition to reducing the structural integrity of the laminate, also results in poor assembly tolerance and has the potential for long-term performance deterioration. Drilling-induced delamination occurs both at the entrance and at the exit planes. This paper presents an analysis of delamination during drilling. The analysis uses a fracture mechanics approach in which the opening-mode delamination fracture toughness, a material parameter, is used with a plate model of the laminate. The analysis predicts an optimal thrust force (defined as the minimum force above which delamination is initiated) as a function of drilled hole depth. Good agreement is achieved with data obtained from drilling carbon fiber-epoxy laminates. An advantage of the model is that it can predict varying degrees of delamination for other materials, such as glass fiber-epoxy, and for hybrid composites. In addition, the optimal thrust force for no delamination can be used to control a drilling machine with thrust force feedback for maximizing productivity.