Journal Articles
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Item Delamination analysis in drilling process of glass fiber reinforced plastic (GFRP) composite materials(2007) Mohan, N.S.; Kulkarni, S.M.; Ramachandra, A.Machining processes are generally used to cut; drill, or contour composite laminates for building products. In fact, drilling is one of the most commonly used manufacturing processes to install fasteners for assembly of laminate composites. The material anisotropy resulting from fiber reinforcement heavily influences the machinability during machining. Machining of fiber reinforced plastic (FRP) components is often needed in spite of the fact that most FRP structures can be made to near-net shape and drilling is the most frequently employed secondary machining process for fiber reinforced materials. Therefore, the precise machining needs to perform to ensure dimensional stability and to obtain a better productivity of the component. The drilling parameters and specimen parameters evaluated were speed, feed rate, drill size and specimen thickness. A series of experiments were conducted using TRIAC VMC CNC machining center to machine the composite laminate specimens at various cutting parameters and material parameters. The measured results of delamination at the entry and exit side of the specimen were measured and analyzed using commercial statistical software MINITAB14. The experimental results indicated that the specimen thickness, feed rate and cutting speed are reckoned to be the most significant factors contributing to the delamination. A signal-to-noise ratio is employed to analyze the influence of various parameters on peel up and push down delamination factor in drilling of glass fibre reinforced plastic (GFRP) composite laminates. The main objective of this study is to determine factors and combination of factors that influence the delamination using Taguchi and response surface methodology and to achieve the optimization machining conditions that would result in minimum delamination. From the analysis it is evident that among the all significant parameters, specimen thickness and cutting speed have significant influence on peel up delamination and the specimen thickness and feed have more significant influence on push down delamination. Confirmation experiments were conducted to verify the predicted optimal parameters with the experimental results, good agreement between the predicted and experimental results obtained to be of the order of 99%. © 2007 Elsevier B.V. All rights reserved.Item An experimental investigation of jack hammer drill noise with special emphasis on drilling in rocks of different compressive strengths(2007) Vardhan, H.; Murthy, Ch.S.N.An attempt has been made in this paper to investigate the influence on sound level due to drilling in rocks of varying physical properties i.e. compressive strength and abrasivity using jackhammer drill. For this purpose, a jackhammer drill setup was fabricated wherein the thrust applied can be varied while drilling vertical holes. The compressive strength and the abrasivity of various rock samples collected from the field were determined in the laboratory. A set of test conditions were defined for measurement of sound level of the jackhammer drill. Also, with the help of the experimental setup, vertical drilling was carried out on the rock samples for varying thrust and air pressure values and the corresponding A-weighted equivalent continuous sound levels were measured. The results of this study indicate that, increase in thrust increases the sound level at higher midband frequencies in the noise spectrum. The study indicated the sound level near the drill rod to be 0.5 to 1.5 dB, 2.0 to 3.0 dB and 4.0 to 6.0 dB higher relative to that at the drill bit, the exhaust and the operator's position respectively at an air pressure of 5 kg/cm2 and 160 N thrust for all the rock samples tested. Both the thrust and air pressure were found to have a significant effect on the sound level produced by jackhammer drill at all the measurement locations. The study further shows that an increase in sound level of the order of 1.5 to 2.5 dB at the operator's position can occur with an increase in air pressure by 2 kg/cm2 at 160 N thrust and with an increase in compressive strength and decrease in abrasivity of rocks. Also, the increase in sound level at the operator's position with increase in compressive strength and decrease in abrasivity of rock is of the order of 1.0 to 2.0 dB. In order to maintain a constant penetration rate in the rocks, both the thrust and air pressure need to be increased with an increase in compressive strength and decrease in rock abrasivity. Therefore, increased compressive strength and lower abrasivity of rocks will require higher air pressure and thrusts to be applied to achieve an optimum penetration rate and therefore will result in higher sound level at the operator's position and at other measurement locations. © 2007 Institute of Noise Control Engineering.Item Acoustic fingerprinting for rock identification during drilling(Inderscience Publishers, 2014) Shreedharan, S.; Hegde, C.; Sharma, S.; Vardhan, H.During the process of mining, it is imperative to know the type and properties of the rocks being handled. The current technology for this involves core drilling, and subsequently subjecting the drilled cores to various tests in the laboratory, to identify the rocks and establish their properties. In many cases, obtaining a sample may be cumbersome and/or non-profitable. This paper presents a novel method to monitor and evaluate the sounds produced as undesirable by-products, at the drill-bit and rock interface, to predict the type of rock being drilled. A rotary drill was fabricated in the laboratory and vertical drilling was carried out on cubical rock samples, keeping various drilling parameters constant. The results obtained are promising and reinforce that it may be possible to extend the proposed methodology in the field as well, with appropriate modifications. This method may be extrapolated further in the estimation of rock properties as well. Copyright © 2014 Inderscience Enterprises Ltd.Item Soft computing techniques during drilling of bi-directional carbon fiber reinforced composite(Elsevier Ltd, 2016) Shetty, N.; Herbert, M.A.; Shetty, R.; Shetty, D.S.; Vijay, G.S.Due to the intricacy of machining processes and inconsistency in material properties, analytical models are often unable to describe the mechanics of machining of carbon fiber reinforced polymer (CFRP) composites. Recently, soft computing techniques are used as alternate modeling and analyzing methods, which are usually robust and capable of yielding comprehensive, precise, and unswerving solutions. In this paper, drilling experiments as per the Taguchi L27 experimental layout are carried out on bi-directional carbon fiber reinforced polymer (BD CFRP) composite laminates using three types of drilling tools: high speed steel (HSS), uncoated solid carbide (USC) and titanium nitride coated SC (TiN-SC). The focus of this work is to determine the best drilling tool that produces good quality drilled holes in BD CFRP composite laminates. This paper proposes a novel prediction model 'genetic algorithm optimised multi-layer perceptron neural network' (GA-MLPNN) in which genetic algorithm (GA) is integrated with Multi-Layer Perceptron Neural Network. The performance capability of response surface methodology (RSM) and GA-MLPNN in prediction of thrust force is investigated. RSM is also used to evaluate the influence of process parameters (spindle speed, feed rate, point angle and drill diameter) on thrust force. GA is used to optimize the thrust force and its optimization performance is compared with that of RSM. It is observed that the GA-MLPNN is better predicting tool than the RSM model. The investigation in this paper demonstrates that TiN-SC is the best tool for drilling BD CFRP composite laminates as minimum thrust force is developed during its use. © 2016 Elsevier B.V. All rights reserved.Item Influence of materials and machining parameters on drilling performance of syntactic foams(ASTM International, 2018) Ashrith, H.S.; Doddamani, M.; Gaitonde, V.N.; Gupta, N.The effects of drilling parameters and material properties are investigated on epoxy matrix syntactic foams reinforced with 20, 40, and 60 volume percent glass microballoon. The influences of cutting speed, feed, drill diameter, and filler content on drilling performance are studied based on the full factorial design of experiments using tungsten carbide twist drills. Based on experimental results, machinability aspects within the range of the chosen input parameters are predicted using response surface methodology-based models, which can guide industrial practitioners for choosing the appropriate process parameters. Microscopy is conducted on the drilled specimens to understand crack initiation and propagation mechanisms. The thrust force and specific cutting coefficient of syntactic foam are 40 % lower as compared to those of neat epoxy. The surface roughness of syntactic foams is higher than that of neat epoxy. The micrographs of drill bits show negligible tool wear. These results show the possibility of using syntactic foams in industrial applications in which the drilling of material is required for reasons such as joining using bolts. © © 2018 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959Item Predictive analysis of peel up delamination in glass fibre reinforced polyester composite drilling(Transstellar Journal Publications and Research Consultancy Private Limited (TJPRC) editor@tjprc.org, 2019) Bhat, R.; Mohan, N.; Kulkarni, S.M.; Sharma, S.Composites are the engineering materials, comprising two constituents: reinforcing and the matrix or binder material. the composite machining, particularly, drilling is a complex process in comparison to the machining of traditionally employed engineering structural materials. Delamination is the most prevalent integrity issue in composite drilling. In the present work, the independent variables are categorized as continuous and categorical variables. Speed and feed are chosen as the continuous variables, whereas, the drill tool diameter and material thickness are considered as categorical variables. The peel up delamination is chosen as the response. The central composite design form of RSM is employed to develop the experimental design and develop the response regression model. The developed model is then validated using an additional set of small number of experiments and the degree of affirmation is determined. The standard error obtained analytically is 5.91%. The experimental mean standard error for the randomly conducted validating experiment obtained is 4.23%. The validation shows a high degree of agreement (99.75%) between the theoretical and analytical values. © TJPRC Pvt. Ltd.Item Effect of wall thickness and cutting parameters on drilling of glass microballoon/epoxy syntactic foam composites(Elsevier Ltd, 2019) Ashrith, H.S.; Doddamani, M.; Gaitonde, V.Effect of glass microballoon (GMB) wall thickness and cutting parameters (cutting speed, feed and drill diameter) on thrust force (Ft), surface roughness (Ra), specific cutting coefficient (Kf), cylindricity (CYL), circularity error (Ce-Exit) and damage factor (Fd-Exit) in drilling of GMB/epoxy syntactic foam is presented. CNC vertical machining centre is utilised for conducting experiments based on full factorial design. Significant process parameters are identified through response surface methodology. Wall thickness significantly affects the Ce-Exit and CYL of the drilled hole. Increasing wall thickness significantly reduces the Ra (30%), CYL (41%) and Ce-Exit (56%) due to the increased thermal stability of syntactic foams. This observation is very crucial for the syntactic foams used in structural applications pertaining to structural stability. Drill diameter is observed to be significant for Ft, Ra, CYL and Fd-Exit; while Kf is governed by feed. Furthermore, grey relation analysis (GRA) is used to identify the specific combination of process parameters to obtain good quality drilled hole. Combination of higher particle wall thickness and feed, lower cutting speed and drill diameter produces a sound hole quality as observed from GRA. Hole quality is highly influenced by drill diameter followed by cutting speed and GMB wall thickness. The present study offers guidelines for the industries (structural applications) to produce quality holes in GMB reinforced epoxy matrix. © 2018 Elsevier LtdItem Point angle effect in drilling of syntactic foams(Elsevier B.V., 2021) Ashrith, H.S.; Doddamani, M.Borosilicate glass microballoons (GMBs) of three different density grades are dispersed in epoxy resin for fabricating syntactic foams. The influence of different twist drill (coated solid tungsten carbide) point angles (85,110, and 135°) in dry drilling is conducted through full factorial design using a vertical machining centre. The influence of various parameters in drilling (point angle, feed, cutting speed) and GMBs density are examined, and their effects are reported. Analysis of variance and response surface methodology is employed to determine the significant parameters influencing the responses. Drill point angle shows a substantial impact on cylindricity (31.81%), circularity error (42.86%) and damage factor at hole exit (34.29%). Feed significantly affects the thrust force (40.76%) and specific cutting coefficient (53.60%), whereas surface roughness is highly influenced by GMBs density (47.05%). Cutting speed governs cylindricity (32.73%) and exit side damage factor (43.38%) of the drilled holes. Multiple response optimization based on grey relational analysis reveals that combining higher feed, lower cutting speed and drill point angle, and intermediate GMBs density is the optimal condition for achieving sound quality hole. Drill point angle has a remarkable impact (88.35%) on hole quality at the optimum condition. Chip morphology of syntactic foams is presented finally. This research may be beneficial for the industrial practitioners in minimizing poor hole quality, thereby saving time and cost in drilling syntactic foams used in weight-sensitive structures. © 2021