Browsing by Subject "Drilling"

Now showing 1 - 10 of 10

Open Access
A hybrid model to analyze stress distributions at the tool and workpiece interface during drilling of thick CFRP laminates
(2024-08) Shariar, Fahim
Drilling is employed as a machining method to meet the demands for producing functional CFRP structures without compromising their unique and desirable material properties. Because of its temperature-dependent properties and drillinduced damages, drilling CFRP remains an ambitious task. This study proposes an analytical drilling model coupled with a finite element-based thermal model to predict the characteristic time point-based thrust force and torque generated during the drilling operation. A better understanding of pressure and tangential stress distribution along the drilling cutting edge is necessary to select process parameters better. The drill margin region, which directly affects the hole wall quality, has also been included in the analysis. Drilling experiments were conducted to measure thrust force, torque, and temperature for five different configurations of feeds and spindle speeds. The workpiece FE model utilizes a Gaussian distributed ring-type heat flux, and the tool uses characteristic time point-based step functions as heat fluxes to emulate the drill’s progress through the CFRP laminate. The finite element-based thermal models have been considered to evaluate the heat partition during the drilling operation and estimate the subsequent temperature profiles on the drill tip and hole wall surface, respectively. The hybrid analytical and computational model has been used to analyze the variation of peak pressure and tangential stress distributions on the tip of the drill as well as the thermomechanical response of CFRP based on experimental measurements of thrust force, torque, and temperature and investigation of the condition of the holes for various drilling configurations.
Open Access
Comparative analysis of PCD drill designs during drilling of CFRP laminates
(Elsevier, 2015) Karpat, Yiğit; Bahtiyar, O.
As a result of increased use of CFRPs in the aerospace industry, the machining of CFRPs has been studied extensively. The majority of these studies consider drilling of CFRPs, since it is the most common process in the machining of structural parts used in aircraft. It has been shown that drilling process parameters and drill geometry significantly influence the quality of holes. In this study, a systematic approach has been used to compare the influence of drill geometry on process outputs such as drilling forces, torques and tool wear. Custom-made double point angle polycrystalline diamond (PCD) drills from the same manufacturer were used in the experiments. The advantage of this approach is that it eliminates the drill material and edge preparation effects on the experimental measurements, thus helps reveal the influence of drill geometry on the process outputs. The pros and cons of different drill designs are discussed and an appropriate design is identified for the drilling of thick CFRP laminate considered in this study.
Open Access
Drilling thick fabric woven CFRP laminates with double point angle drills
(Elsevier, 2012) Karpat, Y.; Değer, B.; Bahtiyar, O.
Carbon fiber reinforced plastics (CFRPs) have many desirable properties, including high strength-to-weight ratio, high stiffness-to-weight ratio, high corrosion resistance, and low thermal expansion. These properties make CFRP suitable for use in structural components for aerospace applications. Drilling is the most common machining process applied to CFRP laminates, and it is difficult due to the extremely abrasive nature of the carbon fibers and low thermal conductivity of CFRP. It is a challenge for manufacturers to drill CFRP materials without causing any delamination on the work part while also considering the economics of the process. The subject of this study is the drilling of fabric woven type CFRP laminates which are known to be more resistant to delamination than unidirectional type CFRP laminates. The objective of this study is to investigate the influence of double point angle drill geometry on drilling performance through an experimental approach. An uncoated carbide and two diamond coated carbide drills with different drill tip angles are employed in drilling experiments of aerospace quality thick fabric woven CFRP laminates. Force and torque measurements are used to investigate appropriate drilling conditions based on drill geometry and ideal drilling parameters are determined. Tool life tests of the drills were conducted and the condition of the diamond coating is examined as a function of drilling operational parameters. High feed rate drilling experiments are observed to be favorable in terms of drill wear. Feed is observed to be more important than speed, and the upper limit of feed is dictated by the drill design and the rigidity of the machine drill. Hole diameter variation due to drill wear is monitored to determine drill life. At high feeds, hole diameter tolerance is observed to be more critical than hole exit delamination during drilling of fabric woven CFRP laminates.
Open Access
Energy based investigation of process parameters while drilling carbon fiber reinforced polymers
(Elsevier B.V., 2016) Karpat, Yiğit; Bahtiyar, O.
Carbon fiber reinforced polymers (CFRPs) are widely used in the aerospace industry due to their light weight, high strength, and low thermal conductivity. Drilling is a critical process that affects the quality of CFRP parts. This work studies the influence of process parameters on delamination and tool wear. Polycrystalline diamond helical drills are used in the experiments. It has been shown that drilling energy calculations can be used to set appropriate feed and speed parameters and for increasing drilling performance of CFRPs. The results also indicate the importance of thermal modeling of CFRP laminate for better understanding of the drilling process. © 2016 The Authors.
Open Access
Experimental evaluation of polycrystalline diamond tool geometries while drilling carbon fiber-reinforced plastics
(Springer, 2014) Karpat, Y.; Deǧer, B.; Bahtiyar, O.
Polycrystalline diamond (PCD) drills are commonly employed in carbon fiber-reinforced plastic (CFRP) drilling to satisfy hole quality conditions with an acceptable tool life and productivity. Despite their common use in industry, only a small number of studies have been reported on drilling CFRPs with PCD drills. In this study, drilling performances of three different PCD drill designs are investigated experimentally using thrust force, torque, and hole exit quality measurements. Results show that work material properties, drilling conditions, and drill design should all be considered together during the selection of process parameters, and the relationships among these factors are quite complex.
Open Access
Heat partition evaluation during dry drilling of thick CFRP laminates with polycrystalline diamond drills
(ELSEVIER, 2024-10) Shariar, Fahim; Karagüzel, Umut; Karpat, Yiğit
Since various material properties of carbon fiber-reinforced polymer (CFRP) are temperature dependent, dry drilling of CFRP is a delicate process. Thermal damage can be caused by a rise in temperature during drilling due to a large portion of heat being transferred into the material. Heat partition is used to quantify this, which represents the percentage of total heat being dissipated into the constituent objects during a machining operation. Drill margin and contact conditions at the tool-workpiece interface significantly affect the drilling of CFRP material. Drilling experiments were performed to measure thrust force, torque, and temperatures for five different sets of feed rates and rotational speeds. This study proposes a method for calculating heat partition values during CFRP drilling by developing a finite element-based thermal model. The FE model employs a Gaussian distributed ring-type heat flux that is a function of the equivalent contact length at the interface between the drill and the material surface and the geometry of the workpiece which operates as a moving heat source, emulating the progress of the drill through the CFRP laminate. The tool implements heat fluxes that use characteristic time-point-based step functions to represent the temperature on the drill as it advances through the workpiece during machining. The temperature profiles obtained from the FE analysis and the experiments for the workpiece and tool were subsequently matched iteratively to determine the corresponding heat partition value
Open Access
A mechanistic approach to investigate drilling of UD-CFRP laminates with PCD drills
(Elsevier, 2014) Karpat, Y.; Bahtiyar, O.; Deǧer, B.; Kaftanoǧlu, B.
Carbon fiber reinforced plastics (CFRPs) possess desirable material properties that satisfy the aerospace industry's high strength to weight ratio objective. Therefore, CFRPs are commonly used in structural parts, either alone or together with aluminum and titanium alloys. Drilling of CFRPs has been studied extensively in the literature in recent years, with special emphasis on process parameters and delamination. This study identifies mechanical properties of uni-directional CFRPs through drilling tests. Drilling of uni-directional CFRP plates with and without pilot holes has been performed, and cutting and edge force coefficients are identified. A polycrystalline diamond (PCD) drill was used in tests since this type of drill is commonly used in practice. Finally, validation tests on multi directional CFRP laminates have been performed and good results have been obtained.
Open Access
A thermo-mechanical model of drill margin-borehole surface interface contact conditions in dry drilling of thick CFRP laminates
(Elsevier, 2020) Karpat, Yiğit; Karagüzel, U.; Bahtiyar, O.
Dry drilling of thick carbon fiber reinforced polymer (CFRP) laminates requires careful selection of process parameters in order to obtain acceptable borehole surface quality. Complex contact conditions between the drill margin and the borehole surface determine the integrity of the borehole surface depending on the process parameters and temperature-dependent viscoelastic material properties. Temperature rise during dry drilling reduces the elastic modulus of the CFRP and causes thermal expansion of the drill, resulting in considerable contact length at the drill margin and borehole surface interface. Manufacturers need a better understanding of the interaction among contact pressure, sliding velocity, temperature at the interface, and temperature-dependent material properties to develop predictive models for drilling CFRPs. To examine this complex interaction, this study develops a novel, hybrid model that combines a time-based analytical modeling of drilling process with a finite element-based modeling of temperature rise. Drilling experiments were performed in which thrust force, torque, and temperature were measured as a function of feed, and these measurements were used to identify unknown hybrid model parameters. The results revealed that a significant change in friction conditions occurs when increased temperatures at the margin and borehole surface interface approach and exceed the glass transition temperature of the CFRP laminate at a large feed rate. These findings show the benefit of increasing feed during dry drilling, which is nonetheless limited by the temperature-dependent material properties of the work material.
Open Access
Tool geometry based prediction of critical thrust force while drilling carbon fiber reinforced polymers
(Shanghai University Press, 2015) Karpat, Y.; Bahtiyar O.
Carbon fiber reinforced polymers (CFRPs) are known to be difficult to cut due to the abrasive nature of carbon fibers and the low thermal conductivity of the polymer matrix. Polycrystalline diamond (PCD) drills are commonly employed in CFRP drilling to satisfy hole quality conditions with an acceptable tool life. Drill geometry is known to be influential on the hole quality and productivity of the process. Considering the variety of CFRP laminates and available PCD drills on the market, selecting the suitable drill design and process parameters for the CFRP material being machined is usually performed through trial and error. In this study, machining performances of four different PCD drills are investigated. A mechanistic model of drilling is used to reveal trade-offs in drill designs and it is shown that it can be used to select suitable feed rate for a given CFRP drilling process. © 2015, Shanghai University and Springer-Verlag Berlin Heidelberg.
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TPAO’nun Lüleburgaz ve sonrası doğal gaz arama-bulma çalışmaları
(Bilkent University, 2020) Mintaş, Batuhan; Yılmaz, Elif; Yalçın, Enes; Yücetürk, Gözde; Sever, Zeynep Yağmur
Türkiye Petrolleri Anonim Ortaklığı 1954 yılında kurulmuştur. Lüleburgaz’daki doğal gaz çalışmalarına 1960’lı yıllarda başlamış, ilerleyen yıllarda ilçe ve Trakya özelinde açtığı doğal gaz kuyuları ile bölgenin kalkınmasında rol oynamıştır. Bölgenin doğal gaz konusunda zenginliği fark edildikten sonra, 1984 yılında Lüleburgaz’da TPAO Trakya Bölge Müdürlüğü kurulmuş ve çalışmalar daha verimli hale getirilmiştir. İlçede elde edilen doğal gaz, çevredeki sanayi kuruluşları başta olmak üzere çeşitli alanlarda kullanılmıştır. Lüleburgaz’da olumlu sonuçlar alınmasının ardından, TPAO Trakya dışında da doğal gaz arama-bulma çalışmalarını hızlandırmıştır. Bu amaç doğrultusunda yurt dışında çalışmalar yapılmış ve bu çalışmalar günümüzde de devam etmektedir.