Browsing by Subject "Machining"

Now showing 1 - 18 of 18

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
Dynamic lot sizing and tool management in automated manufacturing systems
(Elsevier, 2002) Aktürk, M. S.; Önen, S.
The overall aim of this study is to show that there is a critical interface between the lot sizing and tool management decisions, and these two problems cannot be viewed in isolation. We propose "ve alternative algorithms to solve lot sizing, tool allocation and machining conditions optimization problems simultaneously. The "rst algorithm is an exact algorithm which "nds the global optimum solution, and the others are heuristics equipped with a look-ahead mechanism to guarantee at least local optimality. The computational results indicate that the amount of improvement is statistically signi"cant for a set of randomly generated problems. The magnitude of cost savings is dependent on the system parameters.
Open Access
An exact tool allocation approach for CNC machines
(Taylor & Francis, 1999) Aktürk, M. S.
An exact approach is developed to determine the optimum machining conditions and tool allocation decisions simultaneously to minimize the total production cost on a CNC turning machine. There are multiple machining operations and we consider a set of alternative cutting tool types for each operation. The existing tool management approaches at the system level fail to relate the tooling issues to the machining conditions, and ignore the tool availability and tool wear restrictions. Consequently, we not only improve the overall solution by exploiting the interactions between these two decision making problems, but also prevent any unfeasibility that might occur for the tool allocation problem due to tool contention among the operations for a limited number of tool types by considering the machining operation, tool availability and tool life limitations. The computational results indicated that the average computation time to find an optimum solution was 1.11s, whereas the maximum time was 11.45s, for a set of randomly generated problems.
Open Access
Femtosecond laser fabrication of fiber based optofluidic platform for flow cytometry applications
(SPIE, 2017) Serhatlioglu, Murat; Elbuken, Çağlar; Ortac, Bülend; Solmaz, Mehmet E.
Miniaturized optofluidic platforms play an important role in bio-analysis, detection and diagnostic applications. The advantages of such miniaturized devices are extremely low sample requirement, low cost development and rapid analysis capabilities. Fused silica is advantageous for optofluidic systems due to properties such as being chemically inert, mechanically stable, and optically transparent to a wide spectrum of light. As a three dimensional manufacturing method, femtosecond laser scanning followed by chemical etching shows great potential to fabricate glass based optofluidic chips. In this study, we demonstrate fabrication of all-fiber based, optofluidic flow cytometer in fused silica glass by femtosecond laser machining. 3D particle focusing was achieved through a straightforward planar chip design with two separately fabricated fused silica glass slides thermally bonded together. Bioparticles in a fluid stream encounter with optical interrogation region specifically designed to allocate 405nm single mode fiber laser source and two multi-mode collection fibers for forward scattering (FSC) and side scattering (SSC) signals detection. Detected signal data collected with oscilloscope and post processed with MATLAB script file. We were able to count number of events over 4000events/sec, and achieve size distribution for 5.95μm monodisperse polystyrene beads using FSC and SSC signals. Our platform shows promise for optical and fluidic miniaturization of flow cytometry systems. © 2017 SPIE.
Open Access
The impact of reengineering in manufacturing companies: a methodology for operations improvement and manufacturing productivity
(1993) Atceter, Muzaffer
Many manufacturing companies today are facing the problem of loosing their competitive edge in international markets. This is partly due to the outdated manufacturing processes. This study is examining the improvement methods and suggesting a methodology whose scope is wider than small changes. This type of improvements requires a radical change in the manufacturing processes. The word reengineering, meaning process redesign, is used to describe this method for achieving the manufacturing productivity considering the cost, quality, customer service, time and management issues. First chapter is defining reengineering. The techniques, methods and a step-bystep approach for productivity projects are explained in the second chapter. Chapter three includes an analysis of a Turkish case company with the methods given in chapter 2. The thesis questioning the applicability of reengineering projects for manufacturing companies in Turkey in chapter 4. It is examining the difficulties that the project teams would face.
Open Access
Integrated lot sizing and tool management in automated manufacturing systems
(IIE, 1997) Aktürk, Mehmet Selim; Önen, Siraceddin
We propose a new algorithm to solve lot sizing, tool allocation and machining conditions optimization problems simultaneously to minimize total production cost in a CNC environment. Most of the existing lot sizing and tool management methods solve these problems independently using a two-level optimization approach. Thus, we not only improve the overall solution by exploiting the interactions, but also prevent any infeasibility that might occur for the tool management problem due to decisions made at the lot sizing level. We showed that in a set of randomly generated problems 22.5% of solutions found by the two-level approach were infeasible and we improved the solution on the average by 6.79% for the remaining cases with an average computation time of 63.4 seconds.
Open Access
An integrated process planning approach for CNC machine tools
(Springer-Verlag, 1996) Aktürk, M. S.; Avcı, S.
In view of the high investment and tooling cost of a CNC machining centre, the cutting and idle times should be optimised by considering the tool consumption and the non-machining time cost components. In this paper, we propose a detailed mathematical model for the operation of a CNC machine tool which includes the system characterisation, the cutting conditions and tool life relationship, and related constraints. This new module will be a part of an overall computer-aided process planning system to improve the system effectiveness and to provide consistent process plans. A hierarchical approach is presented for finding tool-operation assignments, machining conditions, appropriate tool magazine organisation and an operations sequence which results in the minimum production cost. © 1996 Springer-Verlag London Limited.
Open Access
Integrated scheduling and tool management in flexible manufacturing systems
(Taylor & Francis, 2001) Aktürk, M. S.; Özkan, S.
A multistage algorithm is proposed that will solve the scheduling problem in a flexible manufacturing system by considering the interrelated subproblems of processing time control, tool allocation and machining conditions optimization. The main objective of the proposed algorithm is to minimize total production cost consisting of tooling, operational and tardiness costs. The proposed integrated approach recognizes an important trade-off in automated manufacturing systems that has been largely unrecognized, and which is believed can be effectively exploited to improve production efficiency and lead to substantial cost reductions.
Open Access
Joint lot sizing and tool management in a CNC environment
(Elsevier, 1999) Aktuük, M. S.; Önen, S.
We propose a new algorithm to solve lot sizing, tool allocation and machining conditions optimization problems simultaneously to minimize total production cost in a CNC environment. Most of the existing lot sizing and tool management methods solve these problems independently using a two-level optimization approach. Thus, we not only improve the overall solution by exploiting the interactions among these decision making problems, but also prevent any infeasibility that might occur for the tool management problem due to decisions made at the lot sizing level. The computational experiments showed that in a set of randomly generated problems 22.5% of solutions found by the two-level approach were infeasible and the proposed joint approach improved the solution on the average by 6.79% for the remaining cases.
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
Mechanistic force modeling for milling of carbon fiber reinforced polymers with double helix tools
(Elsevier, 2013) Karpat, Y.; Polat, N.
Carbon fiber reinforced polymers (CFRP) have emerged as the material of choice to satisfy increasing demand for lighter aircrafts. Machinability characteristics of CFRPs are quite different than those of metals; therefore, special tool designs have been developed for CFRP machining. The double helix end mill design compresses the upper and lower sides of the laminate using opposite helix angles that eliminate delamination. A mechanistic force model for double helix tools is developed based on milling force data obtained on flat end mills. The proposed model can be used to improve double helix tool designs and to optimize milling process parameters.
Open Access
Milling force modelling of multidirectional carbon fiber reinforced polymer laminates
(Elsevier, 2012) Karpat, Yiğit; Bahtiyar, O.; Deger, B.
Carbon fiber reinforced polymer (CFRP) usage in the aerospace industry has been steadily increasing due to its superior material properties such as high strength, low weight, high resistance to corrosion, and a low thermal expansion coefficient. In addition, CFRP parts are produced near-net-shape, a process that eliminates rough machining operations. However, machining operations such as drilling, side milling, and slotting are still necessary to give the CFRP parts their final shape. A majority of the studies on machining of CFRP laminates are on drilling. The number of studies on milling of CFRPs is quite limited. In this study, a mechanistic cutting force model for milling CFRPs is proposed based on experimentally collected cutting force data during slot milling of unidirectional CFRP laminates using a polycrystalline diamond cutter. Cutting force coefficients in radial and tangential directions are calculated as a function of fiber cutting angle. The mechanistic model is shown to be capable of predicting cutting forces during milling of multidirectional CFRP laminates and capable of investigating stability of machining. © 2012 The Authors.
Open Access
A model-based investigation of tool-chip friction during precision micro cutting of commercially pure titanium alloy
(Inderscience Publishers, 2022) Aksin, Alp; Karpat, Yiğit
Understanding interaction between the cutting tool edge radius and the work material is essential to identify the conditions leading to superior surface finish during the micromachining process. The interaction between friction angle and effective rake angle has been investigated based on a slip-line field-based machining model from the literature. Machining forces and cut chip thickness values were obtained from orthogonal cutting tests and employed in the process model. The proposed model also allows for calculating material properties such as shear flow stress and fracture toughness. The proposed model can successfully simulate machining forces during shearing-dominated machining conditions. The results showed the importance of flank and rake face friction in micro-scale machining.
Open Access
A modified material model for the finite element simulation of machining titanium alloy Ti-6Al-4V
(Taylor & Francis, 2010) Karpat, Y.
Because of their desirable properties, such as high strength to weight ratio and corrosion resistance, titanium alloys are commonly employed in the aerospace and medical device industries. Titanium alloys are known to be difficult to machine, so the selection of cutting conditions with minimal experimental effort is important for manufacturers. Finite element modeling, which is an indispensable tool to understand the mechanics of machining, can also be utilized as an alternative method of process design as long as the finite element simulation input parameters are well defined. Developing a modified material model for titanium alloy Ti-6Al-4V by considering the relationships between strain, strain rate and temperature is the subject of this study. The flow softening behavior of the material at high strains is also examined. The influences of the material model parameters on the finite element simulation outputs are investigated. The finite element simulation results are found to be in agreement with the data available in the literature.
Open Access
Non-identical parallel CNC machine scheduling
(Taylor & Francis, 2003) Türkcan, A.; Selim Aktürk, M.; Storer, R. H.
In this study, we solve the non-identical parallel CNC machine scheduling problem. We have two objectives: minimizing the manufacturing cost (comprising machining, non-machining and tooling costs) and minimizing the total weighted tardiness. The tooling constraints affect the non-machining times as well as the machining conditions, such as cutting speed and feed rate, which in turn specify the machining times and tool lives. We propose a two-stage algorithm to find optimal machining conditions and to determine machine allocation, tool allocation and part scheduling decisions. The proposed algorithm generates different schedules according to the relative importance of the objectives.
Open Access
Temperature dependent flow softening of titanium alloy Ti6Al4V: An investigation using finite element simulation of machining
(Elsevier, 2011) Karpat, Y.
Titanium alloy Ti6Al4V is the most commonly used titanium alloy in the aerospace and medical device industries due to its superior properties. There has been a considerable amount of research to better understand the serrated chip formation mechanism of titanium alloy Ti6Al4V by using finite element simulation of machining. An accurate representation of the behavior of the material is important in order to obtain reliable results from the finite element simulation. Flow softening behavior has been integrated into the material constitutive models to simulate adiabatic shear bands and serrated chips. Flow softening is usually related to the dynamic recrystallization phenomenon which initiates after a critical temperature. The aim of this study is to investigate the influence of various flow softening conditions on the finite element simulation outputs for machining titanium alloy Ti6Al4V. For this purpose, a new flow softening expression, which allows defining temperature-dependent flow softening behavior, is proposed and integrated into the material constitutive model. The influence of flow softening below the critical temperature, as adopted in recent studies, is also investigated. Various temperature-dependent flow softening scenarios are tested using finite element simulations, and the results are compared with experimental data from the literature. The results showed that the flow softening initiating around 350-500 °C combined with appropriate softening parameters yields simulation outputs that agree well with the experimental measurements.
Open Access
Tool allocation and machining conditions optimization for CNC machines
(Elsevier, 1996) Aktürk, M. S.; Avcı, S.
In the literature, there exist many variations of machining economics problem in terms of modelling approaches and solution methodologies. However most of the existing studies focus on the single machining operation which is seldom in practice. On the other hand, tool management approaches at the system level fail to relate the tooling issues to the machining conditions, and ignore the tool availability and tool wear restrictions. A new solution methodology is developed to determine the optimum machining conditions and tool allocation simultaneously to minimize the production cost of a multiple operation case where there can be alternative tools for each operation. As a result, we can both improve the solution by exploiting the interaction between these two decisions, and also prevent any infeasibility that might occur for the tool allocation problem due to tool contention among the operations for a limited number of tool types by considering the tool availability and tool life limitations.
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.