Alptunc Comak | University of British Columbia (original) (raw)

Papers by Alptunc Comak

Research paper thumbnail of Mechanics of turn-milling operations

Turn-milling machines, which are capable of carrying out turning and milling operations, are wide... more Turn-milling machines, which are capable of carrying out turning and milling operations, are widely used in machining complex parts in one setup. However, due to the complex kinematics and tool-workpiece interaction, turn milling operations are mainly carried out by relying on costly machining trials and experience. This paper presents the mechanics of turn-milling operations to predict cutting forces, torque and power requirements. Typical turn milling process involves three linear (x,y.z) and two rotary drives of the machine tool. The resulting feed vector is modeled as a function of linear velocities of the drives, and angular speeds of workpiece and tool spindles. The generalized chip thickness distribution is modeled as a function of linear feed drive motions, tool and workpiece spindle rotations. The cutting force predictions are experimentally verified for sample cylindrical and ball end mills. The identification of productive tool and workpiece spindle speeds is demonstrated using chip load limit of the tools and torque-power constraints of the turn milling machine tools.

Research paper thumbnail of Stability and high performance machining conditions in simultaneous milling

CIRP Annals - Manufacturing Technology, 2013

Research paper thumbnail of Optimum conditions for increased stability of simultaneous turning processes

Research paper thumbnail of Chatter stability of parallel milling operations

Research paper thumbnail of Paralel tornalama işlevini gerçekleştiren CNC torna tezgahının tasarımı, kesici uç ömrü ve kesme kararlılığı incelemeleri (Cutting tool life, cutting stability and process time review on designed and manufactured CNC turning machine which performs the parallel turning function)

Research paper thumbnail of Eşzamanlı frezeleme operasyonlarının dinamiği ve kararlılığı

Research paper thumbnail of Modeling and simulation based design of variable pitch and variable helix milling tools for increased chatter stability

Research paper thumbnail of Optimum conditions for increased stability of simultaneous turning processes

Research paper thumbnail of Chatter stability of parallel milling operations

Research paper thumbnail of Talaşlı imalat süreçlerinin kararlılığı ve takım tezgah dinamiği (Machining process stability and machine tool dynamics)

Research paper thumbnail of Stability of Milling Operations With Asymmetric Cutter Dynamics in Rotating Coordinates

High-speed machine tools have parts with both stationary and rotating dynamics. While spindle hou... more High-speed machine tools have parts with both stationary and rotating dynamics. While spindle housing, column, and table have stationary dynamics, rotating parts may have both symmetric (i.e., spindle shaft and tool holder) and asymmetric dynamics (i.e., two-fluted end mill) due to uneven geometry in two principal directions. This paper presents a stability model of dynamic milling operations with combined stationary and rotating dynamics. The stationary modes are superposed to two orthogonal directions in rotating frame by considering the time-and speed-dependent, periodic dynamic milling system. The stability of the system is solved in both frequency and semidiscrete time domain. It is shown that the stability pockets differ significantly when the rotating dynamics of the asymmetric tools are considered. The proposed stability model has been experimentally validated in high-speed milling of an aluminum alloy with a two-fluted, asymmetric helical end mill.

Research paper thumbnail of Tuning of tool dynamics for increased stability of parallel (simultaneous) turning processes

Parallel (simultaneous) turning operations make use of more than one cutting tool acting on a com... more Parallel (simultaneous) turning operations make use of more than one cutting tool acting on a common workpiece offering potential for higher productivity. However, dynamic interaction between the tools and workpiece and resulting chatter vibrations may create quality problems on machined surfaces. In order to determine chatter free cutting process parameters, stability models can be employed. In this paper, stability of parallel turning processes is formulated in frequency and time domain for two different parallel turning cases. Predictions of frequency and time domain methods demonstrated reasonable agreement with each other. In addition, the predicted stability limits are also verified experimentally. Simulation and experimental results show multi regional stability diagrams which can be used to select most favorable set of process parameters for higher stable material removal rates. In addition to parameter selection, developed models can be used to determine the best natural frequency ratio of tools resulting in the highest stable depth of cuts. It is concluded that the most stable operations are obtained when natural frequency of the tools are slightly off each other and worst stability occurs when the natural frequency of the tools are exactly the same.

Research paper thumbnail of Stability and high performance machining conditions in simultaneous milling

Parallel milling offers the advantage of simultaneous machining of a workpiece with two milling t... more Parallel milling offers the advantage of simultaneous machining of a workpiece with two milling tools.
Higher material removal rates and machining with fewer fixtures are possible due to the second tool.
These advantages make parallel milling an ideal technology for machining of near net shape structures.
However, parameter selection is quite challenging due to the dynamic interaction between the tools. In
this study, time and frequency domain stability models are developed to aid the process planner. Effects of
process parameters are also investigated and high performance machining conditions are identified. The
experimental cuts are made to verify the presented methodology.

Research paper thumbnail of Modeling dynamics and stability of variable pitch and helix milling tools for development of a design method to maximize chatter stability

Chatter is one of the major limitations in milling operations causing poor quality and reduced pr... more Chatter is one of the major limitations in milling operations causing poor quality and reduced productivity. Stability diagrams can be used to identify deep stable pockets which usually occur at high spindle speeds. However, the required high cutting speeds may not be applied in some cases due to machinability or machine tool limitations. It is known that variable pitch and helix tools help suppressing chatter even at low cutting speeds. These tools may offer high productivity if they are properly designed. The literature on variable geometry milling tools is mainly limited to modelling and simulation whereas for industrial applications design guidelines are needed for selection of variation pattern and amount which is the focus of this paper. Dynamics and stability of variable pitch and helix tools are modelled and solved in frequency domain as well as using Semi-Discretization Method employing multiple delays. A practical but accurate design method is presented for selection of the best variation combination to maximize chatter free material removal rate without using time consuming computer simulations. Increased stability with the tools designed using the proposed method is demonstrated by several examples which are verified experimentally.

articles by Alptunc Comak

Research paper thumbnail of Modeling and simulation based design of variable pitch and variable helix milling tools for increased chatter stability

Research paper thumbnail of Mechanics of turn-milling operations

Turn-milling machines, which are capable of carrying out turning and milling operations, are wide... more Turn-milling machines, which are capable of carrying out turning and milling operations, are widely used in machining complex parts in one setup. However, due to the complex kinematics and tool-workpiece interaction, turn milling operations are mainly carried out by relying on costly machining trials and experience. This paper presents the mechanics of turn-milling operations to predict cutting forces, torque and power requirements. Typical turn milling process involves three linear (x,y.z) and two rotary drives of the machine tool. The resulting feed vector is modeled as a function of linear velocities of the drives, and angular speeds of workpiece and tool spindles. The generalized chip thickness distribution is modeled as a function of linear feed drive motions, tool and workpiece spindle rotations. The cutting force predictions are experimentally verified for sample cylindrical and ball end mills. The identification of productive tool and workpiece spindle speeds is demonstrated using chip load limit of the tools and torque-power constraints of the turn milling machine tools.

Research paper thumbnail of Stability and high performance machining conditions in simultaneous milling

CIRP Annals - Manufacturing Technology, 2013

Research paper thumbnail of Optimum conditions for increased stability of simultaneous turning processes

Research paper thumbnail of Chatter stability of parallel milling operations

Research paper thumbnail of Paralel tornalama işlevini gerçekleştiren CNC torna tezgahının tasarımı, kesici uç ömrü ve kesme kararlılığı incelemeleri (Cutting tool life, cutting stability and process time review on designed and manufactured CNC turning machine which performs the parallel turning function)

Research paper thumbnail of Eşzamanlı frezeleme operasyonlarının dinamiği ve kararlılığı

Research paper thumbnail of Modeling and simulation based design of variable pitch and variable helix milling tools for increased chatter stability

Research paper thumbnail of Optimum conditions for increased stability of simultaneous turning processes

Research paper thumbnail of Chatter stability of parallel milling operations

Research paper thumbnail of Talaşlı imalat süreçlerinin kararlılığı ve takım tezgah dinamiği (Machining process stability and machine tool dynamics)

Research paper thumbnail of Stability of Milling Operations With Asymmetric Cutter Dynamics in Rotating Coordinates

High-speed machine tools have parts with both stationary and rotating dynamics. While spindle hou... more High-speed machine tools have parts with both stationary and rotating dynamics. While spindle housing, column, and table have stationary dynamics, rotating parts may have both symmetric (i.e., spindle shaft and tool holder) and asymmetric dynamics (i.e., two-fluted end mill) due to uneven geometry in two principal directions. This paper presents a stability model of dynamic milling operations with combined stationary and rotating dynamics. The stationary modes are superposed to two orthogonal directions in rotating frame by considering the time-and speed-dependent, periodic dynamic milling system. The stability of the system is solved in both frequency and semidiscrete time domain. It is shown that the stability pockets differ significantly when the rotating dynamics of the asymmetric tools are considered. The proposed stability model has been experimentally validated in high-speed milling of an aluminum alloy with a two-fluted, asymmetric helical end mill.

Research paper thumbnail of Tuning of tool dynamics for increased stability of parallel (simultaneous) turning processes

Parallel (simultaneous) turning operations make use of more than one cutting tool acting on a com... more Parallel (simultaneous) turning operations make use of more than one cutting tool acting on a common workpiece offering potential for higher productivity. However, dynamic interaction between the tools and workpiece and resulting chatter vibrations may create quality problems on machined surfaces. In order to determine chatter free cutting process parameters, stability models can be employed. In this paper, stability of parallel turning processes is formulated in frequency and time domain for two different parallel turning cases. Predictions of frequency and time domain methods demonstrated reasonable agreement with each other. In addition, the predicted stability limits are also verified experimentally. Simulation and experimental results show multi regional stability diagrams which can be used to select most favorable set of process parameters for higher stable material removal rates. In addition to parameter selection, developed models can be used to determine the best natural frequency ratio of tools resulting in the highest stable depth of cuts. It is concluded that the most stable operations are obtained when natural frequency of the tools are slightly off each other and worst stability occurs when the natural frequency of the tools are exactly the same.

Research paper thumbnail of Stability and high performance machining conditions in simultaneous milling

Parallel milling offers the advantage of simultaneous machining of a workpiece with two milling t... more Parallel milling offers the advantage of simultaneous machining of a workpiece with two milling tools.
Higher material removal rates and machining with fewer fixtures are possible due to the second tool.
These advantages make parallel milling an ideal technology for machining of near net shape structures.
However, parameter selection is quite challenging due to the dynamic interaction between the tools. In
this study, time and frequency domain stability models are developed to aid the process planner. Effects of
process parameters are also investigated and high performance machining conditions are identified. The
experimental cuts are made to verify the presented methodology.

Research paper thumbnail of Modeling dynamics and stability of variable pitch and helix milling tools for development of a design method to maximize chatter stability

Chatter is one of the major limitations in milling operations causing poor quality and reduced pr... more Chatter is one of the major limitations in milling operations causing poor quality and reduced productivity. Stability diagrams can be used to identify deep stable pockets which usually occur at high spindle speeds. However, the required high cutting speeds may not be applied in some cases due to machinability or machine tool limitations. It is known that variable pitch and helix tools help suppressing chatter even at low cutting speeds. These tools may offer high productivity if they are properly designed. The literature on variable geometry milling tools is mainly limited to modelling and simulation whereas for industrial applications design guidelines are needed for selection of variation pattern and amount which is the focus of this paper. Dynamics and stability of variable pitch and helix tools are modelled and solved in frequency domain as well as using Semi-Discretization Method employing multiple delays. A practical but accurate design method is presented for selection of the best variation combination to maximize chatter free material removal rate without using time consuming computer simulations. Increased stability with the tools designed using the proposed method is demonstrated by several examples which are verified experimentally.