Stability of Milling Operations With Asymmetric Cutter Dynamics in Rotating Coordinates

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Alptunc Comak ◽  
Orkun Ozsahin ◽  
Yusuf Altintas
Keyword(s):  
Time Domain ◽  
Machine Tools ◽  
High Speed ◽  
End Mill ◽  
Spindle Shaft ◽  
Milling Operations ◽  
Stability Model ◽  
Principal Directions ◽  
The Stability ◽  
Rotating Coordinates

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.

Dynamics and Stability of Turn-Milling Operations With Varying Time Delay in Discrete Time Domain

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Alptunc Comak ◽  
Yusuf Altintas
Keyword(s):  
Time Domain ◽  
Chip Thickness ◽  
Body Motion ◽  
Depth Of Cut ◽  
Time Varying Delay ◽  
Milling Operations ◽  
Varying Time Delay ◽  
The Stability ◽  
Five Axis ◽  
Turn Milling

Turn-milling machines are widely used in industry because of their multifunctional capabilities in producing complex parts in one setup. Both milling cutter and workpiece rotate simultaneously while the machine travels in three Cartesian directions leading to five axis kinematics with complex chip generation mechanism. This paper presents a general mathematical model to predict the chip thickness, cutting force, and chatter stability of turn milling operations. The dynamic chip thickness is modeled by considering the rigid body motion, relative vibrations between the tool and workpiece, and cutter-workpiece engagement geometry. The dynamics of the process are governed by delayed differential equations by time periodic coefficients with a time varying delay contributed by two simultaneously rotating spindles and kinematics of the machine. The stability of the system has been solved in semidiscrete time domain as a function of depth of cut, feed, tool spindle speed, and workpiece speed. The stability model has been experimentally verified in turn milling of Aluminum alloy cut with a helical cylindrical end mill.

A Coupled Theoretical-Experimental Dynamical Model for Chatter Prediction in Milling Processes

2009 ◽  
Author(s):  
Giuseppe Catania ◽  
Nicolo` Mancinelli
Keyword(s):  
High Speed ◽  
Lumped Parameter Model ◽  
Milling Machine ◽  
Beam Shape ◽  
Milling Operations ◽  
Excited Vibration ◽  
Modal Model ◽  
Cutting Force Components ◽  
The Stability ◽  
Delay Differential

Productivity of high speed milling operations can be seriously limited by chatter occurrence. Several studies on this self-excited vibration can be found in the literature: simple models (1 or 2 dofs) are proposed, i.e. a lumped parameter model of the milling machine being excited by regenerative, time-varying cutting forces. In this study, a model of the milling machine is proposed: the machine frame and the spindle were modeled by an experimentally evaluated modal model, while the tool was modeled by a discrete modal approach, based on the continuous beam shape analytical eigenfunctions. The regenerative cutting force components lead to a set of Delay Differential Equations (DDEs) with periodic coefficients; DDEs were numerically integrated for different machining conditions. The stability lobe charts were evaluated using the semi-discretization method [6–7] that was extended to n dofs models (with n >2). Differences between the stability charts obtained by the low dofs models and the stability charts obtained by the new n dofs model are pointed out. Time histories and spectra related to the vibratory behavior of the system were numerically obtained to verify the effectiveness of the stability charts obtained with the n dofs modal model.

scholarly journals Critical Thickness and Dynamic Stiffness for Chatter Avoidance in Thin Floors Milling

2011 ◽  
Vol 188 ◽  
pp. 116-121 ◽  
Author(s):  
Francisco Javier Campa ◽  
Luis Norberto López de Lacalle ◽  
Gorka Urbicain ◽  
Aitzol Lamikiz ◽  
Sébastien Seguy ◽  
...  
Keyword(s):  
Critical Thickness ◽  
Dynamic Stiffness ◽  
Experimental Tests ◽  
Chatter Vibration ◽  
End Mill ◽  
Thin Walls ◽  
Stability Model ◽  
Aeronautical Industry ◽  
The Stability ◽  
Model Algorithm

A common problem in the aeronautical industry is the chatter vibration due to the lack of dynamic stiffness in the milling of thin walls and thin floors. The present work proposes a method for chatter avoidance in the milling of flexible thin floors with a bull nose end mill. It allows the calculation of the thickness previous to finish milling or the minimum dynamic stiffness that the floor must have to avoid the chatter vibration appearance. To obtain these values, the stability model algorithm has been inverted to estimate the thickness or the dynamic stiffness required in a floor to allow a stable milling. This methodology has been validated satisfactorily in several experimental tests.

Chatter Vibration Modeling in High Speed Milling Operations

2008 ◽  
Author(s):  
Giuseppe Catania ◽  
Nicolo` Mancinelli
Keyword(s):  
High Speed ◽  
Removal Rate ◽  
Lumped Parameter Model ◽  
Beam Shape ◽  
Stability Lobe ◽  
Milling Operations ◽  
Excited Vibration ◽  
Cutting Force Components ◽  
The Stability ◽  
High Removal Rate

High removal rate in milling operations can be limited by chatter occurrence. Several studies on this self-excited vibration can be found in the literature: simple models (1 or 2 dofs) are proposed, i.e. a lumped parameter model of the milling machine being excited by regenerative, time-varying cutting forces. In this study, the machine tool spindle was modeled by a discrete modal approach, based on the continuous beam shape, analytical eigenfunctions, while the eigenvalues were mainly experimentally identified. The regenerative cutting force components lend to a set of Delay Differential Equations (DDEs) with periodic coefficients; DDEs were numerically integrated for different machining conditions. The stability lobe chart was evaluated using the semi-discretization method. Time histories, spectra and Poincare´ maps related to the vibratory behavior of the system were numerically obtained and differences with respect to the bifurcations predicted by the simplest models known in literature are pointed out. Some different behaviors in the shape of the stability lobe charts and in the spectra of the chatter vibrations were also observed.

Investigation of Temperature Distribution in High-Speed End Mill Assisted by Heat Pipe Cooling

2011 ◽  
Vol 418-420 ◽  
pp. 1154-1157
Author(s):  
Qing Hua Song ◽  
Hua Wei Ju ◽  
Wei Xiao Tang
Keyword(s):  
Experimental Study ◽  
Temperature Field ◽  
Heat Pipe ◽  
High Speed ◽  
Experimental Studies ◽  
Solid Cylinder ◽  
End Mill ◽  
Milling Operations ◽  
Cylinder Model ◽  
Pipe Mill

A combined numerical and experimental study is performed to analyze the feasibility of using heat pipe cooling in milling applications. In this model, it is assumed that the end mill is subjected to a static heat source which verifies the analysis and feasibility of using heat pipe cooling in milling operations. The performance of heat pipe mill model is approximated using a solid cylinder model of pure conduction. Both the numerical and experimental studies show that the use of a heat pipe in a mill can reduce the temperature field significantly.

Dynamics and Stability of Plunge Milling Operations

2006 ◽  
Vol 129 (1) ◽  
pp. 32-40 ◽  
Author(s):  
Jeong Hoon Ko ◽  
Yusuf Altintas
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Cutting Forces ◽  
Milling Process ◽  
Body Motion ◽  
Plunge Milling ◽  
Milling Operations ◽  
Tool Setting ◽  
The Stability ◽  
The Time Domain

Plunge milling operations are used to remove excess material rapidly in roughing operations. The cutter is fed in the direction of the spindle axis which has the highest structural rigidity. This paper presents a comprehensive model of plunge milling process by considering rigid body motion of the cutter, and three translational and torsional vibrations of the structure. The time domain simulation model allows prediction of cutting forces, torque, and vibrations while considering tool setting errors and time varying process parameters. The stability law is formulated as a four-dimensional eigenvalue problem, and the stability lobes are predicted directly with analytical solution in frequency domain. Time domain prediction of cutting forces and vibrations, as well as the frequency domain and chatter stability solution are verified with a series of plunge milling experiments.

Stability-Based Spindle Design Optimization

2006 ◽  
Vol 129 (2) ◽  
pp. 407-415 ◽  
Author(s):  
Vincent Gagnol ◽  
Belhassen C. Bouzgarrou ◽  
Pascal Ray ◽  
Christian Barra
Keyword(s):  
High Speed ◽  
Modal Identification ◽  
Design Parameters ◽  
Depth Of Cut ◽  
Chatter Vibration ◽  
High Rotational Speed ◽  
Milling Operations ◽  
Critical Requirement ◽  
The Stability ◽  
Gyroscopic Coupling

Prediction of stable cutting regions is a critical requirement for high-speed milling operations. These predictions are generally made using frequency-response measurements of the tool-holder-spindle set obtained from a nonrotating spindle. However, significant changes in system dynamics occur during high-speed rotation. In this paper, a dynamic high-speed spindle-bearing system model is elaborated on the basis of rotor dynamics prediction and readjusted on the basis of experimental modal identification. The dependency of dynamic behavior on speed range is then investigated and determined with accuracy. Dedicated experiments are carried out in order to confirm model results. They show that dynamic effects due to high rotational speed and elastic deformations, such as gyroscopic coupling and spin softening, have a significant influence on spindle behavior. By integrating the modeled speed-dependent spindle transfer function in the chatter vibration stability approach of Altintas and Budak (1995, CIRPS Ann, 44(1), pp. 357–362), a new dynamic stability lobe diagram is predicted. Significant changes are observed in the stability limits constructed using the proposed approach and allow accurate prediction of cutting conditions to be established. Finally, optimization studies are performed on spindle design parameters in order to obtain a chatter vibration-free cutting operation at the desired speed and depth of cut for a given cutter.

Dynamics and Stability of Five-Axis Ball-End Milling

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Erdem Ozturk ◽  
Erhan Budak
Keyword(s):  
Time Domain ◽  
End Milling ◽  
Milling Process ◽  
Ball End Milling ◽  
Part Quality ◽  
Stability Diagrams ◽  
Milling Operations ◽  
The Stability ◽  
Milling Dynamics ◽  
Five Axis

Being one of the most important problems in machining, chatter vibrations must be avoided as they result in high cutting forces, poor surface finish, and unacceptable part quality. Using stability diagrams is an effective method to predict chatter free cutting conditions. Although there have been numerous works in milling dynamics, the stability of five-axis ball-end milling has not been studied in detail. In this paper, the stability of the five-axis ball-end milling is analyzed using analytical (frequency domain), numerical (time-domain), and experimental methods. The models presented consider 3D dynamics of the five-axis ball-end milling process including the effects of all important process parameters such as the lead and tilt angles. Both single- and multi-frequency solutions are presented. Unlike other standard milling cases, it is observed that adding multi-frequency effects in the solution has marginal influence on the stability diagrams for five-axis ball-end milling operations due to effects of the ball-end milling geometry on the engagement region, thus, on the directional coefficients. The stability limits predicted by single- and multi-frequency methods are compared with time-domain simulations and experiments. Using the models and experimental results, the effects of the lead and tilt angles on the stability diagrams are also shown. The presented models can be used in analysis of five-axis ball-end milling dynamics as well as in the selection of the milling conditions for increased stability.

Update on High-Speed Milling Dynamics

1990 ◽  
Vol 112 (2) ◽  
pp. 142-149 ◽  
Author(s):  
S. Smith ◽  
J. Tlusty
Keyword(s):  
High Speed ◽  
Metal Removal ◽  
Removal Rate ◽  
Spindle Speed ◽  
Stability Lobe ◽  
Milling Operations ◽  
Force Signal ◽  
The Stability ◽  
Milling Dynamics ◽  
Selection Of

As spindle speeds and power have increased, the possibility of using the stability lobe phenomena to substantially increase the metal removal rate has become more attractive, and selection of optimum spindle speeds has become an important consideration. It is shown that, for many milling operations, it is desirable to set the tooth frequency equal to the natural frequency. At this spindle speed, the development of resonant forced vibration is actually inhibited by regeneration of waviness. An algorithm is presented for automatically selecting the optimum spindle speed based on the cutting force signal.

A Mixed Frequency/Time-Domain Method to Evaluate the Performance of Semi-Active Steering Damper Control Strategies During Challenging Maneuvers

2011 ◽  
Author(s):  
Pierpaolo De Filippi ◽  
Sergio M. Savaresi
Keyword(s):  
Time Domain ◽  
High Speed ◽  
Control Strategies ◽  
Time Domain Method ◽  
Mixed Frequency ◽  
Active Steering ◽  
Domain Method ◽  
Damper Control ◽  
The Stability ◽  
Wheeled Vehicles

This work presents the validation of control strategies for a semi-active steering damper aimed at improving the stability of two-wheeled vehicles by controlling the weave and wobble modes. A mixed frequency/time-domain method is introduced to evaluate the performance of the control strategies. The proposed cost functions allow one to evaluate the influence of the algorithms on the damping of the weave and wobble modes and also the overall performance in terms of stability of the steering assembly and of the chassis. The performance of the control algorithms is assessed on a multibody motorcycle simulator considering three challenging maneuvers that excite both the weave and wobble modes, such as kick-back and strong braking while cornering at high speed.

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