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.

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.

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.

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.

Investigation of the Dynamics of Microend Milling—Part II: Model Validation and Interpretation

2006 ◽  
Vol 128 (4) ◽  
pp. 901-912 ◽  
Author(s):  
Martin B. G. Jun ◽  
Richard E. DeVor ◽  
Shiv G. Kapoor
Keyword(s):  
Dynamic Model ◽  
End Milling ◽  
Elastic Recovery ◽  
Chip Thickness ◽  
Thickness Effect ◽  
Depth Of Cut ◽  
Minimum Chip Thickness ◽  
Microend Milling ◽  
The Stability ◽  
Cutting Mechanisms

In Part II of this paper, experimental and analytical methods have been developed to estimate the values of the process faults defined in Part I of this paper. The additional faults introduced by the microend mill design are shown to have a significant influence on the total net runout of the microend mill. The dynamic model has been validated through microend milling experiments. Using the dynamic model, the effects of minimum chip thickness and elastic recovery on microend milling stability have been studied over a range of feed rates for which the cutting mechanisms vary from ploughing-dominated to shearing-dominated. The minimum chip thickness effect is found to cause feed rate dependent instability at low feed rates, and the range of unstable feed rates depends on the axial depth of cut. The effects of process faults on microend mill vibrations have also been studied and the influence of the unbalance from the faults is found to be significant as spindle speed is increased. The stability characteristics due to the regenerative effect have been studied. The results show that the stability lobes from the second mode of the microend mill, which are generally neglected in macroscale end milling, affect the microend mill stability significantly.

An Investigation of Workpiece Temperature in Orthogonal Turn-Milling Compound Machining

2015 ◽  
Vol 137 (1) ◽  
Author(s):  
Fangyu Peng ◽  
Yizhi Liu ◽  
Sen Lin ◽  
Rong Yan ◽  
Sheng Yang ◽  
...  
Keyword(s):  
Heat Source ◽  
Orthogonal Experiment ◽  
Test Validity ◽  
Chip Thickness ◽  
Depth Of Cut ◽  
Heat Conducting ◽  
Machining Parameters ◽  
Workpiece Temperature ◽  
Milling Tool ◽  
Turn Milling

A thermal model estimating workpiece temperature in orthogonal turn-milling compound machining for the case with noneccentricity between rotation axes of workpiece and tool has been established in this paper. Milling tool and machining history were discretized into infinitesimal elements of equal size to deal with complicated cutter geometry and intermittent cutting procedure. The geometries of milling tool and workpiece were analyzed to calculate the instantaneous chip thickness, axial depth of cut, and angles of cutting entry and exit. Heat source during cutting process was considered as instantaneous moving rectangular heat source and heat conducting function in infinite solid thermal conductivity was developed. Experiments measuring cutting force and workpiece temperature were launched to test validity of this model and figure out the importance of effects those factors have on workpiece temperature from variance analysis of orthogonal experiment results. Furthermore, simulations to calculate peak temperature of workpiece were carried out by this model with relevant machining parameters and the results matched conclusions from experiment well.

Dynamics of flexible detail milling

2011 ◽  
Vol 225 (4) ◽  
pp. 299-309 ◽  
Author(s):  
S A Voronov ◽  
I A Kiselev
Keyword(s):  
Milling Process ◽  
Machining Process ◽  
Machined Surface ◽  
Workpiece Surface ◽  
Thin Walled Structures ◽  
Milling Operations ◽  
Efficient Processing ◽  
The Stability ◽  
Five Axis

The five-axis milling operations are commonly used in aerospace industry. For example, this operation is the base for the machining process of the turbine blade production. The milling operations of thin-walled structures cause the vibrations of the tool and the workpiece and this turn affect the quality of the workpiece surface. Modelling of the milling process is necessary to determine the proper cutting conditions for the required productivity and the surface quality. In this article, the geometry modelling algorithm for five-axis milling process is proposed. Dynamics of the machined surface is modelled using the finite-element method. The obtained results make possible to conclude about the stability of milling process and to calculate the efficient processing conditions at which the amplitude of the generated vibrations does not exceed the admissible level. The results of this research can be used while the milling process technologies are designed. Especially, it is significant for the machining of hard-to-machine materials and processing of heat-resistant alloys in space and aircraft industries.

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.

scholarly journals Disturbance of the Regenerative Effect by Use of Milling Tools Modified with Asymmetric Dynamic Properties

2020 ◽  
Vol 4 (3) ◽  
pp. 67
Author(s):  
Jonas Baumann ◽  
Andreas Wirtz ◽  
Tobias Siebrecht ◽  
Dirk Biermann
Keyword(s):  
Dynamic Properties ◽  
Constant Width ◽  
Chip Thickness ◽  
Stability Limit ◽  
Dynamic Compliance ◽  
Depth Of Cut ◽  
Regenerative Effect ◽  
The Stability ◽  
Tool Shank ◽  
Milling Tools

Milling processes are often limited by self-excited vibrations of the tool or workpiece, generated by the regenerative effect, especially when using long cantilevered tools or machining thin-walled workpieces. The regenerative effect arises from a periodic modulation of the uncut chip thickness within the frequencies of the eigenmodes, which results in a critical excitation in the consecutive cuts or tooth engagements. This paper presents a new approach for disturbing the regenerative effect by using milling tools which are modified with asymmetric dynamic properties. A four-fluted milling tool was modified with parallel slots in the tool shank in order to establish asymmetric dynamic characteristics or different eigenfrequencies for consecutive tooth engagements, respectively. Measurements of the frequency response functions at the tool tip showed a decrease in the eigenfrequencies as well as an increase in the dynamic compliance in the direction of the grooves. Milling experiments with a constant width of cut and constantly increasing axial depth of cut indicated a significant increase in the stability limit for the specific preparations of up to 69%.

scholarly journals Discrete-time systems with time-varying time delay: Stability and stabilizability

2006 ◽  
Vol 2006 ◽  
pp. 1-10 ◽  
Author(s):  
El-Kébir Boukas
Keyword(s):  
Time Delay ◽  
Discrete Time ◽  
Sufficient Conditions ◽  
Time Varying ◽  
Design Algorithm ◽  
Time Varying Delay ◽  
Discrete Time Systems ◽  
Varying Time Delay ◽  
The Stability ◽  
Time Systems

This paper deals with the class of linear discrete-time systems with varying time delay. The problems of stability and stabilizability for this class of systems are considered. Given an upper bound and a lower bound on the time-varying delay, sufficient conditions for checking the stability of this class of systems are developed. A control design algorithm is also provided. All the results developed in this paper are in the LMI formalism which makes their solvability easier using existing tools. A numerical example is provided to show the effectiveness of the established results.

Kinematic Model of Dynamic Drilling Process

2004 ◽  
Author(s):  
Jochem C. Roukema ◽  
Yusuf Altintas
Keyword(s):  
Mathematical Model ◽  
Rigid Body ◽  
Kinematic Model ◽  
Chip Thickness ◽  
Body Motion ◽  
Depth Of Cut ◽  
Force Model ◽  
Drilling Process ◽  
Structural Vibrations ◽  
Radial Depth

A mathematical model of the torsional-axial chatter vibrations in drilling is presented. The model considers the exact kinematics of both rigid body, and coupled torsional and axial vibrations of the drill. The drill is modeled as a pretwisted beam that exhibits axial deflections due to torque and thrust loading. A mechanistic cutting force model is used to model the cutting torque and thrust as a function of feedrate, speed, radial depth of cut, and drill geometry. The drill rotates and feeds axially into the workpiece while the structural vibrations are excited by the cutting torque and thrust force. The exact location of the drill edge is predicted using the model, and the generated surface is digitized at discrete time intervals. The distribution of chip thickness, which is affected by both rigid body motion and structural vibrations, is evaluated by subtracting the presently generated surface from the previous one. The model considers nonlinearities in cutting coefficients, tool jumping out of cut and overlapping of multiple regeneration waves. The dynamic chip thickness obtained from the true kinematics model allows simultaneous prediction of force, torque, power and dimensional form errors left on the surface. The time domain simulation model allows prediction of stability lobes. The paper provides details of the mathematical model, supported by experimental results of both stable and unstable cuts.

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