Ideko Danobat Group

Elgoibar, Spain

Ideko Danobat Group

Elgoibar, Spain
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Yang Y.,Beihang University | Liu Q.,Beihang University | Jokin M.,Ideko Danobat Group
Zhendong Ceshi Yu Zhenduan/Journal of Vibration, Measurement and Diagnosis | Year: 2010

The orthogonal polynomial method is widely used in the identification of modal parameters performed on the frequency response function (FRF) curves. The disadvantage of this method is difficult to determine the number of modes and the order of the polynomial, while it is difficult to intervene with the identification process by the operator, which can result in the omission of some modes or occurrence of false modes. In this work, based on existing algorithm, the number of modes and poles of the FRF is first determined by use of the stabilization diagram and mode indicator function (MIF) in a combination way, and then the residue is estimated by using linear least square method. Furthermore, this method is extended to the global FRF curve-fitting. A comparison of the modal parameters estimated from a measured FRF by using existing orthogonal polynomial algorithm or the commercial software ME'scope VES to those estimated by the method suggested in this work shows that the phenonmena of false modes and the omission of some modes no longer occur to the results given by the method besides that it can get accurate and stable results, and has great anti-disturbance ability.


Dombovari Z.,Budapest University of Technology and Economics | Dombovari Z.,Ideko Danobat Group | Altintas Y.,University of British Columbia | Stepan G.,Budapest University of Technology and Economics
International Journal of Machine Tools and Manufacture | Year: 2010

The machining behaviour of special serrated milling tools are investigated. These cutters are most commonly used for roughing operations of superalloys such as titanium and nickel based alloys which prevent high cutting speeds due to their high cutting forces and low thermal conductivity. During the experimental study, these drawbacks were avoided with the usage of aluminium alloy that allows more convenient machining circumstances and high tooth passing frequencies compared to the frequencies of the essential vibration modes. By means of a general cutting force model, simulations point out the fact that the serrated cutters require lower drive torque than their non-serrated counterparts, while our corresponding measurements validate our model. A regenerative dynamic model is constructed up directly in the modal space using the modal representation of the tool/toolholder/spindle structure and linear stability analyses are performed by the so-called semi-discretization method. The significantly larger parameter domains of stable cutting and their predicted feed dependency for these serrated mills are confirmed by chatter tests. As a result of these investigations, the practical advantages of the serrated cutters are confirmed: while they remove the same specific amount of materials using lower drive torque, their productivity can also be increased using higher stable depth of cuts compared to their non-serrated counterparts even in case of difficult-to-cut materials like titanium. The constructed mechanical model also provides an adequate tuning of the cutting parameters and the serration waves in order to optimize the process for easy-to-cut materials like aluminium. © 2010 Elsevier Ltd.


Stepan G.,Budapest University of Technology and Economics | Munoa J.,Ideko Danobat Group | Insperger T.,Budapest University of Technology and Economics | Surico M.,Fidia | And 2 more authors.
CIRP Annals - Manufacturing Technology | Year: 2014

Critical comparison is presented related to the stability behaviour of milling processes performed by conventional, variable helix and serrated milling tools. The paper presents a general milling model linked to any non-proportionally damped dynamic system. Extended multi frequency solution and semi-discretization are implemented and used to calculate the stability of stationary milling. Measurements performed in industrial environment validate the general numerical algorithm that is able to predict the stability conditions of milling processes carried out by cylindrical cutters of optional geometry. Both the calculations and the measurements confirm that, for roughing operations, the highest stability gain can be achieved by serrated cutters. It is also demonstrated that variable helix milling tools can achieve better stability behaviour only if their geometry is optimized for the given cutting operation. © 2014 CIRP.


Stepan G.,Budapest University of Technology and Economics | Dombovari Z.,Budapest University of Technology and Economics | Munoa J.,Ideko Danobat Group
CIRP Annals - Manufacturing Technology | Year: 2011

Cutting force coefficients exhibit strong nonlinearity as a function of chip loads, cutting speeds and material imperfections. This paper presents the connection between the sensitivity of the dynamics of regenerative cutting and the cutting force characteristic nonlinearity. The nonlinear milling process is mathematically modelled. The transitions of dynamic cutting process between the stable and unstable zones are considered and experimentally illustrated by applying wavelet transformations on the measurement data. © 2011 CIRP.


Yang Y.,Beihang University | Munoa J.,Ideko Danobat Group | Altintas Y.,University of British Columbia
International Journal of Machine Tools and Manufacture | Year: 2010

Chatter is more detrimental to machining due to its instability than forced vibrations. This paper presents design and optimal tuning of multiple tuned mass dampers (TMDs) to increase chatter resistance of machine tool structures. Chatter free critical depth of cut of a machine is inversely proportional to the negative real part of frequency response function (FRF) at the toolworkpiece interface. Instead of targeting reduction of magnitude, the negative real part of FRF of the machine is reduced by designing single and multiple TMD systems. The TMDs are designed to have equal masses, and their damping and stiffness values are optimized to improve chatter resistance using minimax numerical optimization algorithm. It is shown that multiple TMDs need more accurate tuning of stiffness and natural frequency of each TMD, but are more robust to uncertainties in damping and input dynamic parameters in comparison with single TMD applications. The proposed tuned damper design and optimization strategy is experimentally illustrated to increase chatter free depth of cuts. © 2010 Elsevier Ltd. All rights reserved.


Dombovari Z.,Budapest University of Technology and Economics | Dombovari Z.,Ideko Danobat Group | Barton D.A.W.,University of Bristol | Eddie Wilson R.,University of Bristol | Stepan G.,Budapest University of Technology and Economics
International Journal of Non-Linear Mechanics | Year: 2011

The large-amplitude motions of a one degree-of-freedom model of orthogonal cutting are analysed. The model takes the form of a delay differential equation which is non-smooth at the instant at which the tool loses contact with the workpiece, and which is coupled to an algebraic equation that stores the profile of the cut surface whilst the tool is not in contact. This system is approximated by a smooth delay differential equation without algebraic effects which is analysed with numerical continuation software. The grazing bifurcation that defines the onset of chattering motion is thus analysed as are secondary (period-doubling, etc.) bifurcations of chattering orbits, and convergence of the bifurcation diagrams is established in the vanishing limit of the smoothing parameters. The bifurcation diagrams of the smoothed system are then compared with initial value simulations of the full non-smooth delay differential algebraic equation. These simulations mostly validate the smoothing technique and show in detail how chaotic chattering dynamics emerge from the non-smooth bifurcations of periodic orbits. © 2010 Elsevier Ltd. All rights reserved.


Yang Y.,Beihang University | Liu Q.,Beihang University | Jokin M.,Ideko Danobat Group
Zhendong Ceshi Yu Zhenduan/Journal of Vibration, Measurement and Diagnosis | Year: 2010

A lumped model could extend the application of experimental modal analysis (EMA) and reduce the number of degrees of freedom (DOF) of the original system while the dynamic characteristics were kept. Based on EMA, a lumped model of a vertical milling machine with 7 degrees of freedom was created using the mass and spring- damping elements. The frequency response function (FRF) of the tool point was synthesized and chatter stability was predicted. The relationship between the chatter frequency and the mode shape was revealed. Compared with the FRF derived from the test results, the model presented in this paper was more accurate.

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