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Enhancing dynamic characteristics of fixtures for large workpieces is essential to assure chatter free machining of heavy-duty milling operations. Variable stiffness tuned mass dampers (VSTMD) can effectively improve the dynamic stiffness of modular fixtures by changing their dynamic characteristics. The theory of a new VSTMD concept is presented. Their realisable optimal tuning is determined and the results are compared to the standard constant stiffness TMDs. By means of the developed automatic tuning procedure, stiffness is varied via a rotary spring, while damping is provided by eddy currents. The prototype and the effectiveness of the concept are experimentally validated by heavy-duty milling tests on a modular fixture.

Tuesday, 20 September 2016 11:26

Chatter suppression techniques in metal cutting

The self-excited vibration, called chatter, is one of the main limitations in metal removal processes. Chatter may spoil the surface of the part and can also cause large reduction in the life of the different components of the machine tool including the cutting tool itself. During the last 60 years, several techniques have been proposed to suppress chatter. This keynote paper presents a critical review of the different chatter suppression techniques. Process solutions with design and control approaches are compiled to provide a complete view of the available methods to stabilize the cutting process. The evolution of each technique is described remarking the most important milestones in research and the corresponding industrial application. The selection of the most appropriate technique for each specific chatter problem is also discussed considering various aspects of machining processes.

Scientific pubication by IONAUTICS and IP-ASCR on Time-resolved ion flux and impedance measurements for process characterization in reactive high-power impulse magnetron sputtering. More information: http://scitation.aip.org/content/avs/journal/jvsta/34/4/10.1116/1.4953033

Publication by Ideko on Analytical expressions for chatter analysis in milling operations with one dominant mode. More information: http://www.sciencedirect.com/science/article/pii/S0022460X16300499

New scientific publication by Plasmatrix, University of Oulu, University of Stuttgart and IP-ASCR on High dynamic stiffness mechanical structures with nanostructured composite coatings deposited by high power impulse magnetron sputtering. More information: http://www.sciencedirect.com/science/article/pii/S0008622315303845

A new scientific article by J. Munoa, A. Iglesias, J. Ciurana and Z. Dombovari has been submitted to the International Journal of Machine Tools and Manufacture.

In milling, an accurate prediction of chatter is still one of the most complex problems in the field. The presence of these self-excited vibrations can spoil the surface of the part and can also cause a large reduction in tool life. The stability diagrams provide a practical selection of the optimum cutting conditions determined either by time domain or frequency domain based methods. Applying these methods parametric or parameter traced representations of the linear stability limits can be achieved by solving the corresponding eigenvalue problems. In this work, new analytical formulae are proposed related to the parameter domains of both Hopf and period doubling type stability boundaries emerging in the regenerative mechanical model of time periodical milling processes. These formulae are useful to enrich and speed up the currently used numerical methods. Also, the destabilization mechanism of double period chatter is explained, creating an analogy with the chatter related to the Hopf bifurcation, considering one dominant mode and using concepts established by the Pioneers of chatter research.

 

 

The forced periodic vibrations of milling processes with helical tools are modelled and analysed. By means of analytical and numerical techniques, the so-called superchart of milling is constructed that includes the conventional stability chart with the stability lobes and also the amplitudes of the stable forced vibrations, which is correlated to many surface quality numbers like surface location error, surface waviness and surface roughness. The existences of trivial and non-trivial appropriate axial immersions are presented for a single degree of freedom mechanical model of the machine tool structure. At these appropriate axial immersion parameters, if the cutting is stable, the surface quality parameters will be also optimal even in those spindle speed domains where the system is near to resonance and the cutting efficiency is high. Experiments are performed with a large industrial milling machine using a flexible test rig with an essential flexibility in one direction. The calculated and the measured forced vibration signals in the stable domains of the stability chart are in good correlation, which validates the simple analytical predictions for the non-trivial appropriate axial immersion parameters.

We are happy to announce that Daniel Lundin (Ionautics) , Martin ─îada and Zden─Ťk Hubi─Źka (Fyzik├íln├ş ├║stav) have a joint scientific article published at Plasma Sources Science and Technology! The article presents the Ionization of sputtered Ti, Al, and C coupled with plasma characterization in HiPIMS. Here you can find the link to the article:┬áhttp://iopscience.iop.org/article/10.1088/0963-0252/24/3/035018/meta;jsessionid=C7EC9DE3260570586B7E921921738E10.c1

 

New publications by University of Oulu on The Effect of Al Buffer Layer on the Catalytic Synthesis of Carbon Nanotube Forests. More information about the article: http://link.springer.com/article/10.1007%2Fs11244-015-0479-5

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