[en] Chatter is commonly found when machining slender components on a lathe due to the low stiffness and damping. Aspects such as accuracy and roughness are usually compromised owing to large variation in stiffness along the length of the workpiece, which is a problem for the machining industry. The main contributions of this thesis are the proposal of (I) models for determine the chatter-free cutting conditions in slender workpiece machining and (II) a process monitoring system to detect chatter using available internal signals from the regulator. The clamping of a workpiece in the spindle of a lathe is not completely stiff, so the classical boundary conditions such as clamped–free, are not enough. The natural frequencies of the machine-workpiece system are usually lower than the theoretical ones obtained with classical boundary conditions. As the system is different for each machine and clamping method, it is necessary to characterize them. In order to be industrially feasible, a experimental method based on models with elastic boundary conditions is proposed to identify the system parameters. A exciter tool prototype based on a piezo actuator is developed to excite the system and natural frequencies have been measured by an accelerometer. The system parameters for a specific clamping and machine tool have been identified by means of model updating method. Once the system parameters have been identified, the effective stiffness of the system at each tool position of the workpiece is obtained. In slender workpieces, two nearby local modes appear due to the clamping, so workpiece chatter may occur by mode coupling in addition to regenerative. The stability of the process for a facing operation has been modelled in the state space taking into account both phenomena. An eigenvalue analysis is carried out by freezing the physical parameters of the time varying system at each time instant. The stability of the process is determined for certain cutting conditions. The theoretical results are validated by experimental tests. As the system is variant periodically in time due to the workpiece rotation, a Linear Time Periodic (LTP) stability model for slender workpiece machining has been proposed in order to define the process stability for each cutting condition. The stability is analysed by Floquet theory and the Stability Lobe Diagram (SLD) are obtained. Finally, the development and validation of a process monitoring system using internal signals available in the Computer Numerical Control (CNC) is presented. The feasibility of different internal signals for chatter monitoring are evaluated. An internal signal based monitoring system is implemented on a fast prototyping generic hardware and the monitoring system is experimentally evaluated in a CNC lathe.

[eu] Oso ohikoa da chatterra aurkitzea tornu batean pieza lirainak mekanizatzen direnean, sistemaren zurruntasun eta amortiguazio txikiagatik. Mekanizatzean zehaztasuna oso txikia izan ohi da piezaren zurruntasunaren aldakortasun handiagatik luzeran zehar, eta hori arazo bat da mekanizatu industrian. Tesi honen ekarpen nagusiak (I) pieza lirainak mekanizatzeko chatterrik gabeko ebaketa baldintzak zehazteko modeloak eta (II) erregulatzailean eskuragarri dauden barne seinaleak erabiliz mekanizazio prozesua monitorizatzeko sistema dira. Tornu baten pieza amarratze sistema ez da erabat zurruna, beraz, gainazaleko baldintza klasikoak, ez dira nahikoak. Maiztasun naturalak orokorrean maiztasun teorikoak baino baxuagoak izan ohi dira. Makina eta amarratze metodo bakoitzerako sistema aldatzen denez, beharrezkoa da horiek identifikatzea. Industrialki bideragarria izan dadin, gainazaleko baldintza elastikoak dituen modeloetan oinarritutako metodo esperimental bat proposatzen da, sistemaren parametroak identifikatzeko. Sistema kitzikatzeko, eragingailu piezoelektriko batean oinarritutako erremienta kitzikagailu prototipo bat garatu da, eta maiztasun naturalak azelerometro baten bidez neurtzen dira. Amarre baterako eta makina-erreminta espezifiko baterako sistemaren parametroak identifikatu dira model updating metodoaren bidez. Sistemaren parametroak ezagutu ondoren, sistemaren zurruntasun eraginkorra lortu da piezaren luzeran zehar. Pieza lirainetan, hurbileko bi modu lokal agertzen dira amarratzearen ondorioz. Beraz, chatterra, moduen akoplamenduaren bidez gerta daiteke, birsorkuntza efektuaz gain. Errefrentatze operazio baterako, prozesuaren egonkortasuna modelatu da egoera-eremuan, bi fenomenoak kontuan hartuta. Balio propioak aztertzeko, sistemaren parametro fisikoak izoztu dira une bakoitzean. Ebaketa baldintza jakin batzuetarako prozesuaren egonkortasuna zehaztu da eta emaitza teorikoak proba esperimentalen bidez baliozkotu dira. Sistema denboran zehar aldakorra da periodikoki piezaren errotazioarengatik. Horregatik, denboran zehar periodikoa den egonkortasun modelo bat garatu da pieza lirainentzako eta haren egonkortasuna Floquet teoriaren bidez aztertu da. Ebaketa baldintza bakoitzerako prozesuaren egonkortasuna zehazteko, egonkortasun lobuluen diagrama lortu da. Azkenik, erregulatzailean eskuragarri dauden barne seinaleak erabiliz prozesua monitorizatzeko sistema bat garatu da. Chatterra monitorizatzeko barne seinale desberdinen bideragarritasuna ebaluatu da. Barne seinaleetan oinarritutako monitorizazio sistema implementatu da hardware generiko batean eta monitorizazio sistema esperimentalki balioztatu da tornu batean.