[en] The main objective of this research, in which the present doctoral thesis is contextualized, is the development of strategies for the optimization of the set-up and the analysis of grinding processes, focusing on infeed configurations of cylindrical and centerless grinding and throughfeed and traverse configurations of centerless and cylindrical grinding respectively. Those strategies are based on the application of commanded variable speeds over the main parameters that govern the process: the feed rate, the workpiece speed (or the regulating wheel speed for centerless grinding) and the grinding wheel speed. According to previous studies of the workteam and based on the current state of the art, it has been noticed that the application of a variable workpiece speed is an efficient technology in order to suppress or reduce the dynamic instabilities of the process generated by self-excited vibrations or chatter. To put into practice this technology, it is necessary to know the optimal parameters of the variation (amplitude and frequency for a sinusoidal variation), task that is done so far by methods of trial and error or by using simulation models in the time-domain. As a first work within this thesis, a previous work by the research group comprised of IK4-Ideko and Mondragon Unibertsitatea presented by David Barrenetxea has been completed, in which the variable workpiece speed was applied successfully for suppression of chatter in infeed centerless grinding. To that end and applying a similar methodology, the efficiency of this technology has been validated in the throughfeed configuration of the centerless grinding process, also analyzing the influence in the process behavior (grinding forces, roughness,…) due to the direct relation between the regulating wheel speed and the traverse feed rate. It has been noticed that using a time-domain modeling for the stability analysis with variable parameters supposes a high computing cost. Therefore, the next step of this thesis has focused on the development of a methodology for the stability analysis with variable parameters by means of semidiscretization method. By using this technique a better efficiency related to computing cost is achieved without being detrimental to the results accuracy. This method is based on the analysis of the eigenvalues of the transition matrix that relates the profile defects of the workpiece between two consecutive revolutions and it has been applied and validated in different grinding process configurations. By means of the development of a software based on this methodology, a tool for the achievement of the optimal combinations of workpiece speed variation parameters (amplitude and frequency) to avoid chatter is available. These optimal combinations correspond to frequencies below one hertz and amplitudes higher than a ten per cent of the nominal speed in the analyzed study cases. On the other hand and taking advantage of the developed technology for the continuous variation of the axis controlled by the machine CNC, a software has been implemented with which an ensemble variation of the main parameters of the grinding process is carried out: feed rate, workpiece speed and grinding wheel speed. With this software, infeed cycles can be defined for centerless and cylindrical grinding processes. Prior to the implementation of the software in a grinding machine, a simulation environment has been developed in which different variation strategies can be analyzed and defined in order to achieve optimal grinding cycles according to a theoretical analysis of the influence of the variations in the process behavior, taking into account factors such as surface finish, dimensional tolerances, grinding forces and power, thermal damage or the process stability. Once the combined variation of the three proposed parameters has been defined, these variation strategies have been included in a CNC software and experimental trials have been carried out in which variable cycles and conventional ones (with different constant values of feed rate and workpiece speed) equivalent in cycle time and stock removal have been compared. In these trials, improvements in the final quality of the part have been noticed and the possibility of reducing the cycle time (increasing the productivity) has been analyzed, achieving the same workpiece quality. Besides, it is also remarkable the simplicity of using this software, since it is not necessary to define every stage of the conventional cycle, related to the feed rates, the stocks and the workpiece speeds. Next, the references of the published papers that are part of this thesis by compendium of articles are presented chronologically, in which the developments of the proposed research are exposed. Later in this thesis, the non-published additional work, where defined objectives are completed, is described. It is also noticeable the patent in process to protect the idea.

[eu] Tesi honetako ikerketa lanaren helburu nagusia artezketa prozesuak puntuan jartzeko eta berauen optimizaziorako estrategiak garatzean datza, hurrenez hurren artezketa zilindriko eta zentrorik gabeko artezketetako sartze eta zeharkako prozesuak lantzen direlarik. Estrategia horiek prozesua agintzen duten hiru abiadura nagusien konbinazio eta etengabeko kontrolean oinarritzen dira. Abiadura hauek, sartze (penetrazio) abiadura, piezaren abiadura (harri erregulatzailearen abiadura zentrorik gabeko artezketan) eta artezketa harriaren abiadura direlarik. Lan taldearen aurreragoko ikerketak eta egungo artearen egoera kontuan izanda, piezaren abiadura aldakorraren aplikazioa ezegonkortasun dinamiko edo chattera murrizteko teknika eraginkorra dela baieztatu da. Teknika hau martxan jarri ahal izateko, beharrezkoa da abiadura aldakorraren parametro optimoak ezagutu eta aplikatzea (aldakuntza sinusoidal baten anplitudea eta maiztasuna esaterako), gaur egun hauek proba praktikoen bitartez edo denbora domeinuko simulazio ereduak erabiliz lortzen direlarik. Tesi honetako lehenengo lana IK4-Ideko eta Mondragón Unibertsitateak osatutako lan-taldeak hasitako ikerketa bat burutzea izan da. David Barrenetxea hasitako lan horretan piezaren abiadura aldakorra arrakastaz aplikatzen da zentrorik gabeko artezketako sartze prozesuan ezegonkortasun dinamiko edo chattera murriztuz, eta Tesi honetan antzeko metodologia erabili da eraginkortasun bera zentrugabeko zeharkako artezketan frogatzeko eta baita prozesuko beste emaitza batzuetan duen eragina aztertzeko (zimurtasuna, indarrak..), harri erregulatzailearen abiadura aldakorrak zeharkako abaiduran eta produkzioan duen eragin zuzena dela eta. Egonkortasun analisia burutzeko aurretik garatu zen denbora domeinuko modeloen ebazpenean kostu konputazional handia somatzen zen, batez ere parametro aldakorrak erabiltzean. Berau murrizteko Tesi honetan semidiskretizazioa deritzon metodologia aplikatu da, kostu konputazionala neurri handi batean jeitxi delarik emaitzen zehaztasunari uko egin gabe. Metodo hau piezak jarraian ematen dituen bi biratan dituen akatsak erlazionatzen dituen trantsizio matrizearen autobalioen analisian oinarritzen da eta aipatutako prozesu ezberdinetan aplikatu eta balioztatu da. Metodologia honetan oinarritutako software baten garapena dela medio, chattera murrizteko abiadura aldakorreko konbinazio onenak zehatz eta bizkor ebazteko gai gera une honetan. Aztertu diren kasuetan, konbinazio eta emaitza onenak Hertz baten azpiko maiztasun aldaketa eta abiadura nominalaren ehuneko hamar baino gehiagoko anplitudeak erabiliz lortu dira. Ondoren prozesua agintzen duten hiru abiadura nagusien konbinazioak simulatzen dituen software bat garatu da eta aldi berean makinako ardatzetan konbinazio hauek ahalbidetzen dituzten CNC-rako programak. Simulazio softwarean sartzeko (penetrazio) artezketa eta zentrugabeko artezketa prozesuetako ziklo eta abiadura aldakor estrategia desberdinak aztertu daitezke eta baita konbinazio onenak ebatzi ondoren makinan probatzeko. Simulazioan lortzen diren emaitzak artezketa indarrak, potentzia, pieza erretzeko arriskua, bukaerako zimurtasuna, piezaren azken diametroa, biribiltasuna eta bibrazioa arriskua dira besteak beste. Softwarea erabiliz abiadura aldakorren konbinazio estrategia eta artezketa ziklo desberdinak definitu dira eta ondoren makinan entsegu esperimentalak egin dira. Ziklo berezi hauek, denbora eta artezteko material kantitate berdinak dituzten abiadura Konstantedun ziklo konbentzionalekin konparatu dira. Entseguek simulazioen eta emaitza esperimentalen arteko korrelazio ona egiaztatzeko balio izan dute alde batetik eta are garrantzitsuago, abiadura konbinazio berezidun zikloak piezaren azken kalitatea hobetzeko edo kalitate berdineko ziklo azkarrago edo produktiboagoak lortzeko gai direla. Jarraian, argitalpen laburpen gisako Tesi hau osatzen duten artikuluen zerrenda aurkezten da era kronologikoan. Artikulu hauetan ikerketan lorturiko garapenak aurkezten dira. Jarraian, planteturiko helburuak lortzeko eta argitara eman ez den lan gehigarria ere aurkezten da memorian. Azkenik, aipatzekoa lan honetan aurkezten den etengabeko abiadura aldakor eta konbinazioen estrategiaren ideia patente baten bitartez babestuko dela.