Advances in centerless grinding

La lavorazione di rettifica senza centri a tuffo \ue8 un processo ad alta produttivit\ue0 ma che pu\uf2 soffrire di instabilit\ue0 e condizioni mutevoli, dovuti alla propria configurazione geometrica e alle caratteristiche degli utensili abrasivi. Il presente lavoro si propone di presentare un approccio pratico alla scelta dei parametri di processo con uno studio sperimentale dei loro effetti sulle caratteristiche qualitative tipiche di questa lavorazion

Implicit Subspace Iteration to Improve the Stability Analysis in Grinding Processes

An alternative method is devised for calculating dynamic stability maps in cylindrical and centerless infeed grinding processes. The method is based on the application of the Floquet theorem by repeated time integrations. Without the need of building the transition matrix, this is the most efficient calculation in terms of computation effort compared to previously presented time-domain stability analysis methods (semi-discretization or time-domain simulations). In the analyzed cases, subspace iteration has been up to 130 times faster. One of the advantages of these time-domain methods to the detriment of frequency domain ones is that they can analyze the stability of regenerative chatter with the application of variable workpiece speed, a well-known technique to avoid chatter vibrations in grinding processes so the optimal combination of amplitude and frequency can be selected. Subspace iteration methods also deal with this analysis, providing an efficient solution between 27 and 47 times faster than the abovementioned methods. Validation of this method has been carried out by comparing its accuracy with previous published methods such as semi-discretization, frequency and time-domain simulations, obtaining good correlation in the results of the dynamic stability maps and the instability reduction ratio maps due to the application of variable speed

Modal Identification of Dynamic Properties of the Cylindrical Grinder.

In the paper the method of model identification of the cylindrical grinder dynamic properties by means of experimental modal test was described. The method application, hardware solution as well as the procedure of carrying out the identification modal test of the cylindrical grinder was presented. The experiment was performed in order to acquire the frequency response function (FRF) of the cylindrical grinder. Having obtained the experimental FRF, the mathematical model of the response function was created. That mathematical model of the machine tool dynamic behavior can be applied in grinder and grinding holistic model. The conclusions regarding the application aspects of experimental modal analysis in order to identify dynamic properties of the machine tool were drawn

Desarrollo de nuevos modelos, técnicas y aplicaciones para el aumento de la precisión y productividad en el rectificado sin centros a través de la supresión de inestabilidades dinámicas y la óptima configuración del ciclo de rectificado en sus dos formas de operación: plongée y pasante

Centerless grinding is a manufacturing process widely used as a high-productivity finishing technology. Its specific features regarding the loose work-holding and self-centering confer better performance on centerless grinding when compared with other grinding processes, eliminating clamping and centering operations and allowing the use of fast part loading and unloading systems. However, correct centerless grinding set-up is one of the most problematic operations amongst the machining processes. Apart from thermal, mechanical and tribo-chemical limitations of the cutting and wear mechanisms of a grinding process, centerless grinding set-up has to face the characteristic instabilities or disturbances arising from the above-mentioned kinematic features of this process. These instabilities are geometric lobbing (when the unclamped workpiece oscillates between wheels), chatter (which is more pronounced than in other grinding processes due to the use of wider grinding wheels), and work rotation-driving instability or spinning (which appears when the regulating wheel is unable to maintain the rotation of the workpiece at its peripheral velocity). All such instabilities and restrictions are influenced by a large number of process variables and parameters, which affect them in different ways. This makes it difficult to establish an optimal process configuration to fulfil productivity and precision requirements. Based on the development of simulation models and their experimental validation, this thesis explores on the one hand on the dynamic origin instabilities, a phenomenon particularly marked in centerless grinding due to the use of very wide grinding wheels. The results have allowed to accurately determine what the working configurations free of chatter are in each case and to compare the applicability of the technique of variable workspeed in order to eliminate it. Furthermore, the simulation model development activity and its experimental validation have been conducted also around the rest of characteristic and inherent limitations of the cutting and wear mechanisms in a grinding process. The work has been completed with the one carried out in two parallel Theses around geometric, work rotation-driving and thermal origin instabilities. The developed models and the knowledge gained has enabled an analysis of the influence and coupling of main variables governing the process in both operating forms, infeed and throughfeed as well as for mono and multi-diameter parts. This analysis has enabled the development of optimization algorithms for the optimal configuration of grinding cycles and the selection of working parameters, enforced to fulfil the surface integrity, surface finish, dimensional and geometrical tolerances as well as productivity requirements. The work has resulted in the development of two successive versions of a tool for the set-up and optimization of centerless grinding process. First one implemented in the machines and the later and more complete web support implemented. Both with the name of SUA: Set-up Assistant Estarta. In order to present the work done in the most clear and understandable way, and to argue the coherence and order of the Thesis, following nine articles that represent research conducted throughout this thesis about the stability and optimization of centerless grinding process are referred. In each of the articles the original inputs of said two previous Theses and this third are exposed and argued. The contributions of present thesis are mainly distributed among the papers 3-9. In any case they are the last three papers from the list the ones that must be considered as a compendium and substitute of the traditional PhD dissertation to be the only ones that meet the academical requirements for this.Zentrorik gabeko artezketa, bere lan-konfigurazio bereziagatik, zehaztasun handiko akaberak eta produktibitate-ratio altuak lortzen dituen fabrikazio-prozesua da. Hala ere, konfigurazio berezi hori jatorri geometrikoko, dinamikoko eta arrasteko ezegonkortasun iturri nagusia da baita ere. Maiz agertzen diren eta kontrolatzea zailak diren ezegonkortasun bereizgarri hauei artezte prozesuen berezko mugak gehitu behar zaizkie gainera: kalte termikoa eta gainazaleko segurtasuna, tolerantzia dimentsional, geometriko eta bukatutako gainazalekoak. Hauek guztiek zentrorik gabeko artezketa menderatzeko teknologia konplexua egiten dute. Hala ere, prozesuen martxan jartzea makina-prestatzaileen esperientzia medio eta proba eta akatseko saiakeren bidez egiten jarraitzen da gehienetan, prozesuaren portaeraren ezaguera zientifikoaren aplikazio praktikorik gabe. Simulazio modeloen garapenean eta berauen kontrastatze esperimentalean oinarrituz, Tesi honek batetik jatorri dinamikoko ezegonkortasunen ezagueran sakontzen du, berau, erabiltzen diren zabalera handiko harriek direla eta, zentrorik gabeko artezketan nabarmentzen den fenomenoa delarik. Lortutako emaitzek kasu bakoitzean chatter-etik libreak diren lankonfigurazioak beharrezko eran zehaztea baimendu dute eta baita piezaren abiadura aldakorreko teknikaren aplikazioren ahalmena egiaztatzea chattera ezabatzeko asmotan. Bestalde, simulazio modeloen garapena eta beraien kontrastatze esperimentala, artezketa mekanismoaren ezegonkortasun bereizgarrien eta berezko mugen inguruan ere jorratu da. Lana, jatorri geometriko, arraste eta eta kalte termikoaren inguruan burututako beste bi Tesi paralelotan egindako lanarekin osatu da lehenik. Garatutako modeloek eta lortutako ezaguerak, prozesua gidatzen duten aldagaien eta berauen arteko akoplamenduaren eraginaren analisia baimendu dute, bai barneratze eta baita zeharkako lan egiteko eran eta diametro bakarreko edo diametro anizdun piezatarako. Honek berriz zikloen konfiguraziorako eta aldagaien balio onenak aukeratzeko optimizazio algoritmoen garapena egin du posible, aldi berean inposatzen diren gainazaleko segurtasun baldintzak, tolerantzia dimentsional, geometriko eta produktibitatekoak betetzen direlarik. Lanak, zentrorik gabeko artezketa prozesua puntuan jartzerako eta optimizatzeko erreminta baten bi bertsioren garapena eragin du. Lehenengo bertsioa makinan inplementatua eta bigarrena WEB euskarrian inplementatua. Biak SUA izenekoak: Estarta Set-Up Assistant. Egindako lana erarik argien eta ulergarrienean erakutsi eta Tesiaren koherentzia argudiatzeko asmoz, ondorengo bederatzi artikuluak aipatzen dira. Berauek Tesi honen ildoan zentrorik gabeko artezketa prozesuaren egonkortasun eta optimizazioari buruz burututako ikerkuntza lana irudikatzen dute era kronologikoan. Artikuluetako bakoitzean aipatutako aurreko bi Tesi eta hirugarren honetako ekarpenak erakusten eta argudiatzen dira. Tesi honi dagozkion ekarpenak 3.garren eta 9.garren artikuluetan banatuta aurkitzen dira bereziki. Nolanahi ere zerrendako azken hiru artikuluak dira Tesi tradizionalaren memoriaren ordezko laburpen bezala aurkezten direnak, era honetan aurkezteko beharrezko diren baldintza akademikoak betetzen dituzten bakarrak bait dira.El rectificado sin centros es un proceso de fabricación en el que, debido a su especial configuración de trabajo, es posible lograr acabados de gran precisión con altos ratios de productividad. Sin embargo, esa especial configuración es también la principal fuente de inestabilidades de origen geométrico, dinámico y arrastre. A estas inestabilidades características que aparecen frecuentemente y son difíciles de controlar hay que añadir las limitaciones inherentes al mecanizado de arranque abrasivo: dañado térmico e integridad superficial, tolerancias dimensionales, geométricas y de acabado superficial. Todas ellas hacen del rectificado sin centros una tecnología compleja de dominar. A pesar de ello, la puesta a punto de los procesos continúa realizándose únicamente a través de la experiencia de los preparadores de máquina y mediante métodos de prueba y error, sin la aplicación práctica de un conocimiento científico riguroso del comportamiento del proceso. Basándose en el desarrollo de modelos de simulación y su contrastación experimental, esta Tesis profundiza por un lado en el conocimiento de las inestabilidades de origen dinámico, fenómeno especialmente acusado en el rectificado sin centros debido al empleo de muelas de gran anchura. Los resultados obtenidos han permitido determinar de forma precisa cuáles son las configuraciones de trabajo libres de chatter en cada caso y contrastar la capacidad de aplicación de la técnica de velocidad de giro de pieza variable con el fin de eliminarlo. Por otro lado, la actividad de desarrollo de modelos de simulación y su contrastación experimental se ha llevado a cabo en torno al resto de inestabilidades características y limitaciones inherentes al mecanismo de arranque abrasivo, completándose con el trabajo realizado en otras dos Tesis paralelas llevadas a cabo en torno a las inestabilidades de origen geométrico, arrastre y dañado térmico. Los modelos desarrollados y el conocimiento adquirido han permitido realizar un análisis de la influencia y acoplamiento de las variables que gobiernan el proceso, tanto para las formas de trabajo en plongée y pasante como para piezas monodiámetro y multi-diámetro. Ello a su vez ha hecho posible el desarrollo de algoritmos de optimización para la configuración de ciclos y la selección de variables óptimas de trabajo, al mismo tiempo que se impone el cumplimiento de los requisitos de integridad y acabado superficial, tolerancias dimensionales, geométricas y de productividad requeridas. El trabajo ha dado lugar al desarrollo de dos versiones sucesivas de una herramienta para la puesta a punto y optimización del proceso de rectificado sin centros. La primera de ellas implementada en máquina y una posterior y más completa implementada en soporte WEB, las dos con el nombre de SUA: Estarta Set-up Assistant. Con el fin de exponer el trabajo realizado de la forma más clara y comprensible posibles, así como de argumentar la coherencia y orden de la Tesis, a continuación se hace referencia nueve artículos que de forma cronológica representan el trabajo de investigación llevado a cabo a lo largo de esta Tesis en torno a la estabilidad y optimización del proceso de rectificado sin centros. En cada uno de los artículos se exponen y argumentan las aportaciones originales de las citadas dos Tesis previas y de esta tercera. Las contribuciones correspondientes a la presente Tesis se encuentran distribuidas fundamentalmente entre los artículos 3 a 9. En cualquier caso son los tres últimos artículos de la lista los que deben constar como compendio y sustituto de la memoria de Tesis tradicional por ser los únicos que cumplen con los requisitos establecidos para ello

Grinding and fine finishing of future automotive powertrain components

The automotive industry is undergoing a major transformation driven by regulations and a fast-paced electrification. A critical analysis of technological trends and associated requirements for major automotive powertrain components is carried out in close collaboration with industry – covering the perspectives of OEMs, suppliers, and machine builders. The main focus is to review the state of the art with regard to grinding, dressing, texturing and fine-finishing technologies. A survey of research papers and patents is accompanied by case studies that provide further insights into the production value chain. Finally, key industrial and research challenges are summarized

A STUDY ON MULTI-OBJECTIVE OPTIMIZATION OF PLUNGE CENTERLESS GRINDING PROCESS

ABSTRACT Round component with the minimum value of surface roughness and roundness error is the goal of most of the fine machine processes. This paper presents the research on optimization of plunge centerless grinding process when grinding the 20X-carbon infiltration steel (ГOCT standardRussia) to achieve the minimum value of surface roughness and roundness errors. The input parameters are center height angle of the workpiece ( β ), longitudinal dressing feed-rate ( sd S ), plunge feed-rate ( k S ) and control wheel velocity ( dd v ) using the result of 29 sets in central composite design matrix to show the two second orders of surface rounghness and roundness error models. The final goal of this work focuses on the determination of optimum centerless grinding above the parameters for the minimization of surface roughness ( m R

Dynamic Modeling of Chatter Vibration in Cylindrical Plunge Grinding Process

Cylindrical plunge grinding process is a machining process normally employed as a final stage in precision machining of shafts and sleeves. The occurrence of chatter vibrations in cylindrical plunge grinding limits the ability of the grinding process to achieve the desired accuracy and surface finish. Moreover, chatter vibration leads to high costs of production due to tool breakages. In this paper, a theoretical model for the prediction of chatter vibration in cylindrical grinding is developed. The model is based on the geometric and dynamic interaction of the work piece and the grinding wheel. The model is validated with a series of experiments. Results show that variation in the grinding wheel and work piece speeds, and in-feed lead to changes in the vibration modes and amplitudes of vibration