Contemporary abrasive waterjet (AWJ) cutting processes mostly rely on empirical model of the cutting quality, in terms of the most important process parameters, avoiding any in-line closed-loop control strategy. However, the increasing development of the Industry 4.0 has been representing a driver of change in different manufacturing sectors, like the AWJ technology. In this framework, the physical signals, coming from the process, could represents a valuable set of information for the development of in-line monitoring and diagnostics of the cutting process, which is considered as a cold mechanical material removal process. However, the performance of the cutting, is evaluated on the manufactured part, by measuring its geometrical features. Predictive models of the cutting quality has been developed through the correlation between some control factors of the process and the experimental data. To this purpose, the development of an in-line monitoring strategy of the jet power would improve the supervision of the process with a better control on the cutting quality. The material removal theory in abrasive waterjet cutting has identified the kinetic power of the abrasive particles flow, as the physical quantity which influence the abrasive waterjet cutting capability. Hence, it would be extremely important to monitor and control this quantity during cutting operations. However, a lack of a systematically investigation of the influence of the jet power on the spatial profile of the cutting kerf was found. This thesis work concerns an experimental investigation about the influence of the kinetic power of the abrasive particles flow in the abrasive waterjet (AWJ) cutting process, with application to the effect on the spatial profile of the cutting kerf. Results have strengthened the material removal theory in AWJ, highlighting how the jet power could be considered as a reference energetic parameter which explain different aspects of the AWJ cutting performance, like the kerf width variability along the cutting depth. Said results may be useful for the fundamental comprehension of the material removal process, specifically the understating of the taper angle, is fundamental since it represents a geometrical defect, which is considered a detrimental effect on the quality of the part. The mechanical power of the abrasive water, i-e., the jet power, was found to be a fundamental quantity which explains the temperature distribution during the cutting process. An experimental study of the monitoring of the temperature distribution has been proposed in the present thesis. Results showed how the thermal field resembled the well-known case of a distributed heat source, which plausibly arose through the transfer of a fraction of the jet power as thermal power to the workpiece, because of the continuously friction of the abrasive particles with the target material The second part of the thesis work has been focused on the development of an in-line measure strategy of the jet power, during the abrasive waterjet firing stage, exploiting the vibrations emission from the cutting head. The operational vibration can effectively be exploited as the monitored variable for closing the control loops of the water pump and the abrasive feeder, thus improving the process stability, as well as allowing the process tracking. With respect to the previous state of the art, the present approach does not entail the presence of sensors on the workpiece. This feature is expected to make the setup more robust and compatible with day-to-day operations of a real production environment.
La predizione ed il controllo della qualità nel processo di taglio a getto d’acqua (AWJ), ad oggi, si basa principalmente sull’impiego di modelli empirici connessi ai parametri di processo in grado di correlarne l’effetto con le caratteristiche geometriche del solco di taglio. La teoria della rimozione del materiale nel taglio a getto d'acqua abrasivo ha identificato la potenza cinetica del flusso di particelle abrasive, come la quantità fisica che influenza la capacità di taglio del getto. Pertanto, risulta estremamente importante monitorare e controllare tale quantità durante le operazioni di taglio. A tale proposito, il crescente sviluppo dell'Industria 4.0 ha rappresentato un consistente driver di cambiamento in diversi settori manifatturieri, tra cui la tecnologia AWJ. In questo quadro di riferimento, i segnali fisici, provenienti dal processo, rappresentano un prezioso insieme di informazioni per lo sviluppo di strategie di diagnostica e monitoraggio in tempo reale, volte al miglioramento continuo di processo. A tal fine, lo sviluppo di una strategia di misura della potenza del getto migliorerebbe la supervisione del processo con un miglior controllo sulla qualità del taglio. Tuttavia, è stata riscontrata la mancanza di un'indagine sistematica dell'influenza della potenza del getto sul profilo spaziale del solco di taglio. Questo lavoro di tesi mira a contribuire alla comprensione di tale fenomenologia. I risultati hanno rafforzato la teoria della rimozione del materiale in AWJ, evidenziando come la potenza del getto possa essere considerata un parametro energetico di riferimento che spiega diversi aspetti delle prestazioni di taglio dell'AWJ, come la variabilità della larghezza del solco lungo la profondità di taglio e l’andamento della conicità delle pareti del solco di taglio, la quale rappresenta un difetto geometrico, considerato dannoso per la qualità del pezzo. Inoltre, la potenza del getto, è risultata essere una grandezza fondamentale che spiega la distribuzione della temperatura durante il processo di taglio. Nella presente tesi è stato proposto uno studio sperimentale del monitoraggio della distribuzione della temperatura durante il taglio. I risultati hanno mostrato come il campo termico mostrasse caratteristiche similari al noto caso di una sorgente di calore distribuita ed in movimento. Tale comportamento è plausibilmente dovuto al trasferimento di una frazione della potenza del getto come potenza termica al pezzo, a causa dell'attrito continuo delle particelle abrasive con il bersaglio materiale La seconda parte del lavoro di tesi è stata focalizzata sullo sviluppo di una strategia di misura in linea della potenza del getto, sfruttando l'emissione di vibrazioni dalla testa di taglio. La vibrazione può essere efficacemente sfruttata come variabile monitorata per la realizzazione di un sistema di controllo in anello chiuso migliorando così la stabilità del processo, oltre a consentire il monitoraggio della qualità attesa. Rispetto allo stato dell’arte, la presente soluzione non prevede la presenza di sensori sul pezzo. Questa funzionalità dovrebbe rendere la configurazione più robusta e compatibile con le operazioni quotidiane di un reale ambiente di produzione.
On the role of the abrasive waterjet kinetic power in cutting processes: experimental investigation and modelling
Perotti, Francesco
2021/2022
Abstract
Contemporary abrasive waterjet (AWJ) cutting processes mostly rely on empirical model of the cutting quality, in terms of the most important process parameters, avoiding any in-line closed-loop control strategy. However, the increasing development of the Industry 4.0 has been representing a driver of change in different manufacturing sectors, like the AWJ technology. In this framework, the physical signals, coming from the process, could represents a valuable set of information for the development of in-line monitoring and diagnostics of the cutting process, which is considered as a cold mechanical material removal process. However, the performance of the cutting, is evaluated on the manufactured part, by measuring its geometrical features. Predictive models of the cutting quality has been developed through the correlation between some control factors of the process and the experimental data. To this purpose, the development of an in-line monitoring strategy of the jet power would improve the supervision of the process with a better control on the cutting quality. The material removal theory in abrasive waterjet cutting has identified the kinetic power of the abrasive particles flow, as the physical quantity which influence the abrasive waterjet cutting capability. Hence, it would be extremely important to monitor and control this quantity during cutting operations. However, a lack of a systematically investigation of the influence of the jet power on the spatial profile of the cutting kerf was found. This thesis work concerns an experimental investigation about the influence of the kinetic power of the abrasive particles flow in the abrasive waterjet (AWJ) cutting process, with application to the effect on the spatial profile of the cutting kerf. Results have strengthened the material removal theory in AWJ, highlighting how the jet power could be considered as a reference energetic parameter which explain different aspects of the AWJ cutting performance, like the kerf width variability along the cutting depth. Said results may be useful for the fundamental comprehension of the material removal process, specifically the understating of the taper angle, is fundamental since it represents a geometrical defect, which is considered a detrimental effect on the quality of the part. The mechanical power of the abrasive water, i-e., the jet power, was found to be a fundamental quantity which explains the temperature distribution during the cutting process. An experimental study of the monitoring of the temperature distribution has been proposed in the present thesis. Results showed how the thermal field resembled the well-known case of a distributed heat source, which plausibly arose through the transfer of a fraction of the jet power as thermal power to the workpiece, because of the continuously friction of the abrasive particles with the target material The second part of the thesis work has been focused on the development of an in-line measure strategy of the jet power, during the abrasive waterjet firing stage, exploiting the vibrations emission from the cutting head. The operational vibration can effectively be exploited as the monitored variable for closing the control loops of the water pump and the abrasive feeder, thus improving the process stability, as well as allowing the process tracking. With respect to the previous state of the art, the present approach does not entail the presence of sensors on the workpiece. This feature is expected to make the setup more robust and compatible with day-to-day operations of a real production environment.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/179960