In the whole cutting processing scenario, waterjet can be considered as one of the most flexible non conventional technology. This consideration comes from the fact that it can machine a wide range of materials, geometrical profiles and thicknesses, avoiding to compromise thermally or chemically the resulting workpieces. Therefore, it provides final cut pieces with negligible residual mechanical stresses and deformations. However, this technology is not so spread in the industrial field because it does not guarantee enough accuracy. This aspect becomes crucial when we talk about Micro Abrasive Waterjet, where tolerances are tighter compared to conventional machining. A workpiece obtained from conventional waterjet cutting presents typical defects due to the fact that the jet, facing the material resistance, loses power and is deflected. The effect of this deflection mainly results into sloped part walls and distorted edges. This work starts from the knowledge of a defect compensation model able to reduce the just said defects in macro applications using a 5-axis cutting head. The idea is to apply the same model to micro applications on a conventional machining center. In the beginning of this dissertation, the cutting head kinematic will be discussed and all the modifications performed on the machine will be described. Then, all the limitations of the available equipment will be focused and analyzed to define every source of uncertainty. Afterwards, the whole experimental section will be explained, including the model calibration procedure needed to calculate the kerf taper and jet lag regressions and the subsequent experimental campaigns. The last section will show the followed guideline to limit the defects and meet the tight tolerances typical of fine machining.
Nel mondo delle lavorazioni meccaniche di taglio, il waterjet può essere considerato una delle tecnologie non convenzionali più flessibili. Questa considerazione deriva dal fatto che può lavorare un’ampia gamma di materiali, profili e spessori, evitando di compromettere termicamente e chimicamente il componente lavorato. Quindi, produce componenti con tensioni meccaniche e termiche trascurabili. Nonostante ciò, questa tecnologia non è molto diffusa nel campo industriale perchè non garantisce abbastanza accuratezza. Questo aspetto diventa cruciale specialmente quando parliamo di Micro Abrasive Waterjet, dove le tolleranze sono molto più strette rispetto al taglio waterjet convenzionale. Un componente ottenuto con tecnologia waterjet tradizionale presenta tipici difetti dovuti al fatto che il getto, incontrando la resistenza del materiale, perde potenza e viene deflesso. L’effetto di questa deflessione principalmente risulta in pareti del solco di taglio inclinate e difetti di spigolo. Questo lavoro parte dalla conoscenza di un modello di compensazione dei difetti, capace di ridurre i difetti appena citati nelle applicazioni macro, utilizzando una testa di taglio a 5 assi. L’idea consiste nell’applicare lo stesso modello ad applicazioni micro, utilizzando una macchina per il taglio waterjet convenzionale. All’inizio di questa dissertazione verrà discusso della cinematica della testa di taglio e saranno esposte le modifiche attuate sulla macchina. Successivamente, sarà spiegata la parte sperimentale, incluso il modello di calibrazione necessario per calcolare le regressioni del taper del jet lag e la successiva campagna sperimentale. L’ultima sezione mostrerà la linea guida seguita per limitare i difetti rispettare le ristrette tolleranze tipiche delle lavorazioni di precisione.
Micro abrasive waterjet cutting on a conventional AWJ machining center through defect compensation strategies
LUCENTE, LORENZO
2014/2015
Abstract
In the whole cutting processing scenario, waterjet can be considered as one of the most flexible non conventional technology. This consideration comes from the fact that it can machine a wide range of materials, geometrical profiles and thicknesses, avoiding to compromise thermally or chemically the resulting workpieces. Therefore, it provides final cut pieces with negligible residual mechanical stresses and deformations. However, this technology is not so spread in the industrial field because it does not guarantee enough accuracy. This aspect becomes crucial when we talk about Micro Abrasive Waterjet, where tolerances are tighter compared to conventional machining. A workpiece obtained from conventional waterjet cutting presents typical defects due to the fact that the jet, facing the material resistance, loses power and is deflected. The effect of this deflection mainly results into sloped part walls and distorted edges. This work starts from the knowledge of a defect compensation model able to reduce the just said defects in macro applications using a 5-axis cutting head. The idea is to apply the same model to micro applications on a conventional machining center. In the beginning of this dissertation, the cutting head kinematic will be discussed and all the modifications performed on the machine will be described. Then, all the limitations of the available equipment will be focused and analyzed to define every source of uncertainty. Afterwards, the whole experimental section will be explained, including the model calibration procedure needed to calculate the kerf taper and jet lag regressions and the subsequent experimental campaigns. The last section will show the followed guideline to limit the defects and meet the tight tolerances typical of fine machining.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/116781