Model of vibration assisted deep hole micro drilling

U radu je predstavljen pregled rezultata istraživanja dubokoga mikrobušenja i dubokoga bušenja potpomognutoga vibracijama. Nakon pregleda stanja dosadašnjih istraživanja, preko kinematičke analize trajektorija glavnih oštrica svrdla utvrdio se utjecaj parametara vibracija u ovisnosti o parametrima bušenja na debljinu odvojenih čestica prije deformacije, koja ima utjecaj na sile rezanja i veličinu odvojenih čestica. Provedena je eksperimentalna analiza konvencionalnog i mikrobušenja potpomognutog vibracijama, uz periodičko izvlačenje svrdla, mjerenjem odzivnih veličina aksijalne sile i momenta bušenja preko planiranih eksperimenata. Za analizu utvrđivanja značajnosti utjecaja odabranih parametara na odzivne veličine, koristila se metoda odzivne površine. Za promatrani raspon parametara, izrađeni su matematički modeli odziva aksijalne sile i momenta konvencionalnog i mikrobušenja potpomognutoga vibracijama, u ovisnosti o parametrima bušenja, vibracija i dubine provrta. Usporedbom eksperimentalnih rezultata i oba modela, utvrđeno je kako bušenje potpomognuto vibracijama prvenstveno pogoduje na smanjenje ukupnog momenta mikrobušenja za određeni skup parametara. Smanjenje momenta povezano je s manjim odvojenim česticama i time smanjenom vjerojatnosti začepljenja utora spirale mikrosvrdla i manjim trenjem prilikom dubokoga mikrobušenja. Načinjena je usporedba vijeka trajanja svrdla između konvencionalnog mikrobušenja i onog potpomognutoga vibracijama za proces s većom dubinom koraka ciklusa bušenja s periodičkim izvlačenjem svrdla. Kod dubokoga mikrobušenja potpomognutoga vibracijama ustanovljeno je kako postignuto smanjenje ukupnog momenta bušenja, u kombinaciji s adekvatnom veličinom aksijalne sile, može osigurati prosječno veći broj probušenih provrta prije loma svrdla i time pouzdaniji proces dubokoga mikrobušenja.This work presents research results from the investigation of the deep hole micro drilling and the vibration assisted deep hole micro drilling. Literature survey and the kinematic analysis of the main cutting edges trajectories for the vibration assisted drilling were performed. Influence of the vibration and drilling parameters on undeformed chip thickness is determined, which is directly related with the chip size and the cutting forces. Experimental analysis of conventional and vibration assisted peck micro drilling was performed using the design of experiments. Measured axial force and drilling torque were used as the response variables. Statistical assessment of the significance of the parameters on the response variables is performed with the response surface methodology. For the analysed range of parameters, mathematical models for the axial force and drilling torque of the conventional and vibration assisted micro drilling were created, in relation with the drilling and vibration parameters, as well as the hole depth. Comparison of experimental results and both models showed that, for a certain set of parameters, the vibration assisted drilling has a primary benefit in the form of reduced drilling torque. This is related to smaller chip size, which in turn, leads to reducing the probability of the chip jamming in the micro drill flute and reduced friction during the deep hole micro drilling. For peck drilling, analysis of the drill lifetime for both conventional and vibration assisted micro drilling was performed. It was concluded that for deep hole vibration assisted micro drilling, the reduction in the drilling torque with the combination of adequate axial force, can provide larger number of drilled holes before the drill breaks and thus a more reliable deep hole micro drilling process