Theoretical And Experimental Study On Laser Punching Of Sheet

On the base of analyzing the laser shock processing technology and the punching technology of sheet metal with die at home and abroad, a new metal sheet punching technology based on laser shockwave is presented in this paper. Its mechanism is described as following: When the metal sheet is irradiated by high power (GW/cm~2), short pulse (ns) laser beam, the paint coated on the surface of sheet will be vaporized and ionized instantly because of the absorption of the laser energy, then the high temperature plasma will come into being and it will explode to produce high pressure shock waves which transfer to the sheet, thereafter, the metal sheet will be punched under the co-effect of shock waves and the female die.Firstly, the forming mechanism of the laser-induced shock wave was analyzed theoretically, and then the calculation formulas of the peak pressure of the laser shock wave under two different physical models were put forward, also, some modifications of them were made accordingly. The shock response of materials to pulse laser radiation and high strain-rate effects were discussed. The characteristics of propagation and attenuation of shock waves were studied in the paper, and the effect of the confined layer and the principle for choosing were also discussed.Secondly, according to the mechanism of die punching and some related theory of the shock wave, a punching model based on laser shock wave was established. Afterwards, the theoretic speed of the laser induced shock wave and the momentum transferred to sheet was analyzed, and on the basis of momentum theory, the minimum speed for the sheet to be punched was also deduced.Lastly, through the experiments, the influence on laser punching of the laser parameters, properties of the metal sheet, the dimensions and the profile of the die orifice, and the constraint condition of boundary were investigated, and the thickness change of the hole's edge were measured. Moreover, with the SEM photos, the topographies of the fracture surface were observed, and the fracture characteristics of the nodular cast iron after laser punching were analyzed in detail. It can be concluded from the experimental result that brittle ductile transition takes place in brittle material by laser punching.