Pulse shaping during laser percussion drilling by using fiber laser radiation

Abstract

Laser percussion drilling is commonly used for drilling holes such as cooling holes in the aerospace industry. Flash lamp pumped Nd:YAG laser sources are state of the art for drilling. For a short time pulsed diode pumped laser sources such as fiber lasers with high average power are available coming along with benefits due to the productivity and reproducibility of drilled holes [1]. Pulse shaping can be done easily with these laser sources. The temporal intensity distribution of each pulse - intrapulse shaping - and the intensity in a sequence of pulses - interpulse shaping - can be modulated by the laser control software.The temporal intensity distribution using intrapulse shaping has no visible influence on the drilling results. The same energy is required to get a through hole. Thus using rectangular pulses which can be emitted by fiber lasers the pulse peak power can be lower. Using interpulse shaping by increasing the pulse peak power within a sequence of pulses the hole geometry can be modified due to a smaller diameter and a rectangular hole entrance. Furthermore the spatter on the workpiece surface is less and can be removed by wiping by hand.Thus economic benefits are established by using pulse shaping during laser percussion drilling with fiber lasers due to lower required pulse peak power and the disappearance of finishing steps like grinding.