Drilling and cutting of superalloys with Q-switched and modulated Nd:YAG laser pulses

Abstract

Drilling of holes with large depth/diameter ratio is an important process for aircraft, aerospace and automotive industries. To improve the cooling capacity of turbine components, a large number of effusion holes with small diameter are required. In conventional laser drilling, flashlamp-pumped, pulsed Nd:YAG-lasers with typical mean power of 300-500 W are used for both percussion drilling and trepanning. The pulse repetition frequency (PRF), pulse energy and pulse duration in use in industry are typically in the order of 30 - 50 Hz, 10 J and 1 - 5 ms respectively with oxygen often being used as an assist gas. Problems often encountered are that the holes can be blocked by oxides and dross and that the wall of the holes often contains cracks. The relatively high energy input can also lead to thermal distortion of the components. This paper presents an investigation into the hole drilling process made in order to minimise or eliminate these problems. Our assumption was, that if very short pulses with high pulse repetition frequency and peak power could be generated, the hole drilling process would be improved; every pulse evaporating a small volume of the material with a low total energy input. Oxidation of the walls of the hole was to be prevented by a high pressure inert gas.Drilling of holes with large depth/diameter ratio is an important process for aircraft, aerospace and automotive industries. To improve the cooling capacity of turbine components, a large number of effusion holes with small diameter are required. In conventional laser drilling, flashlamp-pumped, pulsed Nd:YAG-lasers with typical mean power of 300-500 W are used for both percussion drilling and trepanning. The pulse repetition frequency (PRF), pulse energy and pulse duration in use in industry are typically in the order of 30 - 50 Hz, 10 J and 1 - 5 ms respectively with oxygen often being used as an assist gas. Problems often encountered are that the holes can be blocked by oxides and dross and that the wall of the holes often contains cracks. The relatively high energy input can also lead to thermal distortion of the components. This paper presents an investigation into the hole drilling process made in order to minimise or eliminate these problems. Our assumption was, that if very short pulses with high ...