Influence of laser pulse duration on laser drilled hole quality in nickel based super alloy

Abstract

Studies on the title subject have been performed using different commercial and research Nd:YAG laser systems. These systems represent a large range of pulse durations from sub-nanosecond to millisecond (conventional YAG “driller” pulse durations). Correspondingly, the peak powers range from a few kilowatts to over 1 megawatt, which dramatically affect processing times, hole quality and preservation of parent material properties. The different laser systems used to generate the data have similar beam qualities (≤3X diffraction limited), and were selected primarily to contrast peak power effects in a nominally conventional drilling application.The results show that hole quality (taper, recast, and parent metal damage) is significantly affected by the laser pulse duration as varied in these tests. The pulse energy and repetition rate also vary between the test lasers on account of their operational designs, and the effects of these parameters must also be reckoned. However, many of the marked affects can be reasonably attributed to peak power or pulse duration uniquely, and these will be discussed in greater detail below. Depending upon the thermophysical properties of the workpiece material and the design specifications for finished parts, there is probably a pulse duration/repetition rate saddle region where specifications for hole quality and process speed are simultaneously satisfied. In drilling the GE Aircraft Engines (GEAE) N5 alloy an upper bound on the pulsewidth range of ~300 nanoseconds is so identified. In this paper we present results and photomicrographs of these tests, and review the processing potential of “high-performance” lamp and diode pumped Nd:YAG laser devices.Studies on the title subject have been performed using different commercial and research Nd:YAG laser systems. These systems represent a large range of pulse durations from sub-nanosecond to millisecond (conventional YAG “driller” pulse durations). Correspondingly, the peak powers range from a few kilowatts to over 1 megawatt, which dramatically affect processing times, hole quality and preservation of parent material properties. The different laser systems used to generate the data have similar beam qualities (≤3X diffraction limited), and were selected primarily to contrast peak power effects in a nominally conventional drilling application.The results show that hole quality (taper, recast, and parent metal damage) is significantly affected by the laser pulse duration as varied in these tests. The pulse energy and repetition rate also vary between the test lasers on account of their operational designs, and the effects of these parameters must also be reckoned. However, many of the marked affects can be...