Abstract
The availability of commercial ultrafast lasers reaching into the kW power level offers promising potential for high-volume manufacturing applications. Exploiting the available average power is challenging due to process limits imposed by particle shielding, ambient atmosphere breakdown, and heat accumulation effects. We experimentally confirm the validity of a simple thermal model, which can be used for the estimation of a critical heat accumulation threshold for percussion drilling of AISI 304 steel. The limits are summarized in a processing map, which provides selection criteria for process parameters and suitable lasers. The results emphasize the need for process parallelization.
Highlights
The trade-off between quality and productivity is a major challenge in laser material processing, especially with ultra-short pulses
Heat accumulation in pulsed laser processing is approached with varying degrees of accuracy regarding the modelling of the underlying physical effects, ranging from full numerical modelling that allows for the consideration of effects such as electron-ion temperature relaxation [82] and phase transitions, semi numerical methods [72, 80] based on analytical solutions [83] to the heat equation, sometimes extended to more complex geometries of the heat sources [80], to phenomenological models which lend themselves to analytical treatment [75, 76, 79]
This paper focuses on the experimental validation (Sect. 3) of a simple thermal model for the consideration of heat accumulation effects in percussion drilling
Summary
The trade-off between quality and productivity (in terms of processed material volume or mass per unit of time or energy) is a major challenge in laser material processing, especially with ultra-short pulses. Heat accumulation in pulsed laser processing is approached with varying degrees of accuracy regarding the modelling of the underlying physical effects, ranging from full numerical modelling that allows for the consideration of effects such as electron-ion temperature relaxation [82] and phase transitions, semi numerical methods [72, 80] based on analytical solutions [83] to the heat equation, sometimes extended to more complex geometries of the heat sources [80], to phenomenological models which lend themselves to analytical treatment [75, 76, 79] Another limiting aspect is atmosphere breakdown or ionization of the ambient atmosphere, which can lead to absorption of the incident laser radiation prior to reaching the target, and leads to distortion of the beam profile as well as self-focusing [84,85,86,87,88,89]. Atmosphere breakdown can lead to a reduction of the process efficiency due to the attenuation of the beam prior to reaching the target, degraded surface quality due to distortions of the beam profile, and reduced reproducibility because of the random nature of the wavefront distortions
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