Processing of metal
Femtosecond lasers enable the production of complex shapes and features, while also providing the capability to perform black/white marking and coloring without the need for chemical additives.
MHz burst usage in increasing femtosecond removal efficiency in aluminum, copper and stainless steel
Femtosecond processing of materials faces a significant challenge in terms of process throughput. There exists an optimal fluence value at which the most efficient material removal occurs. However, with high average power lasers, achieving this optimal fluence is difficult. In order to achieve the optimal fluence at higher powers, one is forced to increase the repetition rate to values where significant thermal accumulation occurs, often leading to degradation in processing quality. The optimal fluence can be achieved by using MHz burst mode, which splits the high-energy pulse into multiple sub-pulses, enhancing the efficiency of material processing, especially metals, compared to single-pulse mode.
In a recent study by A. Žemaitis et al., the FemtoLux 30 laser was used to optimize machining methods for aluminum, copper, and stainless steel. The researchers conducted material removal optimization by milling 110 cavities in a single metal sample, varying the pulse repetition rate and the number of pulses in the burst. Utilizing MHz burst mode allowed to achieve optimal fluences, resulting in not only high removal efficiency but also great surface roughness. Especially, removal efficiency and rate were increased by 18%, 44.5% and 37% for aluminum, copper and stainless steel accordingly, if compared to the single-pulse operation mode.
Results of processing various metal samples with MHz burst
Material | Removal efficiency | Removal rate | Surface roughness | No. of pulses in burst |
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Aluminum | 7.0 µm3/µJ | 9.2 mm3/min | 1.7 µm | 10 |
Copper | 4.2 µm3/µJ | 5.6 mm3/min | 2 µm | 5 |
Steel | 3.9 µm3/µJ | 5.1 mm3/min | 1.7 µm | 10 |
Material | Removal efficiency | Removal rate | Surface roughness | No. of pulses in burst |
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The ultrafast burst laser ablation of metals: Speed and quality come together
Utilisation of high-power ultrafast laser for ablation-based industrial processes such as milling, drilling or cutting requires high production rates and superior quality. In this paper, we demonstrate highly efficient, rapid and high-quality laser micro-machining of three industrial metals (aluminium, copper, and stainless steel). Our proposed optimisation methods of pulse energy division in time result in simultaneous enhancement of ablation efficiency (volume per energy) and ablation rate (volume per time) while maintaining a focused laser beam on the target surface and high resolution. A high-tech femtosecond burst laser, producing laser pulses of τ = 350 fs duration and intra-burst repetition rates of fP = 50 MHz, was employed in the experiments. Due to the utilisation of bursts, material removal efficiency and removal rate were increased by 18.0 %, 44.5 %, and 37.0 % for aluminium, copper, and stainless steel if compared with the best performance of single-pulses. In addition to the high processing rate, processing by burst mode resulted in lower surface roughness. This technique is believed to be a solution enabling extremely high femtosecond laser powers for precise microfabrication.