LASER DRILLING
percussion drilling, jump delays can represent more than 50% of the total process time.
Figure 3: Drilling of 300 µm thick 5052 aluminum
It is often assumed that focal spot size determines hole diameter, but pulse characteristics also play an important role. With the focus at the material surface, the entrance diameter is usually larger than the exit, resulting in taper. However, exit hole dimensions can be significantly smaller than the focal spot diameter through appropriate selection of pulse duration and repetition rate.
In tests on 300 µm thick 5052 aluminum, consistent exit hole diameters of less than 10 µm were achieved using a focal spot of approximately 30 µm. Full penetration was achieved in under 2 ms with a 20 W laser source, and extending the drilling time to 6 ms resulted in less than 5% variation in exit diameter (Figure 3). This indicates that the process is, to some extent, self-regulating.
THERMAL MANAGEMENT
Although additional pulses may not significantly change hole geometry, they do add heat to the bulk material. This can be problematic for materials with poor thermal
conductivity, such as stainless steel, making thermal management critical. Over-processing should be avoided, and appropriate hole sequencing strategies should be used when drilling large arrays.
Local temperature increases can affect subsequent holes, as pre- heating may result in larger, irregular holes with increased burr formation. One mitigation approach is “on- the-fly” drilling, where the scanner continuously traverses the material and pulse spacing is controlled by scan speed and repetition rate. Multiple aligned passes allow deep hole arrays to be drilled with more uniform heat distribution than conventional static percussion drilling.
ADVANCED DRILLING STRATEGIES
Modern scanners can achieve speeds greater than 10 m/s with positional accuracy of around 5 µm, ensuring good hole alignment. These techniques are widely used in applications such as fuel cell manufacturing. In conventional
For hole diameters larger than the focal spot size, alternative methods such as trepanning are required. In trepanning, a pilot hole is drilled and enlarged using circular beam motion. This approach is generally effective for hole diameters up to around 2.5 times the spot size, but can suffer from heat accumulation and often produces better exit quality than entrance quality.
Helical drilling is another technique in which the beam follows a spiral path to remove material. This method offers improved heat management and is particularly well suited to circular holes larger than about 80 µm, especially in high hole-density applications.
Non-circular holes can also be produced by filling the drill area with a hatch pattern, effectively engraving the required shape. These features typically need to be larger than 100 µm to achieve good definition. Although relatively slow, this method provides excellent thermal control (Figure 4).
For very large holes, multi-pass perimeter cutting offers a flexible, low heat input solution. Only the hole boundary is processed, minimising material impact and enabling dense hole patterns.
CONCLUSION
Ns pulsed fibre lasers provide a flexible and universal drilling solution. When combined with modern scanner systems, they support a wide range of drilling techniques capable of meeting many industrial requirements.
jack.gabzdyl@
trumpf.com
trumpf.com
Jack Gabzdyl is Business Development Manager at TRUMPF promoting and developing
Figure 4: Arrays of 500 µm squares with corner radius of circa 10µm and web widths of <100µm can be made in 300 µm aluminum
applications and sales of TruPulse nano pulsed fibre lasers.
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