Page 30 - MetalForming April 2020

Fabrication: Laser Cutting
Fig. 3—Shown is a comparison of cuts in 100-μm-thick stainless steel using various lasers. The nanosecond-pulse-length laser produced the roughest cut edge, even though it is operating in the ultraviolet (UV) spectrum. The picosecond-regime laser showed a progressively smaller HAZ (darkened area) as wavelength was decreased. The femtosecond laser produced virtually no HAZ and a very clean edge, even when using an infrared (IR) wavelength.
the pulse energy be too high, not all of material removal, and bulk heating and the laser energy is used efficiently for the resulting HAZ again will occur.
There’s typically a sweet-spot maxi- mum material-removal rate for most metals that occurs when laser peak power reaches seven to ten times the material-ablation threshold (Fig. 1).
Once the optimum pulse energy is determined, throughput (material- removal rate) may be increased by increasing the pulse-repetition rate. However, this action impacts other aspects of system operation, in partic- ular the scanning speed or table speed. It’s usually necessary to have the laser beam move rapidly enough across the work surface to avoid a significant amount of pulse overlap. However, when operating at the optimum mate- rial-removal rate doesn’t produce a cut at the necessary depth, multiple passes or some pulse overlap may be necessary.
Pulse Length
Longer-pulse commercial DPSS lasers commonly employ a pulsing technology called q-switching, which delivers pulse lengths in the nanosec-
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