Thermal scribing processes with long-pulse and Q-switch fiberlasers Available to Purchase

In powertrain industry the big eye of the casted steel connecting rod (conrod) is cracked after a laser has scribed two opposite cracking initiation lines (kerf) on the inner surface of the eye. This structure is scribed with pulsed lasers with a production speed of 1000 – 3000 mm/min. Depending on pulse repetition rate and speed, a line of small blind holes or a continuous kerf is produced. Single mode long-pulse fiberlasers create a similar kerf as the standard ms-pulsed Nd:YAG lasers used in the past, but the kerf is deeper and with radii at the bottom which reduce the necessary hydraulic forces for cracking. Also investigated was the use of a more cost effective q-switch fiberlaser. Due to the required production speed and kerf depth of 0.4 – 0.8 mm, ablation-engraving is not the proper strategy. Scribing the conrod with one sweep at low speed and at the high pulse repetition rate of 50 – 200 kHz leads to the fact that scribing is done in a thermal regime where the speed of the heat diffusion is similar or faster than the processing speed. Consequently heat accumulation occurs at the bottom of the continuous notch. The result is a periodic structure in the notch bottom with a repetition rate which is 100 – 500 times slower than the pulse repetition rate. The depth of this structure depends on pulse repetition rate, process speed, pulse energy, pulse intensity, and position of the focal spot.