Machining metals and silicon with GHz bursts: Surprising tremendous reduction of the specific removal rate for surface texturing applications

Bursts of 230 fs pulses with up to 25 pulses having a time spacing of 180 ps were applied to steel AISI304, copper DHP, brass and silicon in real surface texturing (milling) application by machining squares. The previously reported very high removal rates for GHz bursts could not be confirmed, on the contrary, the specific removal rate tremendously drops down to less than 10% for the metals and 25% for silicon when the number of pulses per burst is increased. This drop is fully in line with shielding effects already observed in case of MHz pulses and double pulse experiments. The increase of the number of pulses per burst directly goes with strongly increased melting effects which are assumed to additionally re-fill the already machined areas in this milling application. Calorimetric experiments show an increasing residual heat with higher number of pulses per burst. Further the removal rates of the GHz bursts directly follow the tendency of single pulses of identical duration. This fosters the hypothesis that in case of metals and silicon only melting and melt ejection lead to the high reported removal rates for GHz bursts in punching applications and that no additional "ablation cooling" effect is taking place