A special percussion drilling with “energy ramp” technique has been applied for the machining of high aspect ratio holes in steel plate.

In conventional percussion drilling with constant laser power the energy from successive pulses accumulated in and around the focal volume leads to significant melting, which suspends the advantages of ultrashort pulses. The problem of melting occurs in the first phase of drilling leading to a decreased quality of the entrance side of the drilled hole.

Applying the energy ramp technique improved the overall quality of the hole significantly.

Conventional percussion drilling (left side: hole entrance, right side: hole exit)

Energy ramp drilling: No melting, higher quality