Product Code: ICAL08_303

Precision Trepanning with a Fiber Laser
Authors:
Paul Jacobs, LFI Inc.; Smithfield RI USA
Presented at ICALEO 2008

An analysis is developed to establish the optimal parameters for precision trepanning using a 200 watt average power fiber laser. Recent test results are also presented to document the mean values and standard deviations of fiber laser trepanned holes for a number of materials, hole diameters, and thicknesses. Analytical constraints are established for each of the following: (1) maintaining sufficient laser irradiance to assure rapid trepanning speed without inducing plasma self-absorption, (2) selecting a laser pulse repetition frequency sufficiently high to maintain a molten metal interface and hence increased absorption at the laser wavelength, while not exceeding the kinematic limit of current trepanning heads, (3) selecting an optimum trepanning overlap ratio to minimize perimeter irregularities consistent with high speed operation, (4) optimizing the focused spot diameter to achieve the desired irradiance consistent with modest laser power and cost, (5) choosing a programmable continuous motion trepanning head and a spiral trepanning path to improve precision while minimizing cycle time and perimeter artifacts, and (6) satisfying adiabatic energy requirements in the shortest practical time. The paper also presents important test data indicating initial standard deviations under 3 μm when trepanning 500 μm diameter cylindrical holes with a system not yet fully optimized!