Increasing system stability with tighter tolerances following the Taguchi Robust Design approach on short-pulsed laser helical drilling of stainless steel

Helical drilling promises high quality laser drilling geometries together with a controllable shape (taper, diameter) in multiple materials. Latest research has shown that the use of a short pulsed laser source and an ultra-short pulsed laser source increase those benefits while the process time is increased. However reproductively and stability still remain an issue on these application due to the complex optical alignment and the dynamic beam rotation. The research presented covers a full fractional experimental parameter study of the controllable parameters such as laser power, optical angle and optical offset. Manufacturing deviations and process capability are derived. In addition to that a Taguchi experimental setting with a noise array (temperature, focus drift, change in process gas pressure) has been carried out. The results of five-level factor plan L25(59) with 9 parameters (6 control parameters and 3 noise parameters) is analyzed using ANOVA and Taguchi Robust Design. The outcome is used in an optimization process to identify any parameter combinations that result in decreased deviations from the quality remark (e.g. entrance diameter). Afterwards the control parameter are used to adjust the quality remark to the targeted value. It is shown that this optimized parameter set offers higher stability and therefore an increased process capability.