Time-Optimal Trajectory Generation and Way-Point Sequencing for 5-Axis On-the-Fly and Percussion Laser Drilling

On-the-fly laser drilling provides a highly productive method for producing hole clusters (pre-defined groups of holes to be laser drilled) on freeform surfaced parts, such as gas turbine combustion chambers. Although the process is capable of achieving high throughputs, current machine tool controllers are not equipped with appropriate trajectory functions that can take full advantage of the achievable laser drilling speeds. On-the-fly laser drilling presents new technological requirements, needing the development of new kinds of trajectory optimization and hole sequencing solutions. Work needs to focus on developing minimum snap and minimum jerk time-optimized trajectories for 5-axis on-the-fly laser drilling for predefined sequences of holes, with application to gas turbine combustion chamber panels. Trajectories that minimize the constant laser pulsing period, while ensuring that the axis velocity, acceleration, and jerk limits are considered. The orthogonal component of the part velocity with respect to the beam, at the drilled hole location, also needs to be limited, in order to contain the hole elongation. An ad-hoc stitching algorithm needs to be developed that would allow different cluster trajectories to be connected seamlessly, or looped back onto themselves for repeated laser shots without having to come to a full stop. In this proposal, an improved stitching algorithm is proposed, which would provide a jerk- and time- optimal solution with guaranteed solution feasibility. Furthermore, current algorithms processed all holes inside a given cluster simultaneously. While this may be acceptable for cluster sizes up to 100 holes, the computational efficiency significantly deteriorates when dealing with larger clusters. A windowing scheme development is proposed that would allow the optimization of large clusters to be performed using smaller sequences at a time. This would reduce the off-line processing time needed to run the algorithm and ensure its robustness when dealing with complicated parts that have large numbers of holes. A major bottleneck that determines the highest achievable laser pulsing frequency (i.e., shortest process cycle time) was identified to be the current hole sequencing algorithm used by the industrial partner. This algorithm determines the order and inclusion of hole positions into each drilling cluster. If a single segment contains a turn that is too sharp or holes that are too far apart, this slows down the trajectory for the whole cluster; since all positioning durations have to be equal to the laser pulsing period. This in-turn, increases the total drilling cycle time. It is clear that an efficient hole sequencing algorithm is crucial for obtaining the maximum possible productivity in the laser drilling operation. An efficient sequencing method is proposed to be researched in this proposal