Development of an Intra-Layer Adaptive Toolpath Generation Control Procedure in the Laser Metal Wire Deposition Process

Abstract

Recently developed concentric laser metal wire deposition (LMWD) heads allow metal addition processes which are independent of the deposition direction, thus enabling complex paths to be generated. The sensitivity of the process to height deviations has experimentally been observed to be greater with this type of head than with powder ones, therefore requiring more precise and local process control algorithms to be implemented. This work developed a methodology for measuring the part, layer by layer, using a 3D scanner based on structured laser light. Height corrections were applied to the mean and intra-layer height deviations by recalculating the deposition trajectories of the next layer to be deposited. Local height deviations were adjusted by varying the scanning speed, thus increasing the feed rate in the lower areas and decreasing it in the higher ones. Defects generated in the purpose, with height differences within the layer, were successfully corrected. A flat layer was re-established through the application of the control strategy. The internal integrity of the parts due to the scanning speed variation was analyzed, resulting in fully dense parts. The structured light measurement and height correction systems are found to be an affordable and time-efficient solution that can be integrated into an LMWD environment, thereby improving the process robustness.

Laser Metal Deposition with Coaxial Wire Feeding for the Automated and Reliable Build-Up of Solid Metal Parts

“…However, due to the directional dependency and the process emissions, online measurement is challenging, which is why measurements are usually performed after a layer has been applied. Thus, various layer-to-layer control systems have been developed employing such sensors [37][38][39]. Moreover, several authors have used laterally arranged CCD, CMOS, or IR cameras to detect the height of the bead or the part, respectively [40][41][42].…”

Review on adaptive control of laser-directed energy deposition

“…In these geometry signatures, the widths and heights of the deposited layers 15 and the profile of the molten pool 9,10 can be monitored by a single industrial camera, and the entire outline of the deposited layers are commonly obtained by a 3-D camera. 16,17 To improve the calculation speed and efficiency, Tang et al 18 used a laser-based areal topography measurement sensor to measure the surface and developed a depth image method to process the data and extract the 3-D features. Moreover, a 3-D scanner of structural light was used to measure the height of the deposited layers from an external fixed position by Garmendia et al 17 However, the strong metal vapor in the 3-D reconstruction method based on structural light may contaminate the optical device and affect the monitoring results.…”

“…At the end of each layer, the scanning speed of the next layer was adjusted to compensate the deposition height error according to the height of the previous layer. Another combination of two methods was conducted by Garmendia et al, 16 who used a 3-D scanner based on structured laser light to measure the height of a part. The average height deviation between layers was highly corrected by recalculating the track to be deposited in the next layer, and the local height deviation within the layer was adjusted by simultaneously changing the scanning speed.…”

Influence of a closed-loop controlled laser metal wire deposition process of S Al 5356 on the quality of manufactured parts before and after subsequent machining

“…The difference between controlled and uncontrolled produced cylinders was shown. An intra-layer toolpath generation control procedure to increase the quality of the deposition process was also implemented, where an static camera system was used to observe the process [7]. For the LMWD process in specific, some sources demonstrated a track height control for laser metal deposition with powder [8].…”