Laser weld chaos control for defect reduction

Abstract

Voids caused by the instability of the keyhole are serious defects in partial penetration laser welds. Improving the stability of the keyhole will reduce voids formed by keyhole collapse. In this research, glycerin in a semi-solidified state was used as a medium for performing the welding because its transparency allowed of visualization of the keyhole during control development. Statistical analysis of penetration depth signals for uncontrolled system was performed to verify that the keyhole dynamics was chaotic. One technique applied to control chaotic systems is quasi-sinusoidal power modulation control, and incident leading beam angle was also used to enhance the keyhole stability. The optimum parameters achieved by control methods were 400Hz frequency of quasi-sinusoidal power modulation and 15o incident leading beam angle. Chaos analyses of uncontrolled and controlled signals were performed to demonstrate the effect of the control on keyhole dynamics. Three-dimensional phase plots for uncontrolled and controlled signals illustrate that the chaotic keyhole dynamic system is transformed to regular periodic behavior by the chaos control method applied in this work.Voids caused by the instability of the keyhole are serious defects in partial penetration laser welds. Improving the stability of the keyhole will reduce voids formed by keyhole collapse. In this research, glycerin in a semi-solidified state was used as a medium for performing the welding because its transparency allowed of visualization of the keyhole during control development. Statistical analysis of penetration depth signals for uncontrolled system was performed to verify that the keyhole dynamics was chaotic. One technique applied to control chaotic systems is quasi-sinusoidal power modulation control, and incident leading beam angle was also used to enhance the keyhole stability. The optimum parameters achieved by control methods were 400Hz frequency of quasi-sinusoidal power modulation and 15o incident leading beam angle. Chaos analyses of uncontrolled and controlled signals were performed to demonstrate the effect of the control on keyhole dynamics. Three-dimensional phase plots for uncontrolled a...