Volume 27, Issue 4, November 2015
Index of content:
Characteristics of the effect of swirling gas jet assisted laser percussion drilling based on machine vision27(2015); http://dx.doi.org/10.2351/1.4923019View Description Hide Description
In this paper, a machine vision-based system is used for in-situ monitoring and characterization of the effect of swirling gas jet assisted laser percussion drilling. Feasibility of laser percussion drilling on highly reflective materials, i.e., Al5052 with the implementation of assisting swirling gas jet, was explored. The influence of the gas jet type on the mechanism of material removal and resulting spatter is reported. The authors conclude that the swirling gas jet method greatly reduces spatter formation around the hole exit during the laser-drilling process. Consequently, in order to understand and monitor the gas jet effects in laser drilling, real-time in situ metrology is employed to observe the details. Compared with the results obtained when using a straight gas jet, laser drilling with a swirling gas jet reduces the drilled hole debris by 0.69 and increases the drilled hole efficiency by a factor of up to 1.5. Experimental results show that both the drilling depth and machining quality can be greatly and simultaneously improved. Effects of the swirling flow on the drilling efficiency and spatter thickness of the holes are investigated.
27(2015); http://dx.doi.org/10.2351/1.4923472View Description Hide Description
During laser welding, residual stresses are thermally induced. They can have strong impact on the fatigue behavior and fatigue life. A standardized measurement method for the fatigue crack growth rate was expanded to identify residual stress along the cracking path. The second derivative of the measured crack opening and in turn the crack acceleration corresponded well with distinct acceleration maxima and minima and accordingly with tensile and compressive stress, as was basically proven by numerical simulation. The method is simple and extendable. It provides valuable information, as was demonstrated for various situations.