Effect of Beam Energy on Weld Geometric Characteristics in Nd:YAG Laser Overlapping Spot Welding of Thin AISI 304 Stainl
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LASER welding is a high-power density technology that works with a relatively small but highly focused energy. In comparison with conventional welding processes, less heat is absorbed by the material. A precise amount of energy can be delivered in a short time in laser spot welding. It results in a small heat-affected zone and low final distortions. Thanks to these convenient qualities, laser welding became popular in last 20 years, and its course of use still spreads quickly. Besides welding of large components for automotive or aircraft industry, fine laser welding of heat sensitive components in electronic industry is also desirable.[1–4] For laser continuous welding, beam power density and welding travel speed are the main parameters that define the process. However, when a pulsed laser is used, more variables are involved and must be considered for complete characterization of the welding process. Different combinations of all parameters can lead to similar results. On the contrary, for example, the same peak power density obtained from different settings of energy and pulse duration can lead to evident differences in the weld characteristics. Besides the beam peak power density and welding speed, pulse repetition frequency and pulse duration are the most important parameters in overlapping laser spot welding. The effect of each parameter should be examined. Many authors deal with this problem either experimentally or by using welding simulations or both approaches are combined.[3,5–8] HANA LAPSANSKA, Ph.D. Student, HANA CHMELICKOVA, Research and Development Specialist, and MIROSLAV HRABOVSKY, Professor and Head of the department, are with the Joint Laboratory of Optics, Palacky University and Institute of Physics of the Academy of Sciences of the Czech Republic, 17. listopadu 50a, 77207 Olomouc, Czech Republic. Contact e-mail: [email protected] Manuscript submitted October 22, 2009. Article published online July 13, 2010. 1108—VOLUME 41B, OCTOBER 2010
But, mostly, only a few extreme values of one parameter are investigated, or more parameters are changed within the one experiment. Then, the pure detailed effect of one parameter disappears. This article presents a study of the effect of energy and its small changes in the range of 2.7 J, keeping all other parameters constant.
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PRINCIPAL CHARACTERISTICS OF LASER OVERLAPPING SPOT WELDING
Generally, laser spot welding is much more complicated in comparison with continuous welding. Usually, more pulses affect the area of one beam diameter size on the specimen because pulse overlap is required to achieve continuously penetrated tight welds. The higher the overlap, the more pulses land on the area of one beam cross section. The scheme of pulse overlap is depicted in Figure 1. Let us focus on the dark central spot in Figure 1. This spot is overlapped by another few pulses. However, this pulse overlaps the same number of previous pulses. The number of all these pulses hitting the area of the dark spot depends on the distance between two consecutive pulses a
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