Laser beam shaping and beam swing
Beam shaping, as we call it, often refers to the use of beam shaping lens, lens, microlens or different shapes of optical fiber to achieve the homogenization effect on the spot. This paper introduces a new method: brightline welding technology from Trump, which uses 2 in 1 optical fiber (Fig. 1), which is composed of inner core fiber and outer ring fiber. The two beams are superimposed on the processing area.
Figure 1 2 in 1 fiber technology of trunp
In the process of deep penetration welding, the metal in the micro position absorbs the heat of laser, melts and evaporates, and produces high pressure steam at the bottom of the micro hole. Steam is ejected from the bottom, causing material loss, or splash. The whole process is similar to the process of boiling water at home to produce bubbles. When 2-in-1 beam shaping is used, the outer ring fiber creates a larger "buffer" around the micropore, allowing high-pressure steam to escape. The outer ring beam helps to create a more stable deep penetration welding process.
At the same time, the outer ring beam also changes the flow direction of molten metal (Fig. 2). The molten metal which accelerates to the surface deflects to the side under the influence of the annular beam pulse. Therefore, under the comprehensive influence of the above two changes, the experiment shows that the internal and external fiber shaping technology can reduce the spatter by 90%.
Fig. 2 change of molten pool under the action of internal and external light beams
The beam swing trajectory is shown in the figure below. For some butt welding and lap welding process, due to the gap between parts and no filling material, but the conventional laser welding is along the gap line, can not effectively weld. Therefore, the introduction of beam oscillation (oscillation or wobble) and the superposition of straight line and up and down motion produce helix (Fig. 3) increase the molten pool area, at this time, the metal liquid fills the gap to realize welding. Another advantage of using the beam swing is that it can compensate the size error of the parts, reduce the porosity, increase the beauty of the weld and the stability of the welding process.
Fig. 3 superposition track of linear motion and up and down swing
The application of beam shaping and beam swing at the same time can greatly improve the stability of deep penetration welding process, improve the weldability of aluminum alloy and high strength steel, and effectively avoid micro cracks. However, for some materials, there are still random microcracks. Figure 4-6 below shows the welding effect of 6xxx series aluminum alloy under three conditions of beam shaping, beam swing, and beam shaping and swing.
Figure 4 microscopic effect of beam shaping welding section
Figure 5 microscopic effect of beam swing welding section
Fig. 6 microscopic effect of beam shaping and beam swing welding section