Lightweight aluminum sandwich panels have been widely used on a wide range of vehicles with different speeds: from buses to cars, from cargo planes to flights, from ferries to racing boats. The hardness and strength of these materials are very important properties. Honeycomb sandwich plate structures are often used as skeletons and are bonded together using high performance adhesives. This structure is problematic for many engineers, especially when exposed to fire or when immersed in water. In order to solve these problems, the British Welding Research Institute (TWI) has now developed a laser welded metal sandwich plate structure using an extruded aluminum core material.
According to the Institute, in the experimental study, the aluminum sandwich panel with the trademark Ex-StructTM was composed of a 2 mm thick 5083 aluminum alloy plate and a 6060 aluminum alloy extruded tube. The design of the extrusion die is such that the outer circle of the pipe forms an interlocking connection. The tube has a diameter of 30mm and a wall thickness of 2mm. The tolerances of the male and female connection interfaces are strictly controlled. According to the Welding Institute, they have used laser spot welding and laser post welding to demonstrate the feasibility of manufacturing sandwich panels and identify key factors that affect the quality and distortion of the weld. It is reported that using a 4047 alloy (Al-13% Si) filled wire with a diameter of 1.2 mm can reduce weld solidification cracks and give a smooth beaded surface.
An example board of the Ex-StructTM sandwich panel is manufactured by positioning at the mechanical connection point of the tube and using Nd:NAG laser spot welding. Laser spot welding is performed line by line starting from one side of the sandwich panel in the horizontal direction. The continuous welding operation is performed by controlling the on/off time of the grating at each line of spot welding. In order to avoid welding cracks, the pulse mode is used during spot welding and the power ramp is applied at the end of the pulse to reduce the cooling rate. Controlled ramp-down of laser power can reduce weld crack susceptibility. The same welding operation as described above is then started on the other side of the sandwich panel.
Another example of an Ex-StructTM sandwich panel is manufactured by Nd:NAG laser post brazing. First place the degreasing tube on the bottom plate and make it a whole. Welding proceeds linearly from one edge of the surface to the other, and along the mechanical connection between the weld tubes. This operation is repeated until the welding of the other edge is completed. The other side of the sandwich plate is then subjected to the same welding operation as described above. The weld bead presents relatively smooth beads with no surface defects. The welding speed can reach 2.6mm/min, the laser power is 3kW, and the feeding speed is 3mm/min.
Over the years, the British Welding Institute has been providing solutions for a variety of materials for the civilian and military shipbuilding industry worldwide. With the increasingly fierce international competition and the increasing demand for high-speed ferry users to reduce the weight of aluminum vessels, it is now under tremendous pressure not only to reduce overall life-cycle costs and innovation, but also to increase the cost-effectiveness of manufacturing. Therefore, the strategy of the Welding Research Institute of the United Kingdom is to provide value-added solutions for thin sheets, extruded materials, castings or prefabricated panels for aluminum or aluminium companies, as well as technical solutions for reducing material costs or increasing material functions. The new vision of the connection technology will be the focus of the hospital’s work to meet the current and future market. In addition to the development of connection technologies, the British Welding Institute is now also committed to material development, cladding technology, warpage prediction, simulation work, and prediction of the performance and reliability of ship structures.
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