2 Secrets About Application of Sheet Metal Design in Laser Welding Box Structure

Laser welding has the advantages of fast speed, small deformation, beautiful weld seam, and high strength. It is widely used in aviation, automobile, medical and other fields. Among them, laser self-fusion welding is a non-contact welding process without welding wire, with various welding seam forms and excellent welding seam consistency. In the field of sheet metal manufacturing, it has huge application potential. This article focuses on the application of sheet metal design in the laser welding of the box structure with 45° mitered interface with flanging.

Sheet Metal Design in Laser Welding Box Structure

The material of the box body is 1.5mm thick 304 stainless steel, and the size is 200mm×200mm×115mm. The bending angle of the box is 90°, 90°, and 80° from bottom to top. The box structure is shown in the figure. The laser cutting equipment for product blanking is  Trulaser 3040 laser cutting machine, the bending equipment is BendCell 5130 bending machine, and the laser welding equipment is Trulaser Robot 5020 laser welding machine. The laser welding parameters are shown in the table.

In the traditional welding process of stainless steel box structure, to obtain more beautiful welding products, it is usually necessary to perform grinding and polishing treatment after welding. The follow-up process is cumbersome and time-consuming, and it is easy to produce welding deformation and welding penetration during the welding process. However, laser welding has great application potential in the field of sheet metal welding due to its fast welding speed, small deformation, and beautiful weld seams.

Among them, Trulaser Robot 5020 (hereinafter referred to as TR5020) laser welding equipment has a huge advantage in the welding box structures. TR5020 integrates a high-precision automatic focusing system on its welding head so that it can switch between laser deep penetration welding and laser thermal conductivity welding at any time in the same laser welding procedure, without changing the robot's posture. At the same time, with the high-magnification CCD camera integrated into the welding head, the laser focus position can be adjusted more accurately, so that the laser welding seam has an excellent welding seam consistency. However, how to apply the advantages of high laser welding speed, narrow welding heat-affected zone, small deformation, and high precision to the welding of box structure has become an urgent problem to be solved.

In the welded stainless steel box structure, the box fillet weld occupies most of the entire welding process. In order to obtain a rounded laser welding seam, we optimized the overlap amount of traditional welding, as shown, where t is the thickness of the plate, a is the overlap amount, b is the position of the laser center on the cross-section of the board, and α Is the laser inclination angle.

Improved fillet weld overlap

Laser welding overlap amount

The optimized overlap amount is welded using the laser thermal conduction welding process. Through the TR5020 automatic focusing system, the defocus amount is accurately set to 10.00mm, and the focusing accuracy is 0.01mm. By accurately positioning the b value through a high-power CCD camera, a rounded laser weld can be obtained without adding welding wire, as shown in the figure. The lap margin optimization scheme is suitable for plates with a thickness of 3mm and below, and the values of a, b, and α are determined by the value of t.

Schematic diagram of lap margin optimization and actual laser welding effect

In the welded stainless steel box structure, the optimization of the corner relief groove is also extremely important, which directly affects the bottom effect of the box structure. In the traditional welding process, rectangular or round corner relief grooves are generally used. However, this type of corner relief groove is very easy to cause weld penetration or underfill during laser welding. The schematic diagram of the corner relief groove is shown in the figure below.

Schematic diagram of corner relief groove

The product structure is optimized by calling the laser welding corner relief groove process block. After laser welding, a very full and round welding effect can be obtained, almost no secondary treatment is required, which greatly reduces the time for subsequent processing, as shown in the figure.

Schematic diagram of laser welding design of corner relief groove

Actual laser welding effect of corner relief groove

Design of 45° Bevel Interface For Laser Welding Box Structure Flanging

In the welded stainless steel box structure, due to the bending deformation, it is difficult to close tightly at the 45° bevel interface of the flanging. As shown at A in the figure, laser welding is extremely difficult to handle. Therefore, the design of the interface will directly affect the welding quality of the box structure. At the same time, there will be a large gap at B, which is difficult to handle by direct laser welding.

Schematic diagram of the structure before optimization

For this kind of situation, we optimized the box structure. When designing, cut off the metal of the stepped surface, and then extend two small stepped surfaces, as shown in the figure. Then, when unfolding, use the end surface as a reference to fill in the previously cut part, as shown in the figure. At B in the figure, two stepped surfaces are staggered to increase the amount of metal compensation and make up for the gap produced here, as shown in the figure.

Schematic diagram of sheet metal design for flanged 45° bevel interface

The picture below shows the effect after actual laser welding. It can be seen from the figure that the interface is tightly closed, which fully meets the requirements of the laser welding process. The surface of the welding seam is beautiful, the transition is natural, and there is no phenomenon such as sinking and welding through. The B in the figure is also well filled.