With the mobile phone, Tablet PC, notebook and other consumer electronics product updates and development, a large number of new technology, new materials, new structure has been applied, and aluminum alloy with light weight, high strength, corrosion resistance, good shape, etc. Widely used in the production of various consumer electronics structural parts, and the use of laser pulse spot welding process for further processing. In the use of laser pulse welding, the solder joints are prone to crack, resulting in decreased welding strength, stability is also greatly reduced. However, the traditional laser beam is poor in mass, bulky, high maintenance costs and low photoelectric conversion efficiency, which restricts its consumption in the consumer electronics products to a certain extent. The traditional laser beam, YAG and other continuous laser welding aluminum alloy can avoid the crack. Applications. In particular, the structural parts of consumer electronics products have the characteristics of thin thickness, small volume and high precision. The traditional continuous laser welding is easy to produce large deformation, welding and burning.

The rapid development of fiber lasers to solve this problem has brought opportunities, fiber lasers was born in the 20th century, 60 years, by the technical conditions at that time, the development of relatively slow. Since 1980, Snitzer et al. Proposed double-clad fiber, fiber lasers and amplifiers based on this cladding pump technology have been rapid development, fiber laser output power level of rapid increase, and widely used in high-precision laser processing, laser Medical, optical communications and defense and other fields. Compared with traditional lasers, fiber lasers have good beam quality, small size, high precision, and high photoelectric conversion efficiency. In the welding of consumer electronics products, aluminum alloy structural parts, can be a good way to avoid the traditional laser welding when there are some shortcomings and problems. In this paper, a wide range of pulsed lasers using fiber lasers and aluminum alloy structures in consumer electronics products are compared to determine whether fiber lasers can be successfully applied to such products.

Experimental materials and equipment

1.1 Experimental materials

The representative 5052 aluminum alloy was selected as the material and its chemical composition was analyzed. The results are shown in Table 1. Material thickness of 0.8mm, welded joints for the lap joints.

1.2 Experimental equipment

Experimental pulse laser for the YAG lamp power feedback pulse laser, laser power 300W, its appearance shown in Figure 1. Fiber laser using single-mode fiber laser, laser power 500W, the appearance shown in Figure 2.

During the experiment, the welding quality was evaluated by metallographic analysis, the welding strength was evaluated by the tensile test, and the welding deformation was evaluated by measuring the appearance size of the workpiece after welding. The welding parameters in the experiment are shown in Table 2 and Table 3.

Welding defects

Aluminum alloy laser welding is the main drawback of pores and cracks, which is reflected in the pulse laser welding is particularly evident. It is generally believed that the pores produced by laser welding of aluminum alloy are mainly pores caused by evaporation of hydrogen pores and low melting point alloying elements. Aluminum alloy linear expansion coefficient, welding stress, but also eutectic alloy, easy to produce hot cracks. Especially when the laser pulse spot welding, a single pulse of the short time, thermal cycle speed, crack tendency is great. The use of fiber lasers continuous seam aluminum alloy, due to the existence of a significant extension of the bath to improve the welding stress and low melting point of the impact of welding cracks on the material, greatly reducing the tendency to produce cracks in the welding process. At the same time, the extension of the existence of molten pool is also conducive to the molten pool of gas discharge, reducing the formation of welding pores.

Pulsed laser aluminum alloy spot welding and fiber laser welding seam welding gold compared to Figure 3 shows, Figure 3 shows that fiber laser continuous seam welding conditions, cracks and pores have been significantly improved.

(A: pulsed laser aluminum alloy spot welding spot metallographic)

(B: fiber laser seam welding weld metallographic)

Figure 3: Pulsed laser aluminum alloy spot welding and fiber laser welding seam gold contrast

Strength and stability

Welding cracks will significantly reduce the strength of welded joints, the product of the practicality and reliability of a great impact, is one of the most dangerous welding defects. Aluminum alloy pulse laser spot welding, the crack is an important factor affecting the welding strength, due to the inevitable and irregular cracks, resulting in the strength of aluminum alloy spot welding is much lower than the strength of the material itself, and the welding products The strength difference between the great, poor stability. The continuous welding of fiber laser welding aluminum alloy can avoid the production of welding cracks, effectively improve the strength and stability of the weld.

Fiber lasers and pulsed lasers to weld the same aluminum alloy product. The average pull force of the fiber laser is 3.9 times that of the pulsed laser, and the standard deviation of the tensile data is only 1/3 of the pulsed laser. According to the metallographic analysis of Fig. 3, it can be seen that the width of the weld joint of the fiber laser is much smaller than that of the pulse spot welding, but the pulling force can reach nearly 4 times that of the pulsed laser, because: (1) the length of the fiber laser (2) pulse welding holes and cracks and other welding defects caused by its welding strength is much lower than the base metal strength, and fiber laser weld strength close to the strength of the fiber, Base metal. Therefore, fiber lasers in the welding of this type of product, compared to pulsed lasers can effectively improve the strength and stability.

Welding efficiency

Due to the fact that the tensile strength of the fiber laser is much higher than that of the pulsed laser spot welding, this provides a space for improving the welding efficiency. By reducing the number of welds and the length of the weld, it can be realized with the pulse Laser spot welding the same or even higher welding tension.

In the actual operation process, through the reasonable optimization of welding parameters, the number of welds, length and welding position, fiber laser segmented continuous seam welding process can replace the original pulse laser spot welding process. According to the actual production of statistical data, the process has been the original pulse laser spot welding process more than 3 times the production efficiency, while the welding tension increased to the original pulse laser spot welding process more than 1.5 times. Welding deformation

Aluminum alloy linear expansion coefficient, easy to produce welding deformation. Laser welding aluminum alloy deformation is relatively small, but in the welding of IT components of high precision products, even if the small deformation will still have a greater impact, the need for prevention and control. Generally the traditional continuous laser for seam welding heat input should be greater than the pulse laser spot welding, so the deformation will be larger than the pulse laser spot welding. The fiber laser has a better beam quality, smaller spot, more concentrated energy, can be faster and smaller heat input for welding, so the product deformation relative to the traditional continuous laser smaller.

As the fiber laser has the above characteristics, while the fiber laser welding aluminum alloy IT component product strength is much higher than the pulse laser, by rationally optimizing the fiber laser welding parameters, the number of welds, weld length and distribution position, Strength requirements at the same time, reducing the welding process into the workpiece in the overall heat, in order to further reduce the workpiece welding thermal deformation purposes. The overall welding deformation of the workpiece is improved by 3.5% of the pulse laser spot welding, and the relative pulse laser spot welding process is not obvious, which can meet the actual demand.

Appearance

IT component products have a higher demand for the appearance, and aluminum alloy material by segregation, surface roughness, oxide and other effects, resulting in the workpiece surface laser absorption rate is inconsistent, this phenomenon has a greater impact on laser pulse spot welding. The use of pulsed laser spot welding prone to not welding, splashing, soot and other issues, affecting the appearance and performance of products, the need for secondary cleaning.

Pulsed laser spot welding and fiber laser welding seam appearance comparison shown in Figure 4. Fiber laser continuous seam aluminum alloy, the welding process is more stable, not easy to produce splash and dust, no need for secondary cleaning, in appearance and process are better than pulse lasers.

(A: pulsed laser aluminum spot welding spot)

(A: pulsed laser aluminum spot welding spot)

Figure 4: Pulse laser spot welding and fiber laser seam welding appearance contrast

in conclusion

(1) the use of fiber laser continuous seam welding aluminum alloy IT component products can avoid pulsed laser spot welding often appear welding cracks, pores and other defects, greatly improving the welding strength and stability.

(2) By optimizing the welding parameters, the number of welds, the length of the weld and the distribution position of the fiber laser, the welding deformation can be reduced and the production efficiency can be improved.

(3) fiber laser welding aluminum alloy IT components, the weld smooth and beautiful, not easy to produce splash, soot, etc., do not need to clean up the second, reducing the production process.

(4) fiber laser segmented seam welding process in the welding strength, overall appearance, production efficiency and so on are better than the pulse laser spot welding process, and the amount of deformation and pulse laser equivalent, can replace the ordinary pulse laser in the aluminum alloy IT component products on the application, has a high application value.