Laser welding lead-acid battery terminals and simulation technology

1 Introduction

Since the invention of lead-acid batteries in the 19th century, they have been superior to nickel-metal hydride and lithium-ion batteries in terms of versatility and low cost, and they still play an important role in the industrial field.

As a new trend, although lead-acid batteries have this feature, the so-called high-performance lead-acid batteries should also be adapted to new fields. The use of laser technology to weld the terminals of small-capacity valve-regulated lead-acid batteries is a link in the company's high-tech technology. The trial production reduces the remaining space inside the battery to the limit. The use of laser welding is local heating. In order to reduce the spacing between components, as shown in Figure 1, the remaining space outside the plate has been successfully reduced to less than 7 layers. The result is a leap in volume energy density.

Figure 1 Comparison between the common type and the new structure

This article describes the effects of laser welding on the terminal area of ​​lead-acid batteries. The results of establishing welding conditions are reported by analyzing the temperature during welding using simulation technology.

Figure 2 Laser welding machine structure

The basic laser output procedure during welding is shown in Figure 6. This procedure is that the laser heats the pole for about 2 weeks. The results of this procedure analysis are as follows.

Figure 8 Analysis results of welding range

4 Research on improving welding quality

As shown in Figure 10, the welding depth at each point on the circumference is different. In particular, the required welding depth is not obtained within the range of 10°C to 90°C. The reason is that when the laser is output as a whole, the resin around the pole sleeve can be melted, which affects the airtightness of the battery. Therefore, the required welding depth can be obtained based on simulation analysis, and a new procedure can be obtained in which the heat has no effect on the surrounding resin.

As shown in Figure 12, a new program was finally obtained through the traditional program and the simulation program. The changes in the new program first increased the initial laser output in the second welding cycle to eliminate the previous ambiguous welding depth in the range of 10℃~90℃, and gradually deleted the subsequent output to further control the heating beyond the required level.

Figure 12 Comparison of the old and new laser output programs

In the new program, the simulation analysis results and the actual results are described as follows.

As shown in Figure 13, the new program was used to simulate and analyze the welding depth. Compared with the conventional conditions, the welding depth was the same and the expected welding depth was obtained around. The maximum temperature of the surrounding resin part was about 10°C lower than before, so the possibility of resin melting was very small.

Figure 13 Comparison of welding depth patterns between the new and old procedures Figure 14 Comparison of welding depth test values ​​between the new and old procedures

The rectangular diagram of actual welding measured by the new procedure and the results of the same test according to the previous procedure are shown simultaneously (see Figure 14). Under the traditional conditions, the deviation of the welding depth is large and appears below the standard value, but in the new procedure, the welding depth deviation is less than 1/2 of the traditional deviation, and all samples have reached the standard value. The above results confirm that laser welding has a good effect and simulation technology is a very effective method.

5 Conclusion

Through laser welding, the lead-acid battery terminal parts are highly concentrated, which greatly improves the volume energy density. The laser welding simulation test mode is constructed, and the temperature is significantly improved. In order to achieve a good welding state for laser welding, simulation technology is a very effective way.

Figure 9 Analysis results of welding depth

As shown in Figure 9, the welding range when the model is viewed from the side is selected and indicated in red. From the side, the depth of welding at each time point and each position can be seen. The result of the welding depth at the end of welding is obtained from the angle of the starting welding position, and is shown in Figure 10 together with the actual measured value. It is confirmed that the simulation results and the actual measured values ​​are completely consistent, and the results of the temperature aging of the surrounding resin part are obtained together with the actual measured values. In order to move the heating point above the circumference, the distance between the test point and the heat source is changed, and the two simultaneously form a stage curve. It can be confirmed from the graphical results that the simulation curve is completely consistent with the measured values. The comparison between the above simulation results and the measured values ​​proves that it is effective to use this analysis mode to evaluate the temperature changes during laser welding.

Figure 10 Comparison between the test value and the measured value of welding depth Figure 11 Comparison between the test value and the measured value of the resin part temperature during welding

Figure 4 (a) Solid model; (b) Finite element model Figure 5 Laser heating condition setting

3.2 Analysis results and verification

The temperature distribution of the analysis results is shown in Figure 7. The red area is the range above 327°C, the melting point of lead, and the range of instant melting. Figure 8 shows the distribution of the highest temperature reached at each time point. The red area is the part above 327°C, the melting point of lead, and shows the range of welding at the time point. The green area shown in Figures 7 and 8 is the part with a melting point of the resin above 160°C. At the end of welding, only the part above 160°C reaches the resin, so only this part of the resin melts. If the resin melts, the airtightness of the battery will be destroyed, which will seriously affect the battery performance. The following research was conducted on this.

Figure 6 Laser output program

Figure 7 Temperature distribution analysis results