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Part 2. Technology: aluminum extrusion + friction stir welding as the mainstream, laser welding and FDS or become the future direction

1. Compared with die casting and stamping, aluminum extrusion forming profiles and then welding is the mainstream technology of battery boxes at present.

1) The drawing depth of the shell under the battery pack welded by the stamping aluminum plate, the insufficient vibration and impact strength of the battery pack, and other problems require the automobile enterprises to have strong integrated design ability of the body and chassis;

2) The casting aluminum battery tray in die casting mode adopts the whole one-time molding. The disadvantage is that the aluminum alloy is prone to undercasting, cracks, cold isolation, depression, porosity and other defects in the casting process. The sealing property of the product after casting is poor, and the elongation of the cast aluminum alloy is low, which is prone to deformation after collision;

3) Extruded aluminum alloy battery tray is the current mainstream battery tray design scheme, through the splicing and processing of profiles to meet different needs, has the advantages of flexible design, convenient processing, easy to modify and so on; Performance Extruded aluminum alloy battery tray has high rigidity, vibration resistance, extrusion and impact performance.

2. Specifically, the process of aluminum extrusion to form battery box is as follows:

The bottom plate of the box body is formed by friction stir welding after the aluminum bar is extruded, and the bottom box body is formed by welding with four side plates. At present, the mainstream aluminum profile uses ordinary 6063 or 6016, the tensile strength is basically between 220 ~ 240MPa, if the use of higher strength extruded aluminum, tensile strength can reach more than 400MPa, compared with ordinary aluminum profile box can reduce weight by 20%~30%.

3. Welding technology is also continuously upgrading, the current mainstream is friction stir welding

Due to the need to splice the profile, welding technology has a great impact on the flatness and accuracy of the battery box. Battery box welding technology is divided into traditional welding (TIG welding, CMT), and now the mainstream friction welding (FSW), more advanced laser welding, bolt self-tightening technology (FDS) and bonding technology.

TIG welding is under the protection of inert gas, using the arc generated between tungsten electrode and weldment to heat melt base metal and fill wire, so as to form high quality welds. However, with the evolution of box structure, box size becomes larger, profile structure becomes thinner, and the dimensional accuracy after welding is improved, TIG welding is at a disadvantage.

CMT is a new MIG/MAG welding process, using a large pulse current to make the welding wire arc smoothly, through the material surface tension, gravity and mechanical pumping, forming a continuous weld, with small heat input, no splash, arc stability and fast welding speed and other advantages, can be used for a variety of materials welding. For example, the box structure under the battery package used by BYD and BAIC models mostly adopts CMT welding technology.

4. Traditional fusion welding has problems such as deformation, porosity and low welding joint coefficient caused by large heat input. Therefore, more efficient and green friction stir welding technology with higher welding quality has been widely used.

FSW is based on the heat generated by the friction between the rotating mixing needle and the shaft shoulder and the base metal as the heat source, through the rotation of the mixing needle and the axial force of the shaft shoulder to achieve the plasticization flow of the base metal to obtain the welding joint. FSW welding joint with high strength and good sealing performance is widely used in the field of battery box welding. For example, the battery box of many models of Geely and Xiaopeng adopts double-sided friction stir welding structure.

Laser welding uses a laser beam with high energy density to irradiate the surface of the material to be welded to melt the material and form a reliable joint. Laser welding equipment has not been widely used due to the high cost of initial investment, long return period, and the difficulty of aluminum alloy laser welding.

5. In order to alleviate the impact of welding deformation on box size accuracy, bolt self-tightening technology (FDS) and bonding technology are introduced, among which well-known enterprises are WEBER in Germany and 3M in the United States.

FDS connection technology is a kind of cold forming process of self-tapping screw and bolt connection through tightening shaft of the equipment center to conduct the high-speed rotation of the motor to be connected to the plate friction heat and plastic deformation. It is usually used with robots and has a high degree of automation.

In the field of new energy battery pack manufacturing, the process is mainly applied to the frame structure box, with bonding process, in order to ensure sufficient connection strength while realizing the sealing performance of box. For example, the battery case of a Car model of NIO uses FDS technology and has been quantitatively produced. Although FDS technology has obvious advantages, it also has disadvantages: high equipment cost, high cost of post-weld protrusions and screws, etc., and operating conditions also limit its application.

Part 3. Market Share: battery box market space is large, with rapid compound growth

Pure electric vehicles continue to increase in volume, and the market space of battery boxes for new energy vehicles is rapidly expanding. Based on the domestic and global sales estimates of new energy vehicles, we calculate the domestic market space of new energy vehicle battery boxes by assuming the average per unit value of new energy battery boxes:

Core assumptions:

1) The sales volume of New energy vehicles in China in 2020 is 1.25 million. According to the Medium and Long-term Development Plan of Automobile Industry issued by the three Ministries and commissions, it is reasonable to assume that the sales volume of new energy passenger vehicles in China in 2025 will reach 6.34 million, and the overseas production of new energy vehicles will reach 8.07 million.

2) The domestic sales volume of pure electric vehicles accounts for 77% in 2020, assuming that the sales volume will account for 85% in 2025.

3) The permeability of aluminum alloy battery box and bracket is maintained at 100%, and the value of a single bike is RMB3000.

Calculation results: it is estimated that by 2025, the market space of battery boxes for new energy passenger vehicles in China and overseas will be about RMB 16.2 billion and RMB 24.2 billion, and the compound growth rate from 2020 to 2025 will be 41.2% and 51.7%