In pure electric vehicles, the weight of the battery pack accounts for about 30% of the curb weight. The lightweight of the battery pack is of great significance to improving the cruising range of the vehicle. Therefore, research on the high specific energy of battery packs is one of the current main research directions for new energy vehicles, and it is also the main way to achieve lightweight electric vehicles. The lightweighting of power battery packs can be carried out in two directions: improving single cells The energy density of the battery pack is optimized, and the related accessories of the battery pack are optimized.

The development of multi-material lightweight battery packs aims to reduce the weight of the battery pack, increase energy density and cruising range, while ensuring safety and reliability by using a variety of lightweight materials. Among the main components of the battery pack, the battery cell body has the highest mass, followed by the lower box of the pack, the upper cover, and BMS integrated components.

1-Lightweight design of the battery pack cover

The upper cover of the battery box is located above the power battery box and is not affected by the sides of the power battery box and will not affect the quality of the entire battery pack. Its functions mainly include sealing and protection. In order to improve the energy efficiency of the entire vehicle, lightweight materials will also be considered in the design. The use of lightweight materials, such as aluminum alloys and composite materials (SMC, FRP, etc.), can significantly reduce the weight of the battery pack.

In addition, the structural design of the upper cover also needs to consider manufacturing efficiency and mass production requirements. When the structure is very irregular, it may be difficult to use stamping forming or bending and tailor welding. The design of the upper cover also needs to consider the connection and cooperation with other components such as the lower box and sealing structural parts to ensure the structural stability and reliability of the entire battery box.

2-Lightweight design of the battery pack lower shell

Aluminum alloy is an ideal material for battery pack shells because of its low density, high specific strength, good thermal stability, strong corrosion resistance, good thermal conductivity, non-magnetic, easy molding and high recycling value. Commonly used aluminum alloy materials include 6061-T6, 6005A-T6 and 6063-T6. These materials have different yield strengths and tensile strengths and can meet different structural needs.

The battery pack shell is usually composed of an aluminum alloy profile frame and a bottom plate, which is welded using 6 series aluminum alloy extruded profiles. Factors such as the size and complexity of the profile section, wall thickness, etc. need to be considered during design to adapt to different structural and functional requirements. For example, components such as frames, middle partitions, floor panels, beams, etc. may adopt different cross-section designs.

Through reasonable structural design and connection methods, the overall strength of the shell can be effectively ensured, the processing difficulty can be reduced, and the weight of the shell can be reduced:

l Thin-walled: By adopting a thin-walled design and using stiffeners to meet strength requirements, the weight of the material can be effectively reduced.

l Hollowing: Introducing hollow sections into structural design to reduce material density.

l Size optimization: Optimize the size of the battery pack to reduce unnecessary material usage.

l Topology optimization: Reduce the space occupied by materials by optimizing the layout of internal components of the battery pack.

l Integrated modular design: Integrate cooling plates, battery pack lifting lugs and other components into the box to reduce the number and weight of individual components.

3-Manufacturing lightweight technology

l Material shaping

At present, there are three main categories of battery box material forming processes: stamping, aluminum alloy die-casting and aluminum alloy extrusion. The overall process flow of the power battery box includes material molding and connection processes, among which the material molding process is the key process of the power battery box. At present, the upper casing is mainly stamped, and the main processes of the lower casing are extrusion molding and aluminum alloy die-casting.

l Connection technology

The battery box connection process is crucial in new energy vehicle manufacturing and involves a variety of technologies and methods to ensure the structural strength and sealing of the battery box.

Welding is the main connection process in battery box processing and is widely used. Mainly include the following methods:

① Traditional fusion welding: such as TIG (tungsten inert gas welding) and MIG (metal inert gas welding). TIG welding has low speed and high quality. It is suitable for spot welding and complex trajectory welding. It is often used for frame tailor welding and side beam small piece welding. MIG welding has high speed and strong penetration ability, and is suitable for full-circle welding inside the frame bottom plate assembly.

② Friction stir welding: Welding is achieved by generating heat through friction. It has the characteristics of good joint quality and high production efficiency.

③Cold metal transfer technology: It is suitable for thin plate materials. There is no heat input during the welding process, reducing deformation.

④Laser welding: high precision, high speed, suitable for complex structure welding.

⑤ Stud welding and projection welding: used for quick connection of specific parts. Stud welding is fastened by studs and nuts, and projection welding is connected by pressing bumps.

The mechanical connection method mainly solves the problems of easy welding and thread slippage of thin plate materials during welding, including:

① Blind rivet nut: used to connect the sealing surface of the box frame and the inner cavity bottom plate. It has the advantages of high fastening efficiency and low use cost. Suitable for threaded connections between thin plates and other components.

②Wire thread insert: used to strengthen the screw holes of aluminum or other low-strength bodies, improve the load-bearing capacity of the screws and the force distribution of the threads, and is suitable for battery module mounting holes and sealing surface mounting holes. Compared with blind rivet nuts, wire thread inserts are stronger and easier to repair, but are generally not suitable for thin-wall installations.

We will regularly update you on technologies and information related to thermal design and lightweighting, sharing them for your reference.

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