As a front-line engineer at a battery tray manufacturer, I have participated in multiple new energy vehicle battery shell projects and have a deep understanding of the industry's game in the triangle relationship of "lightweight-safety-cost". This article will analyze the selection logic and industrialization challenges of the current technology route from three dimensions: material route, manufacturing process and future trends, combined with actual cases.

1-Material route: the trade-off between lightweight and cost

The choice of battery shell material directly affects the performance and economy of the whole vehicle. The current mainstream routes can be summarized into three categories: aluminum alloy, high-strength steel and composite materials, each with its own applicable scenarios.

a. Aluminum alloy route: the main force of lightweight

· Extruded aluminum profiles: BYD's battery shells of many models are made of extruded aluminum profiles, which achieve weight reduction by optimizing the cross-sectional shape and improve structural rigidity.

· Die-casting integration: Tesla's 4680 battery is combined with CTC technology to reduce weight by more than 50%, but the mold cost exceeds 200 million yuan, and an annual production of more than 500,000 pieces is required to dilute the cost, which is suitable for large-scale production of leading car companies.

· Composite aluminum: Porsche Taycan adopts an aluminum-carbon fiber hybrid structure, which further reduces weight by 15%, but the cost increases by 30%, which is limited to high-end models.

b. High-strength steel route: counterattack in the cost-sensitive market

Hot-formed steel (such as 22MnB5) has a yield strength of 1500MPa, a penetration rate of over 40% in commercial vehicles, and a single GWh cost that is 40% lower than aluminum, but the energy density is sacrificed by about 8%. Therefore, high-strength steel is generally used in models below 100,000 yuan, taking into account both cost and basic safety.

c. Composite materials: a trial of high-end

· SMC material: The upper shell of the battery pack uses glass fiber reinforced composite materials, which is 30% lighter than steel, but the impact resistance shortcomings need to be compensated by increasing the thickness (3mm+5mm reinforcement).

· Carbon fiber: The shell of the BMW i3 is 50% lighter than aluminum, but the cost is as high as 800 yuan/kg, and it is difficult to mass produce. It is currently only used for luxury models.

Practice summary: Material selection needs to match the model positioning. The mid-range market (200,000-300,000 yuan) is mainly aluminum-based materials, the low-end market relies on high-strength steel, and luxury models explore carbon fiber composite solutions.

2- Manufacturing process: the balance between efficiency and reliability

The manufacturing process of the battery shell directly affects the production efficiency and product reliability. The current mainstream technical routes include die casting, extrusion welding and structural integration technology.

a. Die casting vs. extrusion welding

· Extruded aluminum profiles (used by GM Bolt): The cost of a single piece is about 800 yuan, which is suitable for mass production, but the process is complicated.

· Die-cast aluminum (NIO ET5): The cost of a single piece is 1,500 yuan, but the production efficiency is increased by 5 times, which is suitable for rapid production demand.

· Friction stir welding (FSW): Compared with traditional arc welding, the deformation is reduced by 50%, and the fatigue resistance is improved by 30%, but the equipment investment needs to be increased by 40%, which is suitable for commercial vehicles with high life requirements.

b. Structural integration technology

· CTP modularization (CATL Kirin battery): The space utilization rate is increased from 72% to 85%, and the cost is reduced by 15-20%, but the thermal runaway protection design needs to be strengthened.

· CTC chassis integration (Tesla Model Y): 370 parts are reduced and the battery life is increased by 54%, but the maintenance cost increases by 300%, posing a challenge to the after-sales system.

Key data comparison

Production line experience: CTP technology is still the current mainstream due to its high compatibility; while CTC requires in-depth collaboration between car companies and battery manufacturers and is unlikely to be popularized in the short term.

3- Future trends: technology integration and intelligent upgrade

a. Material composite

Aluminum/carbon fiber hybrid shell (such as Porsche Taycan concept) can reduce weight by 15% and achieve 800MPa compressive strength, but the interface bonding strength needs to be greater than 25MPa (Toyota bZ4X mass production qualification rate is only 65%), and process stability needs to be broken through.

b. Functional integration innovation

· Liquid cooling plate and shell integration (GAC magazine battery): cooling contact area increased by 50%, temperature difference control <5℃, but aluminum-copper dissimilar welding porosity needs to be optimized by laser swing welding.

· Embedded fiber optic sensor (Continental Group solution): real-time monitoring of shell strain and temperature, BMS response speed increased by 30%, but the sensor durability problem needs to be solved.

c. Green circulation system

BMW's closed-loop recycling of recycled aluminum technology reduces carbon emissions by 60%, but the performance loss of recycled materials needs to be controlled within 10%. In addition, large thin-wall die casting (such as LK 9000T die casting machine) requires precise control of mold temperature difference (±5℃), and burr cleaning efficiency becomes a bottleneck for mass production.

Process breakthrough direction:

· Compression of composite material molding cycle (such as LGF-PP injection molding cycle needs to be shortened from 180 seconds to 90 seconds);

· Application of digital twin technology to reduce collision simulation error from ±20% to ±5%, improving design reliability.

4- Market stratification and industrialization outlook

Short term (1-3 years): CTP+ extruded aluminum profiles are still the mainstream, and CATL continues to lead with a 34% market share;

Medium term (5-10 years): CTC and carbon fiber are accelerating their penetration in the high-end market, and it is expected that carbon fiber will account for 25% in 2030;

Long-term goal: Energy density will break through 400Wh/kg, and at the same time, based on the national standard 30-minute thermal runaway protection, further improve safety redundancy.

5-Conclusion

The essence of choosing the technical route of battery housing is "scenario-based adaptation", which requires comprehensive consideration of the positioning of car companies, cost thresholds and supply chain maturity. As engineers, we must embrace innovation in materials and processes, and also focus on the feasibility of mass production, and find the optimal solution in the dynamic balance between lightweight, safety and cost. In the future, with the maturity of intelligent and green manufacturing technologies, battery housings will gradually shift from "passive protection" to "active safety", providing solid support for the full popularization of new energy vehicles.

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