Die Casting Process Analysis for Energy Storage Battery Packs
The core of the energy storage battery PACK package die-casting process is to use high pressure to inject molten aluminum alloy into a precision mold to integrate key structures such as the box and liquid-cooling runner into one-time integration. The core goal is to improve structural rigidity, air tightness and heat dissipation, and adapt to integrated solutions such as CTP/CTC. The following is a comprehensive analysis from the perspective of process positioning, core processes, material selection, defect control, technical difficulties and cutting-edge directions.
- ★Process positioning and core values
Energy storage battery PACK die-casting mainly focuses on structural components such as boxes/trays, liquid-cooling shells and module brackets. The core is "integrated integration": the scattered mounting bosses, sealing grooves, liquid-cooling runners, etc. are formed at one time through the mold, which greatly reduces the welding and assembly processes, improves structural consistency, and reduces cumulative dimensional errors. Compared with stamping welding and profile splicing, die casting has significant advantages:
(1) Strong structural rigidity, good resistance to deformation, suitable for long-term outdoor working conditions of energy storage
(2) Integrated liquid cooling runner forming, high heat dissipation efficiency, ensuring battery temperature control
(3) High dimensional accuracy (IT11 level, CT4-6 for key parts) and excellent surface quality (Ra0.8-3.2μm)
(4) Suitable for mass production, short unit cycle, conducive to cost control
(5) The core limitations are that the molding cost of large parts is high, the uniformity of wall thickness is strict, and defects such as air holes/shrinkage cavities are prone to occur, requiring refined process control.
- ★The entire core process: from design to post-processing
(1) Design and simulation front end (determining air tightness and strength)
The success or failure of die-casting begins with design, which must be combined with simulation to avoid defects.
Structural optimization: uniform wall thickness 2.0-3.5mm, minimum wall thickness ≥1.2mm, gradient transition of stiffeners; topology optimization + MAGMA/ProCAST simulation, optimizing gates, overflow and exhaust to avoid air entrainment/shrinkage holes; integrating liquid cold runners, sealing grooves and installation bosses to reduce subsequent welding
Mold design: H13 hot work mold steel (HRC48-52), multi-slider core pulling to adapt to complex flow channels; point cooling + heat pipe temperature control, mold temperature difference ±5℃; CNC finishing allowance is reserved to ensure the accuracy of key surfaces
(2) Smelting and refining: control impurities and eliminate pores
Porosity is the biggest hidden danger for the airtightness of the energy storage box, and the purity of the melt needs to be strictly controlled.
Alloy selection: energy storage priority A356 (high toughness, suitable for T6 heat treatment), AlSi10Mg (commonly used in integrated die-casting); ADC12 is used for non-load-bearing structural parts. A356 strictly controls Fe≤0.2%, ADC12 strictly controls Fe≤1.3%
Melting and degassing: temperature 680-720°C (closed-loop temperature control ±5°C); rotating injection of argon/nitrogen degassing, hydrogen content ≤0.1ml/100g; adding Al-Ti-B refiner, the grains are refined to less than 15μm, and the elongation is improved.
(3) Core process of die casting: high pressure filling + pressure feeding
Mainstream uses cold chamber high-pressure die casting , with vacuum assistance to increase density, and core parameters are optimized by alloy.
Mold temperature control: 180-220℃ for ADC12/380, 220-250℃ for A356/6061, reducing cold isolation and mucous membrane.
Injection strategy: slow injection (0.1-0.5m/s) to push material smoothly and prevent air entrainment; fast injection (2-5m/s) to quickly fill the mold and prevent cold insulation; boost pressure 80-150MPa, holding time = wall thickness × (3-8)s, dense feeding
Vacuum assistance: The cavity vacuum degree is ≤100mbar (A356≤50mbar), which greatly reduces pores and improves elongation and tensile strength. It is a key process for energy storage airtight parts.
(4) Post-processing: ensuring accuracy, strength and corrosion resistance
Cleaning and processing:removing gates and flash; shot peening (residual compressive stress ≥150MPa); Cnc Precision finishing of sealing grooves and mounting surfaces to ensure assembly accuracy
Heat treatment: A356 can be T6 (solid solution + aging) to improve strength; ADC12 is suitable for T5 artificial aging to avoid full T6 deformation
Surface and air tightness: anodized and passivated to improve corrosion resistance; 100% air tightness test (helium test/air pressure) to ensure there is no leakage in the liquid cooling channel and box
- ★Key defect control: causes and countermeasures of pores, shrinkage cavities, and cold insulation
Energy storage PACK die castings have zero tolerance for defects and focus on controlling three types of problems.
Porosity: The cause is mold filling and entrainment, high hydrogen content in smelting; the countermeasure is high Vacuum Die Casting + rotating degassing + optimized pouring and drainage system
Shrinkage cavities: The cause is insufficient solidification and feeding; the countermeasure is multi-stage pressurization + sufficient pressure holding + local cold iron temperature control
Cold shut/flow marks: The cause is low mold temperature and insufficient injection speed; the countermeasures are to accurately control the mold temperature, optimize the injection curve, and achieve uniform wall thickness
- ★Technical difficulties and cutting-edge breakthroughs
(1) Core difficulties
Large integrated box: large size, complex structure, requires a very large die-casting machine (≥4000 tons), and difficult to control mold thermal balance and deformation
Liquid-cooled runner forming: the internal runner is easy to block and the wall thickness is uneven, requiring multi-slide core pulling + precise mold temperature control + simulation optimization
Batch consistency: wall thickness fluctuations, unstable porosity, reliance on closed-loop process control and online testing
(2) Cutting-edge technology
High vacuum die casting: cavity vacuum degree >90%, porosity <1%, suitable for high airtight energy storage boxes
Semi-solid die casting: high metal slurry viscosity, smooth mold filling, fewer pores/shrinkage holes, suitable for high-precision structural parts
Integrated die-casting + CTC/CTP: Integrate the box, tray, and liquid cooling system to reduce the number of parts and improve energy density and production efficiency.
- ★Suggestions on process selection
Large energy storage liquid cooling box: priority A356 + high vacuum cold chamber die casting + T6 heat treatment to ensure strength, toughness and air tightness
Small module bracket: ADC12 + conventional high-pressure die-casting, cost control, suitable for mass production
Pursuing ultimate lightweight: magnesium alloy die-casting (protection and cost need to be strictly controlled) or aluminum alloy semi-solid die-casting
- ★Summary
The core of energy storage battery PACK die-casting lies in "design simulation first, melt purity as the basis, high-pressure vacuum shape control, and post-processing to ensure performance." Through integrated integration and refined management and control, the rigidity, airtightness, and heat dissipation pain points of traditional processes can be solved, and the needs of large-scale and lightweight energy storage can be adapted. In the future, difficulties such as thermal balance and flow channel consistency of ultra-large molds need to be overcome to promote the deep integration of processes with CTC/CTP technology.