Cylindrical Battery Case Ironing for Low Surface Roughness
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Solution Overview
Problem
Conventional cylindrical battery cases exhibit high surface roughness and poor corrosion resistance, which affects their performance in high-temperature and high-humidity environments, such as electric vehicles, due to inadequate polishing and increased tensile force during the drawing process.
Innovation Solution
A method involving multiple ironing processes during the deep-drawing process to reduce surface roughness, specifically performing primary and secondary ironing steps to achieve a surface roughness of 0.1 μm or less, ensuring uniform thickness reduction and improved polishing of the battery case.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional single ironing process is used during deep-drawing, then the manufacturing process is simple and productivity is high, but the surface roughness remains high and corrosion resistance is poor
Solution Approach 1:
The single ironing process is segmented into multiple ironing passes (first ironing, second ironing, and optionally third ironing). Each pass reduces the wall thickness by a controlled amount and progressively improves the surface finish. This segmentation allows achieving Ra≤0.1μm surface roughness while managing the total manufacturing time by optimizing each individual pass duration.
Solution Approach 2:
The method performs preliminary surface preparation through controlled ironing passes before final battery assembly. By pre-reducing surface roughness during the forming process itself, rather than requiring separate post-processing steps, the method improves corrosion resistance without adding significant manufacturing time.
2Reliability
If multiple ironing processes are performed to reduce surface roughness, then corrosion resistance is improved, but the manufacturing complexity increases
Solution Approach 1:
The method merges multiple ironing operations into a single integrated deep-drawing process. By combining the forming and surface finishing operations into one continuous process flow, the method achieves reduced surface roughness (Ra≤0.1μm) and improved corrosion resistance without requiring separate equipment or process steps, thus avoiding increased manufacturing complexity.
Solution Approach 2:
The method changes the process parameters by performing multiple ironing passes with controlled reduction ratios. Each pass uses optimized parameters (pressure, speed, tool geometry) to progressively reduce surface roughness while maintaining structural integrity. This parameter optimization achieves high corrosion resistance without requiring complex additional equipment.
3Manufacturing precision
If the wall thickness is reduced uniformly through multiple ironing passes, then surface quality is improved, but the structural strength may be compromised
Solution Approach 1:
The method applies different reduction ratios to different regions of the battery case wall during ironing. By controlling the local deformation characteristics, the process achieves uniform surface quality (Ra≤0.1μm) while maintaining adequate wall thickness and structural strength in critical areas. The ironing process is optimized to distribute stress evenly, preventing weak points.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method significantly enhances the corrosion resistance of cylindrical battery cases by reducing surface roughness, preventing spot corrosion and improving the overall performance in harsh conditions, while allowing for increased capacity and efficient charging/discharging characteristics.
Implementation Method 1
an ironing process, which is one of the processes of manufacturing the battery case, a plurality of times in order to decrease the surface roughness of the battery case
Implementation Method 2
performing an ironing process, which is one of the processes of manufacturing the battery case, a plurality of times
Data Source
AI summary
A cylindrical battery case for a secondary battery includes a body having a steel sheet including a nickel coating layer formed thereon, a step portion on the body, and a taper and a flange extending from the body. A surface roughness (Ra) of the battery case ranges from 0.022 μm to 0.040 μm. Also provided is a device including such a secondary battery. The device is selected from a group consisting of an electronic device, an electric vehicle, a hybrid electric vehicle, and a power storage system.