Air tightness and flatness control of battery shell frame mold
The flatness requirement for the sealing surface of the battery case frame is 0.3mm/m, and the airtightness is IP67. The core of the mold is rigid, cooled, and standardized.
Flatness is a prerequisite for sealing
The frame size is often between 1.2-2 meters, and the flatness of long span components is most prone to loss of control. The requirement of 0.3mm/m means that the total deviation on a 2-meter piece does not exceed 0.6mm.
If the flatness exceeds the tolerance and the compression of the sealing strip is uneven, water will seep locally. This type of failure is difficult to repair in the whole vehicle rain test.
The arrangement of support points for the mold directly affects its flatness. If the support spacing is too large, the self weight will cause downward deflection. It is recommended to set a support every 400-500mm.
Test conditions corresponding to the airtightness level
IP67 typically requires immersion in water for 1 meter and no water ingress for 30 minutes. Corresponding to the part level, the air tightness test pressure is mostly between 10-30kPa, and the leakage rate is calculated in cc/min.
The test pressure is much lower than the 0.6-0.8MPa of the wheel hub, but the frame volume is large, and even small leaks accumulate and exceed the standard.
Welding seams and sealing surfaces are the two major sources of leakage. The density requirement of the casting itself is relatively loose, but the sealing surface area must be dense.
Mold rigidity determines dimensional stability
The aspect ratio of the frame mold is large, and the template is prone to deformation. It is recommended to use integral castings or thick plate processing for the mold frame to avoid welding parts.
Xinfeng Mold will perform a stiffness check on the battery shell frame mold to control the maximum deformation within 0.05mm, and then arrange for cavity processing.
The deformation of the mold in the closed state will be directly replicated on the casting. Therefore, stiffness verification should be based on the closed mold condition, not the free state.
The relationship between cooling and deformation
The thickness of the frame wall is thin, the process is long, and uneven cooling can cause warping. It is recommended to control the temperature difference between the upper and lower surfaces of the mold cavity within 8 ℃.
The layout of waterways should be symmetrical. The number of waterways and flow rate of the upper and lower molds should be as consistent as possible, otherwise the shrinkage of the upper and lower surfaces will be different, and warping is inevitable.
The demolding temperature of thin-walled frames should not be too low. Demolding at temperatures below 150 ℃ results in high cooling stress and will continue to deform even after being placed.
Unification of processing standards
The benchmark for casting blanks must be consistent with the machining benchmark. The benchmark is not uniform, and even the best flatness of the blank will exceed the tolerance after processing.
Suggest setting a process protrusion on the mold as a reference and cutting it off after processing is completed. The position of the protrusion should be clearly marked on the drawing.
During coordinate measurement, the assembly state should be simulated and supported by support points before measurement. The measured values in a free state cannot represent the loading status.
Two checks during the trial stage
Measure the gap between the sealing surface in the closed state, and the plug gauge of 0.05mm should not be inserted. If it can be inserted, it indicates that there is a problem with the rigidity or support arrangement of the mold frame.
Perform double inspection of airtightness and flatness for the first piece. The flatness is qualified but the airtightness is unqualified, and the problem often lies in the roughness of the sealing surface or the direction of the knife pattern.
Frequently Asked Questions
Q: What is the flatness requirement for the battery case frame?
Answer: The common deviation is 0.3mm/m, and the total deviation of the long piece is calculated proportionally.
Q: What level of airtightness is used?
Answer: Mostly IP67, part level test pressure 10-30kPa.
Question: How much is the mold deformation control?
Answer: It is recommended to be within 0.05mm under the mold closing condition.
Question: How much is the temperature difference between the upper and lower molds controlled?
Answer: It is recommended to keep the temperature below 8 ℃ to reduce warping.
Question: How to unify the benchmark?
Answer: Set up a process protrusion, which is shared between casting and machining.
Q: What is the appropriate demolding temperature?
Answer: It is not recommended to lower it below 150 ℃ to avoid cooling stress.
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