Meaning
The cumulative variation in dimensions that results from assembling multiple individual components can lead to mechanical interference or clearance issues. This stack-up tolerance dictates the design clearances and manufacturing requirements for battery modules and pack enclosures.
Assembly Variance
Each part in a battery stack, from the cell thickness to the cooling plate flatness, has a specified manufacturing deviation from its nominal dimension. When these parts are assembled, their individual variances can add up to create a significant total variation in the final assembly. Engineers use statistical methods like root-sum-square analysis to predict this total variation.
This prediction helps avoid both over-designing the clearances and incurring high scrap rates during assembly, saving both time and material cost during the manufacturing process.
Quality Influence
Excessive variation in the completed stack can lead to uneven pressure distribution across the cells when the module is clamped. This uneven pressure leads to localized current density variations and accelerates cell degradation during operation. Parts that are too tight can deform the module housing, while parts that are too loose can cause vibration issues.
Sourcing components with tighter individual tolerances reduces this risk but increases the purchase price.
Sourcing Requirement
Sourcing contracts must specify the allowable dimensional variation for each component to ensure compatibility at the pack level. Suppliers must demonstrate capability through statistical process control data to prove they can consistently meet these requirements. Sourcing teams use these metrics to qualify suppliers and to negotiate warranty terms related to dimensional defects.
Clear alignment ensures that assembly line throughput remains high and scrap remains low.
