Statistical Sampling Plans for Incoming Prismatic Lithium Cell Shipments
Incoming prismatic cell sampling relies on ISO 3951-1 variable plans and ISO 2859-1 attribute plans to reject defective lots before module integration.
Terminal Runout
Meaning
Manufacturing variations describe the axial or radial misalignment of cell terminals relative to the nominal centerline of the cylindrical housing. Uncontrolled terminal runout leads to assembly challenges during the high-speed pack manufacturing process where busbars must connect to each cell. This geometric deviation arises from minor tooling wear or inconsistent crimping forces during cell closure.
Mechanical Consequence
Misaligned terminals prevent proper laser welding of the interconnecting busbars. When the welding head cannot make uniform contact, the joint strength is compromised, creating a high-resistance electrical connection. These weak joints can fail under the vibration of transport applications, leading to pack failure.
Production Tolerance
Automated assembly lines require very tight tolerance limits, often limiting this deviation to less than a fraction of a millimeter. High-speed cameras and laser sensors scan each cell before welding to ensure the terminals fall within the required window. If a cell exceeds these limits, the assembly robot automatically rejects it to prevent a line stoppage or a defective weld.
Consistent cell geometry is essential for the high throughput demanded by modern electric vehicle battery plants.
Quality Control
Statistical process control on the assembly line monitors the alignment of cell crimping machines to catch drift before it exceeds the tolerance limits. Regularly scheduled maintenance of the punches and dies prevents tool wear from causing excessive variation. This proactive approach minimizes scrap rates and ensures that all finished modules meet strict structural requirements.