First Article Inspection Protocols for Custom Pack Stamping Dies
First article approval for pack stamping dies requires free-state optical scanning coupled with micro-sectioned edge burr verification below 0.03 mm.
Burnish Zone Fraction
Meaning
This quantitative metric measures the proportion of a cut metal edge that exhibits a smooth and polished appearance resulting from the shearing action of a punch. It represents the area where the material was pressed against the die wall before the final fracture occurred. The value is expressed as a percentage of the total sheet thickness and varies based on the material properties and tool clearance.
Engineers monitor burnish zone fraction to assess the quality of blanking or piercing operations in battery terminal manufacturing. It stops being a reliable indicator if the cutting tool is broken or if the material undergoes a secondary shaving operation. The measurement provides a direct insight into the mechanical interaction between the punch and the workpiece.
Edge Geometry
Characteristics of the cut surface are divided into four distinct regions including the rollover, the burnish, the fracture, and the burr. Because burnish zone fraction identifies the amount of material that has undergone controlled shearing, it serves as an indicator of edge quality for electrical connections. A larger burnish zone typically suggests a tighter tool clearance which produces a more uniform edge for welding.
This smooth surface minimizes the risk of stress concentrations that could lead to cracking under thermal or mechanical loads. The relationship between the burnished area and the fractured area affects the structural integrity of the final component. Engineering specifications often require a minimum burnished depth to ensure proper fitment in high voltage connectors.
This measurement is critical for maintaining the reliability of the battery pack interconnects.
Tooling Interaction
Clearance between the punch and the die determines the flow of the metal and the timing of the crack initiation. Since burnish zone fraction is sensitive to changes in tool sharpess, it provides an early warning system for tool wear during a production run. As the punch edge rounds over, the burnished portion of the edge tends to decrease while the fracture zone and burr height increase.
This change in edge topography can interfere with the automated assembly of the battery cells and busbars. Monitoring this fraction allows maintenance teams to schedule tool regrinding before the part quality falls below the acceptable limit. It also helps in the selection of appropriate lubricants to minimize friction and heat buildup during the stamping process.
Proper tooling management ensures consistent edge quality across millions of produced parts.
Part Reliability
Long term performance of the battery system depends on the absence of sharp edges or microcracks that could cause internal short circuits. While burnish zone fraction is a measure of the shearing process, it has a direct impact on the fatigue life of the metal component. A smooth burnished edge provides a better surface for adhesive bonding or thermal interface material application.
Sourcing teams evaluate the edge quality of supplier parts to ensure that the manufacturing process is stable and repeatable. The data collected from edge measurements supports the optimization of the blanking process for different alloy grades. Proper control of the burnish zone ensures that the mechanical and electrical properties of the battery enclosure are maintained.
Choosing the right stamping parameters prevents the formation of defects that could compromise the safety of the entire pack. .