Busbar brackets: 5,000 pcs/month and a 32% lower unit cost

The problem

A battery pack assembler was buying busbar brackets from two suppliers: one stamped the bracket, the other drilled and tapped the mounting holes. On the drawing each part was in tolerance. Assembled, the hole positions stacked up and roughly one pack in twelve stalled on the line because the busbar would not seat.

The customer had already tried tightening the tolerances on both suppliers, which raised the price and did not fix the stall rate — because the problem was the datum scheme, not the individual dimensions.

What we changed

• One process chain, one PO. Stamping and the secondary CNC operations moved under one roof, so the second operation references the first operation's actual features instead of a nominal drawing.
• Datum rebuilt from function. The assembly locates on two holes and a face. Those three features are now cut in the same set-up as the mounting pattern, so the stack-up that caused the stall is gone rather than reduced.
• In-process SPC on hole position. Ten parts per hour are checked on the CMM; the position data is plotted and the die is adjusted when the trend moves, not when a part fails.
• Progressive die with in-house maintenance. Die wear was the hidden variable — the previous stamper sent dies out for service and lost a week each time.

The result

Hole position Cpk went from 0.9 (marginal) to 1.6. The line stall rate dropped to zero over six months, unit cost fell 32% because the second supplier, the second freight leg and the incoming inspection at the customer's plant all disappeared, and on-time delivery has held at 98% across 30,000 parts.

Volume is 5,000 pcs/month with capacity for 8,000 on the same die.