Re-Slotting Before Peak at an E-Commerce Fulfillment Center
A 3PL operates a 180,000 sq ft e-commerce fulfillment center with 12,000 SKUs, 24 aisles, and six pick levels. Pickers use pick-to-tote carts and travel to packing. Slotting is by product category, so a slow-moving lawn-care SKU may sit in the golden zone while a best-selling phone case is on level 6 at the far end. The top 5% of SKUs account for 58% of picks. Pickers average 85 lines per hour; the target is 110. Travel is 62% of picker time. Aisles 1-4 near packing are congested with both fast movers and bulky oversize items, causing queueing. The operation is entering peak in ten weeks, when volume doubles and temporary labor rises to 40% of the workforce.
1. Quantify the opportunity and prioritize slotting changes.
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At 85 lines per hour, time per line is 60/85 = 0.706 minutes. If travel is 62%, travel time is 0.438 minutes per line and pick/other is 0.268. A 20% travel reduction saves 0.0876 minutes, raising the rate to 60/0.618 = 97 lines per hour. A 30% reduction gives 60/0.575 = 104; reaching 110 needs about a 38% travel cut or gains in pick time too.
The top 5% of SKUs, 600 SKUs, drive 58% of picks; slotting them in the golden zone (waist-to-shoulder, aisle ends near packing) gives the largest return. Prioritize by velocity-cube, not units alone: a high-pick, small item belongs in the prime zone; bulky oversize items should move out of aisles 1-4 to a dedicated bulk area, even if they are fast movers, because they cause congestion that slows everyone. Keep product-family grouping only where it does not override velocity. Measure the change in travel distance per line, not just lines per hour.
2. Propose an implementation plan that does not disrupt peak, including layout and labor considerations.
Read the worked answer
Implement in waves before the peak freeze, not during it. Week 1: extract 12 months of pick data, calculate velocity-cube and affinity (items often picked together), and simulate travel with the WMS slotting module. Week 2: re-slot the top 600 SKUs into the golden zone and move oversize to a bulk bay; keep 10% of prime locations flexible. Weeks 3-5: execute one aisle pair at a time during low-volume shifts, update the location master, and re-label. Weeks 6-8: train pickers on the new flow and post standard work. Do not re-slot the whole building in the last two weeks.
For peak, stage temporary labor on a narrow set of aisles and use zone picking to reduce congestion. Track lines per hour, travel distance, and aisle queue time. Set a go/no-go: if pick rate is below 95 lines per hour or errors rise, pause. The goal is a 20-30% travel reduction before peak, with a second wave after peak. Communicate location changes to customer service so order promises are not affected during the transition.