Put one pallet in the wrong zone at inbound, and automation can't get it out at outbound

The same part ended up in two places: some of it in the standard-parts store, some in the large-parts store.

On paper, there was enough stock. At outbound, automation couldn’t get it out.

In the end we moved the check to the moment the goods arrive: if a part doesn’t belong in this zone, it is rejected right at the entrance. This post starts from that problem and walks through the five inbound steps, the three traps, and the putaway rules.

1. The five WMS inbound steps all pave the way for outbound

From arrival to putaway, a part goes through five steps:

• Receiving: the supplier delivers to the receiving area
• Inspection: quality check; only parts that pass move on. Inspection comes before repalletizing, so we confirm the parts are usable before spending effort on them
• Repalletizing, also called pallet building: moving the parts from the supplier’s packaging onto the AS/RS standard pallet or tote, and binding the pallet number
• Profile check: measuring the pallet’s height, width and weight; anything over the limit can’t enter the AS/RS. An over-height pallet would scrape the racking inside the aisle. This is the AS/RS’s last gate
• Putaway: the system assigns a slot, and the stacker crane puts the pallet in

Different part types also use different entrances. We set up several by part type: the standard-pallet AS/RS, the standard-parts store and the large-parts store, each with its own. Large and small parts differ in size and handling equipment; squeeze them through one entrance and they block each other.

Inbound looks like the warehouse’s own business, but every step paves the way for outbound: a properly standardized pallet is one outbound can move; a part in the right zone is one outbound can call out.

2. AS/RS inbound traps sit up front: packaging, inspection, zones

1. Packaging varies, so repalletizing volume is high. Supplier packaging comes in every shape, and almost every pallet has to be broken down and rebuilt. At this point we don’t stack by the “pieces per pallet” in the PFEP table; that would be too slow. Inbound repalletizing has one standard: get it onto an AS/RS standard pallet, as long as it fits. The PFEP quantities only come into play at outbound, during manual sorting.

2. Partial inspection failures must be put away separately. One batch can contain both good and bad parts. Good parts go away normally; the bad ones are separated and put away on their own, waiting for further checks, and in the end they are either rejected or accepted under concession. Concession means there is a minor issue, but after evaluation it’s agreed the parts can be used for now. Put away mixed together, and outbound may send bad parts to the line.

3. One part spread across several zones means automation can’t get it out. This is the problem from the start. Which zone a part belongs in is set in the system. If someone takes the easy route at inbound and puts it in another zone, the stock still counts on the books. At outbound, automation goes to the part’s assigned zone, and the portion sitting in the other zone can’t be called out: either someone fetches it by hand, or it just sits there.

Our fix was to move the check forward: at goods receipt, the system checks which zone the part should go to, and if it isn’t the current zone, it is rejected at the entrance. Stopping the mistake at the entrance costs far less than finding it at outbound.

3. WMS putaway rules: use all three together, then separate inbound from outbound

For slot assignment we combine three rules, in this order: pick the store, then the area, then the aisle within the area:

• Store by pallet size: large pallet, small pallet, height limit decide which store it can enter
• Area by part type or line section: similar parts stay together
• Spread evenly across aisles within the area: keep the stacker cranes’ workloads about equal, instead of one swamped and one idle

One more that’s easy to overlook: an inbound peak fights outbound for the stacker cranes. When deliveries bunch up, the cranes are all busy putting away, and the line’s material-call outbound tasks have to queue. Our approach was to separate inbound and outbound times so the two don’t collide. Once separated, line outbound tasks no longer wait behind a pile of putaway tasks.

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Parts accepted under concession: do you flag them separately at putaway? And how are they used at outbound?