Changing a BOM line after release is easy. Knowing where the parts are is the hard part

A production order has been released. Then the BOM changes: one part less on this unit, two more on that one.

Changing a line in the system takes a minute. The hard part comes before that: finding out where those parts are right now. Still on the rack, in a picker’s hands, or already at the line.

This post covers the three things that go wrong most often in line-side logistics: calling parts, adding or removing parts after release, and returned parts.

1. First, picking and calling are two steps

Logistics on the production side is usually run by an LES. An LES is a logistics execution system; it manages the stretch from the warehouse to the line.

It splits delivery into two steps:

• Picking: the warehouse creates outbound tasks per production order, picks and sorts the parts, and leaves them in a staging area off the line.
• Calling: only when the line starts work does it call the parts, and they move from staging up to the line.

The staging area works as a buffer between the warehouse and the line. Parts wait there, so they can go up as soon as the line starts, without waiting for the warehouse to pick.

Why not deliver all the way in one go? Line-side space is small, and the plan changes often. Parts staged too early take up the line, and when the plan changes they all have to go back.

So one part on the production side can be sitting in several places: on the rack, in a picker’s hands, in staging, on the delivery vehicle, at the line. When the BOM changes, the first thing to answer is where it is.

2. Adding and removing parts: one change, three states, three ways to handle it

After the BOM of a production order has been released, adding a part at short notice is an add; taking one out is a removal. The change itself is not hard. The timing is: the order is already out, and logistics is already moving on the old BOM.

Before changing anything, each case starts with the same question: how far has this part moved?

① Nothing has started, in the system or physically. The simplest case: change it, let the system recalculate demand, and carry on with the new numbers.

② The task is issued in the system, but the parts have not moved. Here you change the task: for a removal, cancel that outbound task line; for an add, insert one. But before cancelling, go to the floor and confirm the picker really has not picked it yet.

③ The task is issued and the parts are already at the line. For a removal, the extra parts go back to the warehouse. For an add, you raise an urgent delivery. This is where an add is most urgent: the line is waiting to install, the delivery has to jump the queue, and the warehouse needs someone ready to take this kind of order at any time.

Where to look also differs by state:

• To tell whether it is state ① or ②: check the status of the outbound task, then look at the picker’s pick list or handheld to confirm whether that line has been picked
• To tell whether it is state ③: check whether the delivery note has been signed for, and whether the line has a receipt record
• After checking the system, go and look at the box on the floor

Why does this step need a person? Because the system knows tasks, not boxes. A picker may be halfway through while the system still shows “not started”. Whether the pallet on the vehicle has reached the line, the system may not know either. State ② is the most dangerous one: the system says nothing has moved, and on the floor it may already have.

What happens when you get it wrong once? You treat “already picked” as “not moved” and cancel the task, and the parts go up to the line anyway. That box is not on any document. It is extra at the line, nobody claims it, and the month-end count does not reconcile. Some of the gap between book stock and physical stock that I wrote about in my first post comes from exactly this.

3. Returned parts: once back in the warehouse, they must be used first

Returned parts are parts that were delivered to the line, not installed for one reason or another, and sent back to the warehouse. The removals in state ③ above are the most common kind.

There is only one rule: on the next pick, use returned parts first.

For that to work, the system has to recognize them: flag them separately when they come back, and rank them ahead of new stock when allocating the next pick. Without that flag, they get mixed in with new stock, or left in a corner of the warehouse, never allocated, and slowly turn into dead stock. The more returned parts pile up, the more the warehouse carries a block of inventory nobody can account for.

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When returned parts come back to the warehouse, do you re-inspect them before issuing them again? Who makes that call?