Line-side material supply: feeding the station without burying it in stock

Presentation is part of the work design, not an afterthought

How parts face the operator determines reach, grip, orientation and whether the wrong variant can be picked at all. Bins angled toward the worker, parts oriented as they will be fitted, similar-looking variants physically separated, and a fixed address for every item are the fundamentals. Where two visually near-identical parts sit side by side, mis-picks are a matter of time regardless of operator care. Engineering owns this because it is a station design question, but the operators who work there every day will tell you within an hour which bins are wrong if anyone asks them.

The signal that says more is needed

Something has to tell the replenisher that stock is running down, and the mechanism must not depend on an operator remembering to ask. Common approaches are a two-container arrangement where the empty one is the signal, a marked reorder line inside the bin, a call button, or a fixed-clock delivery sized to consumption. The pull disciplines behind these belong to lean practice; the operational question here is response time. A signal that takes longer to answer than the remaining stock will last is not a signal, it is a warning that the line is about to stop.

Floor space at the station is finite and permanently contested

Every additional part presented at a station consumes reach envelope, walking room and sightlines. High-variety assembly hits this wall fastest: the station physically cannot hold every variant of every component. The choices are then real — kit the variable parts and present only common items at line side, sequence deliveries so only the parts for the next few units are there, or split the operation across more stations. Deciding by default means the biggest boxes win the space, which is precisely the wrong criterion, since bulky low-value items are the easiest to deliver more often.

Stockouts, substitutions and the operator workaround

A station stockout rarely stops the line cleanly. More often somebody fetches parts from another station, opens a container reserved for a different order, or fits a similar part that has not been approved for that build. All three cause a second problem later, and none of them appears in the stoppage record. Make the shortage visible instead: a defined call, a recorded event, and an explicit rule that no unapproved substitution happens without the supervisor and quality agreeing it. The pattern of recorded shortages then points at the handful of parts whose supply loop is genuinely broken.

Drawing the line between production and internal logistics

Somebody must own the last leg. When operators fetch their own material, cycle time inflates invisibly, the line loses balance and nobody can say how much labour goes on walking. When a dedicated route runner owns it, the station keeps working and the replenishment workload becomes measurable — but that role has to be resourced and covered on every shift, including breaks. The failure mode is a runner who is also the relief operator, the forklift driver and the first person pulled during a crisis, at which point line-side supply silently reverts to the operators.

Frequently asked questions

How much stock should sit at a workstation?

Enough to cover consumption across the replenishment interval plus a margin for a missed delivery, and no more than the station can present safely. Work it out from actual consumption rate and the route cycle rather than from container size. Shorter, more frequent deliveries let stations hold far less, which is why route reliability and line-side quantity are the same problem. If the calculated quantity will not fit, the answer is more frequent delivery, not a bigger bin.

Should line-side stock be counted as inventory?

It is inventory, though many plants relieve it from the system at issue to the line and treat consumption as backflushed against production. That is workable provided periodic physical checks reconcile what is actually on the floor. Where line-side holdings are large or valuable, the untracked quantity distorts stock accuracy and hides shortages until the line stops. Deciding the accounting point matters less than checking, on a set rhythm, that the record and the floor agree.

What is the fastest way to cut mis-picks at an assembly station?

Separate the confusable items physically and visually before doing anything else — different bin locations, different container colours, an unambiguous label facing the operator. Then remove the choice where you can: sequence the variable part to the station in build order so only one option is present. Poka-yoke devices and pick-to-light help, but a station holding several near-identical variants within arm's reach will keep generating errors no matter how careful the person is.