Spare parts for a factory: critical items and safety stock

A production line stood idle for three days because of one bearing. The part was on the purchasing plan, but nobody noticed that stock had run out, and a replacement from China had to pass through shipping and customs. By the time it arrived, the loss was many times the price of the bearing. A spare parts store is not a raw materials store: usage is low, a stock-out is costly, and the way to manage it is different.

Why spare parts are special

• Low use, high consequence: a part may be used once or twice a year, yet its absence can halt a whole line.
• Long replenishment time: imported parts go through ordering, shipping and customs, which takes weeks or longer.
• Many near-identical items: one series can have a dozen models that look almost the same, so wrong picks are common.
• Scattered storage: parts often sit in the maintenance workshop or a mechanic's cabinet, outside the storekeeper's view.
• Borrowed and not returned: mechanics take parts and tools, put them down after the job, and the books still show them as in stock.

So the aim is twofold: critical parts must never run out, and the records must be believable. The first rests on classification and minimum levels, the second on issue records and regular counts.

Start with criticality

Sit down with the equipment or maintenance manager and answer three questions for each part:

1. If it is missing, will the machine or line stop?
2. How long does replenishment take, and can it be bought locally the same day?
3. Is the unit price high?

Then sort the parts into three classes:

• Critical: a shortage stops the line, or replenishment takes weeks. There must always be stock.
• Important: a shortage slows work, but the part can be obtained within days.
• General: common parts that can be bought locally at any time, such as standard bolts, ordinary bearings and wear items.

Have the maintenance manager sign off the critical list; the store keeps and records, it need not judge importance itself. Do not aim for perfection at first: list the critical parts, even if only twenty or thirty. That already covers the biggest risk.

Setting the minimum level

A simple approach: minimum stock = expected use during the replenishment period + a safety margin.

An invented example: a certain bearing is used 3 times a year, and replenishment takes 8 weeks. Expected use during that time is 3 × 8 ÷ 52, about 0.46 of a piece, less than one. But this is a critical part and a missing one stops the line, so the answer cannot be zero. The rule should be: "always keep at least 2". When one is used and the stock falls to 1, order at once, so that the new one arrives before the last one is used.

For critical parts, err towards holding too much; for general parts follow the formula, or hold none and buy when needed. Review once a year: if the machine runs harder, or has been sold, the minimum should change with it.

Loans, returns and old parts

• Record every issue: who took it, which part, for which machine, and when.
• Return replaced parts to the store, register them and then decide whether to repair, keep or scrap them. Exchanging "old for new" also shows the true consumption and makes it harder for good parts to disappear quietly.
• For borrowed tools and returnable parts, write an expected return date and review the overdue list weekly.
• Mark parts bought for one particular machine with that machine's name on the label. If the machine is disposed of, those parts need a fresh decision from management: reuse, sell or scrap.

Keeping the records matched to the shelf

A spare parts store suits cycle counting. Count critical parts every quarter and the rest every six or twelve months. With few items, the count is quick. Put labels on shelves and bins showing code, Chinese name, model and machine. Someone must also own the room, so it does not become a corner that anybody can enter and nobody looks after.

In short

Records that match the shelf in the spare parts store are part of keeping equipment running. UzWarehouse's counts and warehouse audits can cover a plant's spare parts store: we check issue and loan records, count the stock and trace differences to their source, with practical recommendations to fix them.