A breakdown rarely gives notice. When an axis stops moving or a drive module shuts down, the question is no longer "what failed", but "do we have the part?". And that is where half of the downtime is decided: if the spare is on the shelf, the line can be back in hours; if it has to be ordered, it can be days or weeks. Stocking everything is expensive and unworkable; stocking nothing is a gamble. This guide helps you decide, at plant level and without making up part numbers, which critical robot spares are worth keeping and which are not.
Why your spares stock decides the downtime
The cost of a breakdown is not set by the repair alone, but by the wait for the part. A two-hour job turns into a several-day stoppage when the key part is unavailable and has to be imported or reconditioned. That is why stock is not a warehouse expense: it is a production-continuity decision, tied directly to how much an hour of line downtime costs.
The goal is not to hoard parts, but to cut risk where it hurts most. A good spares plan answers a single question for each component: if this fails tomorrow, how long until we have it and how much does waiting cost us?
How to decide what to keep: criticality × lead time × risk
Rather than a fixed list, score each spare against three simple criteria:
- Criticality: does its failure stop the robot or the whole line, or can the process keep running in a degraded mode?
- Lead time: can you get it in hours, in days, or only to order / by import?
- Obsolescence risk: is it a current, plentiful model, or an older generation that is getting harder to find?
What scores high on all three axes —stops the line, takes time to arrive and is becoming scarce— is a clear candidate for stock. What is cheap, plentiful and quick to deliver almost never pays to store. This is the same reasoning we recommend when planning the life of an older robot, where parts availability weighs as much as mechanical condition.
Critical spares that almost always pay off
Without naming specific part numbers (which depend on each brand and model and must be confirmed against the manufacturer's documentation), these families usually justify keeping a unit available in plants with robots in continuous production:
- Backup / position-keeping batteries: cheap, easy to store and able to leave a robot without referencing if they run flat. It is the textbook example; we cover it in SMB batteries in ABB robots.
- Cabinet fans and filters: low-cost consumables whose failure causes overheating and avoidable thermal stops.
- Connection cables and the dress pack / arm hoses: they suffer fatigue and chafing; breakage is common and replacement is urgent.
- Axis drive / power modules (for example, the KPP/KSP-type assemblies on KUKA): expensive, but their failure stops the robot and lead time can be long. An exchange unit cuts downtime dramatically.
- Teach pendants and their spares: essential to operate and diagnose; without one, the robot is effectively "blind".
- Encoders, brakes and gearboxes for the busiest axes on critical or older-generation robots, where supply is starting to get uncertain.
The exact list changes depending on whether you run ABB robots, KUKA or FANUC and on the models in your fleet. What matters is the criterion, not copying another plant's shelf.
Spares you normally should NOT stock
Hoarding out of fear has a cost too: tied-up capital, space and parts that age unused. As a general rule, avoid stocking:
- Quick-delivery, low-impact components: if it arrives in 24-48 h and the line can tolerate it, order it when you need it.
- Very specific, expensive electronics with low failure probability, unless the lead time is unacceptable; an exchange agreement is usually better there.
- Age-sensitive parts (some seals, certain electrolytics) that degrade in storage as much as in service.
How to manage stock so it does not "expire"
Having the part is useless if it is expired or can't be found. A useful spares stock is a living one:
- Identify and label each spare with its robot model and the purchase date.
- Rotate the perishables: batteries and consumables have a shelf life; use them before they lose capacity and replenish.
- Store electronics properly: in a dry place, free of moisture and dust, with antistatic protection where applicable.
- Tie the stock to the robot documentation: backup, calibration data and serial numbers on hand speed up any replacement.
Exchange and independent service: an alternative to tied-up capital
Not all risk needs to be covered by buying parts you may never use. For expensive, long-lead components, a spare parts and exchange agreement lets you get the unit when you need it —often reconditioned and under warranty— without tying up capital for years. The choice between new, reconditioned and exchange is analysed in original vs. reconditioned parts.
The combination that works best in most plants is simple: your own stock of the cheap, perishable and critical items, and a supply/exchange agreement for the expensive, bulky or uncertain-lead ones. That cuts downtime without turning the store into a graveyard of parts.
Frequently asked questions
How many critical spare parts should I keep in stock?
There is no fixed number: it depends on the number of robots, how critical the line is and each part's lead time. Prioritise what is both hard to get quickly and able to stop production; for the rest, a supply or exchange agreement usually wins.
Do batteries and other spares expire in storage?
Some do. Batteries lose capacity over the years even unused, and some electronics or seals degrade. Rotate the stock, record the purchase date and periodically review what's stored.
Is it worth stocking a drive module or a gearbox?
It depends on the risk. If it stops the line and its lead time is long or the model is obsolete, having a unit available (your own or by exchange) saves days of downtime. If it is easy to source and the line can wait a few hours, tying up that capital usually is not worth it.