Supplier capability assessment: can this plant make your part?

Name the machine the part would run on

Generic capability lists are close to worthless. Ask which specific asset would produce your part, its size and age, what else it runs, whether it is the plant's newest or its oldest, and what the changeover to your job involves. Then look at it. A machine list on a brochure tells you nothing about condition, and condition is what determines whether a tolerance drifts through a shift. Where the answer is that the machine would be purchased if you place the order, you are assessing an intention rather than a capability, and the risk profile changes completely.

Evidence that the process holds, not that a part passed

One good sample proves a plant can make the part once. What matters for series supply is variation over time: does the process sit comfortably inside the tolerance with room to move, or does it pass by measuring at the middle of a distribution that reaches both limits? Ask for capability data on comparable characteristics from parts they already produce, look at how they set control limits, and ask what they do when a trend appears before a part goes out of specification. A plant with no answer to that question is inspecting rather than controlling.

The measurement question decides whether anything else is trustworthy

A supplier cannot demonstrate what it cannot measure. Check that the equipment on site can resolve your tolerances with margin, that it is calibrated to traceable references, that gauges used at the machine are controlled rather than personal property, and that operators measuring parts have been shown how. Where a critical characteristic must be sent out to a laboratory, that is workable but it changes the response time on a problem and it should be known in advance rather than discovered when a shipment is held pending results. Ask to see the calibration record for the specific gauge they intend to use rather than a summary of the system.

Tooling, fixturing and who maintains it

Many part failures trace to tooling rather than to the machine or the operator. Establish what tooling your part requires, who designs and builds it, whether it is made in house or subcontracted, what the maintenance regime is, how wear is monitored, and what spare tooling exists for the elements that break. Ask to see the toolroom. A plant that runs demanding parts on tools it cannot repair itself is dependent on a third party you have not assessed, and that dependency will surface at the worst possible time. A candid answer about tooling lead time also tells you what any future design change will really cost in elapsed weeks.

People, and what happens on the night shift

Capability rests on setters and operators as much as on assets. Ask how many people can set the machine your part would run on, how they are trained and how that training is verified, what the turnover has been, and how the process behaves when the most experienced setter is absent. Visiting during a shift other than the one the sales team scheduled tells you more than the presentation did. Where capability depends on one individual, the plant has a competence risk it may not have recognised, and you have just inherited it.

Frequently asked questions

How is capability assessment different from checking a supplier's certification?

Certification tells you a management system was assessed against a standard by an accredited body. It says nothing about whether a particular machine can hold a particular tolerance on your part. Both matter and neither substitutes for the other: a certified plant can be incapable of your specific requirement, and an uncertified specialist can be entirely capable of it. Assessment is part-specific and technical; certification is system-level and independent of what you happen to be buying.

What evidence should a supplier provide before you commit to tooling?

A stated process route with the machine identified, capability data on comparable characteristics from existing production, the measurement method proposed for your critical features with evidence the equipment resolves them, a tooling plan naming the toolmaker and the maintenance approach, and a view of where they see risk in your drawing. That last item is the most revealing: a supplier that has studied the part will name a feature that worries them, and one that has not will tell you everything is straightforward.

Can a small factory be assessed as capable for a demanding part?

Frequently yes, and small specialists often hold tighter processes than large general plants because the work is concentrated and the people are experienced. What a small firm may lack is depth: one setter who knows the job, one machine that can run it, limited measurement, and no spare capacity when something breaks. Assess capability and resilience separately, then decide whether the depth gap is acceptable or whether it needs mitigating through stock, tooling arrangements or a second source.