Process Capability: the compass of quality in modern manufacturing

maggio 14, 2025

Do you know how much you can trust your production process before you even turn on the machines? Process Capability is the compass of quality in modern manufacturing, especially in the gear industry where precision and reliability are not optional.

What is Process Capability

Process Capability is a statistical measurement that evaluates how much a process is able to produce parts within pre-established tolerance limits. In practice, it tells you whether your process is capable of maintaining the required quality in a repeatable way.

A "capable" process does not make mistakes: it produces components within specifications, every time. Just like a sniper who always hits the target in the same place.

Why the concept of Process Capability was developed

Process Capability was born from the need to guarantee production consistency. It is no longer enough to make a compliant part: you must ensure that every single part, even the 100,000th, respects the specifications. This is why you need a predictive tool that allows you to anticipate problems, not just correct them.

What is it for in practice

Process Capability is essential for:

assessing process stability;
reducing waste, rework and complaints;
selecting truly reliable suppliers;
certifying compliance in the automotive, aerospace and medical sectors.

The two key indices: Cp and Cpk

Process Capability is measured with two indices: Cp and Cpk.

Cp compares the width of the process with the tolerance: it is a signal of precision, but not of centering.
Cpk evaluates how much the process is centered with respect to the target: even if the machine is precise, if it is not well adjusted the Cpk will be low.

Practical example on a gear

Imagine having to produce a gear Ø 50.00 mm ±0.02 mm. Acceptable pieces measure between 49.98 mm and 50.02 mm.

If the standard deviation is 0.005 mm, you get a high Cp: excellent!
But if the average is 49.96 mm, you are off center: low Cpk → parts out of tolerance.

Result? Complaints, rework, extra costs.

Why Process Capability is essential in gears

In the world of gears even a tenth of a millimeter can:

generate metallic noises;
cause premature wear;
compromise the functioning of the system.

Process Capability is not an option. It is a condition of access to work with OEMs, Tier1 and in high responsibility sectors.

In your work they ask you not only for quality, but continuity. Process Capability is the system that allows you to promise reliability, not just compliance. It is your tool to stay on course towards industrial quality.

Do you want to know more about how to control and improve the capability of your processes? Contact GSI Ingranaggi.

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