SPC software

SPC Software for Process Control and Capability

Every part inside tolerance is not the same as a process in control. Control charts show you the difference, and they show it while there is still time to act.

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A control chart screen for bore diameter at operation 20, with an X-bar R chart showing one point beyond the upper control limit, and Cp, Cpk, Pp and Ppk values.

The problem

Tolerance tells you about parts. Control tells you about the process.

A process can produce a hundred conforming parts in a row while walking steadily toward a limit. Judged part by part, everything passes. Judged as a process, it has been sending a signal for two hours. Control limits are calculated from the process’s own variation, which is why they catch things a tolerance check cannot.

The other half of the problem is data entry. If chart data is typed in separately from inspection, charting becomes a task somebody does on Fridays. Drawing charts from the inspection results already recorded is what makes monitoring continuous rather than retrospective.

X̄–R charts

Subgroup means and ranges with control limits calculated from the data using the standard constants.

Nelson rules

Out-of-control signals detected by rule, not by eye — including runs and trends a person would miss.

Capability indices

Cp, Cpk, Pp and Ppk, with the distinction between short-term and long-term kept intact.

Fed from inspection

Charts are built from recorded inspection results rather than a separate data-entry step.

Traceable signals

A signal points back at the characteristic, the operation and the control that should have caught it.

Studies as records

A capability study is a record you can reference from a submission, not a screenshot.

Where it sits

SPC is where the loop closes.

A signal on a chart sends you back up the chain — to the control that missed it, the PFMEA row that specified that control, and the operation where it happens. That path is what makes monitoring actionable.

X̄–R charts with calculated control limits
Nelson rules for out-of-control detection
Cp, Cpk, Pp and Ppk
Charts built from recorded inspection results
Signals traceable to characteristic, operation and control
Capability studies referenced by PPAP submissions

Connected capabilities

Every one of these works on the same record. That is the point of the platform.

Inspection software

Results against specification, with the gauge that took them.

Control plan software

What is measured, how, how often, and what happens on failure.

CAPA software

Corrective and preventive action, verified before closure.

FAQ

Questions about SPC software

What is SPC?

Statistical Process Control uses the statistics of a process’s own output to tell whether it is behaving consistently. Control limits are calculated from the observed variation, not from the drawing tolerance, so a chart can show a process going out of control while every part it makes is still within specification.

What is the difference between Cp and Cpk?

Cp compares the spread of the process to the width of the tolerance — how tight the process is. Cpk also accounts for where the process is centred, so a tight process aimed off-target has a good Cp and a poor Cpk. Both are reported, because the gap between them is the useful information.

What is the difference between Cp/Cpk and Pp/Ppk?

Cp and Cpk are calculated from within-subgroup variation and describe short-term capability — what the process can do when it is behaving. Pp and Ppk use total variation across the whole study and describe actual long-term performance. A large gap between the pairs usually means the process is shifting between subgroups.

Does the software include predictive analytics?

No. It computes the standard control chart and capability statistics from your recorded data and applies the Nelson rules. Predictive quality analytics is on the roadmap and labelled as such — it is not in the product today.

Do we have to enter data twice for inspection and SPC?

No. Charts draw on the inspection results already recorded against the characteristic.

Get started

See variation while you can still do something about it.

Bring APQP, FMEA, PPAP, process flow, control plans, inspection and SPC into one connected platform.

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Questions? support@easyqualityflow.com