Points beyond the control limits catch big changes; run rules catch the small shifts, trends and mixtures that
cause most drift into nonconformity. scripts/we_rules.py applies the Western Electric (and optionally Nelson)
rules, merges overlapping hits so a single shift reports once, and gives the usual cause of each pattern.
Trigger Conditions
Activate this skill when the user:
- Has control chart data and wants to know whether the process is in control
- Sees a pattern (run, trend, saw-tooth, hugging) and asks what it means
- Asks which run rules to use, or why the chart signals so often
- Needs to document special-cause signals for a Phase I study or audit
Limits for the chart: manufacturing-spc-chart-builder.
Workflow
1. LIMITS -> centre and sigma of the plotted statistic from a stable baseline (or the chart's UCL/LCL)
2. CHECK -> python scripts/we_rules.py chart.csv --value xbar --ucl 12.0121 --lcl 12.0063 [--nelson]
3. ORDER -> investigate signals in time order; the first point of a run is where something changed
4. CAUSE -> what changed then (lot, tool, operator, setting, maintenance)? patterns-and-causes.md
5. RESPOND -> contain if needed, fix the cause, annotate the chart; no limit recalculation to hide signalsRules
| Code | Rule | Pattern |
|---|---|---|
| WE1 | 1 point beyond 3 sigma | Sudden special cause |
| WE2 | 2 of 3 beyond 2 sigma, same side | Shift starting |
| WE3 | 4 of 5 beyond 1 sigma, same side | Small shift |
| WE4 / N2 | 8 (Nelson: 9) in a row on one side | Sustained shift |
| N3 | 6 in a row increasing or decreasing | Trend (wear, heating) |
| N4 | 14 alternating | Tampering, two streams |
| N7 | 15 within 1 sigma | Stratification |
| N8 | 8 beyond 1 sigma on both sides | Mixture |
WE3 at 19 (points 15-24): a small sustained shift: tool wear, temperature, gradual change
N2 at 23 (points 15-24): a sustained shift in the mean
N3 at 45 (points 40-47): a trend: tool wear, heating, chemical depletionZones, Nelson numbering, false-alarm rates and ARL, rule choice for Phase I/II, R and attribute charts, autocorrelation: rules-and-false-alarms.md. Pattern-to-cause table and how to respond: patterns-and-causes.md.
Output Format
Deliver:
- Basis - centre and sigma used and where they came from; rule set.
- Signals - rule, span of points, likely cause, in time order.
- Verdict - in control or not; which signals need investigation first.
- Actions - containment (if parts may be bad), cause investigation, chart annotation.
Scripts
python scripts/we_rules.py xbar.csv --value xbar --center 12.0092 --sigma 0.00097
python scripts/we_rules.py xbar.csv --value xbar --ucl 12.0121 --lcl 12.0063 --nelson
python scripts/we_rules.py data.csv --value x --baseline 25 --label sampleExit codes: 0 no signals, 1 signals found, 2 usage or data error (fewer than 8 points, sigma <= 0).
Additional Resources
| File | Content |
|---|---|
| rules-and-false-alarms.md | Zones, WE and Nelson rules, false-alarm rates, rule choice, prerequisites |
| patterns-and-causes.md | Patterns with typical manufacturing causes, first checks, responding without tampering |
8d-problem-solving-report-writer
Write and review 8D problem-solving reports for customer complaints and serious nonconformities (automotive and aerospace practice: Ford Global 8D, VDA, GM, Stellantis formats): D0 emergency response, D1 cross-functional team and champion, D2 problem description with 5W2H and is / is-not and no cause in the statement, D3 interim containment within 24 hours with verification and clean point, D4 verified occurrence and escape (non-detection) root causes plus systemic cause, D5 permanent corrective actions for each cause verified before implementation, D6 implementation, validation with production data and removal of containment, D7 PFMEA, control plan and read-across to similar products, D8 closure and recognition. Checks an 8D discipline by discipline for missing content, human-error root causes, missing escape cause or action, late containment and dates out of order.
acceptance-sampling-plan-selector
Select and evaluate acceptance sampling plans for incoming, in-process and final inspection: ANSI/ASQ Z1.4 / ISO 2859-1 single sampling under normal inspection (code letter from lot size and inspection level I, II, III, S-1 to S-4; sample size, Ac and Re from AQL, following the table's arrows to the correct plan; 100% when n reaches the lot size; AQLs above 10 per 100 units), operating characteristic curves (Pa at any quality, producer's quality level, indifference point, LTPD, AOQ and AOQL, binomial or hypergeometric), plans designed from producer and consumer risk, and c = 0 zero-acceptance plans. Covers AQL choice by defect class, switching rules between normal, tightened and reduced inspection, when sampling is not appropriate, and random sampling.
approved-supplier-list-manager
Manage and audit an approved supplier list (ASL) / external provider register for ISO 9001 8.4.1, IATF 16949 8.4 and AS9100 8.4.1: supplier status (approved, conditional, probation, pending, disqualified), scope of approval by commodity and process, risk class, certification and expiry, re-evaluation intervals by risk, conditions with end dates, single-source contingency, approver and customer-directed sources. Audits the list for expired or expiring certificates, overdue re-evaluations, conditional or probation status past its decision date, high-risk suppliers without the required certification, single-source suppliers without backup and missing approvers, and checks purchase orders for suppliers that are off-list, disqualified or pending, or buying outside the approved scope. Covers ERP blocks, PO requirements, off-list and emergency purchases.
apqp-phase-planner
Plan and track Advanced Product Quality Planning (AIAG APQP 3rd edition, IATF 16949) for a new or changed automotive part: back-schedule the five phases (plan and define, product design, process design, product and process validation, launch and feedback) from the start-of-production date by program complexity, with overlap, PPAP lead and safe-launch period; list the deliverables and gate for each phase (DFMEA, DVP&R, feasibility, process flow, PFMEA, control plans, MSA, Ppk, run at rate, PPAP, safe launch, lessons learned); adjust for build-to-print suppliers; flag compressed timelines and late or untracked deliverables against a status list. Covers gate reviews, red/yellow/green status reporting, run at rate and safe-launch exit criteria.
as9100-gap-analyzer
Run an AS9100D / EN 9100:2018 gap analysis for aviation, space and defence suppliers on the requirements added to ISO 9001: on-time delivery and conformity focus, management representative, ethics and human-factors awareness, operational planning and operational risk management, configuration management, product safety, counterfeit-part prevention, special requirements, critical items and key characteristics, external provider register and flow-down, FOD prevention, tooling and NC program control, special process validation, first article inspection (AS9102), traceability, in-service data and nonconforming product control. Generates and scores a worksheet, grades missing core controls as major, and checks invalid n/a claims. Covers AS9101/AS9104, OASIS, AS9102 FAI forms, counterfeit standards (AS5553, AS6174, AS6081), NADCAP and the planned IA9100 transition.
audit-report-writer
Write internal, supplier and pre-certification audit reports with the content ISO 19011:2018 6.5 expects: audit objectives, scope, criteria with revisions, dates, team and auditees, method and sampling statement, specific strengths, findings table and three-part finding details (requirement, evidence, statement), conclusion on the degree of fulfilment of criteria, diverging opinions, follow-up deadlines and distribution. Builds a Markdown report from a JSON audit record, generates the conclusion from the findings (major / minor / none) and flags reports missing required content or findings without clause or evidence. Covers conclusion wording, closing meetings, response expectations and verifying corrective actions.