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📚 Quality Quick Reference
Control chart constants · AQL sampling · Sigma conversion · 8D · MSA · standard clauses — look it up in seconds
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📊 SPC
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Control Chart Constants (X̄-R chart)
| Subgroup n | A2 | D3 | D4 | E2 | d2 |
|---|---|---|---|---|---|
| 2 | 1.880 | 0 | 3.267 | 2.660 | 1.128 |
| 3 | 1.023 | 0 | 2.574 | 1.772 | 1.693 |
| 4 | 0.729 | 0 | 2.282 | 1.457 | 2.059 |
| 5 | 0.577 | 0 | 2.114 | 1.290 | 2.326 |
| 6 | 0.483 | 0 | 2.004 | 1.184 | 2.534 |
| 7 | 0.419 | 0.076 | 1.924 | 1.109 | 2.704 |
| 8 | 0.373 | 0.136 | 1.864 | 1.054 | 2.847 |
| 9 | 0.337 | 0.184 | 1.816 | 1.010 | 2.970 |
| 10 | 0.308 | 0.223 | 1.777 | 0.975 | 3.078 |
Useful for: Control Chart SPC Generator →
Eight SPC Out-of-Control Rules
1
Point beyond control limit
1 point outside ±3σ (control limit) — special-cause variation, highest priority.
2
9 points on one side
9 consecutive points all on the same side of the center line — process mean may have shifted.
3
6 points trending
6 consecutive points steadily increasing or decreasing — monotonic drift (tool wear, gradual temperature change).
4
14 points alternating
14 consecutive points alternating up and down — two alternating machines/people, or periodic sampling.
5
2 of 3 points beyond 2σ
2 of 3 consecutive points beyond ±2σ on the same side — early signal of a mean shift.
6
4 of 5 points beyond 1σ
4 of 5 consecutive points beyond ±1σ on the same side — distribution off-center.
7
15 points within 1σ
15 consecutive points within ±1σ of the center line on both sides — control limits miscalculated, stratification, or suspected data smoothing/fabrication.
8
8 points outside 1σ
8 consecutive points beyond ±1σ on either side — two different populations (bimodal / mixed distribution).
Useful for: Control Chart SPC Generator →
Control Chart Selection Guide
| Data Type | Suitable Chart | Selection Notes |
|---|---|---|
| Variables | X̄-R chart | Subgroup n=2~9; range monitors within-group dispersion; most common |
| X̄-s chart | Subgroup n≥10 (or use standard deviation for more stability) | |
| I-MR chart | Single parts / slow rate / destructive testing, n=1 | |
| Attributes | p chart | Fraction nonconforming, variable subgroup size |
| np chart | Number nonconforming, fixed subgroup size | |
| c chart | Number of defects, fixed sample area (e.g. per square meter / per lot) | |
| u chart | Defects per unit, variable sample area |
Rule of thumb: for variables data prefer X̄-R (economical, sensitive); for attributes choose among the four by "nonconforming vs defects, fixed vs variable subgroup".
Useful for: Control Chart SPC Generator → Advanced SPC →
Process Capability Grades (Cpk)
| Cpk Range | Grade | Judgment & Action |
|---|---|---|
| < 1.0 | Inadequate | High defect rate, process cannot meet spec; improve as a priority |
| 1.0 – 1.33 | Marginal | Some customers (especially automotive) won't accept; monitor and improve |
| 1.33 – 1.67 | Capable | Lowest acceptable threshold in most industries; maintain and monitor |
| 1.67 – 2.0 | Good | Ample process; maintain as is |
| ≥ 2.0 | Excellent | Near six-sigma level; benchmark and sustain |
Useful for: Normal CpK Calculator →
AQL Inspection Levels
| Level | Description | Applicable |
|---|---|---|
| General I | Small sample | Low inspection cost, high risk tolerance |
| General II | Medium sample (default) | Routine sampling, most common |
| General III | Large sample | Quality-sensitive, risk-averse |
| Special S-1 to S-4 | Very small sample | Destructive / expensive / small lots |
Switching rules: 2 of 5 consecutive lots rejected → switch to tightened; stable production with low historical defects → switch to reduced.
Sample Size Code Letters (lot size × level → letter)
| Lot Size | S-1 | S-2 | S-3 | S-4 | I | II | III |
|---|---|---|---|---|---|---|---|
| 2–8 | A | A | A | A | A | A | B |
| 9–15 | A | A | A | A | A | B | C |
| 16–25 | A | A | B | B | B | C | D |
| 26–50 | A | B | B | C | C | D | E |
| 51–90 | B | B | C | C | C | E | F |
| 91–150 | B | B | C | D | D | F | G |
| 151–280 | B | C | D | E | E | G | H |
| 281–500 | B | C | D | E | F | H | J |
| 501–1200 | C | C | E | F | G | J | K |
| 1201–3200 | C | D | E | G | H | K | L |
| 3201–10000 | C | D | F | G | J | L | M |
| 10001–35000 | C | D | F | H | K | M | N |
| 35000+ | D | E | G | H | L | N | P |
Common Sampling Plans (Normal Inspection)
| AQL | Code | Sample n | Ac | Re |
|---|---|---|---|---|
| 4.0 | H | 50 | 5 | 6 |
| 2.5 | J | 80 | 5 | 6 |
| 1.5 | K | 125 | 5 | 6 |
| 1.0 | J | 80 | 2 | 3 |
| 1.0 | L | 200 | 5 | 6 |
| 0.65 | K | 125 | 2 | 3 |
| 0.65 | L | 200 | 3 | 4 |
Ac = acceptance number, Re = rejection number; defects ≤ Ac accept, ≥ Re reject. Use the main sampling table for exact Ac/Re; use AI lookup or the sampling assistant for complex needs.
Useful for: Sampling Assistant →
Sigma Level ⇄ DPMO ⇄ Cpk
| Sigma level* | DPMO | Approx. Cpk |
|---|---|---|
| 1σ | 691,462 | 0.33 |
| 2σ | 308,537 | 0.67 |
| 3σ | 66,807 | 1.00 |
| 4σ | 6,210 | 1.33 |
| 5σ | 233 | 1.67 |
| 6σ | 3.4 | 2.00 |
* Sigma level includes the 1.5σ process shift (six-sigma convention); approx. Cpk = sigma level ÷ 3.
Useful for: DPMO / Sigma Converter → Normal CpK Calculator →
Cp / Cpk / Pp / Ppk Formula Quick Ref
| Index | Formula | Notes |
|---|---|---|
| Cp | (USL−LSL) / 6σwithin | Spread only, ignores centering |
| Cpk | min[(USL−x̄), (x̄−LSL)] / 3σwithin | Short-term capability after centering offset |
| Pp | (USL−LSL) / 6σoverall | Long-term performance, overall standard deviation |
| Ppk | min[(USL−x̄), (x̄−LSL)] / 3σoverall | Long-term performance, all variation sources |
| σ estimate (R method) | σ = R̄ / d₂ | For X̄-R; look up d₂ in constants table |
| σ estimate (s method) | σ = s̄ / c₄ | For X̄-s; look up c₄ in constants table |
Memory hook: Cp/Pp only ask "how spread"; Cpk/Ppk also ask "is it centered". Cpk ≤ Cp always.
Useful for: Normal CpK Calculator →
MSA / GR&R Criteria (AIAG)
| %GR&R | Decision | Action |
|---|---|---|
| < 10% | Excellent | Acceptable, safe to use for analysis |
| 10%–30% | Marginal | Depends on application importance, gage cost, repair cost; usually usable |
| > 30% | Unacceptable | Must improve the gage or measurement system |
Also check NDC (number of distinct categories) ≥ 5; %Study Var and %Tolerance are also commonly used.
Useful for: Quick Quality Calc →
ISO 9001:2015 Clause Structure
4
Context of the organization
Understand the organization and its context, interested-party needs; determine the QMS scope.
5
Leadership
Top-management commitment, quality policy, roles, responsibilities and authority.
6
Planning
Address risks and opportunities; quality objectives and planning to achieve them.
7
Support
Resources, competence, awareness, communication, documented information.
8
Operation
8.3 design & development · 8.5 production provision · 8.6 release · 8.7 control of nonconforming output.
9
Performance evaluation
9.1 monitoring & measurement (incl. SPC) · 9.2 internal audit · 9.3 management review.
10
Improvement
10.2 nonconformity and corrective action (CAPA) · 10.3 continual improvement.
IATF 16949:2016 (Automotive Supplement)
8.3
Manufacturing process design input
Must consider design output, capacity, cost, special characteristics, FMEA, etc.
8.5.6
Management of temporary changes
Alternative processes/equipment require a list, approval, verification, and control to return to the original process.
9.1.1
Manufacturing process monitoring
Apply SPC etc. to special characteristics per the control plan and keep it effective.
8.4
External provider / sub-supplier control
Supplier selection, evaluation and development; extend to on-site audits of lower-tier suppliers as needed.
Common Related Standards
ISO 14001 environmental management · ISO 45001 occupational health & safety · ISO 17025 testing & calibration laboratories · ISO 13485 medical devices · ISO 27001 information security · ISO 50001 energy management. Note: IATF 16949 only certifies an automotive QMS built on ISO 9001 and cannot replace ISO 9001 on its own.
8D Process Quick Ref (D0–D8)
D0
Preparation & Emergency Response (ERA)
Confirm the problem is real; contain immediately to protect the customer. Common mistake: starting a D without confirmation. Output: initial problem judgment + emergency actions.
D1
Build the team
Cross-functional group (engineering/quality/production/logistics/procurement); name a leader. Common mistake: quality alone. Output: members and roles.
D2
Describe the problem
Quantify with 5W2H (who/what/when/where/why/how/how many) plus data, photos and batches. Common mistake: vague "maybe/about". Output: problem definition.
D3
Interim Containment Action (ICA)
Contain WIP and shipped product; verify it works and introduces no new risk. Common mistake: contain without verification. Output: ICA and verification records.
D4
Root cause analysis
Use 5Why/fishbone to distinguish root cause from escape cause; verify with data and tests. Common mistake: guessing from experience. Output: verified root cause.
D5
Choose permanent actions
Select PCA against the verified root cause; assess feasibility/cost/side effects and compare options. Common mistake: actions not targeting the root cause. Output: PCA plan.
D6
Implement & validate
Deploy the PCA; track that the problem is fully solved with no new defects. Common mistake: closing without long-term verification. Output: effectiveness evidence.
D7
Prevent recurrence
Update FMEA, control plan, work instructions, inspection specs and training; deploy horizontally. Common mistake: fixing only this case without horizontal rollout. Output: system update list.
D8
Recognize & close
Recognize the team, standardize results, archive for traceability. Common mistake: skipping recognition hurts future engagement. Output: closure report.
Useful for: 8D Report Generator → Fishbone Diagram Generator →
Seven Wastes (TIMWOOD)
| # | Waste | Typical Scenario |
|---|---|---|
| 1 | Transport | Material detours, multiple transfers, forklift running back and forth |
| 2 | Inventory | WIP buildup, dead stock, excessive safety stock |
| 3 | Motion | Bending to pick material, walking around, can't find tools |
| 4 | Waiting | Waiting for people/material/equipment/information; downtime waiting for material |
| 5 | Over-processing | Extra operations, over-inspection, beyond-spec machining |
| 6 | Over-production | Producing early or over quantity, masking other wastes |
| 7 | Defects | Rework/repair, scrap, complaint handling |
Mnemonic: Transport, Inventory, Motion, Waiting, Over-processing, Over-production, Defects (TIMWOOD).
Useful for: Value Stream Mapping (VSM) →
OEE Overall Equipment Effectiveness
| Metric | Formula | Notes |
|---|---|---|
| Availability A | Run time / planned time | Deduct downtime, changeover, breakdown |
| Performance P | Actual output × cycle time / run time | Deduct speed loss, micro-stops |
| Quality Q | Good parts / total output | Deduct defects, rework |
| OEE | A × P × Q | World-class ≈ 85% (A=90% × P=95% × Q=99%) |
OEE below 60% is common; first tackle the largest loss item (downtime / slow speed / defects) one by one.
Useful for: TPM Equipment Management →
SMED Four Quick-Change Steps
1
Separate internal/external setup
Internal (only with machine stopped: die removal/installation) vs external (done in advance: find die, preheat, prep materials).
2
Convert internal to external
Move internal steps external where possible: preheat, pre-assemble, pre-adjust, tool positioning.
3
Parallelize & simplify
Two people working at once, fewer bolts, quick clamps instead of screws, eliminate adjustment (shims/locating pins).
4
Standardize & rehearse
Write the best method into work instructions, rehearse until solid, and advance toward "single-touch changeover".
Useful for: SMED / Line Balance / TOC →
Takt Time & Line Balancing
T
Takt = available time / customer demand
Example: shift 8h = 28,800s, demand 1,200 pcs → takt = 24s/pc; the line must output one every 24 seconds to stay on pace.
B
Line balance efficiency = sum of station times / (bottleneck time × number of stations)
Target ≥ 85%; the bottleneck sets whole-line output, so improvement targets the bottleneck first.
Useful for: SMED / Line Balance / TOC →
5S Shop-Floor Steps
1S
Sort (Seiri)
Separate needed from unneeded; remove the unneeded (red-tag campaign).
2S
Set in order (Seiton)
Fixed location, container, quantity and labels; 30-second retrieval.
3S
Shine (Seiso)
Cleaning is inspection; find oil leaks, looseness and abnormalities while cleaning.
4S
Standardize (Seiketsu)
Standardize and visualize 1-3S into rules.
5S
Sustain (Shitsuke)
Build the habit of following standards; everyone continuously improves.
Useful for: 5S Shop-Floor Management →
Quality Abbreviation Glossary
| Abbr. | English Name | Meaning |
|---|---|---|
| SPC | Statistical Process Control | Monitor processes with control charts |
| MSA | Measurement Systems Analysis | Evaluate measurement error |
| Gage R&R | Gage Repeatability & Reproducibility | Gage variation study |
| Cpk/Ppk | Process Capability / Performance index | Short-term vs long-term capability |
| FMEA | Failure Mode & Effects Analysis | Proactive risk prevention |
| APQP | Advanced Product Quality Planning | Structured product planning |
| PPAP | Production Part Approval Process | Customer part approval |
| CP | Control Plan | Process control document |
| DOE | Design of Experiments | Factor screening & optimization |
| OEE | Overall Equipment Effectiveness | A × P × Q |
| AQL | Acceptable Quality Limit | Sampling acceptance threshold |
| DPMO | Defects Per Million Opportunities | Yield in PPM |
| SCAR | Supplier Corrective Action Request | Supplier 8D demand |
| CAPA | Corrective And Preventive Action | Root-cause action loop |
| NCR | Non-Conformance Report | Defect / deviation record |
| FIFO | First In First Out | Material rotation rule |
| PDCA | Plan-Do-Check-Act | Continuous improvement loop |
| Poka-Yoke | Mistake-Proofing | Error-proof devices |
| CTQ | Critical-To-Quality | Key customer attribute |
| SIPOC | Supplier-Input-Process-Output-Customer | Process map overview |
| 5S/6S | Workplace organization | Sort·Set·Shine·Standardize·Sustain (+Safety) |
| 6σ | Six Sigma | 3.4 defects per million |
| VOC | Voice of Customer | Customer requirements |
| VSM | Value Stream Mapping | Material & information flow map |
| SMED | Single-Minute Exchange of Die | Rapid changeover |
| TPM | Total Productive Maintenance | Operator + maintenance ownership |
| KPI | Key Performance Indicator | Performance metric |
| SOP | Standard Operating Procedure | Standardized work |
| WI | Work Instruction | Step-by-step job instruction |
| NDC | Number of Distinct Categories | Gage resolution (≥5) |
| EV/AV/PV | Equipment / Appraiser / Part Variation | GR&R components |
| OBA | Open Box Audit | Outgoing sampling audit |
| FTA | Fault Tree Analysis | Top-down failure logic tree |
| PPM | Parts Per Million | ≈ DPMO |
| KANO | Kano Model | Attractive/expected/must-be classification |
| HACCP | Hazard Analysis & Critical Control Points | Food safety control |
| GMP | Good Manufacturing Practice | Regulated production practice |
| QMS | Quality Management System | ISO 9001 framework |
| LPA | Layered Process Audit | Multi-level process audit |
| CQI | Continuous Quality Improvement | AIAG CQI-x special-process assessment |
| IATF | International Automotive Task Force | Auto QMS owner |
| SIL | Safety Integrity Level | SIL 1–4 |
| MTBF/MTTR | Mean Time Between Failures / To Repair | Reliability metrics |
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About Quality Quick Reference
One-page quality quick reference: SPC control chart constants, Cpk/Ppk formulas, sampling highlights and standard clauses for engineers. Look up anytime.
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