dmaic

DMAIC (Six Sigma Problem Solving)

When to use

Use DMAIC when:

• A problem has recurred multiple times despite previous corrective actions
• The process needs measurable, data-driven capability improvement (Cpk improvement target)
• The root cause is unknown and requires statistical analysis to identify
• A customer requires a Six Sigma approach or asks for a DMAIC report
• The improvement opportunity involves eliminating chronic waste (rework, scrap, test failures)

Use 8D instead when: The problem is a single customer complaint, an escape to the field, or requires immediate containment. 8D is reactive and fast. DMAIC is proactive and thorough — it takes weeks to months.

Use PDCA instead when: The improvement is incremental and the root cause is already known or assumed.

Prerequisites

• A defined problem with measurable impact (reject rate, Cpk, scrap cost, defect count)
• Baseline data available or collectable
• Process owner and cross-functional team assigned
• Management support and a time budget (minimum 4–12 weeks depending on project scope)

Workflow

Phase 1 — DEFINE

Objective: Define the problem, the scope, the team, and the goal in measurable terms.

Key tools and deliverables:

Project Charter — The DMAIC starts and ends here. Contains:

• Problem statement: what is happening, where, since when, how much (measured impact)
• Goal statement: specific, measurable target (e.g., "Reduce connector reject rate from 3.2% to 0.5% by Q3")
• Scope: what is IN and OUT of scope (use Is/Is-Not to define boundaries)
• Business case: financial or customer impact ($, PPM, warranty cost)
• Team: Champion, Black Belt/Green Belt, process owner, operators, engineering

SIPOC diagram:

• Suppliers → Inputs → Process → Outputs → Customers
• Defines the process at a high level before diving into detail
• Identifies all inputs that could affect the output (Y)

Voice of the Customer (VOC) → CTQ:

• What does the customer care about? (VOC)
• Translate to a measurable Critical to Quality (CTQ) characteristic
• The CTQ becomes the Y (output) the project will improve

Gate criteria to exit Define:

• Problem is specific and measurable
• Goal is agreed with the Champion
• Scope is bounded
• Team is assigned and available

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Phase 2 — MEASURE

Objective: Establish the current baseline and validate the measurement system.

Key tools and deliverables:

Process map (detailed):

• Map every step of the process as it IS (not as it should be)
• Identify where defects are created or detected
• Mark each step: Value-Added (VA), Non-Value-Added (NVA), or Required Non-Value-Added

Data collection plan:

• What will be measured? (the Y and key process inputs Xs)
• How will it be measured? (gauge, method)
• How many samples? (for capability: minimum 100 pieces)
• Who will collect data? When? Where?

MSA (Gauge R&R):

• Validate the measurement system for the CTQ before collecting data
• %GRR < 30% required; <10% preferred
• If measurement system is inadequate: fix it before proceeding

Baseline capability:

• Calculate current Cpk/Ppk for the CTQ
• Establish current defect rate (PPM or %)
• This baseline is the MEASURE gate deliverable — do not proceed without it

Gate criteria to exit Measure:

• Baseline Cpk/PPM established with statistical confidence
• MSA complete and measurement system adequate
• Data collection plan executed with sufficient data

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Phase 3 — ANALYZE

Objective: Identify and confirm the root cause(s) of the problem using data.

Key tools and deliverables:

Fishbone / Cause & Effect diagram:

• Brainstorm potential causes using 6M (Man, Machine, Method, Material, Measurement, Mother Nature)
• All potential causes are hypotheses at this stage — none are confirmed

Is/Is-Not analysis:

• Scope the problem precisely — what IS affected vs. what IS NOT
• Narrows the hypothesis list before investing in analysis

Multi-Vari study:

• Understand whether variation is: positional (within-part), cyclical (part-to-part), or temporal (time-based)
• Identifies the dominant family of variation — directs the investigation

Hypothesis testing:

Confirm or reject hypotheses statistically. Selection guide:

| Situation | Tool |

|-----------|------|

| Compare means of 2 groups (continuous Y, e.g., Shift A vs. B) | t-test (paired if same parts measured twice) |

| Compare means of 3+ groups (e.g., 3 machines, 4 operators) | One-way ANOVA |

| Categorical Y (pass/fail) vs. categorical X (supplier, shift) | Chi-square test |

| Continuous Y vs. continuous X (does temperature predict dimension?) | Pearson correlation; then regression to quantify |

| Multiple Xs affecting one Y | Multiple regression; confirm no multicollinearity |

Use p < 0.05 as the significance threshold unless a different risk level is warranted. Always check the test's assumptions (normality for t-test/ANOVA; independence for chi-square).

Root cause confirmation:

• A root cause is NOT confirmed until data proves it
• Reject "human error" as a root cause — it is a symptom; ask why the error was possible
• Confirmed root causes: demonstrate that when the Xs change, the Y changes predictably

Gate criteria to exit Analyze:

• Root cause(s) confirmed with data (not assumed)
• Cause-and-effect quantified (Y = f(X) relationship established)
• Team agrees on which Xs to improve

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Phase 4 — IMPROVE

Objective: Develop, test, and implement solutions that address the confirmed root causes.

Key tools and deliverables:

Solution generation:

• Brainstorm solutions for each confirmed root cause
• Evaluate solutions: impact vs. effort vs. risk
• Do NOT select solutions based on opinion — test them

Pilot / Design of Experiment (DOE):

• Test the proposed solution on a small scale before full implementation
• DOE: systematically vary multiple factors to find the optimal process settings
• Simple experiments: OFAT (One Factor At A Time) for straightforward improvements

Solution validation:

• Run a production pilot with the solution in place
• Collect data: does the Y improve as predicted?
• Calculate new Cpk/PPM — compare to baseline and goal

Implementation plan:

• Who does what, by when, to implement the solution at full scale
• Change management: update Process Flow, PFMEA, Control Plan, Work Instructions, training

Gate criteria to exit Improve:

• Solution tested and statistically validated (not just "it seems better")
• Cpk/PPM improvement demonstrated in pilot data
• Implementation plan complete and approved

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Phase 5 — CONTROL

Objective: Sustain the gains — prevent the process from reverting to the old state.

Key tools and deliverables:

Updated Control Plan:

• Add new controls for the Xs identified in Analyze
• Define monitoring frequency and reaction plan for out-of-control conditions

SPC / Statistical monitoring:

• Install control charts on the critical Xs and the Y
• Set control limits from the improved process data
• Define who monitors and how often

Updated PFMEA:

• New failure modes identified during the project must be added
• Controls added in Improve must be reflected in the PFMEA current controls column

Updated Work Instructions:

• Document the new process steps, settings, or behaviours required
• Train operators and verify understanding

Mistake-proofing (Poka-yoke):

• For any root cause that was behavioural or procedural: add error-proofing to prevent recurrence
• Error-proofing is the highest-reliability control — prefer it over inspection or SPC alone

Project handover:

• Transfer ownership from the project team to the process owner
• Establish a 3–6 month monitoring period with defined Cpk targets; specify the minimum Cpk that constitutes "sustained improvement" (e.g., Cpk ≥ 1.33 for a minimum of 3 consecutive months of production data — not 3 months of calendar time)
• Close the project only when the monitoring criterion is met with actual production data — not lab data or pilot data

Final project report:

• Before and after: Cpk, PPM, financial savings
• Lessons learned for future projects

Gate criteria to close the project:

• Cpk/PPM goal achieved and sustained for minimum 3 months post-implementation
• All documents updated (PFMEA, CP, WIs)
• Process ownership transferred to process owner
• Financial benefits validated by Finance (if business case required it)

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DMAIC vs. 8D — quick reference

| Dimension | 8D | DMAIC |

|-----------|-----|-------|

| Trigger | Customer complaint, single escape | Recurring problem, capability gap |

| Timeline | Days to weeks | Weeks to months |

| Root cause method | 5-Why, Fishbone | Hypothesis testing, statistical analysis |

| Output | Corrective action to prevent recurrence | Optimised process with sustained capability |

| Standards | ISO 9001 §10.2, IATF 16949 §10.2.3 | ISO 9001 §10.3, IATF 16949 §10.1 |

Validation criteria

A DMAIC project is complete when:

• Baseline and improved Cpk/PPM both quantified with data
• Root causes confirmed statistically (not assumed)
• Solution validated in a pilot before full implementation
• PFMEA, Control Plan, and Work Instructions updated
• Improved Cpk sustained for minimum 3 months post-implementation
• Financial or quality benefit measured and reported

Common mistakes

• Jumping to Improve before confirming root cause (the most common DMAIC failure)
• Not performing MSA before collecting baseline data — baseline may be measurement noise
• Selecting the solution in Define before data analysis — biases the entire project
• Closing the project at Implementation without monitoring for sustainability
• Not updating PFMEA and Control Plan — process reverts within months
• Using DMAIC for a single-event problem that needs 8D containment first

Output Format

At the start of each use, ask the user:

> "How would you like to receive the output?

> A — Structured Markdown (formatted tables and sections, ready to copy)

> B — Plain tables (simplified structure for Excel or Word)

> C — Narrative report (flowing text for a formal document or email)

>

> Default: A."

Adapt all output sections to the chosen format. If the platform or session context already defines a format preference, skip this question.

Changelog

| Version | Date | Author | Change |

|---------|------|--------|--------|

| 1.0 | 2026-06-06 | @RBraga01 | Initial release |

| 1.1 | 2026-06-06 | @migmcc | Added hypothesis test selection guide in Phase 3; added monitoring period closure criteria in Phase 5 (Cpk sustained on production data, not pilot) |