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)