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Glossary

What is Six Sigma?

A data-driven methodology for eliminating defects and reducing variation in manufacturing processes.

Six Sigma is a quality management methodology that uses statistical tools and the structured DMAIC problem-solving framework to drive process improvement. A Six Sigma process produces no more than 3.4 defects per million opportunities (DPMO) — achieved when 6 standard deviations (sigma, σ) fit between the process mean and the nearest specification limit.

The DMAIC Framework

DMAIC is the core improvement cycle used in Six Sigma projects:

D

Define

Define the problem, customer requirements (CTQs — Critical To Quality), project scope, and business impact. Create a Project Charter.

M

Measure

Collect baseline process data. Map the process, measure current DPMO/sigma level, quantify the gap between current and target performance.

A

Analyse

Identify root causes of defects and variation. Tools: Fishbone / Ishikawa diagrams, Pareto analysis, hypothesis testing, regression analysis.

I

Improve

Design and implement solutions that address root causes. Tools: Design of Experiments (DOE), pilot studies, error-proofing (Poka-Yoke).

C

Control

Sustain the improvements. Create control charts (SPC), update SOPs, establish monitoring plan, hand over to process owner.

Sigma Levels & DPMO

DPMO = (Defects ÷ (Units × Opportunities per Unit)) × 1,000,000
Sigma Level (σ)DPMOYieldTypical for
2σ308,53769.1%Below average processes
3σ66,80793.3%Average manufacturing (US industry avg ~4.5σ)
4σ6,21099.4%Good manufacturing processes
6σ3.499.9997%World-class quality (6 Sigma target)

Six Sigma and OEE Quality

The Quality component of OEE directly measures Six Sigma performance at the line level:

OEE Quality = Good Parts Produced ÷ Total Parts Started

A line running at 98% OEE Quality is producing 2% defective parts — roughly equivalent to 4σ performance (20,000 DPMO). Improving to 99.9%+ Quality requires Six Sigma-level process control.

The two frameworks are complementary: OEE identifies where losses occur (Availability, Performance, Quality). DMAIC explains why they occur and drives systematic improvement. Shopfloor Copilot's Root Cause Analysis screen surfaces quality deviations from live OEE data — the starting point for any DMAIC project.

Six Sigma Belt Levels

Frequently Asked Questions

What is Lean Six Sigma?
Lean Six Sigma combines Lean Manufacturing (waste elimination — 8 wastes) with Six Sigma (defect reduction — DMAIC). Lean improves flow and speed; Six Sigma improves quality and consistency. Together they address the full range of process losses captured in OEE: Availability (Lean reduces changeovers/downtime), Performance (Lean reduces minor stops, speed losses), Quality (Six Sigma reduces defects).
Is six sigma 99.9% quality?
Not quite. 99.9% quality corresponds to approximately 1,000 DPMO — close to 4.6σ. True Six Sigma (6σ) is 3.4 DPMO, or 99.9997% yield. The difference matters at scale: on a line producing 1 million parts per year, 99.9% quality means 1,000 defects; 6σ quality means just 3 defects.
How do I start a Six Sigma project using OEE data?
Start with the Define phase: identify which production line has the lowest OEE Quality rate. The Measure phase uses your MES OEE data as the baseline. For the Analyse phase, drill into defect categories (scrap, rework, first-pass yield) by shift, operator, and machine. Shopfloor Copilot's Root Cause Analysis screen provides this breakdown automatically from live OPC UA data.

Measure Quality with Real-Time OEE Data

Shopfloor Copilot calculates OEE Quality in real time from OPC UA signals, surfaces defect trends by line and shift, and feeds your Six Sigma DMAIC Measure phase with accurate baseline data.

Explore Root Cause Analysis →