Case Study · 2025
Jominy Hardness Testing Fixture
DMAIC-driven fixture redesign that killed an 80% slice of COPQ
The Problem
An aging Jominy hardness test fixture was driving misfeeds, scrap, and recurring measurement variation , and nobody could agree whether the problem was the fixture, the operator, or the steel.
Approach
1 · Define & Measure
Quantified the baseline with Cp/Cpk on existing fixture data. Once 'the fixture is annoying' became 'the fixture is special-cause variation', the redesign case wrote itself.
2 · Analyze
Ran 5 Why and fishbone analyses with the operators who actually use the rig , surfaced misfeed root causes that the CAD model never showed.
3 · Improve
Redesigned the fixture in SolidWorks with positive part location and DFMEA-informed error-proofing to significantly reduce misfeed paths.
4 · Control
Stood up control charts on the new fixture so the gains stick , and so the next person to touch it can see drift before it becomes scrap.
Model Performance
Results
80%
Reduction in Cost of Poor Quality from the redesigned fixture.
Stable Cp/Cpk
Capability moved from variable to predictable.
Fewer misfeeds
Positive-location design significantly reduced the dominant failure mode.
What I Took Away
- DMAIC is a design tool, not just an ops tool , Measure is where the project actually turns.
- Operators know root causes that don't appear in any CAD model. Ask them first.
- Control charts are how you prove the win wasn't luck.