Level 2: Engineering Diagnosis

From Symptom to Root Cause

Analyst Mode

Diagnosis Decision Tree

Where do we start?

Always check IF the process CAN be good first.

7 QC Tools Playground

Engineer's Swiss Army Knife: When to use what?

Scenario: 1/3

Mission:

"Customer complains: 'Parts are sometimes long, sometimes short'. You want to see the SHAPE of variation."

Accuracy vs Precision

Target Practice: Many engineers confuse these two.

N=10

Select Scenario:

Engineering Insight

Tampering Experiment (Funnel)

Deming's Warning: Adjusting a process for Common Cause variation only INCREASES variation!

Strategy A: Do Nothing

Let it run. Accept natural noise.

σ = 0.00

Strategy B: Tampering

If too high, adjust down for next part. Trying to 'compensate'.

σ = 0.00

Note: Theoretically, tampering doubles variance (σ * √2). The harder you try, the worse it gets.

SPC Challenge: Spot the Pattern

Don't just watch limit lines. Watch patterns (Nelson Rules). STOP immediately when you see non-random behavior!

Score

UCL/LCL Breach

One Side (Shift)

Trend (Drift)

Oscillation

Batch Comparison Simulation

Mission: Choose the supplier with lower long-term risk

Supplier A

5.8σ

Looks like High Cp...

Cp2.1

Cpk0.8

PPM8200

Supplier B

4.2σ

Cpk looks okay...

Cp1.4

Cpk1.35

PPM32

Level 2 Certification Exam

Test your Engineering Judgment

Diagnosis & DecisionQuestion 1 / 2

You are the Quality Engineer. A process has Cpk = 0.8 and Cp = 2.5. The operator asks to stop and replace the tool. What do you do?