Quality Learning Centre

Inspections

Checking parts against the drawing or specification at receiving, in process and before dispatch.

• Inspect the characteristics that matter most (critical and safety) every time; sample the rest.
• Record actual values, not just OK/NOT OK — trends need numbers.
• Photo evidence and a signature make results defensible in audits.

CAPA

Corrective and Preventive Action: removing the cause of a problem so it does not recur, and applying the lesson elsewhere.

• Containment protects the customer today; corrective action protects tomorrow.
• Every action needs an owner and a due date.
• Close only after checking effectiveness with data.

8D problem solving

An eight-discipline method (D1 team → D8 closure) used widely in automotive and with demanding customers.

• D3 containment within 24 hours is usually expected by customers.
• Use 5 Whys and a fishbone for D4 root cause — confirm it with data.
• D6 needs evidence that the fix works, not just that it was done.

SPC (Statistical Process Control)

Using control charts to separate normal process variation from special causes that need action.

X̄ chart limits = X̄̄ ± A₂·R̄ · R chart: UCL = D₄·R̄, LCL = D₃·R̄

• Control limits come from the process; spec limits come from the customer — never mix them.
• React to patterns (e.g. 7 points on one side of the centre line), not only points outside limits.

FPY (First Pass Yield)

The share of units that pass inspection the first time, without rework or scrap.

FPY = (units passed first time ÷ units inspected) × 100%

• Rolled throughput yield = FPY₁ × FPY₂ × … across process steps.
• Track FPY by line and shift to find where losses start.

PPM (parts per million)

Defect rate expressed per million parts — common in customer and supplier agreements.

PPM = (defective units ÷ total units) × 1,000,000

• Agree with the customer whether PPM counts rejected parts or defects.
• Separate internal PPM from customer (external) PPM.

Cpk and Ppk

Capability indices: how well a process fits inside its specification limits.

Cpk = min(USL − μ, μ − LSL) ÷ 3σ (σ within subgroups; Ppk uses overall σ)

• Cpk ≥ 1.33 is a common minimum; 1.67 for critical characteristics.
• Only meaningful when the process is stable (in statistical control).

Traceability

Knowing which material lots went into which products and which customers received them.

• Label every lot at receiving and keep the link at each process step.
• Practise a mock recall: how long does it take to list affected customers?

Audit preparation (ISO 9001)

Showing objective evidence that your quality system is defined, followed and improving.

• Keep controlled documents current and acknowledged by the people who use them.
• Calibration certificates and training records are the most requested evidence.
• Run internal audits and close findings through CAPA before the certification audit.