Basic Quality Control

Inspection Alone Cannot Create Quality

When you first learn about quality control, it's easy to think of it as "selecting defects well." However, inspection only discovers existing defects, it doesn't reduce them. No matter how much you strengthen inspection, the defect rate remains the same.

That's why the fundamental principle of quality control is this:

> Quality is built in, not inspected in (품질은 검사가 아니라 공정에서 만든다)

Two Types of Quality

In the field, we mainly manage conformance quality. If the drawing is wrong, no matter how well you make it, the customer will be dissatisfied. So if you see anything strange in the drawing, ask for sure.

Quality Cost — Prevention is Far More Cost-Effective

1 : 10 : 100 Rule

Caught in the process        1
Caught during pre-shipment inspection   10
Caught after reaching the customer    100

One customer claim not only costs rework, but also trust and the next order. Most manufacturing in Gyeonggi and Busan is under a prime contractor subcontractor structure, so one quality incident can lead to the termination of a contract.

3D 5S is the Starting Point of Quality

In a site that is not organized, mix-up is inevitable.

• Good and defective products in the same box
• Materials with different lot numbers on the same pallet
• Parts from different processes next to each other

Make them visually distinguishable like red sticker (defective), yellow sticker (hold), green (good product).

Four Rules for Newcomers

1. If something seems wrong, stop — If you think something is "a bit strange," don't keep making and inform the team leader. Making 100 more will result in 100 defective items.
2. First piece inspection — After setup, the first product must be confirmed before starting.
3. Isolate defects immediately — Leaving defective products on the workbench will definitely cause them to be mixed in.
4. Record on the spot — Writing them all later is not data, it's a novel.

Frequently Used Terms

• Yield (수율): Ratio of good products to input
• First Time Through (FTT, First Time Through): Ratio of passing without rework — a real indicator of capability
• PPM: Number of defects per 1 million units. For automotive parts, 50PPM or below is usually required
• Process Capability (Cp/Cpk): The ability of the process to meet specifications (covered in the SPC module)