Zero defects is not a slogan about trying harder. It is a decision that every defect which reaches a customer is a process failure that can be designed out, not an operator failure to be corrected with a reminder. The PPM chart tells you which defect types are escaping; the zero-defect mindset says each one gets a permanent fix at the point where it is created.
Error-proofing means building a device or feature into the process that either prevents the defect from being made or detects it automatically before the part moves on. Examples in fastener manufacturing include a length sensor on the cold header that stops the machine when wire feed slips, a go/no-go thread gauge built into the roller exit chute, and a plating-thickness probe that interlocks the unload conveyor. None of these depend on an inspector staying alert through a night shift.
The usual sequence is: rank escaping defect types by PPM contribution, pick the top one, find the process condition that creates it, and install a prevention or detection device there. Then watch that defect type's PPM fall to zero on the chart and move to the next one. Adding more final inspection is the opposite of this approach; it manages defects instead of eliminating them.
Standard Procedure
- 1Break customer PPM down by defect type and rank the types from largest to smallest.
- 2For the top type, trace back to the process step and condition that creates it.
- 3Install a device that prevents the condition or automatically detects and rejects the part at that step.
- 4Track that defect type's PPM separately until it reads zero for several months.
- 5Move to the next defect type on the ranking.
Lesson Summary
- ✓Error-proofing at the source removes a defect type permanently; added inspection only filters it.
- ✓Attack defect types in order of PPM contribution and track each one to zero.