Definition
Internal work must be done with the equipment stopped; external work can be done while the equipment is still running. This is not the difference between in-plant work and outsourcing.
In detail
When separating internal and external work, judge step by step whether the equipment must be stopped, rather than relying on where and when it is currently done out of habit. External work includes preparation before and cleanup after changeover; internal work should be moved outside the shutdown window when safety and quality requirements allow, then the remaining motions simplified. External steps themselves should also be improved; do not simply shift waste to another operator. This is a key analysis method in SMED.
Example in practice
Before changeover, deliver the next die, tools, and materials to the point of use and check their condition; after shutdown, perform only the disassembly, assembly, and confirmation that require shutdown, and tidy the old die after production resumes. The team records downtime and total labor hours separately, and checks whether the improvement satisfies both safety and first-piece quality.