Test the Constraint Before Replacing the Machine
Would improving this machine increase completed good output through the whole line?
The machine with the most visible idle time is not automatically the machine limiting finished output. It may be waiting for product, waiting for downstream space, or stopped by its own problem.
Those conditions suggest different investigations. None, by itself, settles the investment decision.
Follow the same interruption through the line
Choose an interval that materially affects the production plan. Record what the candidate machine was doing, whether usable input was available, and whether the next process could accept output.
Distinguish its own faults from upstream starvation and downstream blockage. Include setup and planned activities rather than forcing every minute into a fault category.
Then trace the initiating event. A downstream stop may propagate through several buffers before the most visible machine stops. Counting every affected station's idle minutes as separate lost line time would exaggerate the opportunity.
Ask the counterfactual
What would the line have shipped during that interval if the candidate machine had performed better and everything else had remained the same?
If the machine lacked input throughout, more instantaneous speed may have little value during that interval. It could still matter later if faster recovery clears a queue. If the next process was full, additional upstream output may only enlarge work in process.
Test the actual mechanism across relevant products and schedules. A constraint can change with mix, shifts, or batch availability. A downtime percentage cannot establish that it never binds.
Compare remedies on the same boundary
Evaluate repair, buffering, sequence changes, improved coverage, and equipment changes where each addresses the identified cause. Include space, quality, maintenance, and operating implications.
Use completed good output and the costs that actually change. A local utilization gain is not automatically a plant throughput gain.
An equipment case should name the condition it improves, the evidence that this condition limits output, and the next limitation after the improvement. It should also state what observation would disprove the diagnosis.
The decision becomes clearer when the team can finish this sentence: improving this asset changes finished output because this specific interruption or rate limit currently prevents it.