1 Disk Drives

This case study looks at a manufacturing operation for disk drives. During the process, a robotic arm picks up a computer hard drive and repositions it for transfer to the next operation. A problem developed where the robotic arm was dropping the disk drives periodically. The operators were becoming frustrated and wanted management to replace the robot. A team was assembled and given the task of improving the robot's operation. They learned that the robot was dropping a disk on the average of one every half hour of operation. When the robot dropped the drive, the operator needed an average of five minutes to reposition and re-index the robot. The operators were asked what would be an acceptable level of performance. After conferring, they replied that they could accept the robot dropping a drive once every two hours.

Let's examine their answer. A dropped drive once every 2 hours in a 24-hour-a-day/7-day-a-week operation adds up to a considerable amount of time. The operators worked a 12-hour shift. One dropped drive every 2 hours at 5 minutes downtime per drop equals 30 minutes downtime per shift. Multiplying this amount times the 14 shifts the robot operates equals 7 hours of downtime per week. In turn, 7 hours of downtime times $10,000 per hour of production output is $70,000 of downtime every week. Finally, multiplying this number times the 50 weeks a year the plant operates leads to an amount of $3,500,000 worth of downtime...