A product requires four steps to complete Step 1 takes 8 min

A product requires four steps to complete.

Step 1 takes 8 minutes
Step 2 takes 6 minutes
Step 3 takes 2 minutes
Step 4 takes 10 minutes

20% of all units produced requires rework. For reworking, they have to revisit steps 3 and 4. Each step is processed by one employee. Rework takes the same processing times as the first pass and always fixes the problem. What is the capacity of the process in units per minute?

Solution

The capacity without rework -

(60/10) = 6 per hour (note that the fourth step is the bottleneck) = 0.10 per minute

Then 20% of them are rejected i.e. 4.8 parts per hour are OK. The remaining 1.2 parts will take 12 min of time. So, in 72 minutes, 6 parts are finally getting out.

The final capacity = 6 / (60+12)

= 0.0833 per minute.

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