PA 3-10 An automated car wash serves customers... An automated car wash serves c

Question

PA 3-10 An automated car wash serves customers... An automated car wash serves customers with the following serial process: pre-treat, wash, rinse, wax, hand dry. Each of these steps is performed by a dedicated machine except for the hand dry step, which is performed manually on each car by one of 4 workers. The steps of the process have the following processing times: Pre-treat: 7 minute per car Wash: 4 minutes per car Rinse: 4 minutes per car Wax: 5 minutes per car Hand dry: 9 minutes per car If the car wash has a demand of 11 cars per hour, what is the a. flow rate of the process? (Do not round intermediate 6.67 cars per hour calculations. Round your answer to 2 decimal places) If the car wash has a demand of 11 cars per hour, what is the utilization of the machine that performs the Wax process? (Round to nearest integer) b. 56 percent

Explanation / Answer

3-10

(a)

Though the hand dry seems to be having the highest cycle time, there are 4 workers deputed for this work. So, the effective average time per car = 9/4 minutes = 2.25 minutes.

So, the bottleneck is not hand drying but Pre-treatment (7 minutes per car).

So, flowrate = min (demand, capacity of bottleneck) = min (11, 60/7) = 8.57 cars per hour

(b)

Utilization of waxing stage = 5 / 7 x 100% = 71%

3-11

Capacity (customers per hr.) = 60 * # resources / Cycle time (minutes)

Bottleneck station is 3 (least capacity)

(a)

Fow rate = min(demand, capacity) = 27 customers per hour

(b)

Now the bottleneck shifts to station 1 and the capacity = 30 customers per hr.

Fow rate = min(demand, capacity) = 30 customers per hour.

Step Cycle time (minutes) # resources Effective capacity (customers per hr.) 1 8 4 30.0 2 2 3 90.0 3 11 5 27.3

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