1. Chapter 7 on Process Interruptions / Batching (20 Points): Metal frames for k

Question

1. Chapter 7 on Process Interruptions / Batching (20 Points): Metal frames for kick scooters are manufactured in two steps: Stamping and assembly. The parts are fabricated by a single stamping machine that requires a set up time of 90 minutes after every 120 parts produced for preventative maintenance. Once the machine is set up, the activity time for parts is 30 seconds each piece. Completed parts move only when the entire batch is produced. At assembly, parts are assembled manually to form the finished products. The part and a number of small purchased components are required for each unit of final product. Each product requires 30 minutes of labor time to assemble. There are 12 workers in assembly. There is sufficient demand to sell every scooter the system can make.

a. (10 points) At the current batch sizes, what is the process capacity in units per hour? Is the bottleneck stamping, assembly, or both?

b. (10 points) What batch size for the stamping machine would minimize inventory without restricting the flow rate?

Explanation / Answer

a) Flow time of Stamping operation = 90 minutes + 120*30/60 = 150 minutes per batch of 120 items

Flow time of Assembly operation = 120*30/12 = 300 minutes per batch of 120 items

Clearly, Assembly operation is bottleneck.

Process capacity = 120 units per 300 minutes = 24 units per hour

Assembly is the bottleneck.

b) Process flow rate is 24 units per hour.

Therefore, flow rate of stamping machine should be 24 units per hour to minimize inventory without restricting the flow rate.

Flow time = 60/24 = 2.5 minutes

Target Setup time per item = 2.5 minutes - 30 seconds = 2 minutes per unit

Batch size = 90 minutes/ 2 minutes = 45 units

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