An injector is produced in two steps: assembly and calibration. This study will focus on the calibration area only. The assembly area can produce a batch of 24 parts in 82 minutes. Each batch is placed on a WIP cart. A batch is only produced if a WIP cart is available. Injectors must be cured for 24 hours after assembly before they can enter the calibration area. To control work in process, the number of WIP carts is limited to the fewest number need to avoid constraining throughput. Only one WIP cart can be in the calibration area at a time. The calibration area consists of four workstations that can be labeled W1, W2, W3, and W4. Each workstation processes one injector at a time. A worker is not needed for automated operations and thus is free to due other tasks. At workstation W1, the worker initiates the injector in 25 seconds. The workstation performs an automated test in 10 seconds. Finally, the worker removes the part in 5 seconds. A manual operation is performed at workstation W2. The operation time is triangularly distributed with minimum 4.0 minutes, mode 5.0 minutes, and maximum 7.8 minutes. At workstation W3, the worker initiates the part in 5 seconds. An automated operation is performed in 4.1 minutes. The worker removes the part in 2 seconds. Workstation W4 is a packing operation performed by the worker in 5 seconds.
The calibration area is served by one worker. Worker walking times between stations are as follows.
Determine the number of WIP carts required. Generate a trace of worker tasks to validate the model.
Case Problem Issues
1. How should the WIP carts be modeled?
2. How should the constraint on the number of WIP carts in the calibration area be modeled?
3. How should the injector curing requirement be modeled?
4. Write down the sequence of tasks for the calibration area worker.
5. Discuss how the number of WIP carts can effect cycle time.
6. Beside throughput, are any other performance measures important? If so, what are they?
7. An entity moving through the assembly area represents a WIP cart while an entity moving through the calibration area represents an individual injector. How is the conversion from WIP cart to injector accomplished?
8. Specify the experimental strategy for determining the number of WIP carts.
9. Discuss how to obtain verification and validation evidence.
10. Determine how to model arrivals to the assembly process.
11. Determine how to model batch processing times in the assembly area. Note that the batch processing times are the sum of 24 individual processing time. Should this sum be explicitly computed? Can the central limit theorem be applied?
12. Compute the expected number of WIP carts needed to maximize throughput.
13. What are the initial conditions for the experiment? Terminating Experiment: The simulation time interval is 5 days (120 hours of work time)