Assignment on simulation (using Operational policies on layout design)
A production line consisting of four stations are connected in series. Their processing times are given in Table 1 as follows.
Table 1 Information of the serial production line
|
Station
|
Processing time (min/part)
|
|
1
|
2.8
|
|
2
|
2.8
|
|
3
|
3.1
|
|
4
|
2.9
|
Basic tasks:
1. Develop a simulation model for this line. Decide on the suitable inventory levels for these stations. Run the model for 10 hours. (You may assume that sufficient number of parts are waiting in front of the production line.) (MODEL 1)
2. Compare the performance of this line (in terms of throughput andWIP) with the theoretical model of the best case given in the discussion on operational policy. Is there any discrepancy between the two? Why?
3. Based on the Model 1, apply the constant WIP (CONWIP) approach to introduce new parts into the production line. (CONWIP: when a part has completed all four stages of processing and leaves the line, a signal will be sent to the buffer in front of the line to allow the release of a new part into the line.) (MODEL 2)
4. Compare Model 1 and Model 2. Is there any discrepancy between the two? Why?
Practical worst case (PWC):
5. (PUSH) Develop a simulation model for this line, with the processing times of all the stations following an exponential distribution. Decide on the suitable inventory levels for these stations. Run the model for 10 hours with 20 repetitions. (MODEL 3)
6. Compare the performance of this line (in terms of throughput, WIP and critical WIP) with the PWC. Is there any discrepancy between the two? Why?
7. Work out the best CONWIP approach for this line. (Start with Model 3, decrease the buffer size of individual stations (say, by 1 or 2). See if any significant effect on throughput. This is an iterative or trial-and-error process.)
Basic tasks:
- Buffer: the heap of jobs sufficient for the line to consume in 10 hours. Do a simple calculation to determine this number plus a few more.
- B2, B3, B4: intermediate buffer. Size could be 20 or some arbitrary value.
- Define a variable WIP to keep track of the WIP. Use "basic statistics" to obtain mean inventory.
Model 2:
CONWIP: constant WIP. A part is admitted into the system only when a part exits the system.
- Just cap the buffers B2, B3 and B4. Try B2,3,4=0,1,2,3. (For B2,3,4=0, you have to get rid of them.)
- More sophisticated methods can be used but that involve more complex logic and unfamiliar statements (order).
Model 3:
Similar to Model 1 except the processing times are exponentially distributed.
Item 7:
- Cap B2-4, and try different inventory levels.