A production process consists of five operations: Preparation, Conditioning, Machining, Painting, and Inspection. The capacity of the Preparation station is 2, the Conditioning station is 1. The machining station consist of 2 machines each with a capacity of 1, the painting station 1 and the inspection machines (machine 1 and 2) each 2. Movement between stations requires times that follow a Triangular distribution with parameters (0.5, 1.0, 1.5) minutes.
The data for arrivals and processing are as follows (all times are in minutes):
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Arrivals
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Exponential
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Mean = 4 minutes
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Preparation
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Triangular
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(2, 3, 4)
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Conditioning
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Uniform
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(4, 8)
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Machining 1, 2
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Weibul
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(2, 4)
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Machining Setup
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Fixed
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0.25
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Painting
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Normal
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Mean = 4, Standard Deviation = 1
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Inspection Machine 1
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Triangular
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(5, 10, 15)
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Inspection Machine 2
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Triangular
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(7, 14, 21)
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Inspection Setup Time
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Fixed
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0.3
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Buffer size behind the first 3 stations (i.e. Preparation, Conditioning and Machining) is limited to 4 parts, and for painting and the inspection stations is 6 parts. Parts arriving at a full queue are ejected from the system.
Forty percent of the jobs are type 1, the rest are type 2. Type 1 jobs arrive to be served at preparation, then move to conditioning, followed by machining 1, then painting, then to the inspection station and then leave the system. Type 2 jobs arrive to be processed at preparation, then move to machining (both machines can process type 2 jobs), but job type 1 has priority to access Machine 1. After that the Type 2 parts go to conditioning, then painting, back to conditioning and then to the inspection station and then leave the system. At conditioning station, type 1 jobs have higher priority than type 2 jobs. There is no priority system at inspection. Jobs fail inspection with a 10% probability. 50% of the failed jobs are returned to conditioning, and the rest are scrapped.
Using Arena, simulate the system for four weeks of five and a half days of three 8 hour shifts with a coffee break of 30 minutes at hour two of production and a 30 minute of lunch/dinner break. In the simulation allow a one-day warm-up period. The WIP will remain in the system and parts under process in the machines will be pre-empted before shifts change.
Ensure you replicate the simulation to acceptable statistical levels for statistical validation and verification. You need to include a separate section for model validation and verification analysis.
Questions
Part 1:
Report on the results of the simulation:
1. How many good jobs are made of each type? How many reworks occur?
2. How many jobs are ejected and how many are scrapped?
3. What is the average throughput time for each type?
4. What is the utilisation of each station?
5. Discuss the effect of Job priorities and their effect on the performance of the system. Explore the possibility of changing priorities or no priorities.
6. How many jobs are ejected from the system in front of each cell?
7. What is the average queue time behind each cell?
8. What is the average WIP?
9. Add a conveyor system that connects all the stations to each other starting from a start station and a leave station. The parameters access rules, spacing, and load-unload time is left to your choice. Ensure that the transport time remains
Part 2:
The management believes that the system is sub-optimal and there is room for improvement. These improvements could be done in quality management, improving utilisation of the resources in the system, reducing ejections, reducing throughput time etc.
As a manufacturing systems consultant what are your proposals to management? Analyse the current situation and simulate your proposed system(s), comparing it to the actual system as proof of concept.
This part of the assignment should be analytical; your report on it should be in the form of a short essay.