Additional Problems with solutions The Rocky Mountain Arsenal, formerly a chemical warfare manufacturing site, is said to be one of the most polluted locations in the United States. Cleanup of chemical waste storage basins will involve two operations.  Operation 1: Drain and dredge basin.  Operation 2: Incinerate materials. Management estimates that each operation will require the following amounts of time (in days): A Dredge 3 Incinerate 1

B 4 4

C

D

3 2

6 1

Storage Basin E F G 1 3 2 2 6 4

H 1 1

I 8 2

J 4 8

Management’s objective is to minimize the makespan of the cleanup operations. All storage basins are available for processing right now. First, find a schedule that minimizes the makespan. Then calculate the average flow time of a storage basin through the two operations. What is the total elapsed time for cleaning all 10 basins? SOLUTION We can use Johnson’s rule to find the schedule that minimizes the total makespan. Four jobs are tied for the shortest process time: A, D, E, and H. E and H are tied for first place, while A and D are tied for last place. We arbitrarily choose to start with basin E, the first on the list for the drain and dredge operation. The final sequence is shown below: EHGFBJICDA Note: Several optimal solutions are available to this problem because of the ties at the start of the scheduling procedure. However, all have the same makespan. The schedule would be as follows: Basin E H G F B J I C D A

Dredging Start Finish 0 1 1 2 2 4 4 7 7 11 11 15 15 23 23 26 26 32 32 35

Incineration Start Finish 1 3 3 4 4 8 8 14 14 18 18 26 26 28 28 30 32 33 35 36 TOTAL 200

The makespan is 36 days. The average flow time is the sum of incineration finish times divided by 10, or 200/10 = 20 days. Note: Work out the above problem using FCFS rule and compare the same with Johnsons rule with respect to makespan and average flow time.

Problem on MRP MRP has to be developed for a company that is making a telephone for the next 8 weeks planning horizon. The bill of material for a phone assembly is shown below: The numbers that are shown along the side of each symbol represent the code number of the parts, while the number listed below the symbol represent the quantity required to make the telephone.

The quantities of telephones to be produced from Week 2 to Week 8 are 600, 1000, 1000, 2000, 2000, 2000 and 2000 respectively. (Note: You need not make a level 0 plan, as it is already given here). The inventory and scheduled order receipts details for other components and parts are given below: Part No. 11 (handset assembly)

Current inventory 1200

12

800

121 123 1211

500 15000 1200

Scheduled receipts 400 in week 1 700 in week 2 200 in week 3 400 in week 1 400 in week 2 400 in week 3 10000 in week 2 1500 in week 1

Remarks fixed lot size of 3000 lead time is 2 weeks fixed lot size of 3000 lot for lot lot for lot lot for lot

Assume that lead time for all the components listed above in the table is one week (other than part 11). Prepare the MRP for the above-mentioned components.

Solution Part 11 gross requirements scheduled receipts projected inventory balance net requirements planned receipts planned order release

current

Part 12 gross requirements scheduled receipts projected inventory balance

current

net requirements planned receipts planned order release

1200

400 1600 0

2 600 700 1700 0

3 1000 200 900 0

0

0

3000

0

800

400 1200

2 600 400 1000

0

0 0 0

0 0 0

Part 121 gross requirements scheduled receipts projected inventory balance net requirements planned receipts planned order release

current 0

1

1

6 2000

7 2000

8 2000

2900 100 3000 3000

900 0

2900 900 3000 0

900 0

3000

1900 1100 3000 0

3 1000 400 400

4 1000

5 2000

6 2000

7 2000

8 2000

2400

400

1400

2400

400

0 0 3000

600 3000 0

0 0 3000

1600 3000 3000

600 3000 0

0 0 0

0

0

500

500 0 0 0

500 0 0 2500

0 2500 2500 0

Part 123 gross requirements scheduled receipts projected inventory balance net requirements planned receipts planned order release

current 0

1

Part 1211 gross requirements scheduled receipts projected inventory balance net requirements planned receipts planned order release

current 0 1200

2

5 2000

3 3000

15000

1

4 1000

2 0

15000 0 0 0 1 0 1500 2700 0 0 0

0 10000 25000 0 0 0 2 2500

3

200 0 0 0

4 0

5 3000

6 3000

7 0

8 0

0 0 0 3000

0 0 3000 3000

0 0 3000 0

0 0 0 0

0 0 0 0

3 12000

4

13000 0 0 0

0

0

5 12000

6 12000

7 0

8 0

13000 0 0 0

1000 0 0 11000

0 11000 11000 0

0 0 0 0

0 0 0 0

0

4 3000

5 3000

6 0

7 0

8 0

200 0 0 2800

0 2800 2800 3000

0 3000 3000 0

0 0 0 0

0 0 0 0

0 0 0 0