Simulation of production systems- final report
- 1. COURSE: IE 682 PROJECT REPORT OF ASSIGNMENT NUMBER: 15 MANUFACTURING MADNESS: SIMULATION EXPERTS NEEDED TO IMPROVE HIGHLY VARIABLE SYSTREM DATE OF SUBMISSION: 12/4/2011 SUBMITTED BY: SATHEESH KUMAR CHANDRAN AND LUN LI.
- 2. EXECUTIVE SUMMARY: The facility that has been evaluated produces sections with units that are inserted into the section. There are two areas in the facility, namely Cell A(custom made products) and Cell G(pre-engineered orders). Both of them operate independently and do not share workers or machines. In each cell there is a section assembly area where in sections are assembled according to the order received, a unit build line and a final assembly area where in the sections and their corresponding units are assembled together to form the final product. Meeting the demand with minimum operating cost is the goal of the company. The areas of concern standing in the paths are missing parts, wrong parts and engineering changes that are required to be done before the raw products and the time taken for the corrections to be made for the above mentioned. Of all the three failures, the percentage of clean units arriving in the unit assembly area is very low and the time taken for its replacement is also high. Thus the time taken to replace the missing units should be reduced to keep up the production pace. By simulating the base configuration the number of total completed products produced is equal to 11467. This is due to some of the following problems. There is a limited space to hold the sections before the final assembly. The entire production ceases if the buffer space is full. Rather than increasing the buffer space that requires changes in the facility layout and in order to make it available for most of the time, the number of workers in the final assembly area right after the section rack is to be increased from five to ten, so as to ensure the continuous production. Bottle necks also occur in some of the work station due to the lack of optimum recourse. This can be resolved by increasing the workers by 52 in number. The idea of combining both the Cell A and Cell G and the idea of having a common queue for all the lines and high priority for Cell G also is not recommended.
- 3. PROBLEM STATEMENT: The facility under study produces sections with units that are inserted into the sections as required by the order. The facility contains two production areas, Cell A (custom made products) and Cell G(Pre engineered products). In both the cells there is a section assembly area, a unit assembly area and a final assembly area. Both sections and units are assembled together in the final assembly. The facility finds it difficult to meet the required demand due to various factors like Determining the capacity to meet the demand. Missing parts (section and units) and the time taken to replace them. Wrong parts (section and units) and the time taken to replace them. Section rack capacity before final assembly. OBJECTIVES OF SIMULATION: Simulating the provided system in its current situation, finding the bottle necks and getting rid of it, so as to meet the demand and ensuring minimum production cost will be basic objective of the study. Also there are certain parameters that are to recorded for managerial purpose is also required. These performance measures are Time taken for section and unit builds. Number of section shells produced per day. Number of units produced per day. Number of sections with the unit inserted produced per day. Number of units that are tested and the number that required re-work. Number of waiting items for testing. (Testing queue length). Total time spent on board testing Total final assembly hours. Time taken for assembling a section.
- 4. PROCESS DESCRIPTION: Note: There are two areas in the facility under study, Cell A and Cell G. Each area has its own Section assembly area, unit build area and a final assemble area. In Cell A and Cell G the process can be described in short by the following diagram SECTION ASSEMBLY: Cell A has one section assembly area and Cell G has one section assembly area. The processes carried out in the section assembly area are the same in both Cell A and Cell G. The section assembly area has five work stations in total. Station 1: Has 1 worker and 1 part is processed at a time. Has a processing time distributed asTRIA(5,10,13). Station 2: Has 1 worker and 1 part is processed at a time. Has a processing time distributed as TRIA(5,7,13). Station 3: Has 2 workers and 1(10% likely) or 2(30 % likely) or 3(30% likely) or 4(20% likely) or 6(10% likely) parts simultaneously. When more than one section is processed, they are represented as items with their percentage likely as mentioned above. The entities come out of the third station as an item. The processing time is distributed as TRIA(8,10,13) Station 4: Has 1 worker and 1 item is processed at a time with a processing time distributed as TRIA(8,15,20). Station 5: Has 1 worker and 1 item is processed at a time with a processing time distributed as TRIA(5,20,120). Section Shell assembly Final Assembly (section+units) Unit Assembly
- 5. There are two types of failures that occur in the section assembly area. They are Missing parts: Parts required to build the sections are missing for 4% of the total time. If they are found missing they are put at the end of the WIP queue and the work on the next order is carried out. They are replaced up front in the queue after a delay time distributer as TRIA(1,5,30 days). Wrong parts: Usually 3% of parts wrongly arrive in the section assembly area to which the same process is carried out as missing parts. They are usually replaced in a time distributed as TRIA(1,2.5,30 days). The section buffer space before Cell A is 20 and 5 before Cell G. If this buffer space is full, the entire section production is stopped. UNIT ASSEMBLY: There are 4 unit build lines in Cell A and 1 unit build line in Cell G. Unit inserts for a particular section are build on the same line. There are failures also in the unit build areas. Usually the kits that has all the components required to build the units have missing parts. The kit that contains all the parts are called clean kits. The percentage of Clean kits arriving per week are given as graph1 and are replaced with a time distributed as TRIA(1,5,30 days). 0 20 40 60 80 100 120 WEEK 1 WEEK 2 WEEK 3 WEEK 4 WEEK 5 WEEK 6 WEEK 7 WEEK 8 WEEK 9 WEEK 10 WEEK 11 WEEK 12 WEEK 13 WEEK 14 WEEK 1 CELL G CELL A
- 6. There are also cases in which the wrong parts arrive for assembly. They are placed at the end of the queue until they are replaced with the correct ones. Its replacement time is TRIA(1,2.5,30). Once the correct parts are arrived they are put in front of the assembly line.. Also 10% of the units arriving for assembly requires engineering changes to be made. It usually takes UNIF(1,3). Followed by assembly a testing process is carried out and rework is carried out on the units that fail the testing. About 90% of the total units pass testing. The units are classified according to the complexity of their processing. Their differentiation in terms of processing time and the time required for testing and rework are tabulated. TABLE 1: UNIT TYPE CELL A BREAKDOWN CELL G BREAKDOWN BUILD TIME (HRS) TEST REWORK TIME(H) TIME(MIN) LEVEL 1 30% 45% .75-1.5 .15-0.3 5-30 LEVEL 2 53% 55% 1.6-4 .15-0.3 5-30 LEVEL 3 14% 0 4.1-7 .15-0.3 5-30 LEVEL 4 3% 0 7.1-13 .15-0.3 5-30 FINAL ASSEMBLY: In the final assembly area in both Cell A and Cell G, initially assembly takes place, followed by wiring and then inspection. 90% of the completed sections pass the inspection. 80% of the failures are due to wiring. The processing time distribution for assembly, wiring and inspection are provided along with the capacity for assembly, wiring and inspection.
- 7. CELL A CELL G FINAL ASSEMBLY 60% 85% WIRING 30% 5% INSPECTION 10% 10% TABLE 2: CELL A CAPACITY CELL G CAPACITY FINAL ASSEMBLY 5 INFINITE 5 INFINITE WIRING 8 INFINITE 8 INFINITE INSPECTION 2 INFINITE 2 INFINITE TABLE 3: CALCULATIONS: To calculate the percentage of clean parts of units in cell A and Cell G, graph 1 was used in input analyzer and the distribution was obtained. And the best fit was to be Normal distribution. Pic-1 Pic-2:
- 8. Data’s for performance measures for a random 42 days have been provided in an excel sheet. Of these the time distribution for final assembly is calculated by dividing the total sections completed by the total final assembly hours. The rework time distribution is also calculated the data given in the excel file. The distribution was found to be triangular as shown in pic 3. The entity creation is made from the demand statistics. The demand is 20.000 for 252x18 hours. So the production for one hour is 20000 over 252x18. And the time between arrival is 1 over (20000/252x18) multiplied by 0.85, because 15% of the total sections are considered structural. The demand swings over 20%, so to obtain the maximum and minimum demand, the above value is multiplied by 1.2 and 0.8.
- 9. FINDINGS: THE BASE CONFIGURATION: The base configuration is simulated and the results are obtained. The important observations are Total production numbers – 11,467 Total Cost(labor cost) - $19,276,475 Total profit – (11,467*8250)-( 19,276,475)= $75326275 There is a drop in production due to the bottle necks in the following areas The Final Assembly process The work Station 1 in section production area. The work Station 5 in section production and unit production lines.
- 10. EXPERIMENTATION: SCENARIO 1: In this scenario, the production areas Cell A and Cell G are combined together. It means there is no independent line for producing the pre-engineered sections and their corresponding units. One of the lines of Cell A is dedicated to the production of pre-engineered products. Its assumed that the same number of workers used for Cell G, in the previous case are used here too (22). The simulation was run in these conditions and the results were obtained. It is observed that the number of total sections produced is = 10250. Which is way too less than the base configuration. The total cost of The WIP at section production was almost double (8748) the base configuration. Which means it’s in no way useful in increasing the production. So it’s a clear “no” for the management to combine both Cell A and Cell G. SCENARIO 2: In scenario 2 the management plans to combine both Cell A and Cell G, but with a common queue for all the four line for custom made products. And the pre-engineered sections also can be produced in any of the four lines. But all the sections and their corresponding units are produced in the same line. In this condition selection of items out of the queue is of the most important. The decision of queue is made on its length. When its stated that orders can occupy any of the four lines, under this scenario, the decision has been made such that, the order first in the queue gets to occupy the line that has finished the previous order. The number of completed products is only one third of the base production. Its because Cell G has the lowest operating cycle time and it’s the most efficient, as the number of workers are more for a single line. Also the number of Clean kits for unit production arriving are very much higher than Cell A. When the priority is high for Cell G, the numbers out is increased to 7640 from 6000. Still the production is not up to the required level. So still a “no” for scenario two.
- 11. The best production by obtaining the optimized number of resources is done by the process analyzer
- 12. CONCLUSION: The demand is not fulfilled with the base configuration. It is only 11469 products instead of 20400. The profit obtained is $75326275. The labor cost is $19,276,475 The production is at its maximized when the recourses are of the following capacity, 1. Final worker A- 10 2. Section 1A operator- 5 3. Worker 5A- 3 4. Production worker all four lines- 19 5. Unit testing A worker-5 6. Section 2A operator- 3 7. Section 3A operator-3 8. Wiring worker A-9 The change in buffer space is not recommended as its problem is solved once there is an addition of 52 workers. Scenario 1 and 2 are not recommended because of low production s.