|To: |Positrol Workholding |
|From: | |
|CC: | |
|Date: | |
|Re: |Job Process Scheduling |
| | |
Introduction
The difference in the job process scheduling will be measured based on table 1 that was given. We are comparing the differences between First Come, First Served (FCFS), Shortest Operating Time (SOT) and Earliest Due Date (EDD) to find which sequencing rule may work the best.
Highlights
Lateness: The findings (SOT) had the best average of lateness (-3.8), but would still have 3 jobs come up short. On the other hand (EDD) had a slightly lower average at (-2.1), but had no jobs arrive late. With that being said both of these alternative had better averages than the (FCFS) method that positrol workholding is currently using.
Jobs: To have the best efficiency and make sure the customers are happy, most jobs should be completed on time which is not the case for the methods (FCFS) and (SOT). They both would have 3 late jobs, whereas (EDD) method would have 0 late jobs, meaning they would all be completed on time.
Flow Time: The last key finding would be to look at the average flow time for each of the three methods to come to an overall consensus in which sequencing rule may work the best, whether it is (FCFS) or one of the two alternatives in (SOT) and (EDD). Once again in the findings the (FCFS) method was the worst with an average flow time of 14.16 followed by (EDD) at 13.98 and then (SOT) at 11.4. (EDD) is the best option and what we should use.
Discussion
Method: As mentioned above, there were three methods used in order to find the most effective and efficient job sequencing rule. The first being what Positrol Workholding already had in place being the (FCFS) method which is pretty easily explained. Which ever job were to come in first would be the first one started and completed, following that would be the same pattern with the following jobs. The next method would be the (SOT), which is the shortest operating time, meaning the jobs that took the shortest amount of time to complete would be started first to get them out of the way, and then continue down the list of jobs. The last method and most effective to some degree would be the (EDD) example, meaning which ever job had the soonest due date would be started on first and once again move down the list until completed. This method allowed for every job to be done on time. We got these results from the data that was provided in which Positrol was using the first come first serve method. Using those numbers we were able to calculate the other alternatives.
Results: Following will be the results of each method so it is easier to see each of the side by side and compare. What we want to look for to be able to determine the most effective method is average flow time, average lateness and number of late jobs.
First Come First Served (FCFS)
Table 1.1
|Job |Date Received |Flow Time |Due Date |Lateness |
|ABC |2/2 |4.5 |10 |4.5 – 10 = -5.5 |
|RBP |2/11 |4.5 + 6 = 10.5 |16 |10.5 – 16 = -5.5 |
|XC |3/3 |10.5 + 5.1 = 15.6 |12 |15.6 -12 = 3.6 * |
|SDS |3/8 |15.6 + 2.9 = 18.5 |18 |18.5 – 18 = .5 * |
|EFF |3/20 |18.5 + 3.2 = 21.7 |20 |21.7 – 20 = 1.7 * |
AVG = 14.16 AVG = -1.04
Key Finding(s): By starting on the jobs that we get first we end up with a high flow time and three jobs being late.
Shortest Operating Time (SOT)
Table 1.2
|Job |Operating Time |Flow Time |Due Date |Lateness |
|SDS |2.9 |2.9 |18 |2.9 – 18 = -15.1 |
|EFF |3.2 |2.9 + 3.2 = 6.1 |20 |6.1 – 20 = -13.9 |
|ABC |4.5 |6.1 + 4.5 = 10.6 |10 |10.6 – 10 = .6 * |
|XC |5.1 |10.6 + 5.1 = 15.7 |12 |15.7 – 12 = 3.7 * |
|RBP |6.0 |15.7 + 6.0 = 21.7 |16 |21.7 -16 = 5.7 * |
AVG = 11.4 AVG = -3.8
Key Finding(s): When going by the shortest operating time and getting the smaller jobs out of the way we end up with the shortest flow time and with the best average for lateness, meaning the job is on time. There was still three late jobs, two of the five jobs were just finished really early.
Earliest Due Date (EDD)
Table 1.3
|Job |Operating Time |Flow Time |Due Date** |Lateness |
|ABC |4.5 |4.5 |10 |4.5 – 10 = -5.5 |
|XC |5.1 |4.5 + 5.1 = 9.6 |12 |9.6 – 12 = -2.4 |
|RPB |6.0 |9.6 + 6.0 = 15.6 |16 |15.6 – 16 = -.4 |
|SDS |2.9 |15.6 + 2.9 = 18.5 |18 |18.5 – 18 = -.5 |
|EFF |3.2 |18.5 + 3.2 = 21.7 |20 |21.7 – 20 = -1.7 |
AVG = 13.98 AVG = -1.2
Key Finding(s): By completing the jobs by their due date, we come to most effective technique. Even though the flow time is still kind of high, not one of our jobs end up late, and that is what we are looking for. We want to make everyone happy, not just certain clients.
* denotes late job
** ranked based upon
Analysis/Recommendation: In conclusion of Job Process Scheduling for Positrol Workholding, the best way to simply decide if one of the alternatives is better than the job sequence the are currently using is to compare to goodness of all of them. Simple meaning to compare each of the average flow times, number of late jobs, and the average lateness, which can be seen at the chart below. Comparison Table 1.4
|Category |(FCFS) |(SOT) |(EDD) |
|Average Flow Time |14.16 |11.4 |13.98 |
|Number of Late Jobs |3 |3 |0 |
|Average Lateness |-1.04 |-3.8 |-2.1 |
Continued: As it can be seen in the chart, both alternatives look to be a better option than the (FCFS) method that Positrol is currently using. Both (SOT) and (EDD) have lower average flow times and a better average lateness. That being said it becomes hard to determine which of the alternatives would be the better option. The (SOT) method has a lower average flow time and a better average lateness, but on the other hand it will still have three late jobs, which can cause some friction with current customers and within the job process. Therefore, the (EDD) sequence would be the best option in result because it causes no late jobs at all while still maintaining a better average flow time and average lateness then the current method being used. We will now start to use the (EDD) Earliest Due Date method in order to maintain a happy clientele; only in certain circumstances will we drift outside of this method, or on special orders. 