Case Study
This section lists the specific examples for a better understanding in how to find an optimal schedule by deducing cycle time or shortening the project duration using suitable software. Methods and coding will be different based on the schedule procedure required and the constrains needed for each process in different cases.
Cycle time reduction and component testing
Problem definition
In cycle time reduction case study, the schedule required is to do an optimal testing plan for a project with 240 pcs new developed sensors. The testing requires 3 steps: Visual inspection, measurement process and baking process.
For the first step, there is only one high-power scope that is in new product inspection lab and only available 4 hours per day from every Monday to Wednesday. An engineer needs around 4 to 8 minutes per piece to finish the inspection process, after inspection, parts will be sent for measurement process.
The second step is measurement process which included GRR testing, Dark current measurement and Optical testing. Benchtop Chamber is required in this step. There are two chambers available to use, one is in Singapore, and the other is in Zurich. Transition time between these two locations is 3 days from Mondays to Wednesdays, 5 days on Thursdays and Fridays. The operating hours for chambers depend on engineer’s working hours, engineers are working 6 hours per day and 5 days per week. The software used in measurement need around 5 minutes set-up time. To start the measurement process, a GRR testing is required once per day using standard GRR module, this is to ensure the stability of machine condition. These quantity needs additional timing apart from the testing population. Each GRR module needs a 5-minute processing time and 4 GRR modules are needed every day every time before Dark current and optical testing starts. Dark current and Optical measurement need two different setup and software script, so there’s a 2 to 3 minutes setup time between these two processes. Loading and unloading modules in measurement step ranges from 6 to 9 minutes due to the skillfulness difference between engineers. Processing time for Dark current process and optical process is 5 minutes and 20 minutes per piece. After measurement process finished, 50 sec is needed to unload module from the chamber.
Baking process is the next step once measurement done. There will be two heating and drying ovens allocated to this project, one in Singapore and the other in Zurich. Both ovens can be used 24 hours 7 days. Above three processes need to repeat 6 times as the baking condition in each time is different. In the first round, parts are required to do 168 hours baking under temperature of 85 degree, in the second round, baking time is 332 hours under temperature of 85 degree, in the third round, baking temperature changed to 125 degree with baking time 168 hours, in the fourth round, baking time is 332 hours under temperature of 125 degree, in the fifth round, baking temperature is changed from –40 degree to 85 degree with cycle time 0.5 hours per cycle, 500 cycles are needed in this process, in the last round, 250 cycles are needed under same temperature range. The location for measurement process and baking process can be randomly chosen as long as the machines are available. And dark current process and optical test process in the measurement step can also be done using two Benchtop chambers. After baking process, a visual inspection for all quantity is needed, until now, this project is called finished.
In this project, only 3 engineers in Singapore and 2 engineers in Zurich are available daily, their working hours is from 8:30am to 5:30 pm, with lunch break 1.5 hours start from 12pm. Machine condition used in Measurement step is not stable, so machine breakdown will happen randomly, each breakdown requires an engineer 1.5 hours to repair and once machine breakdown, the whole project will be delayed 2.5 hours per day.
Figure 3.1.1.1 shows the process flow.
Figure 3.1.1.1
Figure 3.1.1.2
Analysis study
Before the simulation model is built, the first step to do is to make an analysis, below figure shows the model structure for this case study:
•Process time:
•Inspection: process for t 4, 5, 8 min
•Transition: wait for u 4, 1 day (for machine 2)
•Measurement: Set up for u 4, 1 min
•Measurement: GRR runs for e 5 min
•Measurement: Remove for t 6, 8, 9 min
•Measurement: Dark current run for e 5 min
•Measurement: Software set up for u 2.5, 0.5 min
•Measurement: Optical run for e 20 min
•Measurement: remove for e 50 sec
•Baking: 168h/85degree (1st time); 332h/85degree (2nd time); 168h/125degree (3rd time); 332h/125degree (4th time); 250h/-40~85degree (5th time); 125h/-40~85degree (6th time)
•Territories (Queues)
•Inspection: wait (∞)/process (1)
•Measurement: wait (2)/process (1)
•Baking: wait (2)/process (1)
•Resource
•Inspection: (1)
•Measurement: (2)
•Baking: (2)
•Break down
•Engineer
•Lunch, 3.5 hours, 1.5 hours
•6 hours per day
•Measurement
•Break down u 3, 3 hr
•Repair e 1.5 hr
Simulation modelling
Since this case is to find out the total number of parts per batch, so the sequence of whether a part is measured in SG or ZRH or baked in any of these two places are not important, the routine for the measuring and baking process should be randomly picked making each location has the equal chance to be selected. Based on the structure shown in 3.1.2, the model can be drawn easily, model structure shown in below figure and the logic file with simulation coding will be attached in appendix afterwards.
Conclusion
What’s the conclusion?
Shortest path Algorithms
Problem definition
In shortest path Algorithms case study, the schedule required is to find an optimal solution for a project so that the project duration can be minimized. The testing orders and which part should go to which location for a measurement test and baking process to achieve a shortest project duration will be studied via Automod simulation software.
The total test quantity is still 240 pcs but is divided into three equal quantity batches. These three batches will be sent for inspection together and then do the measurement, after measurement process, these three batches of parts will go through a baking process under three baking conditions and each batch will do their own inspection, measurement and baking process again.
There will be two Benchtop chambers available in Singapore and Zurich for measurement procedure with transition time 3 days from Mondays to Wednesdays, 5 days on Thursdays and 4 days on Fridays.
Batch 1 after measurement process requires 168 hours baking under temperature of 85 degree, and this batch will then go back to inspection process and measurement process, followed by a baking process of 332 hours under same temperature. Batch 2 requires 168 hours baking under temperature of 125 degree, and then goes back to inspection process and measurement process, followed by a baking process of 332 hours under same temperature. Batch 3 requires 100 baking cycle with temperature range from -40 degree to 85 degree, and this batch will also do the inspection process and measurement process, followed by a 400-baking cycle with same temperature range of 332 hours under same temperature. Later this batch need a third time inspection checking and measurement testing followed by another 250-baking cycle of the same temperature range. The baking cycle time is 0.5 hours per cycle for each baking process. The conditions of time used in each procedure, machine stability, and engineer working hours are all same with the one in cycle time reduction case.
Below is the figure for overall scheduling network of this shortest path Algorithms case.
Analysis study
Similarly, we draw the flow diagram for this case:
•Process time:
•Inspection: process for t 4, 5, 8 min
•Transition: wait for u 4, 1 day (for machine 2)
•Measurement: Set up for u 4, 1 min
•Measurement: GRR runs for e 5 min
•Measurement: Remove for t 6, 8, 9 min
•Measurement: Dark current run for e 5 min
•Measurement: Software set up for u 2.5, 0.5 min
•Measurement: Optical run for e 20 min
•Measurement: remove for e 50 sec
•Baking: 168h/85degree (1st time 1st batch); 332h/85degree (2nd time 1st batch); 168h/125degree (1st time 2nd batch); 332h/125degree (2nd time 2nd batch); 50h/-40~85degree (1st time 3rd batch), 200h/-40~85degree (2nd time 3rd batch); 125h/-40~85degree (3rd time 3rd batch)
•Territories (Queues)
•Inspection: wait (∞)/process (1)
•Measurement: wait (2)/process (1)
•Baking: wait (2)/process (1)
•Resource
•Inspection: (1)
•Measurement: (2)
•Baking: (2)
•Break down
•Engineer
•Lunch, 3.5 hours, 1.5 hours
•6 hours per day
•Measurement
•Break down u 3, 3 hr
•Repair e 1.5 hr
Different from previous case in section 3.1, shortest path Algorithms case need the model choose the measurement and baking process through a certain routine. After comparing the
Simulation modelling
The best way to solve this time deduction problem is to build a simulation model, based on the requirement in problem definition part, the simulation model is shown as below:
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