Supply Chain and TOM Analytics Flashcards
What is the CYCLE TIME of a operation?
The Cycle TIme is the gap between items coming out of the end of the operation.
It is the reciprocal of the OUTPUT RATE
In the following serial system, the numbers in the boxes represent the CYCLE TIMES of each stage.
Which of the two stages will act as the bottleneck?
FORMATTING
(The bottleneck will be the operation with the longest cycle time).
In the following serial system, the numbers in the boxes represent the OUTPUT RATES of each stage.
Which of the two stages will act as the bottleneck?
INITIAL DATA ENTRY
(The bottleneck will be the operation with the lowest output rate).
In the following combined system product can flow through either the top or bottom branches. The figures in the boxes are cycle times in minutes.
What is the cycle time for the combined system?
Through top route: 15 per hour (because 60/4 = 15)
Through bottom route: 12 per hour (because 60/12 = 5)
So combined output = 27 per hour = 27/60 per minute = 9/20 per minute = 0.45 per minute
So combined cycle time = 20/9 minutes = 2.2 minutes
In the following combined system product can flow through either the top or bottom branches. The figures in the boxes are cycle times in minutes.
What is the cycle time for the combined system?
Through top route: 2 per hour (because 60/30 = 2)
Through bottom route: 1 per hour (because 60/60 = 1)
So combined output = 3 per hour = 3/60 per minute = 1/20 per minute
So combined cycle time = 20 minutes
What is the leadtime for the following process (the figures in the boxes are cycle times in minutes).
13
In steady state, it will take 13 minutes for an item to get from one end of the process to the other.
For Little’s Law to apply, what are the two key assumptions we must use?
‘Steady State’ and ‘on average’.
Little’s Law says that if we’re considering the steady state, the work-in-progress in a system will be equal to the leadtime (also known as the throughput time) multiplied by the output rate.
What goes in and out of the boxes in an IDEF0 diagram?
What is ‘Backward Scheduling’?
BACKWARD SCHEDULING:
starts from the required time, and works backwards to determine the latest possible time that a job can start.
In steady state, what is the average work-in-progress for the following system? (The figures in the boxes are cycle times in minutes)
In steady state, it will take 13 minutes for an item to get from one end of the process to the other, so the leadtime is 13.
The output rate will be 1/3 items per minute, because the bottleneck cycle time is 3 minutes.
Using Little’s Law, average WIP will therefore be 13/3 = 4.33.
What is ‘Forward Scheduling’?
FORWARD SCHEDULING:
This starts from ‘now’, and works forward to find out when things will be finished.
What is the bottleneck stage in this process?
(The numbers in the boxes are cycle times in minutes).
WRAPPING
(cycle time = 4 minutes)
What is the combined cycle time for this system?
(Figures in boxes are cycle times in minutes).
The combined cycle time is 3.33
The drilling stage is the bottleneck: every 10 minutes, three items emerge from this stage, so its output rate is 3/10 items per minute = 0.3. This is lower than the output rate of of the other stages (0.33 for unpacking, wrapping and labelling; 1 per minute for cleaning).
So bottleneck output rate = 0.3 items per minute, so combined cycle time is 1/0.3 = 3.33
In this system, in steady state, how long will an item spend in packing as a percentage of its total leadtime in the system?
(Figures in boxes are cycle times in minutes).
3.03%
Total leadtime will be 33 minutes.
So item will spend 1/33 of its time in the system in the packing operation = 3.03%
In this system, in steady state, what will be the utilization of Station D? (In other words, for what percentage of the time will it be busy?)
(Numbers given are cycle times in minutes).
87%
Station D will be only be working for 5.4 minutes in every 6.2 minute cycle (set by Station A, which is the bottleneck), so its utilization will be 5.4/6.2 = 87%
In this system, which station is the bottleneck operation?
(Numbers given are cycle times in minutes).
Station A is the bottleneck, because it has the longest cycle time (6.2 minutes).
In this system, what is the leadtime for an item going through the system?
(Numbers given are cycle times in minutes).
The leadtime = 27.5 minutes
6.2 + 5.6 + 6.0 + 5.4 + 4.3 =27.5
In this system, the figures in the boxes are the output rates of the individual stage. Which stage acts as the bottleneck?
Station B
Station B has the lowest output rate.
In this system, the figures in the boxes are the output rates of the individual stage. Would increasing the capacity of Station D increase the capcity of the overall system?
No.
Station B has the lowest output rate, and is the bottleneck in the system, Increasing the capacity of a non-bottleneck will not increase the capacity of the overall system.
