Week 8 - Little’s Law And Theory Of Constraints Flashcards
What is the difference between lead time and cycle time?
Lead time is measured by elapsed time (minutes, hours etc) but cycle time is measured by the amount of time per unit (e.g minutes per hours/customer/unit etc)
Formula for throughput efficiency
Work content (time to build a unit) / lead time x 100
What was Shingo’s P-D ratio?
The time to Produce a product / the time given by the customer to Deliver the product
What is the formula for throughput rate?
1/cycle time
Formulas for lead time (2)
• Cycle time x WIP
• Wip/throughput rate
Formula for Little’s law in operations (2)
• L = λW
• L is the average number of customers in a stable system, λ is equal to the throughput rate, W is the time a customer spends in the system
What is meant in theory of constraints?
The speed at which an operation can run is determined by one step which is the bottleneck - bottlenecks limit the speed of an entire operation
Why is a bottleneck an important focus area?
Because if a bottleneck’s capacity can be increased it will increase the system capacity
Example of a bottleneck
The dryer is the bottleneck as it is slower than the process in front of it
Define lead time
Is the average length of time it will take a new set of inputs to move all the way through the operation, assuming no unusual measures are taken
Formula for direct labour utilisation
WIP / Number of operators
Little’s law applied to a balanced line:
What is throughput rate?
What is the cycle time?
What is the WIP?
• Throughput rate is 20 units per hour
• Lead time is 15 minutes
• Wip is = number of operators
How do you calculate the balancing loss? (3)
• Sum the difference between the balance cycle time and the unbalanced cycle time
• The divide that by number of operators multiplied by the balance cycle time for one operator
• Then get a percentage which shows the amount of employee and working time lost
