2. CH7 Flashcards
(24 cards)
Little’s Law
WIP = TH•CT
The average quantity of good (non-defective) parts produced per unit time
Throughput (TH)
Material stocked at beginning of routing
Raw material inventory
Material held in a stock-point at the beginning of a routing
Crib inventory
Material held in inventory prior to shipping to the customer
Finished goods inventory (FGI)
Time between release of the jobs at the beginning of the routing until it reaches an inventory point at the end of the routing
Cycle Time (CT)
Service Level
Pr(Cycle Time <= Lead Time)
A manufacturing system is a goal-oriented network of process through which parts flow
Factory Physics Definition
Plant is made up of routing (lines), which in turn are made up if processes
Factory Physics Structure
Rate (parts or jobs/unit of time) of the process center having the highest long-term utilization
Bottleneck rate (rb)
Sum of the long-term average process times of each station in the line
Raw Process Time (T0)
A unit-less measure of congestion
Congestion coefficient (alpha)
Alpha = 0
Zero variability case
Alpha = 1
Practical worst case
Alpha = Critical WIP (W0)
Worst possible case
Maximum throughput with minimum cycle time
Critical WIP (W0)
Critical WIP (W0)
W0 = rb•T0
Max TH, min CT, no randomness
Best case performance
Min TH, max CT, no randomness
Worst case performance
In a balanced line, Critical WIP (W0) = Number of machines
In an unbalanced line, Critical WIP (W0) < Number of machines
Maximum randomness
Practical worst case (PWC)
Conditions for PWC
- Balanced line
- Single machines
- Memoryless
If we improve the non-bottleneck
Then rb does not change, but it serves to reduce randomness
Unbalanced lines exhibit
Less congestion than balanced lines
