Slide 1
A required slow stage can limit the whole line
In a simple production line, every finished item must pass through each required stage. A stage with limited effective capacity can restrict the whole line’s output.
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For stages capable of 12, 8 and 10 items per hour, sustained output cannot exceed 8 without changing the constraint. This ideal example assumes comparable items and no additional losses.
Slide 2
Keeping an upstream machine busy may only create a queue
Producing faster before a bottleneck can increase waiting stock without increasing finished output.
Local utilization means how busy a stage is; system throughput measures output from the whole line.
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The extra work in progress occupies space and can delay detection of defects. Improving every machine’s apparent busyness may therefore make the overall operation harder to manage.
Slide 3
Protect the bottleneck from avoidable stops
A bottleneck loses valuable output when it waits for material or stops for avoidable reasons. Reliable supply, maintenance and quality checks can improve its effective capacity.
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Processing defective inputs consumes scarce time that cannot be recovered downstream. Checking quality before the constrained step can be more valuable than discovering the defect after it.
Slide 4
A buffer absorbs interruptions, not a permanent rate mismatch
A buffer can keep one short interruption from immediately stopping another stage. It cannot permanently overcome a slower average processing rate.
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Larger buffers can reduce starvation or blocking but also increase inventory and waiting time. Their value depends on variability and the cost of interruptions, not simply on available floor space.
Slide 5
Improvement can move the bottleneck elsewhere
After a constraint improves, another stage may become the limiting step. Different product mixes and downtime patterns can also change where the restriction occurs.
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A one-time capacity calculation should therefore be checked against operating data. The useful question is which improvement raises the system’s output under the conditions actually expected.
Sources
- Multi-Job Production Systems: Definition, Problems, Analysis, and Product-Mix Performance Portrait of Serial Lines
National Institute of Standards and Technology
- An Examination of National Supply-Chain Flow Time
National Institute of Standards and Technology