Manufacturing Systems
Manufacturing Systems tests how you design and run the flow of work: capacity, takt, line balancing, lean pull, MRP, and the metrics - OEE, WIP, lead time - that expose problems. Expect calculation items, not just definitions.
Flow fundamentals
Takt time = available production time / customer demand. It sets the pace, not the cycle time of any single station. Line balancing assigns tasks so no station exceeds takt; the theoretical minimum number of stations is total task time divided by takt, rounded up. Real lines add stations for precedence and balance delay.
Little's Law: WIP = throughput × lead time. Cutting WIP is the fastest way to shorten lead time, which is why pull systems cap WIP with kanban rather than pushing work into the floor.
MRP versus lean: MRP explodes a bill of materials against demand and lead times; it performs well with stable demand and known lead times. Kanban pull performs well with repetitive demand and fast replenishment. Pushing MRP into a volatile mix generates expediting and excess inventory.
OEE
OEE = Availability × Performance × Quality.
- Availability = run time / planned production time. Planned breaks and preventive maintenance are excluded from planned time; breakdowns and changeovers are losses.
- Performance = (ideal cycle time × total count) / run time.
- Quality = good count / total count.
Worked example
Planned time 480 min, unplanned downtime 48 min, ideal cycle 1.0 min, 380 units produced, 12 scrapped. Availability = (480 − 48)/480 = 0.900. Performance = (1.0 × 380)/432 = 0.880. Quality = 368/380 = 0.968. OEE = 0.900 × 0.880 × 0.968 ≈ 0.767, or 76.7%.
Traps
Counting planned breaks as availability loss. Using actual instead of ideal cycle time in Performance, which hides slowdowns. Treating takt as a number you may round to whatever the fastest machine does. Forgetting that eliminating rework raises Performance as well as Quality when rework consumes run time.