Manufacturing Processes and Production: Flow, Pace, and the Constraint
Production questions test flow
Understand how customer demand sets the pace, and where work actually piles up.
Demand and pace. Takt time = available production time ÷ customer demand - the rate you must produce to satisfy the customer, not the rate you currently achieve. Cycle time is how long one unit actually takes at a station. If a station's cycle time exceeds takt, it cannot keep up and becomes the constraint. The bottleneck - the slowest step - sets the output of the entire line. Improving a non-bottleneck adds work-in-process, not throughput.
Lean building blocks. Standard work fixes the best-known method and sequence. 5S organizes the workplace. Poka-yoke (error-proofing) prevents mistakes at the source instead of catching them in inspection. Kanban signals replenishment in a pull system, so material is produced to replace what was consumed rather than pushed by forecast. Setup reduction (SMED) converts internal setup, done with the machine stopped, into external setup, done while it runs - shrinking economic lot sizes.
OEE = Availability × Performance × Quality, each as a fraction. A line 90% available, 95% performance, 98% quality runs at 0.90 × 0.95 × 0.98 ≈ 0.838, or about 84%.
Documentation. The work order authorizes and tracks production; the bill of materials lists components and quantities; the routing lists operations and sequence. Reading a print means handling views, dimensions, tolerances, and surface finish callouts.
Rule of thumb: when a line misses output, find the constraint first. Speeding up everything else raises inventory and cost without raising good output.