Facilities and Logistics
What to master
Layout types and when each fits: process (job shop, high variety), product (flow line, high volume), fixed-position (large assemblies), and cellular. Know the tools - from-to charts, closeness/relationship charts from systematic layout planning, activity relationship diagrams, and the load-distance model. For line balancing: cycle time = available time / required output; minimum stations = ceiling of (sum of task times / cycle time); efficiency = sum of task times / (actual stations x cycle time). Understand material handling, storage and AS/RS, warehouse design, cross-docking, order picking, and transportation basics (center of gravity, transportation model, milk runs). Dock queueing and equipment counts round out the quantitative side.
Traps
- Rounding the minimum number of stations down instead of up.
- Choosing a cycle time smaller than the largest task time, making the line infeasible.
- Ignoring precedence constraints when assigning tasks to stations.
- Comparing layouts on distance alone without weighting by load.
- Confusing aisle space, cube utilization, and footprint when sizing storage.
- Forgetting that center-of-gravity solutions ignore real road networks.
Worked example
Available time 450 min/day, demand 900 units: cycle time = 0.5 min. Total task time = 4.0 min, so minimum stations = ceiling(4.0/0.5) = 8, giving efficiency 4.0/(8 x 0.5) = 100%. If precedence forces 9 stations, efficiency falls to 4.0/4.5 = 89%.
Rule of thumb
Closeness ratings and from-to charts answer "adjacent or apart"; load-distance answers "how much movement." Use the first for relationship-driven layouts, the second for cost-driven ones.