Lean Principles and Waste Elimination
What the exam tests
This domain tests whether you can define value from the customer's perspective, separate value-adding from non-value-adding work, and select the right Lean countermeasure. Expect items on the eight wastes, takt time, value stream mapping, flow, pull, 5S, and kaizen.
Core rules
- Value is customer-defined: a step adds value only if the customer would pay for it, it is done right the first time, and it physically changes the product or service.
- The eight wastes are defects, overproduction, waiting, non-utilized talent, transportation, inventory, motion, and extra processing (TIMWOODS). Overproduction is often called the worst because it creates or hides the others.
- Takt time = available production time / customer demand. It sets the required pace, not the capacity of any single machine.
- A value stream map shows material and information flow, lead time, and process time; the future-state map targets flow and pull.
- 5S (sort, set in order, shine, standardize, sustain) is a foundation for visual control, not a one-time cleanup.
Worked example
A plant runs two 480-minute shifts with 30 minutes of breaks each and must ship 900 units per day. Available time = 2 x (480 - 30) = 900 minutes, so takt = 900 / 900 = 1.0 minute per unit. A bottleneck with a 75-second cycle time cannot meet takt: it needs 900 x 75 = 67,500 seconds = 1,125 minutes, or 225 minutes of overtime. The reasoning matters: takt is demand-driven, and you compare it with cycle time at the constraint, not with an average across the line.
Traps
Confusing takt with cycle time; treating all inventory as waste when a deliberate buffer protects flow; using local efficiency as a proxy for flow; and listing transportation when the real issue is layout-driven motion.