Lean Systems and Value Stream Management
Domain 4: Lean Systems and Value Stream Management
This domain tests end-to-end design: value stream mapping, takt, flow, pull, leveling, kanban, standard work, jidoka, SMED, TPM, and the value stream manager's role. Questions ask you to choose the system design that meets customer demand with the least waste.
Core rules
- A value stream is the end-to-end sequence of value-adding and non-value-adding steps; map material and information flow.
- Takt time equals available work time divided by customer demand; it sets the pace, not the actual cycle time.
- Flow where you can, pull where you cannot flow; supermarkets and FIFO lanes control inventory.
- Level demand and level work to reduce Mura; variation creates Muri and Muda.
- Standard work defines the current best method, sequence, and takt-based cycle time.
- Jidoka stops the process at abnormality; andon and poka-yoke make defects visible at the source.
- A value stream manager owns the whole stream, not one department's efficiency.
Worked example
Available time is 27,000 seconds per day; demand is 450 units. Takt equals 27,000 ÷ 450 = 60 seconds. The bottleneck runs at 75 seconds, so the stream cannot meet demand even if other steps are faster. The future state should reduce the bottleneck to below 60 seconds through SMED, TPM, or work redistribution, then connect steps with a FIFO lane and a supermarket kanban where flow is interrupted. Reasoning: improving a non-bottleneck adds cost, not throughput; the system constraint sets output.
Traps
- Confusing takt with cycle time or lead time.
- Improving a non-bottleneck and claiming throughput gains.
- Installing kanban without stabilizing demand, quality, or replenishment.
- Mapping only material flow and ignoring information flow.
- Optimizing departmental efficiency instead of value stream flow.