W1: The Principle of WIP Constraints: Constrain WIP to control cycle time and flow.
Limiting work-in-process (WIP) prevents the catastrophic high-queue states described in Q15: The Diffusion Principle.
WIP constraints work by blocking new work when queue size reaches a predetermined limit (k), creating an M/M/1/k queueing system. This creates three effects, one positive and two negative. The positive is dramatically reduced average cycle time by preventing queue explosions.
The negative effects are rejected potentially valuable work during congestion periods and reduced capacity utilization when demand is blocked.
The cycle time reduction typically provides 10x more economic value than the costs of blocked demand and capacity underutilization.
W2: The Principle of Rate-Matching: WIP constraints force rate-matching.
W3: The Principle of Global Constraints: Use global constraints for predictable and permanent bottlenecks.
W4: The Principle of Local Constraints: If possible, constrain local WIP pools.
W5: The Batch Size Decoupling Principle: Use WIP ranges to decouple the batch sizes of adjacent processes.
W6: The Principle of Demand Blocking: Block all demand when WIP reaches its upper limit.
W7: The Principle of WIP Purging: When WIP is high, purge low-value projects.
W8: The Principle of Flexible Requirements: Control WIP by shedding requirements.
W10: The Principle of Part-Time Resources: Use part-time resources for high variability tasks.
W11: The Big Gun Principle: Pull high-powered experts to emerging bottlenecks.
W12: The Principle of T-Shaped Resources: Develop people who are deep in one area and broad in many.
W13: The Principle of Skill Overlap: Cross-train resources at adjacent processes.
W14: The Mix Change Principle: Use upstream mix changes to regulate queue size.
W15: The Aging Principle: Watch the outliers.
W16: The Escalation Principle: Create a preplanned escalation process for outliers.
W17: The Principle of Progressive Throttling: Increase throttling as you approach the queue limit.
W18: The Principle of Differential Service: Differentiate quality of service by workstream.
W19: The Principle of Adaptive WIP Constraints: Adjust WIP constraints as capacity changes.
W20: The Expansion Control Principle: Prevent uncontrolled expansion of work.
W21: The Principle of the Critical Queue: Constrain WIP in the section of the system where the queue is most expensive.
W22: The Cumulative Reduction Principle: Small WIP reductions accumulate.
W23: The Principle of Visual WIP: Make WIP continuously visible.