2. The fusion of Lean and Six Sigma is required because: Lean cannot bring a process under statistical control Six Sigma alone cannot dramatically improve process speed or reduce Invested Capital Lean is used to drive out wasted time, achieve non-stop operations for maximum efficiency and throughput of production. Lean means reducing Non-value add by streamlining internal (and external) processes. Six Sigma tools & techniques reduce process variability (six sigma levels of process capability) - key element required to achieve lean manufacturing and to ensure ongoing consistent, peak quality.