Continuous Improvement
What to master
This domain rewards fluency in improvement methodologies and knowing which one a scenario calls for. Expect PDCA and DMAIC (define, measure, analyze, improve, control) contrasted with DMADV for new design; DMAIC assumes an existing process with data.
Lean targets waste and flow. Memorize the seven wastes - transport, inventory, motion, waiting, overproduction, overprocessing, defects - and note that overproduction is usually called the worst because it hides the others. Lean tools: 5S, value stream mapping, kanban, standard work, SMED, TPM, poka-yoke (error-proofing), jidoka, heijunka, and kaizen (small, continuous, everyone) versus kaikaku (radical). Distinguish muda (waste), mura (unevenness), and muri (overburden) - a frequent distractor.
Six Sigma targets variation and defect reduction; the benchmark is 3.4 defects per million opportunities. Know the belt roles (champion/sponsor, master black belt, black belt, green belt) and that the champion removes barriers and owns the project charter. Also know the Theory of Constraints sequence: identify, exploit, subordinate, elevate, repeat - and that improvement elsewhere does not help the bottleneck.
Worked example. A cell produces 2,000 units, each with 5 opportunities for a defect, and inspection finds 4 defects. Opportunities = 2,000 × 5 = 10,000; DPMO = (4 / 10,000) × 1,000,000 = 400. Compare that with the 3.4 DPMO six-sigma benchmark to see the gap. Forgetting to multiply by opportunities is the standard error.