Kaizen is more of philosophy than a specific tool. The word, in Japanese, simply means “good change” or improvement. Adopting a Kaizen mindset means acknowledging that everything can be improved and made to perform more efficiently and with better quality. The Kaizen approach can be applied to small opportunities for improvement addressed by individual, front line employees, or to larger more complex problems which are addressed by teams and sometimes called, “Kaizen events.” Kaizen is an ideal every-day philosophy for organizations. It leverages the insight of employees at all levels to identify and act on opportunities for improvement, big or small.
Lean is a business philosophy and methodology that is focused on improving business results by identifying and eliminating waste and maximizing the value delivered to customers -- delivering the best quality on time or as quickly as possible. Any energy, money, and time that are used on processes or activities that do not provide value to the customer are targeted for reduction through various methods. Practitioners use a variety of tools including value stream maps, and gemba walks to organize the improvement effort. Lean provides excellent tools not only for improving existing processes, but also for designing and developing processes when there aren’t any processes in place or when major overhauls are necessary.
Six Sigma is an approach to limiting defects and variability in business process in order to achieve quality outcomes. It offers two project methodologies, DMAIC (define, measure, analyze, improve and control) and DMADV (define, measure, analyze, design, and verify). These are based on the Plan-Do-Check-Act approach made popular by W. Edwards Deming. Six Sigma is ideal for optimizing and maintaining processes that are generally effective to begin with.
So which one is best? It's sort of a trick question, and not necessarily the right one to ask. The question is valid, it’s but a bit like asking, “Which hand tool is best?” It might be a hammer or it might be a screwdriver; it depends on whether you are trying to hang a picture or fix a loose doorknob. Each approach is well suited for different situations and problems.
The important thing is to pick the right tool for the job. Or to combine them, as many of our customers do.