In their ground-breaking book, Learning to See, Mike Rother and John Shook introduced the world to a new value-identifying and value-creating tool called the value stream map. Actually, Toyota had been using a variation of Rother and Shook’s technique long before, but it was Rother and Shook that launched American businesses and the rest of the world on their journey to first identify and then eliminate all forms of waste through the eyes of this tool. Toyota refers to it as “material and information flow mapping,” and it clearly serves a vital function. It allows you to view and depict the total process as it exists today and then imagine the future, or ideal state, as you would like it to be. If used as intended, this tool will tell you how your own flow of material, information, and people is and might be. To quote Rother and Shook, “Whenever there is a product for a customer, there is a value stream. The challenge lies in seeing it.”
I think most of you understand the concept of value and what a value stream is, but in case you have missed it along the way or have not been exposed to it, in simplistic terms, the value stream is all those things you do to convert raw materials into a finished product that creates value. Value is simply all of those things that a customer is willing to pay for. Rother and Shook tell us, “Taking a value stream perspective means working on the big picture, not just individual processes, and improving the whole, not just optimizing the parts.” As I’ve said many times in other postings, my emphasis is always on improving the system, not just optimizing parts of it. In fact, this focus on system rather than parts of it is paramount to the success of any for-profit business or organization.
As a tool or technique, the value stream map (VSM) uses a variety of symbols, or a sort of shorthand notation, if you will, to depict various elements within the process. For example, a triangle with a capital “I” inside of it represents inventory, with the amount of inventory entered directly beneath the triangle. There are various material flow icons, general icons, and information flow icons used to represent all the specific elements within the process. I highly recommend Rother and Shook’s Learning to See for details on the specifics of their methods and styles for producing a VSM and the various icons they use. However, from my perspective, it is not as important to get the VSM perfect as it is to get it functional.
So one question you might ask is why is value stream mapping such an essential tool? Rother and Shook have answered that question with a list of eight reasons:
· It helps you visualize more than just the single-process level (i.e., assembly, welding) in production. You can see the flow of the process and the information.
· Mapping helps you see the sources of waste in your value stream that may not be obvious to you without visualizing it.
· It provides a common language for talking about manufacturing processes.
· It makes decisions about the flow apparent, so you can discuss them. Otherwise, many details and decisions on your shop floor just happen by default.
· It ties together Lean concepts and techniques, which help you avoid cherry-picking.
· It forms the basis of an implementation plan. By helping you design how the whole door-to-door flow should operate—a missing piece in so many Lean efforts—value stream maps become a blueprint for Lean implementation. Imagine trying to build a house without a blueprint.
· It shows linkage between the information flow and the material flow. No other tool does this.
· It is much more useful than quantitative tools and layout diagrams that produce a tally of non-value-added steps, lead time, distance traveled, the amount of inventory, and so on. In other words, value stream mapping is a qualitative tool by which you describe in detail how your facility should operate in order to create flow. Numbers are good for creating a sense of urgency or as before and after measures. Value stream mapping is good for describing what you are actually going to do to affect those numbers.
Although I agree with most, if not all of these eight reasons, I have added a ninth reason to this list: The VSM can be used to identify the current and next constraint. This, I might add, is actually first on my list because it trumps the first eight reasons. My motivation for considering this step the most important is because it is the quintessential starting point in any improvement process. As I’ve said many times before, improvements in non-constraints are typically wasted effort because the real improvement comes when the constraint capacity is improved. The constraint controls the flow and throughput of the system. This is yet another example of why it is so important to combine or integrate Lean and Six Sigma with the Theory of Constraints.