Value stream analysis is conducted typically for one specific product or service family at a time. In order to identify and distinguish families, lean practitioners use what is called a product family analysis matrix (a.k.a. product quantity process matrix (PQPr)). Many times the families can be easily discerned once the matrix is populated, other times, it is more difficult. The application of a dendogram or binary sort, can be helpful in these situations. Value stream analysis and, with it, flow kaizen, is central to any lean transformation and is specific to product or service families.
Value stream analysis is an effective way to identify improvement opportunities within a product or service family’s value stream, envision a leaner future state and develop an actionable value stream improvement plan to achieve the future state. It's bread and butter stuff for the lean practitioner. Most folks are well acquainted with the value stream map’s lead time ladder. And many people are familiar with the concept of rolled throughput yield.
A rather simple sounding but often vexing challenge that faces lean practitioners is: What is the optimal physical route for pickups and/or deliveries? This is especially true for a fixed interval, variable quantity material replenishment system design for water spider (a.k.a., waterspider, material handler, mizusumashi, etc.) conveyance.
Interestingly enough, the same question and logic applies when designing the best neighborhood snow plow route.
From my experience, there are a handful of pull system design steps. This post seeks to "simply" outline those steps and some of the math that should be considered.
However, don't let the brevity of this post mislead you. It isn't necessarily simple.
We will address more and more of the referenced math through future Lean Math posts.
Lean practitioners must properly identify product families in order to value stream map a given family’s flow of material and information. That’s very important, but not always simple.
In order to illustrate how to identify product families and thus value streams, consider the following example. Three different patient groups go to a hospital. The treatment for patient groups 1 and 2 consists of three steps A, B, and C. However, the treatment for patient group 3 consists of only step D.
Recently a reader posed the following value stream mapping lead time related question(s). My experience, after facilitating more value stream mapping activities than I care to remember, is that it's not an uncommon question. In fact, it's a very good question.
I provided a quick answer...supplemented by a very sophisticated graphic (recently enhanced, in red, based on a comment from Sandor).
Here's some often overlooked and misunderstood value stream mapping math.
The lead time ladder has two levels or “rungs.” The bottom rung is the process or processing rung on which the relevant process time is dropped down. This is usually pretty straightforward...unless there is a split or branch in the material, service or knowledge flow within the value stream.