In my last post, I wandered around, "covering" some of the "why's" of Value Stream Mapping (VSM).  I gave some illustrations as to how most manufacturing processes lose time, not in the actual task steps but in between those steps.  So, long wait times are a problem. (I'll have more to say about this later, maybe in a subsequent post.)  Variable wait times are just as important an issue.

Remember that machine shop I talked about in my last post?  Sometimes they managed to get a batch of parts to the next step in the process within a minute, other times it took a few weeks.  Mostly it took about an hour or less. 

Why the variability?  What's keeping that shop from getting the parts to the next operation within a minute all the time?  They do it when "they really need the part"?  Why not each and every time?

The answer to that question is to uncover just about every ill and affliction experienced by the shop.  Wrong material.  Bad material. Poor planning and scheduling.  Lack of availability of tools, tooling, equipment, personnel, machinery, supplies or information.   Poor order entry.  Making unreasonable and unrealistic promises to customers (that cause the unreasonable and unrealistic promises they made last week to get broken).

(You'll notice that few of these causes go directly back to operator performance.  Time and motion studies always go back to operator performance.)

There's another reason this variability exists...management and ownership's worldview is deficient and faulty. In their view, the time an unfinished product spends sitting and waiting doesn't matter because it's "free", i.e., no resources (aka, labor) are being put into it. 

I consulted for a company that made overhead cranes for the steel and other heavy industries.  Building a large overhead crane is like building a house; it's a construction project in which many subassemblies that can be fabricated separately are brought together into one big assembly late in the process.  I ultimately failed in getting the production manager and supervisors to take a "value stream" approach to the planning and execution of crane building.  Their view was that, if a specific subassembly was delayed for any reason, they could assign the workers to a different subassembly.  Rarely were delays such that workers were altogether idle.  They just did not view work that sat for days, weeks, and even months as a problem so long as they were able to have workers attend to other duties.

VSM mapping, then, is a powerful tool but only in the hands of folks who will treat the information it provides seriously.