More on Single Piece Flow
Have had a wonderful series of conversations with one of our production associates over the past 10 days. She has read a fair amount about Lean Manufacturing and wants to learn more.
Her question: "Joe, just how small must lot size be to get to single piece flow?"
Very perceptive. And there is not a clear answer.
Consider a process in which a five-foot pipe is cut into one foot sections. Is single piece flow 5 one-foot pieces? Isn't 5 more than 1? But if flow is 1 one-foot piece, what do you do with the rest of the raw material, which is now four feet long? Do you minimize scrap by always making a "batch" (gasp) of 5?
Before she asked me the question, our associate was already grappling with these questions. My response to her was "Well, it depends." Other factors play in; cost of the raw material, impact of scrap, processing time, overall demand of the customer, and so on. Single piece flow is one important part of the equation...but only one part.
In any event, we want to get lot sizes to their smallest logical level. And that level demands clear-headed thinking. And, never, ever, ever forget to listen carefully to the person actually touching the material.
I hope this is helpful.