I'm about to sign off for the Memorial Day weekend, visiting Washington DC, which seems like a moving time to visit. Best wishes to all, particularly any military veterans reading the blog. Thanks for your service.
I presented at a lean workshop for medical professionals this week and was asked a question afterward:
“The arguments for lean and flow seem so obvious, it really makes sense. So how did the manufacturing world end up with batch?”
I had my answers for that, the long story short is that we could point to a number of factors, including:
- cost accounting encourages “spreading” fixed costs across large production runs
- the U.S. being the only real manufacturing power after WWII, we were successful in spite of batch thinking and mass production, so it was hard to get past
- Sub-optimization encourages departments to crank out parts to keep costs down, accounting systems don't penalize us enough for inventory (calling it an “asset”)
- human nature seems to think batching is “efficient”, doing the same thing over and over is more efficient
How would you have answered her? Would you add points or amplify any of the points above? (This is the audience participation section, feel free to click on “Comments” to chime in).
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Here’s what I would call the simple answer. You can’t just implement flow as a choice. You have to remove barriers to achieve it and the magic is in removing those barriers. Until you can see a way through barriers, you end up with batch.
A little more complicated though is also that you don’t have EITHER batch OR flow. Most ‘lean’ organizations strive towards but don’t achieve complete one-piece flow throughout the entire process. So we all have batch – it’s just a matter of how close to the ideal we get.
The 4 bullets cover pretty well, I think. Sub-optimization along with the desire to reduce the “direct labor component” leads to batching in order to achieve lowest per-unit cost for each department.
I can’t remember who it was (amid the lean blogs) who offered the idea that humans will intuitively batch processes. The analogy of the example was the author’s kid who was entrusted with processing the christmas card list. The child began batching the job instinctively. First putting all the stamps on, sticking in each card, then sealing them up, all in batch mode. Maybe we’re fighting our genetic instincts; in light of that, it’s no wonder lean can seem counterintuitive.
That’s probably a story that is attributed to every lean author at some point, about the kids and the envelopes. I was thinking about that story when I wrote the blog posting. For some reason Jim Womack pops to mind, that he mentioned that in Lean Thinking or I’ve heard him talk about it, but maybe he was quoting someone else.
I think the bullets are pretty accurate. In addition I agree with Jamie- basically batch allows problems to exist and isolates each part of the operation so that a problem in one area does not impact another. Of course this is a fallacy when we see from the waste perspective the added effort and cost (which is hard to see when the cost accounting model is used to measure “efficiency” of individual operations). Perhaps the most simple reason for batching is/was “Because we can.” Toyota really had no choice and had to develop a new reality.
By the way- there are limits to single piece flow and the overriding theme needs to be “total cost” and “overall efficiency.” I have done the Christmas cards and I can do it faster overall by batching because of the inherent waste in handling within that process (picking up the secondary items such as stamps and pens). I like the quote in The Toyota Way (pg. 87) that states flow is not necessarily intended to be “better” for manufacturing, but when a problem occurs people are forced to solve problems and in the process become more capable (my paraphrase). This is why flow is “better” but some sense is still required to understand the overall situation.
To some extent “batch” happens just because we know it can. The truck still leaves at 5:00 p.m. so small batches or 1 piece flow, (either way) will get the order out the door.
Since level-loaded production is a pipe dream for most shops and micro-lead-times are generally not required (yet,) batching is not causing enough perceived pain or inefficiency yet.
I think there is still a disconnect between the real cost of raw vs. WIP & finished goods inventory. People say “well, we already have the materials here so the money is spent.”
We also see important batch processes around most plants, i.e., annealing, curing, and thermal cycle processes etc. Some batches just make sense but wrongly encourage further batch processing.
When I help a company implement Lean I start with 1 piece flow (in most cases) and then work my way backwards if warranted. Generally speaking 1 piece will work most of the time. If I help install KanBans I likewise start with a KanBan of 1 and adjust as needed. Surprisingly enough a KanBan of 1 piece usually works just fine and is often eliminated.
There’s much more I could say on this topic but I won’t right now. I hope my rambling makes sense ; – )
Mark, thanks again for the terrific blog and have a great holiday folks!