Nov 10 2014
Change your production leveling strategy to achieve flow | Ian Glenday | Planet Lean
“…What I came to call Repetitive and Flexible Supply (RFS) is based on the idea of manufacturing the largest products in the same sequence at the same time every week. To many people, this sounds ridiculous and stupid at first.
My analysis consistently showed that, typically, 6% of a company’s products represent 50% of the volume it produces.
I started to see this happen in every factory, hospital, or office I went to. And that’s when it hit me – why not simply focus on stabilizing the plan for that 6% of the products?…”
Ian Glenday’s idea of RFS is fine, but not quite as original as presented in the article. Making it easy to do what you do the most often is the motivation behind the Product-Quantity (P-Q) analysis I learned in Japan in the 1980s.
To use the terminology introduced in the UK by Lucas Industries about that time, it breaks the product mix into Runners, Repeaters, and Strangers. You make each Runner is an dedicated production line, because it has a volume that justifies it.
Then you group Repeaters in families and make them in flexible lines, and you keep a residual job-shop to make the Strangers — the long tail of your demand — products in large numbers but with low and sporadic demand.
This method is described, as prior work, in Lean Assembly as a foundation for assembly line design, and in Lean Logistics for warehouse/supermarket design and for production scheduling, in particular heijunka.
See on Scoop.it – lean manufacturing
Rob van Stekelenborg | Dumontis
November 13, 2014 @ 1:53 am
Having read the book, I was surprised to find that the first step of the advocated RfS approach in fact constitues pure push flow! A fixed sequence, fixed frequency, fixed quantity schedule where all variability should be absorbed by inventory. I am not sure whether this is truly where we want and need and are even allowed by our companies to start… The risk also is that the first step already takes quite a while and we get into a new status quo that hasn’t got anything to do with pull flow and that will last for years
A second thing I noted is that “the sieve” is nothing new and has existed since the 1950’s I believe (H.F. Dickie, 1951 if I’m correct). And in my experience, the volume analysis alone also doesn’t provide all the inisghts you need. I always add a frequency analysis (how often shipped to/ordered by the customer) as I have come across situations with high volume low frequency shipments that also need to be dealt with (eg interregional/export supply).
Now I know we don’t want that, but leveling it ourselves over long intervals does create inventory and blocks sometimes sparce surface during long periods, and customers do not always just change their ways overnight. In the mean time, we have to manage these situations as well.
Anyway, I was somewhat disappointed by the whole book and the related articles. I do however understand that companies embrace it, as it is an easier way to say we’re doing “Lean” in supply chain (although I personally don’t consider it Lean).
November 13, 2014 @ 10:51 pm
You are ahead of me here, since I have not read the RFS book. I was only reacting to the article.
When you schedule production in a fixed, repeating sequence, I like to think of it as a reservation system. A time slot is reserved for a particular product, based on its history of capacity requirements, but this slot is used as planned only is some sort of pull signal confirms the reservation.
You also try to make the sequence as short as possible. If your setup times are 0, you can change product with every unit, as happens with heijunka in final assembly of cars. The sequence is calculated for one shift. Given that the order fulfillment lead times are in days it makes no difference to the customer whether one unit is assembled at 7:43AM or 1:16PM the same day. It will be delivered at the same time anyway.
That the time horizon for sequencing the line is short with respect to the order fulfillment lead time gives you the freedom to pursue goals that are indifferent to customers. The direct purpose of heijunka is not related to customers; it is instead to smooth the workload of feeder lines and immediate suppliers. It is to dampen or eliminate the bullwhip effect upstream in the supply chain.