“…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.
“Apparently the folks writing about stratifying inventory into A, B and C items and building calculations of such into ERP packages didn’t get the lean memo.
Wikipedia is typical of such thinkers when they describe the ABC thought process as:
‘A’ items – 20% of the items accounts for 70% of the annual consumption value of the items.
‘B’ items – 30% of the items accounts for 25% of the annual consumption value of the items.
‘C’ items – 50% of the items accounts for 5% of the annual consumption value of the items.
The idea of micromanaging some items and slacking off on others based on purchase price is the very same theory they taught me at the University of Cincinnati back in the days when … ”
Michel Baudin‘s comments:
I agree with Bill that, from the point of view of manufacturing operations, the purchase price of materials is not the most important parameter. because the lack of a nail can prevent the completion of a product as effectively as the lack of a pump costing 1,000 times more.
It doesn’t mean, however, that classifying items to treat them differently is wrong, but it must be done by frequency of use rather than price, and I prefer to call the categories “Runners,” “Repeaters,” and “Strangers” rather than A, B, and C.
As a function of rank, I then look for the percentage of units actually built that can be fully assembled with only the items of this rank and higher. It starts at 0%, and, as long as it stays at 0%, I consider the items to be Runners, essentially items you can’t build any product without. At the other end of the spectrum, I call Strangers all the items without which you can make 95% of the units. And everything in-between is a Repeater.
Then you may decide, for example, to dedicate an easily accessible storage location to each Runner, and make special arrangements with suppliers. For Repeaters, you may use the Kanban system, with smaller dedicated locations. And you don’t keep any stock of Strangers, but order them as needed and store them, if at all, in dynamically allocated slots.
In the TPS Principles and Practices discussion group on LinkedIn, Brian Miller initiated a discussion on “How do you create standard work for a customized product that has over a billion combinations?” It has had 31 comments so far, and I would like to share here a few that I made.
Even in a plant that is perceived to be focused on low-volume/high-mix production, you usually have an uneven demand pattern, calling for different approaches to standard work by product category.
You start with a Runner/Repeater/Stranger analysis to determine what it is we do often and what not. Without this analysis, we commingle in the same lines products made every day with other products made sporadically (See Lean Assembly). In Japan, this is called P-Q, or Product-Quantity analysis, with the categories called A, B and C. The more vivid Runner/Repeater/Stranger terminology comes from Lucas Industries in the UK. You then use a dedicated, integrated production line for each Runners, a flexible line for each family of Repeaters, and a job-shop with functional groupings of equipment for Strangers.
Then, obviously, you face different challenges for developing standard work in each category:
In a runner line, you can post A3 sheets above each workstations with instructions for the purpose of allowing supervisors to monitor how the work is being done. This is the normal situation of high-volume production.The operators themselves do not need to read the instructions for every workpiece; as soon as they are proficient in the job, they work from memory.
A repeater line is for a family of products with variants but with a high commonality of materials and processes. The instructions that can be posted on A3 sheets are then limited to the common processes, but the operator needs to read what is specific to each workpiece. For final assembly of cars, Toyota has provided “build manifests” printed on larger sheets mounted on car bodies and bearing all the option information. The kitting of workpiece-specific components also helps. In computer assembly, workpiece specifics are shown on electronic displays, with component picks validated by auto-ID technology, including bar codes, QR-codes, or RFID chips.
Kit trays with instructions for repeaters in electronics assembly
Strangers are the odds and ends with sporadic demand, one-of-a-kind systems, or new product prototypes. For strangers, you cannot rely on operator memory or habit. For one-of-a-kind systems or prototypes, you cannot even assume you have the knowledge needed to produce workable detailed instructions. Each stranger is a job in a job shop and requires instructions on a traveller that moves with the workpiece. The traveller may be hardcopy or electronic. An electronic traveller may either be a device containing all the instructions or an ID that triggers the download of appropriate instructions at each station. Strangers are usually built by skilled craftsmen able to work directly from engineering drawings. Given the nature of strangers, however, the time required cannot be precisely known and sequencing mistakes will happen, making rework inevitable.