“Flow and Pull Value” is a principle in the Continuous Improvement dimension of the Shingo Model. This principle seems to be the most difficult for students of the Model to understand. The confusion experienced in learning this principle has caused us deep reflection on how we might better explain and teach this principle.
Causes
In looking at the causes of the confusion, we realized some problems in the way we describe this principle, which, in turn, affects how we teach this principle. Specifically, we noted four problem areas:
It is easy to see how students of the Model might get confused when studying these principles.
Improvement
To improve this confusing situation, we will do the following:
We propose the following wording of these two principles:
“Increase Flow”
“Flow” refers to the movement of the product or service through the value stream. “Flow” is increased by identifying and removing anything from the process that does not add value. “Flow” can be measured by the total elapsed time from start-to-finish, including value-adding work and necessary non-value-added items, including the following delays:
Process Delay. Commonly referred to as “Queue Time,” process delay occurs when a lot arrives at the next process before the process needs it. Process delay has many causes including scheduling issues, part shortages, equipment breakdowns, or quality problems.[1]
Lot Delay. This occurs when all items in a lot must wait for the entire lot to be completed before they are transferred to the next process. The ideal lot size is one – i.e., one product at a time, one operation at a time, one procedure at a time, one transaction at a time, etc., as this reduces lot delay to one piece. To effectively reduce lot delay, set-up times and transportation time must be reduced.[2]
Transport. Time taken to convey material (including patients in the case of healthcare) between operations is often significant. Transport time can be reduced to seconds if all operations are placed right next to each other, creating a flow configuration referred to as a cell. When one-piece flow is achieved, both process and lot delays are reduced to the minimum level, and the cell is said to have continuous flow – that is the ability to process one-by-one, thereby leveling production by product, and creating a high level of just-in-time production.
Inspection. Inability to assure quality at the source adds many inspection points in a process. Cellular arrangement facilitates inspection at the source, and tightly links all operations in the process providing immediate feedback to upstream operations, thereby reducing additional inspection time.
“Respond to Pull”
Shigeo Shingo referred to products and services produced as needed by the customer as “authorized” because production was triggered by an actual purchase order, or “pull,” by the customer. In this way, only needed items are produced as opposed to items produced to a forecast ahead of actual customer need. Producing to forecast was described by Dr. Shingo as “speculative,” and is also referred to as “push,” because items are produced by an upstream process and then “pushed” downstream whether they are needed or not. “Push” often results in inventory and overproduction waste. Pull production conserves valuable resources, shortens customer lead-time, and increases value to the customer. “Pull” can only be achieved when the lead time (i.e., the “flow” of the product or service) is less than the customers’ expected delivery time. Responding to pull is the only way to ensure that the right product or service is provided at the right time, and in the right amount.
Interestingly, performing work without a pull from the market is primarily a manufacturing issue. In healthcare, one would not consider performing surgery on a patient in anticipation of future demand. In financial services, one would not consider processing a transaction for a client in anticipation of future demand. Many organizations naturally adhere to this principle.
Summary
[1] Adapted from Shingo, Shigeo, Non-Stock Production: The Shingo System for Continuous Improvement, Productivity Press, 1988, p. 8-9
[2] Adapted from Shingo, Shigeo, Non-Stock Production: The Shingo System for Continuous Improvement, Productivity Press, 1988, p. 9
