ONE PIECE FLOW - ANOTHER VIEW ON PRODUCTION FLOW
Michal MARTON, Iveta PAULOVÁ
One-piece flow describes the sequence of product or of transactional activities through a
process one unit at a time. In contrast, batch processing creates a large number of products or
works on a large number of transactions at one time – sending them together as a group
through each operational step. In one-piece flow, focus is on the product or on the transactional
process, rather than on the waiting, transporting, and storage of either. One-piece flow methods
need short changeover times and are conducive to a pull system.
Achieving one-piece flow
While many are familiar with the terminology, there is still a significant amount of
confusion regarding what one-piece flow means and, more importantly, how to achieve it. Let
us begin by stepping back and attempting to understand the concept of “connected flow.”
Achieving connected flow means implementing a means of connecting each process step
within a value stream. In a typical MRP batch-and-queue manufacturing environment as
illustrated below, parts move from functional area to functional area in batches, and each
processing step or set of processing steps is controlled independently by a schedule.
There is little relationship between each manufacturing step and the steps immediately
Large amounts of scrap when a defect is found because of large batches of WIP,
Long manufacturing lead time,
Poor on-time delivery and/or lots of finished goods inventory to compensate,
Large amounts of WIP.
When we achieve connected flow, there is a relationship between processing steps: That
relationship is either a pull system such as a supermarket or FIFO lane or a direct link
(one-piece flow). As illustrated below, one-piece flow is the ideal method for creating
connected flow because product is moved from step to step with essentially no waiting (zero
Fig. 2 One-piece flow manufacturing environment
Why would we not always create one-piece flow for every set of processes within a value
stream? To be good candidates for one-piece flow, we must have the following conditions:
Processes must be able to consistently produce good product. If there are many quality
Equipment must have very high (near 100 percent) uptime. Equipment must always be
piece flow will be impossible.
Processes must be able to be scaled to tact time, or the rate of customer demand. For
every 10 minutes.
Without the above conditions in place, some other form of connecting flow must be
used. This means that there will be a buffer of inventory typically in the form of a supermarket
or FIFO lane between processes; the goal would be to eventually achieve one-piece flow (no
buffer) by improving the processes.
If a set of processes is determined to a candidate for one-piece flow, then the next step is to
begin implementation of a one-piece flow cell.
Implementing one-piece flow
The first step in implementing a one-piece flow cell is to decide which products or product
families will go into the cells, and determine the type of cell: Product-focused or mixed
model. For product focused cells to work correctly, demand needs to be high enough for an
individual product. For mixed model cells to work, changeover times must be kept short; a
general rule of thumb is that changeover time must be less than one tact time.
The next step is to calculate tact time for the set of products that will go into the cell. Tact time
is a measure of customer demand expressed in units of time and is calculated as follows:
Next, determine the work elements and time required for making one piece. In much detail,
list each step and its associated time. Time each step separately several times and use the
lowest repeatable time. Then, determine if the equipment to be used within the cell can meet
tact time. Considerations here include changeover times, load and unload times, and downtime.
The next step is to create a lean layout. Using the principles of 5-S (eliminating those items
that are not needed and locating all items/equipment/materials that are needed at their points of
use in the proper sequence), design a layout. Space between processes within a one-piece flow
cell must be limited to eliminate motion waste and to prevent unwanted WIP accumulation. U-
shaped cells are generally best; however, if this is impossible due to factory floor limitations,
other shapes will do. For example, I have implemented S-shaped cells in areas were a large U-
shape is physically impossible.
Finally, balance the cell and create standardized work for each operator within the
cell. Determine how many operators are needed to meet tact time and then split the work
between operators. Use the following equation:
Number of operators = Total work content / Tact time
In most cases, an “inconvenient” remainder term will result (e.g., you will end up with
Number of Operators = 4.4 or 2.3 or 3.6 instead of 2.0, 3.0, or 4.0). If there is a remainder term,
it may be necessary to kaizen the process and reduce the work content. Other possibilities
include moving operations to the supplying process to balance the line.
Why is important using One-Piece Flow in production?
The following illustration shows the impact of batch size reduction when comparing batch-
How we can see differences between these both flow systems is very enormous. One-piece
flow system saved 18 minutes for to same batch of 10 pieces. With this system can be produced
rather 3 times more as batch and queue system. Next, first piece was in processes only 3
minutes. Does it mean that system or operator can check part immediately in every process (A,
B and C). Batch and queue system allowed produce many parts after every process. If will be
occurred failure in the system than will be detected too late and many parts will be damaged.
On the next table I want to you introduce next differences and advantages of one-piece flow
DIFFERENCES AND ADVANTAGES OF ONE-PIECE FLOW Table 1
The authors described in this research theoretical and practical knowledge about one-piece
flow system. Results from this research give an impulse for next working out about continues
process improvement in manufacturing companies. In the present all companies solving impact
of the global crisis and try to reducing costs. On the table above are described basic advantages
of one-piece flow and how can be increase efficiency of production system at companies.
So far this paper has focused on explaining of another sight of production flow. One-piece
flow is one of the key concepts within lean manufacturing; in most cases, a piece of a value
stream can be transformed into a one-piece flow operation. While one-piece flow is not always
achievable for an entire door-to-door value stream, manufacturers must continually improve
their processes in an attempt to get closer and closer to true one-piece flow. This will reduce
inventory levels, reduce manufacturing lead time, and improve customer service levels.
Kenichi Sekine One-Piece Flow: Cell Design for Transforming the Production Process.
Productivity Press, 2005. ISBN 0-88427-061-0
Arzet, Harry. Bases of the One Piece flow. Berlin: Rhombos, 2005. ISBN 3-937231-97-8
Takeda, Hitoshi. The synchronous production system. Landsberg: MI-publishing house,