Implementing
Continuous Flow Cells
March
1, 2005
After you’ve mapped your value streams,
you are ready to setup continuous flow manufacturing cells.
Most cells that have been set up in the past ten years do not have
continuous flow; most changes to cells have been a layout change only.
That is, machines were moved in a cellular arrangement and nothing more
was changed. A change in layout
alone does not create continuous flow. This
article will discuss seven steps to creating continuous flow manufacturing
cells.
1.
Decide which products or product families will go into your cells, and
determine the type of cell: Product-focused or Group Technology (mixed model).
For product focused cells to work correctly, demand needs to be high
enough for an individual product. For
mixed model or group technology cells to work, changeover times must be kept
short.
To learn more
about the types of cells and their appropriate application, read our article
entitled, “Types of Manufacturing Cells.”
2.
Calculate Takt Time. Takt
time, often mistaken for cycle time, is not dependent on your productivity- it
is a measure of customer demand expressed in units of time:
Takt Time =
Available work-time per shift / Customer demand per shift
Ex:
Work time/Shift = 27,600
seconds
Demand/Shift
= 690 units
Takt
Time = 27,600/690 = 40 sec.
The
customer demands one unit every 40 seconds.
What if your demand is unpredictable and relatively low volume?
Typically, demand is unpredictable; however, aggregate demand (that is,
demand of a group of products that would run through a cell) is much more
predictable. Takt time should
generally not be adjusted more than monthly.
Furthermore, holding finished goods inventory will help in handling
fluctuating demand.
3.
Determine the work elements and time required for making one piece.
In much detail, document all of the actual work that goes into making
one unit. Time each element
separately several times and use the lowest repeatable time.
Do not include wasteful elements such as walking and waiting time.
4.
Determine if your equipment can meet takt time.
Using a spreadsheet
determine if each piece of equipment that will be required for the cell you are
setting up is capable of meeting takt time.
5.
Create a lean layout.
More than likely, you will have more than one person working in your cell
(this depends on takt time); however, you should arrange the cell such that one
person can do it. This will
ensure that the least possible space is consumed.
Less space translates to less walking, movement of parts, and waste.
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 where a large U-shape is
physically impossible.
6.
Balance the cell. This
involves determining how many operators are needed to meet takt time.
Number
of Operators
= Total Work content / Takt time
Ex.:
Total work content: 49 minutes
Takt time: 12 minutes
Number of operators:
49/12 = 4.08 (4 operators)
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. For example, one of my
clients moved simple assembly operations from their assembly line to their
injection molding operation to reduce work content and balance the line.
7.
Determine how the work will be divided among the operators.
There are several approaches. Some
include:
After you’ve
determined the above 7 elements, you will have gathered much of the necessary
data required to begin drawing and laying out your continuous flow manufacturing
cell.
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About the Author
Darren Dolcemascolo is an
internationally recognized lecturer, author, and consultant. As Sr. Partner and
co-founder of EMS Consulting Group, he specializes in productivity and quality
improvement through lean manufacturing. Mr. Dolcemascolo has written
the book
Improving the
Extended Value Stream: Lean for the Entire Supply Chain, published by
Productivity Press in 2006. He has also been published in several
manufacturing publications and has spoken at such venues as the Lean Management
Solutions Conference, Outsourcing World Summit, Biophex, APICS, and ASQ. He has a BS in Industrial Engineering
from Columbia University and an MBA with Graduate Honors from San Diego State
University.
