Lean Manufacturing Implementation
The Lean Manufacturing Handbook
Part 2
The Lean Manufacturing Handbook
by Tom Epply
Assisted by Judy Nagengast
Second Edition
At any given time there may be hundreds or even thousands of parts in various stages
of production. If we were to track a given part through its production, we would see that
the part was in production for possibly 48 hours from start to finish, but that the actual
time that it was being processed, or value was being added to it, was only 8 minutes. The
rest of the time was spent waiting for the next process or moving the part from Process
A to Process B.
Another problem with the batch-and-queue system is when a defect occurs in Process B,
but is not discovered until Process C or later. If there are 500 parts in the batch affected
by the defect, then they all must be scrapped or reworked. This can add up to a great deal
of waste.
Lean differs from traditional batch-and-queue manufacturing because the system strives
for a ONE PIECE FLOW.
One Piece Flow means just what it says. One part is put through Process A and immediately
handed off to Process B. Process B is completed on the part and it is given to Process
C, which is then completed and so on. Ideally there is no batch or build-up of parts at
any given point in the process. The part does not wait for the next process. Ideally the
workload is balanced so that each operator is doing his fair share of the work. This is
called operator balancing.
The whole operation is set up so that Process A is next to Process B, which is located
as close as possible to Process C and so on. This is usually done in a U configuration,
which is called a production cell. Therefore the part does not have to travel long distances
throughout the plant to get to the next process. Of course this is in an ideal state and
one must still contend with large equipment such as ovens or paint processes, which cannot
be easily moved. But the emphasis of Lean is for a one-piece-flow process that covers the
least amount of floor space possible.
If we were to track a given part through the Lean Manufacturing cycle, we would see
that a part that takes 8 minutes to be produced would take only about 9 or 10 minutes to
process from start to finish. The number of parts in process would drop from hundreds (or
even thousands) to single or double digits, depending on the number and complexity of the
processes. As you can easily see, the savings in inventory alone would be significant.
In a perfect world the number of pieces in the flow is equal to the number of operations.
Example: Your production flow goes from OP(operation) 10 to OP 20, etc. through OP 150.
You have fifteen total operations and the ideal WIP (Work In Process) inventory or number
of parts in the assembly cycle would be 15.
If this is your case you have one piece flow. If you have multiple pieces between each
operation, you have batch or traditional manufacturing. In Lean, one strives for one-piece
flow and continually improves the operation until it is achieved.
McDonald's vs. Wendy's
A simple example of Traditional Manufacturing vs. One Piece Flow is the production lines
at McDonald's vs. Wendy's. When you arrive at McDonald's, you will see stacks of hamburgers,
cheeseburgers and quarter pounders, etc. stacked in the burger chutes behind the front
counter. These have been made in batches and are ready to deliver to the customer. This
system works as long as there are sufficient customers who demand the types of burgers
that are prepared and waiting before the burgers get cold or dried out. (One has to wonder
what McDonald's standard is on this). However, if you ask for your burger with no pickles
or fried with no salt, you may be in for a long wait. This is a good example of traditional
manufacturing.
Conversely, when you go to Wendy's for a hamburger, you will not see stacks of product
waiting for customers. When you place your order, the cashier announces it to the food
preparers, who then "build" your burger to order. If you ask for no pickles and
extra onions, you will receive it in the same amount of time it takes for you to get a
standard burger. This is one-piece flow. You will see similar systems in place at Taco
Bell and Arby's.
What does "Just-In-Time" mean?
Just in time refers to producing and delivering goods in the amount required when the
customer requires it and not before. An example of just in time delivery would be the new
service of purchasing dogfood, over the Internet, that is delivered to your home via UPS.
A person who has two dogs that each eat a can of dogfood a day would need 14 cans of dogfood
a week. If the dogfood comes in cases of 24, they would have dogfood shipped every 12 days
or so. This may be adjusted somewhat to allow for weekends and shipping delays. This system
would allow for an adequate supply of dogfood without tying up too much money or space
with excess dogfood.
Of course daily delivery of dogfood would be closer to an ideal state of just in time,
but would be too costly in shipping charges. The optimum delivery of dogfood would be determined
by need and shipping costs.
One could purchase a year's supply of dogfood (roughly 30 cases) to save on shipping
costs, but this would tie up money and a good portion of the garage on storage. As absurd
as this example sounds, many manufacturers do just that. They devote large portions of
their facilities to raw materials storage or storage for finished goods. This adds up to
a great deal of waste in inventory and space costs.
Another example of waste that is the opposite of just-in-time principles is the production
practices of traditional manufacturing. Traditional manufacturing plants often produce
all they can of a given product for the marketplace so as to never let the equipment be
idle. These goods then need to be warehoused or shipped out to a customer who may not be
ready for them. If more is produced than can be sold, the products will be sold at a deep
discount (often a loss) or simply scrapped. This can add up to an enormous amount of waste.
How does a plant produce "Just-In-Time"?
In Lean Manufacturing, the manufacturer only produces what the customer wants, when
they want it. A key element of Lean is to produce to TAKT time. TAKT time is a German word
for pace or rhythm. The pace is determined by a simple calculation of the number of parts
required by the customer divided by the production time available.
For example: your customer wants 1080 parts per day. You are working one shift of 10
hours. When you subtract lunchtime and breaks, you arrive at a time of 9 hours of actual
time that work can be done. Convert 9 hours to minutes by multiplying 9 times 60 minutes
to get 540 minutes. If you take 1080 parts and divide by 540 minutes you discover that
you need a part made every 1/2 minute or 30 seconds. So your pace or TAKT time is 30 seconds.
Your TAKT time will drive your production process and flow. You will want to develop
your processes to produce one piece every 30 seconds. You will also want to make it flexible
enough so that you can adjust the processes as the TAKT time goes up or down depending
on customer requirements. This is done by adding or subtracting operators, adding or subtracting
shifts or even adding a duplicate line if the customer demand increases significantly.
This is often a much more cost effective way of manufacturing when compared to high priced,
high volume equipment.
Lean Manufacturing Handbook Menu
- The Lean Manufacturing Handbook
- What does "Just-In-Time" mean?
- How was Lean Manufacturing Developed?
- How do I implement Lean Manufacturing?
- Do we need outside help to get Lean Manufacturing?
- Tell me more about the Lean Implementation Workshop you offer
- About the Author - Tom Epply
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