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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
  1. The Lean Manufacturing Handbook
  2. What does "Just-In-Time" mean?
  3. How was Lean Manufacturing Developed?
  4. How do I implement Lean Manufacturing?
  5. Do we need outside help to get Lean Manufacturing?
  6. Tell me more about the Lean Implementation Workshop you offer
  7. About the Author - Tom Epply

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