Q: We are in the planning stages of a new factory to replace our existing plant, which was built in the 1940s. I'm sending you a CAD detailed drawing of the present plan and would like your input. A big concern for us is part flow, and getting it as short as possible. Any suggestions would be appreciated.

A: While working on this question with the writer, I was reminded of an incident that occurred about seven years ago. I had two students working for me during the summer at a factory. This was one of the shops where we had broken all the standard thinking about how a plant should be set up to try and turn it around. One of the concepts that we adopted from the Japanese Kaizen techniques was the idea of shortening parts travel distances. In a lot of instances, workers would take the part they had just made and hand it directly to the next operator.

To make a long story short, one of the students, who was taking a summer course on plant layout, used our plant as a model to layout the class assignment. As I recall, he used only about 25 percent of the allotted space. I figured he would get a really good grade for such an original design.

You guessed it, he had to re-do the layout, including more room for inventory between operations and laying out his machines in neat orderly rows. And we wonder why original thinking seems so rare in this business.

But to the question itself. First, we need to put to rest an erroneous concept that flow manufacturing deals with parts flow and plant layout. Those who have read this column as well as the book, A Better Way, know that I haven't written very much at all about plant layout. Layout is not a consideration in implementing flow manufacturing. Your time is best spent in first implementing flow manufacturing concepts (and your reward will be much greater).

However, there is nothing wrong with wanting to revise the layout of your factory, so let's discuss some ways you can do that. Most industrial engineers have some basic background in plant layout, but if they are like me, and the student above, they may have been taught the old school methods. Therefore, I'm going to cover some methods that I've used to break the old "grid" style of thinking about plant layouts.

The Spaghetti Method  

Back when I first started using the concepts of work cells and nonlinear parts flow, CAD systems were still not all that common, especially in furniture plants. So I had to use noncomputerized ways to analyze parts flow. One of these is what I call the Spaghetti Method.

I started with a blueprint of the plant layout. This blueprint should just show the bare floor, with no equipment on it. I would attach this to a piece of foam board or, if that wasn't available, a sheet of drywall. You should then make a template of each machine to the correct scale. I would then divide the parts that we run through the plant into major groups or families (I should mention that we'll focus on the layout of the machining areas in this article). For example, let's say that you have a typical casegoods plant. I would break down the parts into the following families:

  • Doors
  • Drawer fronts
  • Drawer boxes
  • End panels
  • Tops
  • Shelves and bottom panels
  • Mouldings
  • Back panels

Your own list for your plant may vary, depending on your particular products. You also may have to group some "oddball" parts into a grouping based on the process they go through. For example, a solid wood pencil tray would not normally be considered a moulding, but because in goes through a similar process I would probably put it with that family.

The next step would be to assign a color code for each family of parts. Here's my list:

  • Doors - red
  • Drawer fronts - blue
  • Drawer boxes - green
  • End panels - brown
  • Tops - yellow
  • Shelves and bottom panels - purple
  • Mouldings - white
  • Back panels - black

I would then run down to the local crafts store and buy a box of stick pins and a roll of colored yarn for each color I had assigned. If you have a choice, get as thin a brand of yarn as you can, for reasons that will become clear soon. Next I would use the push pins to locate each machine in its present position, and then run the yarn through the various machines for each family. In other words, for each machine that doors go through, I would string the red yarn around each of the push pins for those machines. Since some machines (e.g. widebelt sander) might process parts for every family, that is why it it is best to get as thin a yarn as you can get. As you process each family, you will begin to get a feel for how parts travel through your plant. If it's like most of the plants I tried this at, the initial layout will look like a big plate of rainbow colored spaghetti, hence the name.

Once you've done this analysis, you should bring in workers from the floor, managers, maintenance, engineers, purchasing - in short anyone who can add some insight to improving part flow. There are a few guidelines you need to keep in mind as you do your analysis.

1. Forget about keeping like machines together - put machines where they are needed for better flow, not so they are in nice straight lines.

2. Where feasible, consider dedicating machines to families of parts and setting up work cells.

3. Do bring in your dust collection specialist to give their input before you commit to a final layout.

4. Keep in mind as you do your layout where some additional cheap, dedicated machines might help to improve parts flow even more and reduce cycle time.

5. Allow enough room for the needed inventory buffers to protect throughput, but not a single piece more. If you leave an empty hole, it will get filled up.

A plant layout for improved part flow isn't the most vital thing you can do to improve profitability, but it is a step you will want to take on your path to world class excellence.

Have something to say? Share your thoughts with us in the comments below.