By Gerald Najarian
Here’s a question for you: who created the first cellular factory? Hint – it was an automobile company. We’ll come back to the answer later in the article but first let’s look at cellular organization in the lean factory.
Why organize in cells? In a lean factory, cells, in fact, create little factories within the big factory (not exactly like the fad a few years back called “factory within a factory,” but similar) that allow a mixed model product line to be manufactured as an island by itself. Cells, when organized and balanced properly, permit product to “flow” in one piece production from the first part to the final product without stopping to become a subassembly so there is no WIP inventory between the work stations in a cell.
To start out we should be clear that not every part of the typical fabrication/assembly plant or process plant can be completely organized in product oriented cells. For example, imagine the plant that assembles products from injected plastic and stamped metal components. It would be impractical and cost prohibitive to have injection molding machines and stamping presses for each of a multitude of product family cells, but the final assembly operations can be organized by product family and buffered with components to ensure availability and flow. Similarly in a process type operation such as private label foods, bottling or canning lines are organized in product family cells yet produce the actual food in common “vessel and pipe” centers with very small buffers if any. Here are the attributes of a lean oriented cellular operation:
- No subassemblies – operations in sequence. There are no subassemblies made in a lean cell. If the BOM calls for a subassembly, we incorporate the subassembly into the overall process of putting out a final product from the cell. The previously “batched” subassembly (whether component or final assembly), as it is made is passed on, in the right sequence, immediately for the next operation on its way to the final operation.
- One-piece production. Frequently dismissed as an ideal for which to strive, one-piece production is a must in cellular operations. There are no queues between operations in a lean cell. No queue means that the varying speeds of each machine or manual operation must be keyed to a demand rate of the customer or operation it is feeding that doesn’t exceed the rate of slowest machine or operation.
- Flexible layout – worker proximity. One of the prime objectives of a cellular layout is to be able to flex the output of the cell according to the demand rate. Flexing almost always has to do with the amount of labor assigned to the cell. Therefore, a flexible layout should accommodate changes in its worker compliment to make the best use of the total factory labor force. Cells that are “U” or “J” shaped facilitate such flexibility by allowing workers to stand back to back as well as side by side and thereby have easy mobility in the cell to perform multiple operations when necessary. Such layouts are in contrast to the traditional layout in long assembly lines in which workers in side by side formation cannot simply turn around to do another task making it almost impossible to flex down the labor force.
- Worker in motion multitasking. In an advanced well laid out lean cell, workers are doing more than one specialized task whether operating a machine or performing manual tasks or functioning as the material handler. The idea here is have mobile workers moving about in a limited area of the cell. This mobility avoids the mental fatigue inherent in doing a monolithic task repeatedly in the same space and saves labor cost.
With these types of cells, we abandon the paradigm of functional organization and layout of plants recognizing that the functions, once grouped into centers of functional activity are now resident the product cells. Where there is not enough functional equipment to deploy in product cells or it is truly impractical to do so, cells are simulated using a pull system.
So, think Henry Ford when you think cells. Yes, it was Ford who created the first cellular factory long before there even was a Toyota Motor Company. The famous Ford “assembly line” was, in fact, a cell – parts were assembled in a balanced sequence with no queues between stations in one car (piece) production in an uninterrupted flow. Of course, the worker in motion part wasn’t in existence back then. The cellular flow line concept had made its debut at the turn of the twentieth century and is making an encore now at the turn of the twenty first century.
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