Work Cells – A building block of lean manufacturing

If Lean Manufacturing were a building, then the bricks that lay the foundation of lean manufacturing, particularly with assembly lines, would be work cells. The fruit of the work cell implementation is a more efficient, stronger assembly line with higher quality products, happier employees, and a safer work environment.

Work cells belong to a type of manufacturing referred to as cellular manufacturing. The concept behind this type of setup is exactly how it sounds: on a certain floor or line, there exists a string of equipment and workstations that promotes an efficient flow of inventory and materials from raw material to final, assembled product. The important aspect to note about cellular manufacturing is the idea that it minimizes transportation and waiting time, which makes the process ideal for quality leaders to implement.

Using the concept of cellular manufacturing as a base, then the work cell is a group of equipment, workstations, and/or personnel that are physically located in a single area and allows for the group of workers and equipment to produce an entire product or group of products completely from start to finish. It can be thought of as a small version of the entire assembly line, complete with its own specific processes, teams, equipment, operating guidelines, and quality standards.

The alternative to cellular manufacturing is the “batch and queue” system, in which the product is produced in stages, then allowed to sit for a period of time in a queue while it is waiting to get to the next workstation, as can be seen in Figure (1). If the production line is large enough, this leads to large amounts of inventory waiting in various queues, incurring costs to the company and taking resources away from the production line. Additionally, the line must become much more complex because additional machines and personnel are needed to transport the product between batches. With cellular manufacturing, the work cell absorbs the queue and ensures that inventory is kept to a minimum by constantly producing a quality product inside of the cell, which is demonstrated in the bottom half of Figure (1).

Work Cells and Batch and Queue Operation Compared

The company that should be most interested in using this tool is the one that finds themselves bogged down by excess inventory and slow processes. Another, less obvious telltale sign that cellular manufacturing is necessary is workers that are unhappy with their job, because production is directly proportional to job satisfaction. The company will also find themselves very slow to react to demand changes and cost reduction techniques. The excess inventory directly drives these factors.

Not every company is a good candidate for shifting to work cells and cellular manufacturing. Some companies simply do not have a manufacturing process that is long and complicated enough to justify work cells. Other companies produce products that are not able to be split into different assembly steps, leading to a convergent line at the very end of the line, and not allowing any room for work cells. While these are a couple of situations in which work cells will not necessarily be the best choice for a company, a large majority of companies would benefit greatly from the positive impact this model has on their inventory and production costs and times.

A good example of the work cell model is with a generator manufacturer. In its most simple form, a generator consists of a rotor, a stator, the casing, and the control systems. Each part consists of many subassemblies that are reflected in Figure (1) by the different processes, Processes A-C.

Up until now, the manufacturer was using the batch and queue model of manufacturing in which each station puts out its product, and then sits in the “up and coming queue” of the next process. These queues are represented by the yellow boxes in Figure (1). As you can see, with the batch and queue process, there is a lot of inventory sitting around for no reason other than waiting for the next process to take care of it and process it.

The second part of the diagram, the work cell, is the model that the manufacturing plant moved to when they decided to finally lean out their processes. The work cells are constantly processing product, and don’t have a “queue”. There may be a few times where a bottleneck happens and there is an excess inventory because of a slow workstation, but in general, there should be no inventory stacking up in a work cell system.

This is all because the work cell is constantly running their process, and the previous and next work cells are taking their inventory, also completing their processes on a continual basis. If running correctly, the work cell method should resemble a conveyer belt or assembly line, with a few stops for the processes, but otherwise running fluidly and continuously.

Work cells should be designed at the highest levels. While the workers must be trained in the conduct of business inside of the work cells, the actual system should be designed with a 30,000 foot view. Managers should also be trained to operate their cells efficiently to keep the bottlenecks to a minimum.

If utilized properly, a work cell system can reduce and possibly eliminate the need for inventory. It will also foster higher quality due to constant improvement and a continuous worker from one end of the cell to the other.

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