characteristics. Traditional batch production is not equipped to deal with product variety; furthermore, move and wait time are sources of waste. Batches must wait for a preceding batch and a subsequent setup before beginning a process. Once a batch starts a process, units are processed sequentially; as units are finished they must wait for other units in the batch to be finished before the entire batch moves to the next process. For example, if a department can process one unit every five minutes, then the first unit of a batch of 10 will be completed after five minutes but must then wait an additional 45 minutes for the remaining units to be completed before mov-ing to the next process. Thus, there is pre-process waiting and post-process waiting. Lean manufacturing reduces wait and move time dramatically and allows the produc-tion of small batches (low volume) of differing products (high variety). The key fac-tors in achieving these outcomes are lower setup times and cellular manufacturing.
Reduced Setup/Changeover Times With large batches, setups are infrequent and the fixed cost of a setup is spread out over many units. Typical results produce complexity in scheduling and large work in process and finished goods inventories. Reducing the time to configure equipment to produce a different type of product enables smaller batches in greater variety to be produced. It also decreases the time it takes to produce a unit of output, thus increasing the ability to respond to customer demand. Customers do not value changeover and therefore it represents waste. While reducing setup times is important, even more critical is the use of cellular or contin-uous flow manufacturing.
Cellular Manufacturing Lean manufacturing uses a series of cells to produce families of similar products. A lean manufacturing system replaces the traditional plant layout with a pattern of manufacturing cells. Cell structure is chosen over departmental structure because it reduces lead time, decreases product cost, improves quality, and increases on-time delivery. Manufacturing cells contain all the opera-tions in close proximity that are needed to produce a family of products. The machines used are typically grouped in a semicircle. The reason for locating processes close to one another is to minimize move time and to keep a continuous flow between operations while maintaining zero inventory between any two operations. The cell is usually dedicated to producing products that require similar operations.
Panel A of Exhibit 16-3 shows the departmental, large-batch-orientation for one of Allen Autoparts’ aluminum wheel products (Model A). The move time, wait time, and unit processing time are included. An interesting question is: How long does it take to produce a batch of 10 units in the traditional batch-production setting? Panel A addresses this question: The traditional system takes 190 minutes to produce a batch