In my last post, I introduced the concept of cellular manufacturing and discussed the design and implementation of work cells. I talked about the deleterious effects on production times of protracted distance traveled and large batch sizes for products in manufacturing processes. I also suggested that we finally do away with the large batch efficiency myth that has plagued manufacturing for decades.
In Part 2 of this series, I will complete this discussion on cellular manufacturing. As in my previous series on cycle time, much of what I will be presenting in this series of posts is taken from my second book, The Ultimate Improvement Cycle—Maximizing Profits Through the Integration of Lean, Six Sigma and the Theory of Constraints.
Cellular manufacturing and work cells lie at the heart of lean manufacturing
The general benefits of cellular manufacturing include simplified flow, cycle time reductions, improved quality, and improved intra-process communication. In cellular manufacturing, equipment and workstations are arranged in close proximity to one another in the normal process sequence. Once processing begins, products move directly from work station to work station. The typical result is significant improvements in overall cycle times and vastly improved teamwork and quality. This arrangement of workstations supports a smooth flow of products and components through the process with minimal transport and delays. In addition, arranging the equipment into manufacturing cells makes it much easier to reduce the transfer batch size.
The positive results from cellular manufacturing are numerous and substantial
A manufacturing cell is comprised of the people, equipment, and work stations arranged in the logical sequence required for producing the end product. The positive effects of cellular manufacturing, if implemented correctly, include improved quality, immediate identification of problems, smaller batch sizes, one-piece flow, flexible production, and less of each of the following:
- travel time for parts
- equivalent manpower
- damaged product
- required space
- walking time
- lead time
All of these results distill down into decreased cycle time, increased throughput, and reduced inventory and operating expense.
Work cells + one-piece flow = maximized production efficiency
I mentioned that one-piece flow is one of the positive benefits of cellular manufacturing. In a one-piece flow production environment, parts are moved immediately to the next operation for processing, which makes it arguably the most efficient way to process material through a factory. When done in conjunction with the establishment of work cells, one-piece flow works very well. Imagine what happens to the lead time of products being produced in work cells with one-piece flow, assuming we have calculated the correct critical WIP.
I recognize that some equipment is simply too large and bulky to be moved into and included in a cell, but even with this scenario, there is a solution. If a piece of equipment is too large and difficult to maneuver, then we may be able to build the work cell around this limiting piece of equipment. Large screw machines or stamping presses, for example, might not be possible to move, but we should not be deterred from implementing a cellular manufacturing process. We can either arrange the equipment around these machines or arrange the equipment that can be moved into a cellular arrangement.
In the French company I recalled in Part 1, we faced precisely this situation. We simply left the large screw machines where they were and arranged the remainder of the equipment (i.e. drilling, hobbing, grinding, reaming, washing and crack detection machines) into functional cells. The results were significantly reduced space, less cycle time, increased throughput, improved quality, reduced inventory, and much improved on-time delivery. As a matter of fact, on-time deliveries improved from approximately 70% to more than 90% of orders, while PPMs decreased from more than 20,000 to roughly 200 in just over three months.
Multiple paths of variation can increase the variability of the process
One other positive effect that typically results from cellular manufacturing has a positive theoretical impact on variation. When multiple machines performing the same function are used to produce identical products, there are potentially multiple paths that parts can take from beginning to end (Note: See Posts 78 - 80 for details on paths of variation). There are, therefore, multiple paths of variation. These multiple paths of variation can significantly increase the overall variability of the process.
Even with reductions in variation, real improvement might not be realized because of the number of paths of variation that exist within a process. Paths of variation are simply the number of opportunities for variation to occur within a process. The paths of variation in a process are increased by the number of individual process steps and/or the complexity of the steps (i.e. number of sub-processes within a process).
The answer to reducing the effects of paths of variation lies in the process and product design stage of the manufacturing processes. That is, processes must be designed with reduced complexity and products should be designed that are more robust. The payback for reducing the number of paths of variation is an overall reduction in the amount of process variation and ultimately more consistent and robust products.
Coming in the next post
In the next post, I will begin a new series on continuous improvement.
Until next time.
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