This Focused Performance Weblog is a "business management blog" containing links and commentary related primarily to organizational effectiveness with a "Theory of Constraints" perspective. TOC is noted for its applications in Project Management and Multi-Project Management (Critical Chain) and Operations Management (Drum-Buffer-Rope), as well as in Marketing, Strategic Planning and Change Management (TOC Thinking Processes). If you are on an archive page, current postings are found here.
Wednesday, October 23, 2002
• Using Drum-Buffer-Rope Scheduling Rather Than Just-In-Time Production - A comparison of JIT (Lean) production and TOC-driven DBR scheduling by Patricia Huff in the Management Accounting Quarterly highlights benefits of the latter approach to production management. In it, Huff points to...
"...several studies that compare the performance of JIT and DBR. D.W. Fogarty, J.H. Blackstone, and T. R. Hoffman found that TOC processing, using DBR scheduling, "gives superior performance with less effort." DBR produced approximately 2% more units of output than the JIT production.
"In a simulation study by Cook, DBR and JIT performed better than traditional processing. However, DBR outperformed JIT in a number of categories. DBR required less inventory, which led to reduced manufacturing costs, better responsiveness to customer requirements, and the opportunity for better product quality. DBR also produced more product with a lower standard deviation of flow time. Cook defined this benefit as better due-date performance. Such performance resulted because it was easier to determine when the product would be ready for shipment."
"Based on the information presented, it appears that DBR scheduling can achieve a higher level of performance. Because it doesn't require a balanced set of production tasks, DBR lends itself to a larger number of processing situations. As in the case of a job order shop, DBR can be used in situations that allow for different sizes of batches to be processed. The evidence also indicates that DBR scheduling results in lower WIP inventories, which leads to lower investment in manufacturing costs. Compared to JIT, Drum-Buffer-Rope scheduling is clearly the superior production method."
The simplicity of DBR's reliance on letting processes work to their natural pacing while controlling WIP (and at the same time minimizing production lead time) through the release of material to the shop floor should be evident. It avoids the complexity of managing Kanbans as well as the difficulties of dealing with the potential brittleness of balanced production systems associated with JIT and its Lean progeny. It also, in implementation, provides pinpointed targets for improvements through it's execution control mechanism, Buffer Management. The "efficiency" of targeted improvement efforts cand result in fast and deep bottom line impacts. Production performance is not so much about driving out waste as it is maximizing speed, reliability and throughput.
I'm going to be facilitating a DBR implementation in a small machine shop in a few weeks. If I get the permission of the client, I'll blog a journal of the experience here. Watch this space.
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