Theory of Constraints Handbook - James Cox Iii [119]
TOC and Other Modern Philosophies10
TOC and Lean
Dettmer (undated) states that the Toyota Production System is better known than TOC primarily because it is a much older system (development started in the 1950s) versus TOC in the 1980s). He continues by saying that both systems use continuous improvement and have the goal of obtaining higher profits. Both methods recognize that the customer is the final arbiter of what value is.
Berry and Smith (2005) provide a comparison of TOC with Lean and with several other approaches—MRP, MRP II, ERP, and Supply Chain Management.
Sale and Inman (2003) surveyed over 900 firms and received 93 responses. They found that firms using TOC had significantly higher performance improvement than firms using JIT and traditional manufacturing.
Moore and Scheinkopf (1998) compare TOC and Lean. Both TOC and Lean concentrate on continuous improvement and control the flow of material on the shop floor. Both have had dramatic improvements of profitability and lead times and have resulted in operations being drastically simplified.
TOC and TQM
Lepore and Cohen (1999) suggest there are many synergies between TOC and Total Quality Management (TQM). Cohen is one of Goldratt’s early partners. Lepore is an academic specializing in Total Quality Management. They suggest a 10-step strategy for implementing the two philosophies together. Step 4 is to implement the 5FS. Step 5 is to implement Buffer Management. However, the book contains little specifics on DBR, per se.
TOC, Lean, and Six Sigma
Pirasteh and Farah (2006, 32–33) state that the top elements of TOC, Lean and Six Sigma work well together. They report on a company that combined the “best components” of these three approaches into what they called TLS. They applied Six Sigma alone to 11 plants, Lean alone to 4 plants, and TLS to 6 plants. They measured plant performance regarding “on-time delivery, warranty costs, customer returns, Inventory reduction, cycle time reduction, and scrap expense.” The company concluded that “the TLS process improvement methodology delivered considerably higher cost savings to the company.”
Problems with DBR
One of the most frequently mentioned conceptual problems with DBR is the issue of wandering bottlenecks, that is, frequent changes in the resource constraint station. The usual cause for this is given that in the case of job shops, shifting of the order mix causes such shifts in the most overloaded resource. Goldratt disputes this issue as a problem out of both his experience and using the logic that even in a job shop there is usually one primary machine or skill that is driving the bulk of orders. An occasional shift in bottlenecks is not a problem as the shop can change its focus occasionally. Hurley and Kadipasaoglu (1998) speculate on the causes of wandering bottlenecks. They demonstrate that changing product mix is a minor contributor to this problem and that the primary cause is management actions in response to inappropriate performance measures. One such policy is the continuing use of non-bottleneck utilization as a performance measure—seeing unused protective capacity as a waste. Releasing material faster than the rope requires builds up inventory at many stations and disrupts the drum schedule with unneeded work delaying needed work. Increasing batch sizes to minimize setups can lead to large jobs at non-bottlenecks clogging the shop and creating an unnecessary shift of the bottleneck. They conclude that only in