Theory of Constraints Handbook - James Cox Iii [687]
The TOC replenishment algorithm was used to manage the material requirements for the entire company. This requirement is a Type 3 variation, subject to rapidly changing requirements of the product development cycle. The quantity of material being held in stock was significantly reduced, which made it easier to manage. The different sizes of the product being manufactured changed often; this is equivalent to the product mix changing often, and the replenishment solution allowed the plant to be visibly more responsive.
The next application of this approach, depicted in Fig. 35-10, is at the United States Marine Corps (USMC) Maintenance Center in Albany, GA. They are one of two maintenance repair and overhaul (MRO) activities that service all of the USMC tracked vehicles.
The vehicles are returned to be serviced after many years of use in the field, much of which has been in very demanding environments. The mission is to return the vehicles to almost new condition, as quickly as possible and at the lowest cost. In addition, many upgrades are designed, manufactured, and concurrently installed as part of the total effort. In addition, the condition of the vehicles is unknown until inspected. Furthermore, the demand pattern is unpredictable, which only adds to the uncertainty in an already complex scheduling environment.
The vehicle itself is scheduled as depicted in Fig. 35-10 as a nominal 14-task critical chain project because it experiences Type 1 variation. The actual number of tasks is much greater because it covers the major events, such as inspection, disassembly (in many cases, only the nameplate will remain on the production line), assembly, corrosion, paint, testing, etc.
FIGURE 35-10 The integrated scheduling algorithm in an MRO environment.
Some of the major components removed for repair and overhaul such as the engine are scheduled using a subordinate critical chain schedule since again this is a Type 1 environment. The many other components that are removed from the vehicle are sent to the support shop and scheduled using DBR since this a Type 2 environment.
The TOC replenishment algorithm is used to schedule and manage the shop consumable items and replacement parts. This is extremely challenging in a complex, high-mix, constantly changing MRO environment. This is an extremely demanding Type 3 environment of high and low product volume demand that changes on a daily basis.
All of the work has to be synchronized and come together at final assembly. This is only possible by scheduling backward from the vehicle delivery date and subordinating all efforts to the needs of the master critical chain. The uncertainty encountered in the Maintenance Center at Albany, GA is much greater than a repetitive manufacturing environment such as when the vehicle is originally produced.
The Maintenance Center’s results over the last seven years have been phenomenal. Some of the results were chronicled in the March 2005 APICS magazine. They were the first recipient of the U.S. Department of Defense’s Robert Mason award in 2005 and again in 2007; and were the first recipient of the TOC International Certification Organization (TOCICO) Award for Excellence in 2008. They reduced the cycle time of every one of the 20 major products they support by at least half and in some instances even more. They doubled the Throughput of the organization within an 18-month period without hiring any additional personnel. They have a very ambitious process of ongoing improvement in place, which is continually raising the bar. In summary, the productivity increased dramatically, they were making their promised delivery dates, and customer satisfaction was very high.
Summary and Discussion
All of the TOC solutions use the concept of time buffers to provide protection against variability in execution. Therefore, for the first time we have system and operational metrics that link to each other and can be used in conjunction with the three scheduling algorithms. These horizontal and vertical linkages