APORTACIÓN DE LAS TEORÍAS DE ENFERMER Í A

1. Implement the policies required to subordinate to market requirements.

 Eliminate measurement of local efficiencies. It’s crucial to get out of the local efficiency syndrome if the market constraint is to be effectively exploited. This is a three-step process. First, manage-ment must embrace the idea, thoroughly rationalized earlier in this book, that measuring local efficiencies actually motivates employee behavior inimical to achievement of the company’s goal. Second, this message must be formally communicated throughout the pro-duction and information systems departments. Re-education of both managers and hourly employees may be necessary. The new focus should be on Throughput-Based Decision Support (TBDS), as introduced in Chapter 3 and described in detail in Chapter 13.

Figure 10.6 S-DBR: A Graphic Depiction

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 Use small production batches. Production employees should not be reluctant to accept the increased number of set-ups that pro-cessing smaller batches will require, but reduce process batches only down to a size that will not turn a resource into a bottleneck.

In other words, the change in process batch size policy should not create a capacity constraint.

 Transfer work-in-process between stations in batches that are as small as practical. In other words, transfer batches will not likely be the same size as process batches — they’ll probably be much smaller. This may not mean transferring in batches of one unit, but it doesn’t mean batches of hundreds or thousands, either.

 Give priority to work orders with the earliest due dates. Remember, we’re subordinating internal efficiency to customer requirements, one of which we assume to be high delivery date reliability. The exception to this rule is made at a resource that may become a bottleneck because of excessive set-up time.

2. Establish close coordination between sales/marketing and production.

While this is not, strictly speaking, necessary for successfully applying S-DBR, it is necessary to fully exploit both a market constraint and an interactive CCR. Close coordination between sales/marketing and production provides the following advantages:

 Production and sales reach consensus on the optimal product mix

— the one that delivers the highest throughput. Sales will then know which products to emphasize.

 Production capacity will not be over-committed. Sales will know what the current load on production capacity is at any given time.

Knowing how much excess capacity exists is crucial to using pro-duction capacity as a competitive advantage in the marketplace.

By coordinating closely with production, sales representatives know what promises they can safely make to customers and what kinds of orders may over-commit production capacity.

 When a CCR becomes active, sales representatives will be able to refine quoted lead times (either upward or downward) to ensure delivery reliability. They’ll know when not to promise capacity-con-suming product customization, and when to quote longer lead times if the customer really needs such customization. Moreover, knowing when the CCR is nearly fully loaded (or overloaded) allows sales representatives to selectively inhibit the demand for products that consume significant amounts of CCR time. Doing so preserves pro-duction’s capability to respond to sales’ high priority needs.

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166 Manufacturing at Warp Speed

3. Identify the CCR. If the production process is already fully loaded, we’ll be looking for an active CCR. If it isn’t fully loaded, we’ll deter-mine which resource should reach full load first, if demand were to increase. Note that it’s possible to influence where the CCR will be in two ways: (a) selective capacity management (purchasing capacity for work centers that should not be CCRs), and (b) selective market-ing (emphasizmarket-ing certain products to drive demand distribution to a desired profile, or product mix). It’s also important to remember that verifying the CCR is a regular, recurring activity. Any significant change in either demand or capacity has a high probability of shifting the location of the system’s constraint.

4. Determine the size of the shipping buffer. This is a key decision. Prod-ucts with very different production routings may need shipping buff-ers of different sizes. The shipping buffer depends on the amount of excess capacity in the system (e.g., less capacity, larger shipping buffer). Since excess capacity varies over time, the adequacy of ship-ping buffers should be reviewed frequently. However, this is not to say that shipping buffers should be frequently changed. Only signif-icant changes in excess capacity should trigger a change in buffer size.

So how do we determine how long the shipping buffer should be?

Most production managers have a reasonably good idea what their current manufacturing lead time is for delivering an order. A nice, conservative rule-of-thumb is to start with a shipping buffer that is 75% of the current lead time. As the transition to S-DBR matures and the kinks are worked out, this will probably be too high. The shipping buffer can be decreased incrementally as long as there are no red-line penetrations (holes in the Zone-1 buffer). Pilots use a similar concept in landing an airplane: They don’t dive vertically at the runway from 30,000 feet, expecting to make one pullout at the precise time required for a smooth landing. Instead, they reduce their altitude in gradual steps, until they reach the final approach. We want to ease into the right shipping buffer size in the same way, because we don’t want the undesirable effects of a late delivery.

5. Determine the red-line zone. The concept of a red line, similar to Zone-1 in traditional DBR, is explained in greater detail later (see Chapter 11, “Controlling Uncertainty and Variation: The S-DBR Approach”).

This, too, is a parameter that should not change too frequently. Unlike Zone 1 in traditional DBR, the red line is not a fixed ratio of the buffer, so a change in the shipping buffer size doesn’t necessarily mean

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that the red-line point must also change. If the shipping buffer changes by 50% or more, we should consider adjusting the red line.

Once these five steps have been accomplished, general planning and prep-aration are complete. Now we’re ready to execute.