Page 415 - Orlicky's Material Requirements Planning

394 PART 4 Looking Backward and Forward

a gross underestimation of how long it takes to reliably produce a Part 101. Experienced
planning personnel are very aware of this phenomenon and have developed alternative
processes to work around the issue. One option is to stock every component. Another is
an adjustment of manufacturing lead times in order to try to reflect the reality in respond-
ing to an order.
In this example, using CLT is not realistic either. The CLT path revealed in the fig-
ure has two stocked components on the path (Parts 301 and 501P). On average, parts
probably will be available more often than they are not. These stocked positions essen-
tially “decouple” the CLT path, making 26 days a significant overestimation for Part 101.
This is demonstrated in Figure 23-4. Once again, planners tend to adjust the lead times to
plan these items effectively. Every planner knows intuitively that in most cases the real-
istic reliable lead time is neither the MLT nor the CLT; it is something in between. This
realization opens the door for a new type of calculated lead time and a different way to
perceive, analyze, and control a BOM.
Figure 23-5 shows that the realistic lead time can be determined by the MLT of the
immediate component part that is not stocked. In this case, it is defined by the path
through Part 204 (the bold line). This path is broken at a stocked position (Part 304P). The
true, realistic lead time is defined by the longest unprotected or unbuffered sequence in
the BOM for a particular parent (in this case Part 101). This is called the actively synchro-
nized replenishment lead time (ASR lead time), which is the core concept behind DDMRP.
This will be described further in Chapter 26.
With the BOM decoupled by possibly several embedded stock positions, there will
be several ASR lead times (ASRLT). In Figure 23-6, the BOM for Part 101 has three inde-
pendent ASRLT stratifications or layers. Part 101 has an ASRLT of 8 days. Part 203 has an

FIGURE 23-4
Realistic Lead Time CLT
Stocked
components that 101
decouple CLT.

5 201 203 204

4 301 302 303P 304P

401P 402 403P 404P

4
501P 11