Page 475 - Orlicky's Material Requirements Planning

CHAPTER 26 Demand-Driven Planning 453

The size of the time buffer varies according to the length on the path that is being
buffered. In Figure 26-24, time buffers have been sized to be one-quarter the length of the
activity or sequence of activities being buffered. The gray boxes of varying sizes indicate
those buffers. Two types of buffer placement strategies also are illustrated. The first is
buffering all purchased parts that do not lie on the ASRLT chain. Parts PPG, PPF, PPE,
PPI, PPJ, PPK, PPA, and PPD all have buffers placed immediately behind them. This
means that variability will be absorbed only from the external sources. There are still sub-
assemblies (e.g., SAZ, SAC, and SAX) where internal variability can be encountered and
transferred to the ASRLT chain.
A superior time buffering strategy involves placing the time buffer where a BOM leg
merges with the ASRLT chain. This buffer is sized by the BOM sequence of that path. In
Figure 26-24, there is a larger time buffer after SAE. That buffer is sized by calculating the
longest sequence in that BOM leg—58 days. The buffer is set to one-quarter of 58 days
15 days. This buffer is designed to protect against variability in that entire leg from pass-
ing through to the ASRLT chain to affect the delivery date of the end item.
Figure 26-25 is an example of the planning screen for all non-ASRLT parts for FPZ.
Note the existence of a new column called “Buffer.” That column is not populated when
a buffer exists either in front of that activity or after that activity (inserted after the last
part on the BOM leg).
There are obvious implications to this type of planning method for engineer to order
(ETO) environments. ETO environments struggle with MRP, yet, typically, most of these Downloaded by [ Singapore Polytechnic Library 176.79.113.174] at [06/05/21]. Copyright © McGraw-Hill Global Education Holdings, LLC. Not to be redistributed or modified in any way without permission.
companies have and use MRP systems. See Chapter 16 for a discussion of the current
tools. A major milestone for these environments is to complete and enter a BOM into
MRP so that purchasing and scheduling activity can occur.
An alternative strategy, as discussed in Chapter 16, is to purchase all materials to
support the earliest possible start date. In environments that are hybrids between project
and manufacturing, there is usually the assumption that the sooner something starts, the

FIGURE 26-25
Planning screen for FPZ with buffer column.
Order Request Promise
Part Number Profile Start Date Buffer ASRLT Date Date Late Quantity Vendor Customer Source
PPG PO-000590 LTM 1/19 40 2/28 2/28 1 Siemens Driven by WO-000589, SAA
PPE PO-000592 LTM 2/08 5 20 3/05 3/05 1 Sony Driven by WO-000587, SAB
PPF PO-000593 LTM 2/14 4 15 3/05 3/05 1 SpaceTech Driven by WO-000587, SAB
PPC PO-000594 LTM 2/18 25 3/15 3/15 1 Boeing Driven by WO-000582, SAY
PPI PO-000596 LTM 2/26 6 25 3/28 3/28 1 Raytheon Driven by WO-000588, SAZ
PPD PO-000595 LTM 3/04 5 18 3/27 3/27 1 MicroTech Driven by WO-000583, SAD
PPJ PO-000598 LTM 3/10 5 20 4/04 4/04 1 SpaceTech Driven by WO-000586, SAC
SAY WO-000582 NB 3/04 11 45 4/04 4/04 1 Driven by WO-000580, SAE
PPK PO-000599 LTM 3/13 5 20 4/07 4/07 1 Siemens Driven by WO-000584, SAX
PPB PO-000597 LTM 3/20 15 4/04 4/04 1 Sony Driven by WO-000580, SAE
SAZ WO-000588 NB 3/28 32 4/04 4/04 1 Driven by WO-000586, SAC
SAE WO-000580 NB 3/20 15 58 4/17 4/17 1 Driven by WO-000579, FPA
SAC WO-000586 NB 4/04 35 4/07 4/07 1 Driven by WO-000584, SAX
SAX WO-000584 NB 4/07 10 39 4/11 4/11 1 Driven by WO-000581, SAF
SAX WO-000584 NB 4/07 39 4/11 4/11 1 Driven by WO-000581, SAF
PPA PO-000600 LTM 4/11 1 5 4/17 4/17 1 SpaceTech Driven by WO-000579, FPA