Page 110 - Orlicky's Material Requirements Planning

CHAPTER 5 Principles of Materials Requirements Planning 89

Proponents of significant digits argue that current computer systems handle longer
numbers with ease. They overlook the work of adding more new numbers (features
change much more frequently than form, fit, or function), correcting more errors, and
needing even longer numbers (a single digit can handle only 10 varieties of a character-
istic). They also forget that computers can access subordinate files of code numbers for
descriptive data without needing those codes in part numbers.
It is difficult to argue against semi-significant numbers where only two or three dig-
its identify families of parts. Those desiring such numbers should be responsible for justi-
fying them by showing that advantages outweigh disadvantages. It is rarely possible to
replace existing part numbers in a going concern; costs and other demands on scarce
resources are prohibitive. The simple solution is to adopt short, serial, nonsignificant num-
bers for all new items, deleting old ones as they become obsolete. Changes now prolifer-
ating in most businesses will lead them to make the conversion in a remarkably short time.

BILLS OF MATERIAL (BOMS)
Each item in the master production schedule (MPS) must have a unique identifying num-
ber and be associated with a BOM specifying its components to be planned and con-
trolled by MRP. BOMs identify the component(s) needed to make parent items. A parent
may be as complex as a product assembled from many components or as simple as a sin-
gle part made from some raw material.
Product structure data can be stored in computers using BOM processing software
commonly supplied by computer manufacturers and com mercial sources. These use
computer storage efficiently, avoid dupli cation of data, and apply fast retrieval for
“assembly” by the computer of BOMs in the various formats desired by different users.
Unfortunately, in practice, some parent items may have as many as five different BOMs:
■ A design parts list. Simply listing the component items, this BOM is the last step in
engineering design. It is the engineer’s way of telling the rest of the organization
how many of which components make up a product. Parts lists may show how
engineering thinks the parent should be put together, but this is usually not the
design engineer’s responsibility. Engineering specifications accompany BOMs
and carry other information needed to produce, inspect, and test complete, func-
tioning products. Parts lists often do not include packaging materials and usual-
ly omit such items as glue, grease, and paint, for which it is difficult to specify a
quantity needed.
■ A manufacturing BOM. In addition to listing all components of a product, BOMs
must be structured to show production people how to put the product together.
Production may require subassemblies for proper welding or ease of assembly.
Semi-finished parts (unpainted, not plated, incom plete machining) may reduce
complexity and increase planning and production flexibility. Sales of field-
replacement spare parts may be assemblies made only for this purpose.
Engineering usually has no interest in these needs.