Part numbering systems and document identification design for PLM software
PDXpert PLM software has been designed to support a wide variety of part numbering
systems, including manually-assigned intelligent part numbers, category-based
semi-significant part numbers, and easy-to-manage sequential part numbers. This
topic explains why most industries have adopted sequential identifiers as part
numbering system best practice. We'd be happy to explain how PDXpert PLM
software's item identification capabilities, coupled with its flexible sourcing
relationships, can help companies transition an existing part numbering system
to a simpler design.
Part numbering system origins
Traditional
part numbering systems and document identification schemes originated over 50
years ago. At the time, a basic consideration was that unstructured information
was very difficult to find, and it was therefore necessary to overload document
identifiers and part numbers with search-related "helper" data. In the absence
of better alternatives, this approach and the resulting practices represented
reasonable, though costly and cumbersome, compromises. But times and technology have changed.
Part numbering system design concepts
Let's step back a moment and consider our essential requirements for a part
numbering system.
The goal of any part numbering system is to uniquely identify the
component approved for a specific application. Accurate, consistent,
unambiguous part identification is essential for correct
product assembly, testing and maintenance.
We must ensure that a
new identifier is assigned whenever a variation in attributes has a material effect on the
item's form, fit, or function in the application.
A part number allows us to clearly distinguish one part from other parts
when the difference is meaningful, and to ignore irrelevant differences. This is
what distinguishes non-interchangeable changes from interchangeable changes. We also need to ensure that
parts with non-meaningful variations can be used for the same application.
Part revisions are not included in the identification of the physical part
because, by definition and best practice, all revisions of a single part number
are interchangeable. Consequently, all revisions of a part number can be intermixed in a
single inventory location. (If this isn't true, then you don't have
interchangeable parts, and they require distinct part numbers and inventory
bins.) Since part revisions merely distinguish one interchangeable part (and its
PLM data
record) from another, the revision identifier format will not influence our part
numbering system design.
Part numbering system constraints
Any part numbering system design must also consider some purely human
elements.
A practical part numbering system design should account for the limits of short-term memory.
Many years of academic study, verified by real-world experience, proves that
data entry errors increase as the number of characters increase and, after a
certain length, errors increase at an increasing rate. The "magic limit" is
typically considered to be 7†. Anything longer than this
(a) requires most users to write down, rather than simply remember, the part number
for even short-term usage; and (b) increases the likelihood of data-entry errors.
Another part numbering system design consideration is eye-hand
coordination, i.e., "clerical speed and accuracy". Many of our users will prefer using only the characters commonly available
on a computer's numeric keypad. This allows single-hand operation, and the
layout is easily memorized and generally independent of local language
variations (e.g., if you out-source to another country, how easy is it to enter
your non-numeric characters on their keyboards?). Restricting our part numbers to numeric characters will provide the
fastest data entry for heavy users in purchasing, manufacturing scheduling,
receiving and other places where employees constantly work with a wide variety
of part numbers.
So, practical constraints suggest that part numbering systems using 7 or
fewer numeric characters are the easiest to manage for the majority of our
users.
† See G. A. Miller, "The magical number seven, plus or
minus two: some limits on our capacity for processing information."
Psychological Review (1956)
Intelligent part numbering systems: problems and costs
To encode or not to encode?
There's an almost magical fascination, even an obsession, with designing the
perfect part numbering system. Everyone starts by envisioning how convenient it
would be to tell, at a glance, the important characteristics of a part, or the
document number that describes the part. Yet, a century after the development of
mass production, the goal remains elusive because each person has a different
idea of what part attributes are important — and that person's opinion will
change over time. This fluid set of usefully encoded properties inherently
conflicts with the part numbering system's essential role in establishing an
unchanging reference to an item.
Recall that our basic part numbering system requirement is to distinguish
parts, based on their meaningful attributes for the application. Let's first
examine the two possible extremes: encode all meaningful attributes in the part
numbering system, or encode no attributes. Obviously, a part numbering system
that encodes all meaningful attributes of each part would be impossible to
manage. So, if we are forced to the extremes, only a non-significant part number
is viable provided that the attributes are otherwise available for look-up.
Restricting encoded attributes reduces the problems, and usefulness, of
intelligent part numbers
However, suppose we take a middle path, encoding only certain attributes in
the part numbering system, and leaving other attributes as "look ups". Which of
these attributes shall be favored? Clearly, whoever designs the part numbering
system will decide the "most important" attributes: engineers will focus on
technical properties (size, weight, power, tolerance, material, etc.);
purchasing agents may prefer procurement attributes (make/buy, vendor, and
commodity codes); production may desire handling codes, bin locations and shelf-life limits;
and finance may want to encode general ledger accounts and purchase authority.
Quality, marketing, field service, and customer support will have their own
competing views.
Since the part numbering system must be skewed to serve one group at the cost
of another, one group will have a useful part numbering system and everyone else
will be dealing with an overly-long, error-prone and costly system. The only
consolation may be knowing that even the favored group's part numbering system
won't last forever: initial design assumptions, practical day-to-day decisions, and the march
of technology inevitably make the original categorizations obsolete. Repeated
part numbering system tweaks and, finally, redesign are inevitable because (1)
mistakes are often made in part number assignments (e.g., is an LED a "display"
or a "diode"?); (2) some categories
become over-used, ambiguous or irrelevant; and (3) encoded attributes may change
despite the on-going interchangeability of the diverging parts (for instance, an
encoded dimension forces an identifier change even though the new part is
interchangeable in the application).
Avoiding these errors requires additional processes, which adds cost, time
and management resources. The cost of processing a single engineering change to
re-issue an incorrectly-categorized part may wipe out any perceived value in the
intelligent part numbering system.
Part number best practice: avoid intelligent part numbering systems
Obviously, the simpler path is to avoid an intelligent part numbering
system. Most attributes that people typically want to encode in their part
number system can be either explicitly defined within the PLM system attributes
(such as document and part type, make or buy sources, commodity codes, component
versus assembly, etc.) or in the item description (part name or document title).
If we record all meaningful part attributes within a database, and use the part number
simply as an index to that data, then our part numbering system goals can easily
be met using only 5 to 7 digits, which can represent 100,000 to 10 million
unique part numbers. Relying on a Google-like free-form text search to find part
data shortens the part length, speeds data entry, reduces clerical errors, and
eliminates the need to periodically redesign an attribute-based part numbering
system as usage and technology alter the initial categorization.
Should part numbering systems influence document identification?
At one time, it was sensible for documents and
parts to share identifying numbers; after all, it could be difficult to
determine which document defined a specific part. The document number typically was embedded within the part number,
and a series of parts could be documented on a single engineering drawing. An
example of these "tabulated parts" would be where document
12345 described parts
12345-01 and
12345-02.
However, documents
and parts have different lifecycles. Part interchangeability rules may force a
new part number where only a document revision is required; likewise, for
clarity a new document may be created to describe one or more existing parts.
And a specific set of documents (for fabrication, plating, assembly, testing,
adjustment, inspection, etc.) may be applied to a variety of different parts.
Another document identification approach assigns related design document types
a common root, and extensions ("tabulated drawings") indicate a particular
document type. For example, a
circuit schematic might be 45678-01, printed circuit layout
45678-02, and printed circuit board (PCB)
drill pattern 45678-03. But you may later need to "upsize" the schematic with a
new document number to cover an entire product family with other PCB layouts and
drill patterns, or an alternative PCB layout based on the same schematic, and the original relationships would no longer exist.
All PLM systems let you make document and part relationships
explicit, independent of their identifying numbers. You no longer need to try maintaining these
relationships through item identifiers. So, engineering drawing identification
should follow our previously-established part numbering system goals and
constraints: purely numeric characters with a length of no more than seven
characters.
Part numbering system best practices for PLM
Product lifecycle management software provides a significant level of
automation, and will influence how your part numbering system is defined.
A good part list tool will automatically assign an appropriate part number,
prompt users with how the part should be described, provide information on the
part supplier sources, permit user-attached specification and process files, and
track the part release history. The best parts list software is part of a
complete PLM system that includes bill of
materials management, document & file control, and change control.
In a computer-based item numbering system, use a short, non-significant
number for all document numbers and part numbers. Use the product structure to
manage the relationships of documents-to-documents (i.e., a "data list"),
parts-to-parts ("bill of materials"), and parts-to-documents ("part control
data"). Other item identifiers defined within the PLM database can be used to
satisfy almost any user's information or query needs.
For more information, please download our free whitepaper Best Practices for Item
Identification.
Part numbering systems supported by PDXpert PLM software
Like most part
numbering software, PDXpert PLM software can follow industry part number
best practices by sequentially assigning document and part numbers. If you help
your users by separating your part numbers into short groups (e.g.,
123-456), PDXpert PLM software will ignore the delimiting
characters when incrementing: 1234-999 will become
1235-000.
If your part numbering system uses a "semi-significant" scheme, PDXpert
PLM software
can assign document and part numbers based on your defined item types. Each part
and document template can "subscribe" to a unique or shared item numbering
format that permits category prefix (e.g., "HW-"), sequentially-assigned
base number, and a fixed
suffix (such as "-01"); the next
part number from HW-12345-01 will be
HW-12346-01. Users can
edit or replace these assigned values as
needed.
And, if your company must use a "intelligent part numbering system" that
requires human interpretation and assignment, you can configure PDXpert
PLM software to only accept manually-entered document and part numbers for all
of your items.
In addition to accommodating your specific part numbering system, PDXpert
PLM software supports all organizational
stakeholders:
- When creating a new part record, users are prompted for consistent item
descriptions using "text templates" based on the part type.
- A specifying designer can provide both budgetary and current unit costs for
part list roll-ups.
- Each part can have its own supplier source parts list, which includes
the ability to rank preferred usage.
- Users can add a virtually unlimited number of file attachments that are
either "locked down" on item release, or can be modified throughout the entire
part life cycle.
- Even non-technical users can easily find parts by relying on
familiar "Google-like" free-form text searches that not only return the most
relevant parts, but also can return similar items that may be substituted, with
the resulting part list ranked by relevance.
- Complete part histories are tracked by releasing and canceling parts
revision records using change forms.
PDXpert PLM software manages parts and part numbering, and so much more. Register now to
download your free, fully-functional PLM evaluation software.
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