Applying principles of interchangeability to your bill of materials
PDXpert PLM software simplifies bill of materials
management by automatically displaying the currently-released item on an
assembly. As new item revisions are released, PDXpert applies
the basic rule of interchangeability to ensure the latest revision is used. We
discuss how the benefits of item interchangeability rules, as well as the
alternatives if your bill of materials don't apply these
common "form-fit-function" rules.
Part interchangeability definition
A
part is interchangeable with another part when (a) the relevant functional and physical
properties are equivalent in performance, reliability and maintainability, and (b)
can be used without requiring special procedures (such as selecting for fit or performance)
and without altering the part itself or any other part.
A part is often considered
interchangeable with another when the form, fit and function
are identical:
- Form The unique and relevant physical characteristics (shape,
size, mass) that characterize a part for a particular use.
- Fit The ability of a part to physically mate with, interconnect
to, or become integrated with another part.
- Function The action that a part is expected to perform in fulfilling
its purpose.
Practically speaking, if a new
part can be intermingled in production inventory with previous iterations of that part without any negative
effect, then the parts are interchangeable and the part number remains
unchanged. Conversely, if you need
to stock a new iteration of a part in a different inventory bin because it is not
compatible with previous iterations (or you simply want to track its usage
because you're not sure of its effect), then it's not interchangeable and you must issue
a new part number.
When you're considering interchangeability, it's important to emphasize that
"the relevant functional and physical properties are
equivalent". The interchangeability decision should account for how the item
is used in your specific application. For example, the particular shade of green on a
wire's insulation may not be relevant, yet a precise green is completely
relevant when evaluating an automobile trim panel. Likewise, you may not care
whether your capacitor's rating is revised from 20WVDC to 10WVDC if all of your
designs operate at 5VDC; or, it might be show-stopper if you also produce 12
volt designs.
Unlike some PLM software that draws firm lines between internal "home" parts
and supply chain "partner" parts, PDXpert software treats
partner parts as peers to home parts. Therefore, any interchangeable
home or partner item can be a source for another item. This allows you to easily consume existing
obsolete stock or switch to a new part numbering system.
Document revisions and new document numbers
Document identifying numbers may be changed less frequently than part numbers. A
document is assigned a new revision identifier when its technical content
changes without forcing a new part number to a currently-produced part. This
happens in two instances:
- The document describes an existing part, and (a) the document and part
numbers are related and (b) the revision does not cause
an non-interchangeable change. In other words, the part remains
interchangeable before and after the document's contents change.
- The document adds a new part to an existing series of similar parts. For
example, a supplier specification lists all available 0.1 watt, 2% axial
lead resistors; when the supplier adds a new value, say 1.8MΩ, the
document can be revised since the addition doesn't affect any existing
product.
Notice that if your document numbers are independent of the parts they
describe, you won't necessarily need to change document numbers when your
revisions affect part interchangeability. You can reduce the bill of materials
that must be manually updated, and change forms that must be processed, simply
by assigning document numbers without regard to how the related parts are
identified. Click here for a
more complete discussion of document and part numbering systems.
Using interchangeability rules to auto-update bills of materials
PDXpert PLM software helps prevent part interchangeability problems
while reducing the number of engineering change orders required to manage the
product life cycle. When you follow the standard interchangeability rules, then
any interchangeable changes you make will be immediate reflected on every bill
of materials upon release of the new item revision.
Similarly, when a supplier part record revision changes while retaining the
previous part number, the Source list on the consuming part will be updated
without requiring an explicit ECO.
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