This paper will provide practical approaches to implementing and managing
engineering changes and explore Product Data Management (PDM) or Product
Information Management (PIM) and Enterprise Resource Planning (ERP) can be
used as a tool to support configuration management and engineering change control.
Complex products such as automobiles, aircraft, and major capital equipment
and systems sometimes consist of thousands to hundreds of thousands of parts.
In addition, there are related tooling, fixtures, gauges, templates, test
equipment and software. One estimate was that a part may undergo ten engineering
changes or more over its life. This suggests that a company may evaluate and
process many thousands of engineering changes for a complex product. Over the
life cycle of the product, the manufacturer must assure that the as-designed
configuration at any point in time will satisfy functional requirements and
that the hardware and software actually delivered (as-built configuration)
corresponds to the approved as-designed configuration.
As a result, the configuration management effort required for a complex
product is significant. Computerized systems including PDM/PIM and ERP are
required to support configuration management if a company is to avoid being
drowned in a sea of paper and non-value-added administration.
Engineering drawings and parts lists when linked together in a drawing tree
or engineering product structure form an engineering bill of material or as-designed
configuration. This representation of how materials, components, sub-assemblies
and assemblies come together to form the end product is based on the designers'
visualization of the product and its stages of production or based on a functional
subsystems-oriented view of product assemblies.
It is likely that the representation of the assembly levels and relationships
will be different from the way Manufacturing actually builds the product.
Additional differences will result from Manufacturing and Materiel deciding
to stock components and assemblies at different stages of completion than may
be represented on a drawing. This may be done to provide flexibility to the
manufacturing process or flexibility to support spares requirements. Finally,
not all data may be provided to support manufacturing needs. For example,
item requirements on drawings are stated as "as required" and left to Manufacturing
to define the needed quantity.
These product structure differences may require the definition of
additional manufacturing part numbers that will never be represented on
an engineering drawing, but are required to uniquely identify an item for
planning within ERP; for receipt, stocking and issuing; and for quality assurance.
It may also be necessary to re-assign parts to different assemblies or different
levels to define a manufacturing bill of material. In addition, tooling,
fixtures, gauges, templates, test equipment and software may also be added to
the bill to support acquisition, manufacture or development of these assets and
plan for their availability to support production. When these re-structuring
activities are performed on an engineering bill of material, the result is a
manufacturing bill of material or as-planned configuration.
The as-designed and as-planned configurations should be reconcilable.
The end-item as well as the lowest level (purchased materials, components
and assemblies) in each of these bills should be the same except for quantities
which may not have been defined in the as-designed configuration and the
additional tooling, test equipment and software items, etc. When a PDM/PIM
system is in place that provides for both an engineering and manufacturing
view of the product structure from the same database, this issue of reconciliation
A complete design baseline, including both the engineering and
manufacturing bills, must be established as a starting point for configuration
control. If the design baseline is not complete or not thoroughly documented,
subsequent changes will become extremely difficult to manage.
Where a partial design release is necessary to support long lead procurement
or fabrication, partial engineering and manufacturing bills can be established,
reconciled and controlled. As the rest of the bill of material items are
released, the remaining structure can be added and linked to the previous
RULES FOR CONFIGURATION CHANGES
The discipline required with complex products such as defense systems
provides an excellent basis for considering rules related to configuration
changes. As a prerequisite to configuration control, it is important to
understand the classes of change and the implications of these changes on
the bill of material structure. Class I changes affect an item's fit, form
or function. These are changes that affect an item's specifications, weight,
interchangeability, interfacing, reliability, safety, schedule, cost, etc.
Class II changes are changes to correct documentation or changes to hardware
not otherwise defined as a Class I change.
Another concept that will affect the implementation of changes is
interchangeability. Interchangeability is defined as when two parts possess
such functional and physical characteristics as to be equivalent in performance,
reliability, maintainability, etc. These parts should be able to be exchanged
one for another without selection for fit or performance and without alteration
of the item itself or of adjoining items.
The Telecommunications Industry Item Interchangeability Guideline
(TCIF-97-001) defines when manufacturers/suppliers should change part
numbers. A new ID number is assigned any time an item cannot be co-mingled
in an inventory bin or is not acceptable to the customer in all applications.
An item is interchangeable if it can be co-mingled in inventory and selected
without regard for which item is picked.
A Class I change is implemented by changing an item's part number.
This is done because, by definition, the change affects fit, form or function.
The new version of the item is no longer interchangeable with the old item.
Therefore, this item must be uniquely identified for planning, procurement,
stocking, manufacture and support because it is distinct and different in how
it can be used.
If a Class I change is made to an item at a lower level in the product
structure, the part number of the new item changes. In addition, the part
number of each higher level assembly where that part is used also changes
until an assembly level is reached where interchangeability is re-established
with the old version of the assembly.
If interchangeability is re-established at the first parent assembly level,
then only the new item's part number would change. However, it is very conceivable
that a change could be made to a raw material, component or assembly that would
affect the specified fit, form and function of the end-item itself. This would
result in part numbers changing all the way up the product structure to a new
end-item part number.
Determination of when interchangeability is re-established is a matter of
judgment. Strictly speaking, it could be argued that in many of cases that
a change is made, a subtle effect on specified fit, form or function could be
identified in the end-item itself (i.e., interchangeability is not re-established
at the end-item level). Practically, Engineering and other functions will make a
judgment that interchangeability is reestablished at the lowest possible level in
the product structure to avoid the impact of the change on logistics, tech manuals
When interchangeability is re-established at a higher assembly level for a
Class I change, the revision letter for that part number is rolled to the next
level to reflect a change in documentation, i.e., a change to the assembly's parts
list. A Class II change which does not affect fit, form or function generally is
also implemented by rolling the revision letter to the next higher level.
Because a Class II change has much less impact on the product, the change approval
process is not as complex. This leads to the infamous Class 1.5 change, a Class I
change that affects fit, form or function, etc., and is treated as a Class II change
by rolling the revision level rather than changing the part number. This type of
change is done to shortcut the engineering change process and should be avoided.
In a complex product with a high volume of changes, changes should be grouped
together and implemented in blocks to improve control over these changes and
minimize the overall effect of changing part numbers and revision levels.
The demand for a configuration or engineering change can be generated
either from within the company or externally from the customer or a supplier.
- Correct a drawing or engineering document error
- Correct a usability, reliability or safety
- Fix a bug or product defect
- Improve performance and/or functionality
- Improve producibility
- Lower cost
- Incorporate new customer requirements
- Specify a new supplier or supplier part/material
- Enhance installation, service, or maintenance
- Respond to regulatory requirements
An engineering change proposal or request (ECP or ECR) is typically prepared
and then analyzed and evaluated. The analysis and evaluation results in a
recommendation by the Configuration Control Board or Change Control Board (CCB)
on when a change is to be made (effectivity) and what should be done to existing
inventory of the old configuration assemblies and components (disposition). ERP
provides data to support this evaluation.
When a change is being evaluated, the following must be considered:
- Inventory status of the new and old item. How many of the old item are in
inventory? Must they be scrapped or can they be used on other products or reworked?
What is the cost to rework or scrap? Is the new item in inventory?
- Production status of the new and old item. How many of the old items are
in work-in-process? Can they be reworked to the new configuration considering
their current stage of completion, completed and used up before the change is
effective, or must they be scrapped? Has production of the new items begun? What
is the leadtime and cost for production of the new item? What is the additional
leadtime for building tooling, fixtures and test equipment?
- Procurement status of the new and old item. Is the old item on order?
Can it be cancelled or reworked? At what cost? What is the leadtime for
procuring the new item? Are new suppliers required?
- The impact on the distributors, dealers, customers and field service organizations.
What notification is required? How long will the process take? What documentation,
manuals and catalogs need to be updated? What are the implications on spare parts
- Testing and regulatory requirements. Are the changes significant enough to require
retesting? What testing needs to be performed? Does the product need to be recertified?
What regulatory approvals are required?
Based on this information, a decision will be made on when a change is to
become effective. A change plan may be required to
identify all of the required actions, the responsibility, and the timing.
Within PDM/PIM and ERP, the effectivity of the configuration
change typically will be specified through one of two basic techniques: date
effectivity or serial effectivity.
Date effectivity has been the traditional approach to defining effectivity
with ERP. With this approach, a change implementation date is used as the basis
for planning when the new item will be phased into the bill of material and the
old item phased out of the bill of material. Dates can be associated with the
start of production lots to control the configuration of the lot and the of the
serialized assemblies within a lot. In a low volume environment, this can be a
very satisfactory method of maintaining configuration control over even complex
Serial effectivity works in a similar way, but the change is tied typically
to the end-item serial number. Serial effectivity is sometimes the preferred
effectivity technique because the planned configuration of each end-item serial
number is pre-defined and not subject to shifting schedules.
In a situation with a large number of changes, a complex product structure,
and low rate production, the result could be a unique configuration for each
end item serial number unless block changes are utilized. With block changes,
there could be a unique end-item at each blockpoint. In this situation, the
Master Production Schedule with unique end-item part numbers controls
EXECUTING THE CONFIGURATION PLAN
Based on the as-planned configuration, ERP will develop a material plan.
Even in the best ERP environment, problems will occur in executing the material
plan and it may be necessary to use other materials. Alternate parts defined
on engineering drawings provide planners the flexibility to use different
materials without prior approval. Substitute parts are items that are approved
on a case by case basis for use in a product.
A deviation provides before-the-fact approval of a substitute or discrepant part.
A waiver provides after-the-fact approval of a product not built according to the
required configuration and specifications.
These single level order bills can be linked together as the product is
manufactured to represent the overall as-built configuration. If the organization
is involved in maintenance, overhauls or modifications, there will be a need to
maintain the as-supported configuration. Future business demands may require the
communication of changes between supplier and customer that affect the as-supported
Regardless of the circumstances, if a product is to be built to other than the
as-planned configuration, a mechanism is needed to plan and document these
differences in configuration. This mechanism is the order bill of material or the
dependent requirements list associated with each MRP order.
As MRP orders are planned, the single level of the as-planned bill of material
related to the order is copied and associated to the order. This order bill of
material or dependent requirements list is usually updated with any subsequent
configuration changes where the effectivity of the change impacts this order based
on date or serial number until the order is firmed. In addition, the order bill
can be maintained for any other changes in configuration, e.g., when a planner
faces a shortage of the primary part and specifies an alternate. The planner
can modify the order at any point and have lower levels of the product structure
planned based on the modified order bill. However, to prevent the order configuration
from being over-ridden by a change to the bill of material with effectivity techniques,
the order should be firmed.
Since the order bill of material will be used to maintain information on
temporary changes in configuration, it should also maintain information on the
authorization for this temporary change if applicable. For example, if the change
in configuration was authorized by a deviation or waiver, the deviation or waiver
identification and date should be maintained in the order bill to provide a
logical audit trail in reconciling the as-built configuration to the as-designed
The order bill can be used to track what is actually issued against an order.
It can also be used to accumulate the as-built configuration information on a
level-by-level basis. As actual parts are issued, the issued part numbers,
quantities, lot numbers and serial numbers are recorded. If multiple serialized
assemblies are built on an order, the order bill can be copied for each serial number
and the as-built configuration information recorded for each serial number. Since
serialized component assignment to a serialized assembly may not be made until
during production, an assignment transaction is needed to identify the serialized
component or component lot to the serialized assembly. This transaction would
update the as-built configuration maintained in the order bill of material.
The alternative would be to limit an order to a single serialized assembly so
that serialized component issues could be automatically associated to a serialized
STATUS ACCOUNTINGConfiguration control
requires that both proposed and approved engineering changes be tracked
and identified to the affected items. ERP needs a robust capability to
track and support engineering changes. A product data management system or
engineering document control system is a logical approach to addressing
this and other documentation needs.
As changes are requested or proposed, a unique identifier is assigned to the
ECP/ECR. The ECP/ECR information should be maintained in a PDM/PIM and/or ERP
system. As the proposed change moves through the evaluation and approval process,
its status should be tracked using this system(s). Status information would include
not only completed steps and the information accumulated at each step, but
information on the physical location of the ECP/ECR should also be maintained.
When the change is approved, an Engineering Change Order or Engineering Change
Notice (ECO/ECN) is prepared and distributed. Information related to this document
should also be maintained in the PDM/PIM and/or ERP system.
These documents should be linked to the item numbers affected by them in the
product structures records for both the as-designed and as-planned configurations
with effectivity techniques. In this way, the PDM/PIM and/or ERP system, the
product structure with its effectivity information, and the order bill of material
with information on waivers and deviations provide some of the necessary information
to support configuration status accounting. This would include:
- As-designed and as-planned configurations: historically for items already built
as well as prospectively for items planned to be built
- As-built configurations including authorizations for any variances from the
- The status of both proposed and approved changes
- Change traceability: changes proposed, approved, and implemented for an
item number (including effectivity); and the items affected by a given proposed,
approved or obsoleted change
A PDM/PIM and ERP system that captures the data described can play a key role
in the configuration verification process. The goal of configuration verification
is to assure that the as-built configuration can be reconciled to the as-designed
configuration. (The need to reconcile the as-designed and as-planned configurations
was previously discussed.)
If the as-planned bill of material and order bill of material can capture
information about deviations and waivers which temporarily authorize a change
in configuration, then the data exists to support the next step in the
configuration verification process, reconciliation of the as-planned and as-built
configuration. The final step is the physical verification of the product to the
as-built configuration records through inspection or product tear-downs if required.
Configuration management is a critical discipline in delivering products that
meet customer requirements and that are built according to approved design
documentation. PDM/PIM and ERP systems can provide the tools to support