This paper will provide practical approaches to implementing and managing engineering changes and explore Product Data Management (PDM) or Product Lifecycle Management (PLM) 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/PLM 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/PLM 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 is overcome.
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 partial structure.
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 and maintenance.
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.
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:
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/PLM 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 assemblies.
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 effectivity.
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 configuration.
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 configuration.
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 assembly.
Configuration 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/PLM 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/PLM 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/PLM 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:
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/PLM and ERP systems can provide the tools to support configuration management.