CAD-BOM Alignment: CAD-Driven BOM vs BOM-Driven CAD

Lionel Grealou CAx, Data, ERP, PLM 1 Comment

The need for BOM-CAD alignment and associated challenges

Bill of Materials (BOMs) typically contain parts / items which are grouped into component and sub-component assemblies based on fit-form-function factors and other usage & market specification requirements. These components and sub-components are “used” and revised in assemblies (context), structured through object relationships which represent functions and data mastership dependencies. These objects are architected in such a way to combine, integrate, mature and align across multiple enterprise data models. In the manufacturing industry, these support business collaboration across organizational boundaries.

A Bill of Materials (BOM) is often compared to a recipe – both engineering and manufacturing BOMs identify and list the components of a finished product.


There are different schools of thought with regards to EBOM and MBOM alignment. Synchronising and maintaining EBOM and MBOM alignment throughout the lifecycle of a product requires a lot of preparation; what is managed on the Engineering side differs significantly from the Manufacturing side (approach, usage, lifecycle, dependencies, etc.); the two need constant alignment and maintenance to ensure seamless business continuity. The utopian schools of thought prone a monolithic or single master BoM vision which would remove the need for continuous alignment – this is however not practical due to integration complexity of multi-purpose requirements which by nature contradict each other.

The physical product design and engineering is initially conceptualised and developed using 3D digital representation: this constitutes the digital mock-up (DMU) or virtual representation of the product.

Creating a BOM is not only a necessary step in the product realization cycle, it is also what makes a product a reality. Different functions in the organization have different definitions of the product should be viewed. This is typically illustrated by how product engineers and manufacturing engineers collaborate. Engineers typically operate in a CAD-driven BOM (often referred as the engineering BOM), while manufacturing engineers operate in context of a BOM-driven CAD structure (which can be referred as the manufacturing BOM). They must align on common interfaces which rely on specific data maturity states.

Aligning BOM and CAD structures over time poses important business challenges, which are intrinsically linked to how engineering data is matured and decimated across the business.

  • Revision changes are impacting relative CAD positioning
  • Enterprise BOM synchronization introduces inaccuracies at the CAD structure level
  • Relinking parts and components is a time consuming ENVA which impacts design-in-context and DMU work
  • CAD and BOM maturity and version are misaligned
  • CAD and enterprise features are not matching and must be manually validated and corrected
  • Broken links and multi-model dependencies (3D-3D, 2D-3D, document-3D)
  • Part child-parent relationships broken or incorrect
  • Wrong quantities
  • Part duplicates or gaps
  • Manually intensive corrections
  • Failed delivery gateway due to data accuracy and trust issues
  • Excel based BOM compare or “hidden factories” (uncontrolled) reports

BOM-driven CAD: robust business control, typically the manufacturing view

Broadly speaking, BOMs drive change traceability, cost management and multi-function collaboration. Yet, in the early design stages, they can add complexity to the creative design and engineer process where multiple CAD instances, positioning and contextual history is very important. BOMs can be difficult to navigate from one function to another, especially in the context of navigating CAD product structures.

Expecting engineers to work in a BOM-driven CAD context is often utopian in the early stages of the product development lifecycle. As the product matures and manufacturing “takes over” from engineering, parts are selected for a particular product configuration by defining features and timing.

  • Managing what is visible to engineering in a manufacturing context with a BOM-driven CAD structure can hinder the “creative process”.
  • EBOM / CAD structures and MBOM have to align at multiple touch points and in multiple repetitive handshakes (not necessarily at all times).
  • The BOM top levels are to be controlled by manufacturing, while the bottom levels can have different freeze points controlled by engineering.
  • Engineers often chose to operate in a perpetual non-revised level CAD components, under the mastership or an enterprise BOM; for them, it translates into operating in a CAD-driven BOM which gradually handover product data to manufacturing.

CAD-driven BOM: flexibility, yet gradual control, for engineers to create

Engineers and project engineers require “simpler” product structures to navigate through instance paths which can be retained for a given part regardless of changes to BOM lines of usage. They need to experiment and test design options without the burden of advanced change management constrains.

It is important to have CAD versions aligned to configured product structure or variants aligned to time-bound effectivities; as CAD data mature, work-in-progress product structures are updated with latest released and validated components and parts. Metadata and attributes are gradually updated to reflect simulated and calculated properties: e.g. calculated weight, material properties, etc.

After the creation of the part structure, Engineers can add non-geometric information, as well as options and variants assigned to the existing designs. Simulation parameters and results, issues and design review mark-up can be added to the data set for traceability. Change request and notices can then be tracked at the EBOM level and synchronised with the MBOM at different maturity gates. The EBOM is then aligned with the MBOM at multiple touch points, and more regularly when transitioning from development to manufacturing. The BOM mastership is therefore expected to transition from the EBOM to MBOM as soon as the product moves into industrialization and start-of-production (SOP). Based on the manufacturing or assembly complexity, there is also a process BOM which sits between the EBOM and the MBOM to simulate and optimise how the product is produced.

This BOM-CAD alignment is critical to avoid late uncontrolled engineering changes leading to expensive manufacturing or production implications. This can also be a consequence to analysis based on an out-of-date engineering data or conflicting recommendations between design and manufacturing requirements.

The ongoing engineering-manufacturing handshake often require a hybrid CAD structure which evolves from a CAD-driven BOM into a BOM-driven CAD structure. The gradual transition and level of BOM-CAD alignment is often dependent on the product complexity, the industry in which the product is manufactured or assembled, and the target market into which the product is sold, distributed and maintained. Achieving this alignment often requires a robust and seamless PLM-ERP integration

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