What is Flattened BOM?

Flattened BOM Definition

A flattened bill of materials (flattened BOM or flat BOM) is a depiction of a multi-level BOM consolidated into a singular, non-hierarchical list of components, where each distinct part is listed just once, accompanied by its total number across all levels. A flattened BOM consolidates the structure, presenting all components, including subassemblies and top-level assemblies, in a single, unembellished spreadsheet or view, rather than depicting parent-child relationships and nested assemblies.

Key characteristics of a flattened BOM include:

  • The consolidated BOM reflects the total consumption of a component when it is used multiple times across various subassemblies
  • No hierarchy or parent-child relationships are displayed; the emphasis is only on part numbers
  • A simplified procurement approach – an optimized bill of materials (BOM) facilitates use by procurement, purchasing, and supply chain teams, since they focus solely on the quantity and kind of parts, rather than structural intricacies
  • The flattened view is derived from a multi-level BOM, which is in turn derived from a more complex hierarchical BOM; it does not supplant the foundational structure.
  • Flattened BOMs are frequently utilized for comparisons, cost analysis, quotations, and part sourcing, particularly when evaluating alternatives, producing cost roll-ups, or exporting to ERP or procurement systems

A flattened BOM abstracts structural details, serving as a valuable “reporting/export view” rather than the principal engineering or design BOM.

Role of Flattened BOM in PLM, QMS, NPI & BOM Management

Flattened BOM in NPI & BOM Management

During new product introduction (NPI), engineers and product managers usually use detailed bills of materials (BOMs) to show the design, structure of modules, and how parts fit together. However, when planning for procurement, cost estimation, or validating part quantities, a flattened bill of materials (BOM) offers a concise and streamlined list of components. It assists with supplier proposals, material cost aggregations, inventory management, and order scheduling.

From a bill of materials management standpoint, the flattened BOM simplifies complexity for several users. Procurement can swiftly assess overall part utilization, recognize duplication, or evaluate alternative parts without needing to access deep hierarchies. It facilitates downstream processes, including cost estimate, parts consolidation, component substitution, and order generation.

Consequently, the flattened bill of materials (BOM) provides a supplementary perspective inside the BOM management lifecycle: structural (hierarchical) views for design and assembly, and flattened views for procurement, cost, and supply chain considerations.

Flattened BOM & PLM / QMS / Change Control

In a PLM (product lifecycle management) system, the flattened BOM view often serves as an alternative representation of the standard multi-level BOM. The PLM system maintains the complete assembly hierarchy (including engineering, design, and assembly sequence) while providing a simplified perspective for downstream stakeholders (such as procurement, cost analysis, and supplier interaction). The controls of the quality management system (QMS) remain applicable: any modifications to the foundational bill of materials (BOM) must undergo change control, and the flattened view must remain synchronized as a derivative representation.

Upon implementing a change (ECO), the system must recalculate the flattened BOM to accurately represent revised quantities or components, ensuring consistency. The flattened BOM functions as a verifiable document in audits and quality assessments.

FAQs

When is a flattened BOM preferable over a hierarchical BOM?

A flattened BOM is advantageous for obtaining a consolidated list of components for procurement, cost roll-ups, or item ordering, eliminating the complexity of traversing parent/child relationships. It enhances transparency for procurement, forecasting, and supplier interaction.

Does a flattened BOM replace the need for a multi-level BOM?

No. A flattened bill of materials (BOM) is a derivative representation used for reporting or subsequent procedures. The multi-level BOM (hierarchical) is crucial for documenting assembly structure, design rationale, and manufacturing sequences.

How are changes to the design BOM reflected in the flattened BOM?

Upon modifications through ECOs or revisions in the PLM, the system reconstructs the flattened BOM to ensure that quantities and components accurately represent the current status. The flattened view is recalibrated based on the revised hierarchical structure.

What are the risks or pitfalls when relying on flattened BOMs?

The loss of structure obscures context, including the origin of a component (its subassembly) and constraints (which components are optional versus mandatory). Users may misunderstand the total amounts or fail to recognize the dependencies between variations. Furthermore, change propagation must be meticulously managed to prevent drift.