What are Bill of Materials (BOM)?

Bill of Materials (BOM) Definition

A bill of materials (BOM) is a comprehensive list of parts, items, assemblies, subassemblies, intermediate assemblies, and other materials required to create a product, as well as instructions required for gathering and using the required materials. A BOM can be thought of as the recipe and shopping list for the creation of a product, presented in a hierarchical format. The bill of materials includes instructions for how to assemble the product from the various parts that need to be sourced and built. 

Bill of Materials illustration


What is BOM structure?

A BOM can be structured as either single-level a multilevel BOM. A multilevel BOM includes parent-child relationships between each level of the assembly and shows the hierarchical structure for each subassembly that makes up the finished product. A single-level BOM shows all of the parts that make up a single lower-level assembly.

How do I create a bill of materials?

Depending on where you create the BOM, the process may be slightly different. If you use a PLM, QMS, or ERP software system for instance, then you normally first create the item master (part/component) record first. Then you create the BOM (assembly) by including all the components and/or subassemblies that comprise the BOM. You will also show the detailed BOM information below for quantities, reference designators, and other key information required to design and build the assembly.

If any of the items happen to have their own assemblies (with existing BOM structures), then the software system will automatically leverage the subassembly BOM to create a multilevel BOM.

If you are creating a BOM using a manual approach like spreadsheets or other types of documents, you will need to identify and add all of the components and subassemblies that comprise the BOM structure.

Whether you create the BOM using software or manually in a spreadsheet, you will need to make sure the following information is created:

  • Assign each part or assembly a number to indicate the level at which it resides in the BOM (software will help automate population of lower level subassembly BOMs).
  • Create, then assign a part number for every component that comprises the BOM.
  • Record the unique name of each part or assembly (this is done on the part record or item master for software and automatically reflected in the BOM when you add a component).
  • Record what lifecycle status/stage each part is at in its lifecycle (e.g., Unreleased, In Design, Prototype, Production). Note: This is done in a more automated and controlled fashion in PLM or QMS systems and managed by the change orders (ECOs) that formally release each part or assembly.
  • Provide a detailed description of each part (software systems manage description in the item master/part record).
  • Record the quantity of each component needed to be create the BOM (each assembly). For example, a bicycle BOM would need to list 2 tires, 1 seat, 1 chain, 2 rims, 1 frame, and 1 handlebar.
  • Classify the unit of measure (UoM) that will be used to purchase a part. UoMs can be each (EA), inch (IN), feet (FT), and others for liquids or other consumables.
  • Document how each part is purchased or made (i.e., purchased, make, off-the-shelf, or made-to-specification).
  • If the product contains printed circuit board assemblies (PCBAs), include reference designators that detail where the part fits on the board.
  • Include any relevant notes for each part.
  • In ERP systems, routing information may also be added to show the process used to make a given item/component/subassembly on the production floor.
What are the types of bill of materials?

There are three main types of BOMs:

  1. Manufacturing bill of materials (MBOM) – An MBOM consists of a structured list of subassemblies that are needed to produce a shippable product. It includes information on the parts that need processing prior to assembly and shows how the different parts are interrelated within a product.
  2. Engineering bill of materials (EBOM) – An EBOM specifies parts or assemblies that are designed by the engineering team. It shows the component structure from a functional perspective and typically includes a technical or mechanical drawing of the product.
  3. Sales bill of materials (SBOM) – An SBOM provides details of a finished product prior to its assembly during the sales phase. Both the finished product and components appear as separate items in the sales order document.

*Source: cadtalk.com

What's the difference between BOQ and BOM?

A bill of quantities (BOQ) is a document which itemizes materials, parts, labor, and their associated costs. A BOQ is used primarily in the construction industry for bidding projects. A bill of materials (BOM) is more hierarchical in nature—providing a detailed list of raw materials, parts, subassemblies, and quantities that are needed to build a finished product. A BOM is used primarily for product manufacturing.

*Source: omniaccounts.co.za

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