Bill of Materials- Definition, Components & Types

In order for manufacturers to begin their assembly or production process, they must establish a bill of materials (BOM). Also referred to as a production recipe or assembly component list, a BOM ensures that teams have accurate instructions on hand, as well as the proper supplies and materials to begin construction.

A well-defined BOM will drive companies to success as it enables business owners to effectively conduct inventory management, reduce waste, and maintain records of their operations.

What is a Bill of Materials (BOM)?

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A bill of materials is an extensive list of raw materials, assemblies, and parts that are necessary to construct or manufacture a product. It also includes the quantity needed for each component and thorough instructions on how to make the final output.

For example, a children's toy manufacturer that must produce 50,000 plush animals would have a BOM that details how much cotton, fabric, thread, and buttons are needed, and how to sew and structure the plush toy.

With a comprehensive BOM, production teams will be able to operate efficiently without any delays caused by low supply levels or missing inventory. This will save businesses time and can minimize extra operating costs.

3 Types of a BOM

There are various forms of production recipes that range in level of detail and structure. Depending on the business model and project, a BOM will typically be one of the 3 main types.

1. Manufacturing

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The manufacturing bill of materials, also known as MBOM, is a full list of all the subassemblies and components that are needed to create a finished product. This type of BOM is extensive, as it usually includes detailed information about individual parts and instructions on how to prepare certain materials before they are assembled.

All information included in the MBOM is exchanged with all staff that is involved with inventory and production. It is also shared with integrated business management systems, such as inventory software, which is a solution that helps companies manage their daily stock levels. By updating these resources with the MBOM, manufacturing processes will be efficient and productive.

2. Engineering

An engineering BOM, or EBOM, details the assemblies of a product by designing its structure from a functional perspective. These often include technical or mechanical pictures or computer aided drawings of a product. Engineers will often create an EBOM using digital tools, such as electronic design automation (EDA).

Companies may have multiple engineering bills of materials for one product due to changes or revisions in design.

3. Sales

Also referred to as SBOM, a sales BOM provides details about a product before it is assembled. It contains two separate lists, with one indicating the finished output and the other detailing the different components that were used to produce it.

Components of an Effective BOM

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To ensure that products are built correctly, a BOM must be well defined. When developing or revising an assembly component list, organizations should include-

  • BOM Level - Each assembly or part should be numbered to indicate its rank in the BOM.
  • Part Number - Another number should be assigned to each part so that users can quickly reference and identify it. It is important that organizations utilize a numbering scheme that does not generate different numbers for the same component.
  • Part Name - To further make the identification process easier, a name should be assigned to the assembly or part.
  • Phase - Each stage of the production process that a product is in should be recorded. Organizations will often use in production to indicate what phase a product is currently in, while unused parts are labeled as in design. By tracking the progress of a product, businesses can forecast accurate timelines.
  • Description - All parts of a product should be described in detail so that staff can identify and distinguish them easily.
  • Quantity - Recording the quantity of all parts used during production or assembly will help management teams accurately replenish inventory.
  • Unit of Measure - Components that are purchased or used in measurements, such as inches, ounces, or pounds, should also be recorded. It is important that businesses be consistent and utilize the same unit of measurement across similar types of parts. This will help ensure accuracy when ordering inventory.
  • Procurement Type - Including where the part was purchased or how it was made will enable manufacturers to efficiently plan their production and procurement activities.
  • BOM Notes - Adding additional notes, such as how an assembly should best be used, will keep staff updated about the production process.

Key Questions to Answer When Creating a BOM

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When developing an effective BOM, organizations should consider these questions-

1. Do Consumables in the BOM Need to be Recorded?

Oftentimes, consumables, such as glue, paper labels, and wires are not included in the BOM record. It is important to document these materials to make sure that it is procured and included in production.

2. Will Files be Attached to the BOM?

A BOM should have supporting documents, such as instructions, part datasheets, and design drawings. These files can be placed according to the BOM level it is associated with.

3. Who Will Use the BOM?

BOM developers should identify everyone who will be using the BOM so that they can include all the necessary information those people may need about the product's lifecycle.

4. What Happens When a BOM is Revised?

A BOM will typically be revised during the design phase; therefore, organizations need to keep track of the different versions of the BOM. There should be a label or identification method that helps staff distinguish the different versions. This will ensure the correct version is being consulted during production.

Creating a comprehensive bill of materials that includes all of the necessary information will help drive the creation of the final product.