Bill of Materials (BOM) and its importance

bill of materials

A product is made up made up multiple parts. These parts which help in building the finished product, can itself be manufactured using several other raw materials. A product’s hierarchical structure defines the list of parts or components that were used to manufacture the same. In theory, we call this as Bill of Materials (BOM). A BOM lists down the raw materials, sub-assemblies and components that is used to build the product, including its quantities and other attributes such as labor required, unit of measure, effective date etc.

Until the modern PLM systems were bought into service, these structures were maintained mostly in Excel sheets. Maintaining a Bill of Material in spreadsheets were seen widely easy, as it requires very less training for the end users. However, in a large scale discrete manufacturing company, maintaining these excel sheets in the long run itself turned out to be a tedious job. In addition, there were also other disadvantages like tracking, revision control etc.

In the longer run, these organizations required automation in maintaining Bill of Materials. A PLM system help to streamline this process and help the administrators to create, edit, and maintain a Bill of Material with much ease. A PLM software tool is so important for an efficient PLM practice as it ease the change management with respect to BOMs, avoid errors and provide feasibility to track back in time on various versions of Bill of Materials.

Types of Bill of Materials (BOM):

Theoretically, companies use different notations to define bill of materials.  The types of bill of materials are generally based on the primary purpose for which it is created. For instance, a Single-level BOM is defined for an easy representation of the finished product. This does not list down the sub-assemblies or other raw materials used to build the sub-assemblies itself. On the other hand, a Multi-level BOM defines the complete hierarchical structure of the leaf level sub-components and raw-materials used to manufacture the finished good. It is self-understood that it is easy to build a single level BOM from a multilevel but not vice versa. The different representations used to define the bill of materials are listed below.

Engineering Bill of Materials (eBOM)

A product is first designed using a Computer-aided design (CAD) software where it is conceptualized digitally, and the various parts and components are defined in the system. The design team defines the Engineering bill of materials in the form of 2D or 3D drawings and this lists down all the items, at sub-assembly level to prepare the design. The eBOM is then passed on to shopfloor for manufacturing.

engineering bill of materials

Manufacturing Bill of Materials (mBOM)

While the eBOM focuses on the detailed design of the product at sub-assembly level, it cannot be directly used to manufacture a finished product. An eBOM gets converted to mBOM for production in the manufacturing floor. A mBOM contains more details of the assembled product before it is shipped for end customer. For example, unlike the eBOM which details the detailed drawing to manufacture the product, it cannot be directly shipped to the customer. A mBOM should include additional details such as the packaging materials used for shipping, user manuals to be shipped along etc.

Configurable Bill of Materials (cBOM)

A Configurable Bill of Material (cBOM) is also known by its other name “Super BOM” or “150% BOM” by PLM practitioners. In early days, when a standard product is manufactured by a company, most of its components and subassemblies were fixed. However, this does not work in all the cases. Modern consumers look for variants, choices to choose from depending on their taste. For example, there are multiple variants of a refrigerator or an air conditioner manufactured by an appliance company. Though the core hardware design of these variants does not vary in most of the cases, there may be very minor deviations such as the color, graphics etc. In more complex scenarios, a consumer can choose from combinations of multiple options and choices provided by the manufacturing company while purchasing the product. In these cases, it is not possible for the organizations to keep up hundreds and thousands of BOMs that results based on the permutations and combinations of the choices provided. So, the company maintains only one BOM with all the possible combinations of the components. Based on the select conditions chosen a cBOM (150%) gets converted to a mBOM(100%) with only the precise parts that is required for manufacturing the finished goods. (We will discuss more in detail about the Super BOM and why it is so important in modern manufacturing practice, in a separate blog)

Configurable bill of materials

In addition to the above three core types of BOMs, there are also other types which are used with respect to the organization’s specialized practice or departments. A “Service BOM” is a term used by service-based companies that list down the repair instructions, installation guide etc. when the product is serviced at customer’s place by service engineers. A “Software BOM” is used in a software industry that lists down various dlls, exe, patches, user guides etc that is required before the software is shipped for end customer.

A Bill of material is a vital constituent of any manufacturing process an it makes sure all the department in the company are working as one and introduce the product to the consumer use.


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