Bill of materials (BOM)

What is a bill of materials (BOM)?

A bill of materials (BOM) is used within a manufacturing or production environment. It’s used to list all the parts and their features required to produce a sub-assembly or product. It’s effectively a shopping list of requirements to complete a product.

To put this into context, if planning and production are to make 100 tables as a finished product, they will require components of:

• 100 x tabletops
• 400 x table legs
• 400 x brackets for bolting each leg to the table
• 800 x bolts (2 for each table leg fixing)

How to make a bill of materials

To generate a bill of materials, it requires data to be extracted from a planning system, such as an MRP or ERP operating system. Each system will have its own way of extracting the data.

There are several different types of BOM which are:

• A Single level BOM is used for simple products or one-stage production.
• A Multi-level BOM (or indented BOM) is required for more complex assemblies often with a mix of elements in the structure. Such as raw materials and sub-assemblies produced in-house rather than externally sourced. These are often referred to as parent /child levels.
• A configurable BOM (CBOM) allows businesses to design and manufacture end products that may have slight changes to accommodate specific customer requirements, such as colour choice or accessories selection. It can be used for products that are highly configurable such as telecom systems or cars.
• A BOM explosion is a full list of all the parts including all those in sub-assemblies. It is the means of calculating all the material requirements and individual component parts to satisfy a specific customer order. The opposite, where a long list of parts can be reduced to the hierarchy level of major assemblies is called a BOM implosion.

As BOM’s have become more complex because of mass customisation, a ‘generic bill of materials’ concept has been introduced to avoid an exhaustive description of all components and end products when this level of detail is not required.

What is a bill of materials used for?

Once the BOM has been exploded down to components level, procurement can identify all the component parts that need to be on site, for the production run to take place.  Procurement can identify existing stock availability. Any components that are not available, procurement can then look to source from the market and place orders with the manufacturers.

The BOM plays a huge role and is a ‘go to’ for many areas of the business too, such as:

• Production:
  The BOM provides the list of components used on the shop floor to make the product and the number of components required. Production planners can then ensure all the required components are available before production goes ahead.
• Logistics:
  The BOM information is used by procurement for re-ordering, by warehousing and transportation for storage planning requirements such as size or perishability and onward shipping to the customer including special packaging.
• Customer/product support:
  Details of all the parts that make up an assembly and their source are held in the BOM so that exact replacement parts or spares can be made available as part of after sales support.
• Quality assurance:
  The quality team can track and trace components for compliance or legal purposes.

Does a bill of material include labour?

A standard Bill of Materials (BoM) does not factor in labour requirements. However, it can be linked to production scheduling and can incorporate equipment capacity and availability. It also can be fully integrated into a manufacturing resource planning (MRP) module.

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