The Association for Operations Management defines a BOM as “a listing of all the sub-assemblies, intermediates, parts, and raw materials that go into making the parent assembly showing the quantities of each required to make an assembly”.
The BOM shows all the parts required to make one of the item. Each part or an item has only one part number. A specific number is unique to one part and is not assigned to any other part. A part is defined by its form, fit, or function. If any of these change then it is not the same part and it must have a different part number.
The BOM shows the components that go into making the parent. It does not show the steps or process used to make the parent or the components. That information is recorded in a Routing File.
Structure of BOM
Structure of BOM refers to the overall design for the arrangement of bills of material files. There can be several formats, or ways, to present the bill. Some of the important formats for bills are Product Tree and Parent Component Relationship.
Multilevel Bills are formed as logical groupings of parts into subassemblies based on the way the product is assembled. Each of these forms a logical group of components and parts and, in turn, has its own BOM.
One convention with multilevel BOM is that the last items on the tree are all purchased items. Generally, a BOM is not complete until all branches of the product structure tree end in a purchased part.
A multiple bill is used when companies usually make more than one product, and the same components are often used in several products. This is particularly true with families of products. They are similar except the tops are different.
Single Level Bills
A single level bill of material contains only the parent and its immediate components, which is why it is called a single-level bill.