In brief
A bill of materials (BOM) is a structured list of all assemblies, components and quantities that make up a product or a machine.
Contents
What is Bill of materials?
The bill of materials (BOM) describes which parts a product is made of. Each line usually contains the part number, description, quantity and unit of measure. BOMs are the basis for design, manufacturing, material requirements planning and costing.
Several types are distinguished according to structure. The summarised BOM lists all parts with their total quantity, without hierarchy. The indented (multi-level) BOM shows the complete structure across all production levels. The single-level BOM describes only one level at a time and refers to separate BOMs for the assemblies. In addition, there are variant and manufacturing BOMs for specific purposes. Which form is used depends on the purpose and on the system in place.
For maintenance, the spare parts list, also called the spare parts BOM, is particularly important. It contains the parts that are usually replaced, often with item numbers and exploded drawings. An up-to-date BOM is often the quickest way to identify a spare part unambiguously, especially when nameplates are missing or illegible. Outdated lists, on the other hand, easily lead to wrong orders.
In practice: maintenance and procurement
Spare parts lists should be updated whenever equipment is modified or rebuilt or alternative parts are used. For a spare parts enquiry, the machine type, serial number, BOM item number and, if available, the manufacturer part number of the component are particularly helpful.
Synonyms and abbreviations: BOM · parts list · spare parts list · spare parts BOM · illustrated parts list
Frequently asked questions
What types of bill of materials are there?
The most important are the summarised BOM, which lists all parts with total quantities and no structure, the indented BOM with the complete hierarchical structure, and the single-level BOM, which shows only one level. For spare parts, the spare parts list is also relevant; it contains replaceable parts with item numbers and drawings.
What is the difference between a bill of materials and a spare parts list?
The bill of materials describes the complete structure of a product for design and manufacturing. The spare parts list is an extract for service and maintenance. It contains only the parts that can or should be replaced, usually supplemented by exploded drawings and order numbers.
Who provides the spare parts list for a machine?
As a rule, the machine manufacturer supplies the spare parts list as part of the technical documentation. If it is missing or outdated, it is worth contacting the manufacturer, quoting the machine type and serial number. In addition, in-house lists can be built up on the basis of nameplates and maintenance experience.