Bill of materials

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A bill of materials or bill of material (abbreviated "BOM") describes a product in terms of its assemblies, sub-assemblies, and basic parts. Basically consisting of a list of parts, a BOM is an essential part of the design and manufacture of any product.

Often, BOMs contain hierarchical information with the master, or top level, BOM describing a list of components and sub-assemblies. Take a PC, for example: the top level BOM might list the shipping box, manual, packaging, packaging labels and the actual PC. The BOM for the PC itself is referenced in the top level BOM and would contain its own list of sub-assemblies like power supply, motherboard, case, etc.

This increasing level of detail continues for all sub-assemblies until it reaches its constituent parts (like resistors or processors), or modules that are out of the scope of the BOM (like the parts that make up a fan that is brought in as a module from another manufacturer).

BOMs are important, since without a basic knowledge of how many parts a product needs, there is no way of knowing how many units of that part you need to buy.

A bill of material can define products as they are designed, as they are manufactured, as they are ordered, as they are built, or as they are maintained. There are different types of bills of materials dependent upon the discipline that generates them and the purpose for which they are intended. It is important to ensure the type of bill of material that you have and its intended use prior to working with a bill of material.

A bill of material can be displayed in following formats:

  • the single-level bill of material,
  • indented bill of material,
  • matrix bill of material,
  • transient bill of material,
  • modular (planning) bill of material, and
  • costed bill of material.

Other terms by which a bill of material is known include the formula, recipe, or ingredients list in certain process industries.

.... With regard to any process industry this is a set of engineering documents containing information for identification, fabrication and construction of equipment, piping and piping components for a project or part of a project.

Separate BOMs are prepared for the different material used for construction, e.g. carbon steel, stainless steel, Glass-reinforced plastic, insulating material, cladding etc.

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