The Elements of a Manufacturing Bill of Material

If you are working in manufacturing or you are new to manufacturing, you may have heard many times the terms bill of material or “BOM” regularly. A bill of material is a structured arrangement of components or parts of a larger object, in particular, particularly complex products or assemblies.

The “Bill of Material” is the skeleton of a product defining every part comprising it. It is often represented in the form of a tree showing which components are part of each subassembly from the top-most finished good down through all subassemblies to the purchased raw materials.The bill of materials contains all the components, sub-components, and raw materials necessary to produce a good or provide a service, providing valuable aid in the management of the warehouse and the organization of supplies. It allows for a concrete framework on the raw materials needed for the production of a finished manufactured product.

BOM information is one of the most important data structures of a manufacturing company because it documents components for every particular product manufactured and sold by the organization. The bill of material is needed not only for manufacturing planning but also for purchasing and scheduling since many items the bill of material do not need to be on-hand or in stock when new manufacturing orders are released because the bill of material is time-phased and parts are ordered or manufactured just in time for the next operation requiring their use.

Basic principles

The BOM will follow particular principles:

• It will bring together all the components necessary for the manufacture of a product.
• Each component, subassembly, and raw material will be identified by product code.
• A specific product code must identify each product variant described in a BOM.
• The BOM also defines the quantities required per component. For example, it may take 4 screws or bolts to fasten a part to a larger assembly.
• The BOM may also contain data for the materials used that is essential for engineering. For example, the tensile strength or chemical composition of some materials (or lots of material) may need to be defined for particular assemblies. This is especially true in highly regulated industries such as nuclear, automotive, aerospace and defense, etc.

The bill of material may also contain other data helpful for manufacturing planning. For example, some items must be sourced or purchased from specific vendors. As such, the BOM may reference a particular supplier. Some BOMs must also utilize materials with specific attributes. These materials are purchased or manufactured to inventory and then the attributes of those inventory lots are used to determine which specific materials to utilize in work orders referencing the specific bill of materials with attribute requirements. For example, a specific bill of material may require the use of metal products with at least 5% zinc content.

The bill of material presents a uniform product structure with common product-related data that is supplemented by user-specific data. The common product-related data includes the part number, the parts designation, the unit of measure, and the respectively required number or quantity as well as the hierarchical arrangements of the components.

All users from the various specialist areas of a company (production, procurement, logistics, sales, finance, etc.) access this uniform product structure, while the respective departments can only access the application-specific data. For reasons of security and clarity, the departments have different access rights and one each application-specific view of the BOM data.

BOMs can be evaluated and sorted by product and application according to various criteria. Variant BOMs must obtain only the required information for each product variant. BOMs are especially needed for deterministic needs assessment, work planning and preparation, and the creation of work instructions.

BOM Types

Bills of material often start during the original part design process in computer aided design (CAD) systems. These engineering bills of material (also known as eBOMs) represent the designed structure of the item. They are then recreated manually in an enterprise resources planning or ERP business system as the manufacturing bill of material or mBOM. There could, and often are, differences between the eBOM and mBOM. For example, the engineer may have used a generic part or component as a placeholder during the engineering process but the manufacturing bill of material may define the exact parts to be used. Further, an engineering drawing may utilize a stocked subassembly which is not necessarily defined down to it’s individual components in the CAD application. But in ERP, the subassembly bill of materials must be defined in the mBOM for accurate material planning and production scheduling.

Some ERP systems utilize other types of bills of material. These can range from a sales BOM which is sometimes called a kit containing components that are typically not “assembled” until ordered by the customer as well as template bills of material which are used as a basis for creating new bills of material for similar items. Another bill of material type commonly used in manufacturing is the phantom bill of material. Phantom bills of material represents the components for an assembly that is never manufactured to stock. Instead, the bill structure is inserted into other bills of material to manufacture the assembly during the larger production of a finished good. For example, you may have a phantom bill of material for a power supply. You never create work orders to make the power supply by itself but every time you create a work order to make any type of machinery or equipment the bill of material will reference the phantom BOM and insert the components and operations required to make the power supply during the overall manufacturing process. Phantoms are sometimes also known as blow-through, transient, or pseudo bills of material.

Looking at the physical structure, the basic types of BOM includes the structure BOM, the modular BOM, the single-level BOM, and the complex or multi-level BOM. The distinction mainly refers to the concrete representation on the screen or in an expression. ERP systems generally store parts list information in the form of a building block BOM, because all other required types can be generated from this by vertical BOM.

For complex products that are produced in flow production (e.g., automotive industry), you can often find the structured BOM from which you can also generate building block BOMs and usage statements.

Structural BOM

A structural parts list contains all assemblies, individual parts, and raw materials of a product and shows the composition of a product in tabular form across all production stages. It corresponds in its information content to the product structure. The quantities refer to the total product or each unit of quantity.

Single-level BOM

Single-level or building block BOMs are distinguished by the fact that only one level of the product structure is considered at a time.

Modular BOM

In a modular bill of materials, several bills of material are summarized on a form according to DIN 199-1: 2002-03 to be able to list different objects with a mostly high proportion of identical components. In an electronic parts list system, the various product variants are stored together with the different options of the parts and assemblies. One or more attributes distinguish each product variant.

These respectively applicable attributes are then stored in the corresponding parts and assembly variants, so that a correct assignment to the product variant is possible.

Configurable BOM

The configurable BOM also called selection BOM or maximum BOM, is a variant of the variant BOM in which all variants of a product or assembly are mapped together. To be able to differentiate between the configurable and to assign the parts and assemblies to a single, specific product variant, these must be provided with product-related attributes. These attributes are features that describe the product in more detail.

A particularly useful type of attribution is the specification of an algebraic expression that refers to a set or subset of the product variants. It requires an algebraic product definition (product encryption) with the help of features. Depending on which product is concerned, features can relate to the equipment, functions, colors, materials, or even geometric, physical or chemical properties of a product.

The features may either have only a loose relationship with each other or form a structure in the form of an algebraic union. This type of product definition is found mainly in industries producing complex and varied products. In the automotive manufacturing industry, the vehicles are described by a large number of features that can be selected with the aid of product configurators. Accordingly, many vehicle manufacturers use algebraic complex parts lists. Depending on the specific form of the product definition, these then differ in the type of attribution.

Multi-Level BOM

A multi-level bill of materials is a bill of materials that lists the components, assemblies, and parts essential to make a product in a parent-child, top-down method. From a specific lot size, the quantities of one or more materials change, or new components are added, then this multi-level BOM is converted into a multiple BOM. Thus, alternatives to the original parts list are formed. These are also called multi-level BOMs.

As a whole, the BOM makes it possible to monitor the costs for the procurement of raw materials and labor (based on the time needed to complete the production process).

Conclusion

There are a lot of different types of bills of material and CADTALK works with all of them. CADTALK leverages artificial intelligence to transform the eBOM from CAD to mBOMs in your ERP system in seconds allowing your engineers to do what they do best –create great products.