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Written by

Anne Mulvenna

How to Make a Bill of Materials (BOM) the Right Way

Genius ERP: ready out-of-the-box for custom manufacturing.

What is a Bill of Materials (BOM)?

A bill of materials, also known as a BOM, is the comprehensive list of all required parts, items, raw materials, and assemblies that you need to manufacture a product. A BOM also includes instructions on how to use the required parts, as well as instructions on procuring the materials. A BOM is one of the most important documents for a custom manufacturer—think of it as a recipe—as it includes all of the components and steps you need to take to manufacture your product.

MBOMs vs EBOMs

There are two subsets of types of BOMs that product manufacturers will use in their shops to create a finished product: EBOMs and MBOMs. 

EBOMs, or engineering bill or materials (EBOM) are used specifically by engineers when they are designing a product, and are often created in a CAD (computer aided design) system. MBOM stands for the manufacturing bill of materials (MBOM), and is the document that contains all the parts and assemblies required to build a complete and shippable finished product. 

MBOMs are more detailed than EBOMs in both structure and depth, as MBOMs need to include a line for every materials required part or assembly on the supply chain, along with instructions on how the part is to be used. For example, if the product you are building needs 12 of a certain type of screw, each screw will be listed in the manufacturing BOM, along with the subassembly where it is to be used. On the other hand, the EBOM for your finished product will only include a line that lists that 12 screws are required from the supply chain.

As the MBOM is the master document that your entire shop will use to build a product, including a comprehensive list of all components and the detailed instructions about how each part or material will be used—including how to procure each part—your MBOM needs to be detailed, accurate, organized, and up-to-date.




Necessary Elements of a Good BOM

To create an accurate, detailed and effective BOM, you will need to include the following elements:

1. BOM level:

Assign each part or assembly a number to detail where it fits in the hierarchy of the BOM. The BOM level will make it easy for anyone to understand the structure and all of the elements of the BOM.


2. Part number:

Give each item within the BOM a unique part number, which allows anyone involved in the manufacturing cycle to reference and identify parts easily. 


3. Part name:

Each part, material, or assembly should include a detailed and unique name that allows anyone in your shop to identify the part, without having to cross-reference other sources.

4. Description:

Provide each material or part within a BOM with a comprehensive, informative description. The description helps you and others identify parts and distinguish between similar parts and materials.


5. Phase:

Record what stage each part is at in its lifecycle. For example, for parts in production, it is common to use a term like ‘In Production’ to indicate the stage of the part, or new parts that have not yet been approved can be classified as 'Unreleased' or 'In Design'. 


6. Procurement type:

This refers to the method in which each part is obtained. For example, indicate if a part should be purchased off-the-shelf or manufactured according to project specifications.


7. Quantity:

Specify the number of each part used in each assembly for the BOM. 


8. Unit of measure:

The BOM should outline what unit of measure is being used to quantify the part or material. For example, terms like ‘each,’ ‘inches,’ ‘millimeters,’ ‘ounces’ can be used. This ensures that accurate quantities are purchased and delivered to the shop floor.


9. BOM notes:

Include any additional information or supporting documentation necessary, aside from the other elements of the BOM, to build the finished product.

How to Create BOMs Quickly & Effectively

As you can see, creating and managing a BOM as a custom manufacturer and according to your supply chain is no easy task, as the level of accuracy and detail that is required is immense. 


Creating a bill of materials is not only a necessary step in the product development process, it is also what makes your product design a reality. Most bills of materials go through multiple iterations as your finished product and manufacturing processes evolve, which means it’s also likely to be handled by multiple people. As such, using only a spreadsheet to manage a BOM is not ideal, because information will constantly need to be re-entered—opening you up to costly human errors that can throw off your entire production—and it is difficult to track what version of the document is being shared and used by your staff. 


Effective BOM management means you need to establish a fail-proof system that ensures that the latest version is always in use by anyone accessing it. 


ERP systems built for manufacturers are the best way for custom manufacturers to create and manage BOMs. ERPs act as a single source of truth for your company, meaning that you can be assured that everyone is working off of the same, and most up-to-date, version of a BOM. Using an ERP to manage your BOM will eliminate headaches and get everyone on the same page. 


How to Make the Most of your BOMs

Some custom manufacturing ERPs, like Genius ERP, will also include proprietary features that will make it simple to create and manage BOMs. For example Genius ERPs CAD2BOM feature makes it simple for a manufacturer to directly transfer their BOM from their CAD program to their ERP with a click of a button, creating a fully itemized, complex BOM conforms to the supply chain. Not only does this save you time, it ensures that you eliminate human error that can occur from having to re-enter data. 


Genius ERP also makes it easy to manage complex types of BOMs, letting you edit and manage your imported BOM with ease, adding the required layers of detail that you need. And because your BOM is housed within your ERP you can ensure everyone on your shop is working off of the latest and most accurate version. 


Using an ERP to create and manage your BOM also makes procurement of parts easy. During the design phase, while your engineering department is still busy at work designing and engineering a new product, your procurement team can have access to the EBOM to see what important long-lead items are needed, and can place the order early on, giving you time to get your hands on these parts before production begins. And again, because everything is managed in one system that it automatically linked to your inventory, your purchasing department will always know what is needed, and what is already sitting on your shelves, ready for production.


Want to learn more about how Genius ERP can help you create and manage accurate BOMs? Check out our Product Engineering Features, including CAD2BOM.

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