The bill of materials (BOM) is a list of things. In manufacturing, it is the recipe ingredients for producing (and repairing) equipment and machinery. It lists the raw material, parts, sub-assemblies, purchased items, and everything else that goes into the product.

The BOM acts as a key communication piece between departments. It contains the items designed by engineering. A BOM provides the list of items to be purchased and the items that must be manufactured. It contains the identifiers (part numbers, stock numbers), the descriptions, quantities, purchasing details, manufacturer information, costs, and other key attributes.

Inventor Bill of Materials

The BOM is the single source of truth between so many systems. From sales (CRM) to engineering (PDM), production (ERP, MRP), and product lifecycle management (PLM). 

It is the most important piece of information in manufacturing. I’ve seen it multiple times where the material is ordered, received, assembled, and shipped to the customer all without the drawing being opened one time.

Different Things for Different People

The BOM provides the who, what, and how. However, the level of detail and the required information differs with who’s touching it.

Probably the best breakdown and explanation I’ve seen regarding how various departments utilize the bill of materials comes from PTC (What IS BOM ). To summarize, they present three main BOMs within the life of a product: Engineering (eBOM), Manufacturing (mBOM), and Service (sBOM). 

Even within a certain type, you may provide different views. We use Inventor’s BOM to populate the Vault’s Item BOM, however, within the drawing, the Part’s List view does not contain the purchasing comments that are passed along to Vault. In the drawing, we use the comments for assembly-specific assembly instructions.

A Drawing – BOM and Balloons

It’s still the same piece of equipment, just different groups need a different view. The easiest way to explain this is by looking at the day in the life of a bill of materials and how it goes from sales to the product’s end of life.

A Day in the Life…

Here’s a typical day-in-the-life of a bill of materials.

Sales start with a rough higher-level view, which is the start of the eBOM. They are not concerned about all the nuts and bolts but with providing the customer with the outline of the solution. Engineering may be involved at this time, but typically providing chunky proposals and mockups.

Next quoting and inside sales take over. Between them and engineering, they add the key (costly) components and estimate production time. We need to know what it costs before we can quote it, right?

With the sale won, engineering takes over and adds all the required components. Now the engineering bill of material takes shape with part numbers and descriptions and important information like the required quantities and manufacturer specifics.

With engineering complete, production takes over. The eBOM represents how the product is designed but doesn’t necessarily work to get it manufactured. The planning group will slice and dice the BOM, restructuring it to work within the manufacturing processes. They add information like instructions on how to assemble. Procurement additionally includes important purchasing information. 

Now after engineering is done…

The result of production’s efforts is the manufacturing bill of materials (mBOM). The mBOM is what the system schedules against. It is what MRP (material resource planning) utilizes to calculate the demand.

Next, the product ships. Now you need the service bill of materials (sBOM) to manage the product from the start of use to the end of life. This BOM will populate parts catalogs, be the basis for preventative maintenance schedules, and provide the customer with the list of important components for suggested spares and replacement part ordering.

Why a different BOM for service? Think of it this way. Just because a part is manufactured a certain way, doesn’t mean that’s how you want to sell it as a replacement to the customer. Take the mirror on your car for an example. It contains the mirror, the bracket to hold the mirror, the housing, and the hardware to install it on the car. The mBOM would list all those components, however, when you stroll into your auto-dealer for a replacement you are buying a singular item.

How Do We Manage This?

Microsoft Excel is where many start, but it is definitely not the right answer.

Your CAD and PDM systems will be able to export to Excel, but how do you manage this change in Excel as the BOM changes in the other?

You should treat your BOM no differently than a drawing. It will go through several iterations, and how do you manage these revisions? How do you ensure everyone is working from the correct version?

How do you tie a spreadsheet into PDM, ERP, MRP, and/or PLM?

So, what do you do?

Look for a standalone system, designed specifically for bills of materials. Something like OpenBOM, “a digital network platform that manages product data and connects manufacturers and their supply networks” is an option. This provides a standalone platform to manage and present the BOM. 

You can also look to your software provider for a solution. You may find that your PDM, ERP, or PLM system provides all the controls you need to both manage and present the information. 

Or perhaps it’s a combination of a bunch of things? We model in Inventor and manage the eBOM in Vault Professional. Then CADLink transfers the information into ERP where we manage the mBOM via the embedded Method of Manufacturing (MOM) tools. We are currently using Excel (gasp!) to manage the sBOM, but are transitioning this into Fusion Manage (PLM).

What is Important?

The main purpose of the bill of materials, which is important to not lose sight of, is ensuring the product is built right. So at a minimum, your BOM needs some type of unique identifier (part number typically), the required quantity, and the quantity’s unit of measure.. [I personally prefer a sequential numbering scheme and hate smart part numbering systems… but this is a conversation for another time]

Next, ask yourself, who is going to use this BOM? You want to include the details making it possible to complete a task. Ideally, the information flows, conveying the information, without any interaction.

A description, summarizing the part, is extremely useful. It should be simple so that even with a quick glance anyone has an understanding of what the part is and how it differs from the others in the assembly.

The BOM Level indicates the hierarchy of the components within the equipment. This allows anyone to quickly understand the grouping of components. This is typically presented in the #.#.# format, like 1, 1.1, 1.1.1, 1.1.2, 1.1.3, etc.

Many bills of materials contain notes or comments to pass along additional information. This could be specific to the assembly, say assembly instructions, pass along purchasing requirements, or really anything important to the construction of the equipment.

That is the bare-bones and the basis for many BOMs. However, the type of equipment, the manufacturing process, and other factors lead to additional information presented. For example, printed circuit boards (PCBs) require Reference Designators to detail where the part fits on the board.

Now What?

Already managing bills of materials? Take the opportunity to take a step back and take a hard look. Are you managing it efficiently? Missing information? Presenting the information concisely? Need different views for different groups? Can you expand on the BOMs use?

Keep reading. This is one post in a series of managing BOMs where we explore options on managing the BOM efficiently.

Feature Image Shortbread Recipe courteous of Craig Murphy via Flickr