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Bill of Materials

What should be included on the Bill of Materials?

By     OCTOBER 12, 2016

Do we have the pieces

When one opens up a box of IKEA furniture—say, a coffee table—they’ll quickly find a small booklet containing two key pieces of information: a list of all the parts contained inside the box, and instructions on how to assemble the table. Without this document, would-be assemblers would be lost without much of an idea of what goes where, and how, and why. In the product development lifecycle, the bill of materials (BOM) serves much the same function: a document that teaches manufacturing operations how to actually create the product the design team has dreamed up. In starting product development, companies need to not only create a BOM, but also be aware of some crucial questions.

What should we include in the BOM? Here’s one place the BOM differs from IKEA instructions: the BOM needs to contain a whole lot more than quantities and little pictures of various parts. It’s important to include quantities, part numbers (to an intelligent or non-intelligent numbering scheme), descriptions, part names, the BOM level, how it will be procured, additional relevant notes, and more. Different products require BOMs with different items—for example, electronics will require references to how circuit boards fit on the bigger product, plus firmware information. As long as it isn’t difficult to manage, it’s likely better to include more information in the BOM than less—manufacturing won’t suffer if they know too much, only too little.

How much detail is needed in the BOM? This is less about the complexity of detail, but rather what kinds of details should be included in the BOM. This depends on who will be touching the BOM or trying to read it later on. IKEA spends a lot of time and money ensuring their instructions are foolproof for almost any would-be assembler, and while companies don’t need to make their BOM comprehensible for anyone, they should ensure it offers all the context necessary to build the product, particularly if the design and manufacturing teams don’t actually ever sit down in the same room to collaborate on the handoff. These details often include CAD work, or documentation about how assembly should happen.

Are consumables part of the BOM? Companies need to determine whether or not they want to include something like glue or Loctite, which is to be used to assemble the product, in the BOM. Some think this would fill up the BOM with excess material that manufacturing should be able to figure out nonetheless, but that mindset creates potential risk. If something isn’t in the BOM, manufacturing just might not include it, which would lead to a faulty product. That said, if design and manufacturing collaborate regularly, this might be an issue that’s solved elsewhere.

How does the BOM deal with change? The BOM is not something that’s created once and never touched again—it’s subject to enormous change throughout the product development lifecycle. Companies need to come up with established processes for dealing with change, whether that’s a supplier who can’t deliver the requested part, or an engineer who has noticed that a material used breaks compliance with certain key regulations. If the company works with contract manufacturers, this becomes doubly important, because while it’s one thing to catch a problem internally, once a poorly-managed BOM has been received by a third party, the risk for error is high.

What is our BOM management strategy (and software)? This question takes the previous one further, and deals with the core of the product development lifecycle. Will the company use a homegrown solution of paper and data entry specialists? Will they use an Excel sheet on a networked drive? Will they use a product lifecycle management (PLM) solution that offers features like engineering change order management and complex BOM hierarchies? Every company has different needs, but the BOM needs only to be carefully managed, regardless of its complexity.

Will the BOM be flat or hierarchical? Sometimes, companies like to manage the BOM so that parts within a certain assembly are grouped together under their parent, which creates a hierarchical BOM. This can make certain management tasks easier, but adds to the overall complexity, particularly if a company is using Excel for their BOM management strategy. A flat BOM, where everything is given the same priority, might be good for electrical engineers and for simpler management, but it doesn’t allow for complex relationships between products and makes working with contract manufacturers slightly more complex.

Even with detailed instructions, many of us share in the experience of accidentally assembling a bookshelf incorrectly, or finishing assembly and having a few too many extra small parts. It’s not difficult to imagine how complex the process would become without the instructions, which IKEA has spent a great deal of time and money developing. A manufacturer should consider their BOM much the same way—if they can’t answer the above questions as they’re creating the BOM, the plant floor team is going to struggle. And when it’s a matter of producing a whole run of the product, an accident in assembly is going to be much, much more than an inconvenience.

– Tyler Beck, Technical Marketing