Rectifying the Bill of Materials with the Bill of Process: A Story of Nouns and Verbs

Rectifying the Bill of Materials with the Bill of Process:  A Story of Nouns and Verbs

The following is a story of an aggressive startup company that was developing, and hoping to move a highly complex, electromechanical product into scale production.

From a design engineering standpoint, the Bill of Materials (BOM) was derived from the CAD documents.The BOM was then scrubbed to identify make, buy, and phantom parts and passed to ERP to procure the necessary parts.

In parallel, a team of fabricators who created the prototypes worked with manufacturing engineers to focus on building production units―documenting the process steps as they went along.
Sounds great? Well, production utopia was not achieved. The first problem that emerged was the fabricators were requesting parts from the warehouse that weren’t there. Why? Well, Engineering had no knowledge that they were ever used. The second problem that became quickly apparent was the rapidly growing pile of scrap that containing “production parts” that didn’t seem to actually be used to build the units.

It was at this point that I developed a working theory. Either we needed to:

  1. Understand every part that was needed, and where and how to install it, or
  2. Document the steps needed to build each unit and establish a complete list of parts that were required to complete the process plan

A 70% understanding of either of these data definitions was clearly not going to work. At this point it became clear that Design Engineering was responsible for defining the parts for the system (the Nouns) and Manufacturing was responsible for the correlating process steps (the Verbs) of how the parts are assembled. This is when the blame game traditionally starts. Design Engineering insists that Manufacturing Engineering just build according to the CAD dataset, and Manufacturing insists that there are parts missing or unnecessary to complete the assembly tasks.

It became clear that what appeared to be a full CAD dataset was insufficient to manufacture a product. It similarly became clear that a manufacturing plan could not be enacted without all of the parts being specified and ordered.

Engineering produced a Bill of Materials (BOM), Manufacturing developed a Bill of Process (BOP), and at the end of the day these two “lists” needed to be rectified. If a part in the BOM (nouns) did not have a correlating step on the process (verbs), it did not get installed. If the BOP called for parts not in the BOM, they were not available for manufacturing to assemble because they had not been purchased.

Moreover, add rapid engineering design changes, an email-based release system, and variability between units, and you have the scenario for a complete production nightmare.

Engineering release into Production

Traditional design methodology has an initial release from design data into a manufacturing environment where manufacturing engineers dig through the assembly to establish how the product gets assembled. At this point a manufacturing process plan is born. Historical “Over the Wall” methodology demands that the entire product is released at once, and this creates a hurry up and wait scenario for manufacturing planners. Of course, there are several benefits to be had if Design and Manufacturing disciplines are working in the same system. First, manufacturing engineers can begin to build out process plans (BOPs) as the design evolves, and second, they can let the designers know in advance if any of the design parameters are difficult or impossible to manufacture and offer alternatives earlier in the design process, thus avoiding rework.

Most importantly, if every part on the Engineering BOM (eBOM) is used by a process step, it is marked as “consumed” by the BOP. If a process step needs parts that do not exist in the eBOM these parts can be requested while the design is still ongoing. If a step requires more of a particular part, such as a sensor, fastener, wire, or hose, the parts are considered “overconsumed,”, meaning the eBOM has to take into account more of that part.

In this way, design and manufacturing engineers working together early and often ensures that a product will launch in an optimal time. Most importantly, the parts that make up the product need to equal the parts needed to build the product, and this rectification is critical.


One challenge with working in parallel is managing the release process and engineering change orders. In a pre-release and launch scenario change happens rapidly and it is positively impossible to link the changed parts to the changed processes, and the other way around. On-demand, real-time rectification of parts to processes is crucial to ensure that changes flow to production without creating piles of scrap or further propagation of known quality issues. Systematic rectification of designed parts with manufacturing plans is crucial. A view into how Aras manages this rectification is available in a short video here.

At the end of the day, you either need to know 100% what you are making, and parse that into steps, OR you need to know all of the steps needed to make something and have access to all of the correct parts to complete the steps. Of course, in the real world, both methods are identical! You have both the parts and the process defined. When either your BOM (nouns) or your BOP (verbs) don’t align, clearly action needs to be taken, designs or processes need to be modified, and everything needs to balance out.

Sean Coleman
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