Why engineering Bill of Materials is complex

Why engineering Bill of Materials is complex


For the last year, I had chance to talk many manufacturing companies in range from small hardware startups to large manufacturing companies with billion dollar revenues and production facilities across the world.

I’ve learned that one simple question that can help you to understand all engineering and manufacturing processes in the company – Bill of Materials. By asking about BOM, you will be immediately exposed to a variety of topics that will tell you about how any company design, manufacture and service its products.

Brian Soaper’s article – Beginning BOM Management discussion reminded me many conversations about Bill of Materials I had with manufacturing companies. In this blog, I want to start from Engineering BOM. According to Brian, engineering is straightforward. Here is a passage from the article explaining that:

The engineering BOM is pretty straight forward and I think that many understand what it is and how it is used. However, I do get into conversations explaining how the CAD structure is different than the engineering BOM. I have seen companies with very detailed CAD structures where the non-geometric items are included (oil, tape, glue …). Other companies do not even model the fasteners in CAD. The majority of companies model only the geometric items. In the engineering BOM’s, they include the fasteners and other geometric items if they were not part of the CAD structure. I have found few companies that link the BOM items to the raw materials used to create them.

It made me think about 3 specific aspects of engineering BOM management I’ve observed. For the purpose of the conversation, let’s call them – Part List, Structures Transformation and Configurations. There is no canonic way to call them and I found the level of diversification is very high.

Part List. This is a simplest way to manage engineering BOM. Usually done by exporting information from CAD system and adding non-geometrical items. It is a very typical way to create a list that can be used for ordering purposes and /or communication with contractors.

Structure transformation. CAD structure is not engineering BOM. Restructuring is one of the most complicated processes to create engineering BOM. From my experience, this process can not be easy automated (if at all) and demand lot of human involvement. Mapping between structures is hard and to make references between two structures is even harder. But this is an absolutely important process to make engineering BOM right.

Configurations. Most of products today are demanding configurations – models, options, etc. Management of configurations in CAD system is complex and sometimes even confusing topic. If you try to apply configurations on structure transformation the chances are you can get lost. The best results can be achieved if a system used to manage engineering BOM is capable to model configurations, but very often it is not a case and companies are ending up with complex spreadsheets.

What is my conclusion? Some PLM pundits are saying “engineering BOM is a problem that was created by 3D CAD systems”. Because before that, engineering BOM was the first one to be created based on 2D drawings. In my view, 3D CAD added an additional information level that before was only captured in engineers’ minds. The old 2D process was a source for many mistakes and problems that were resolved by 3D CAD systems. However, to manage Engineering BOM is still a challenge in manufacturing organization, which can be resolved by careful alignment between design and engineering processes. Just my thoughts…

Best, Oleg

Want to learn more about PLM? Check out my new PLM Book website.

Disclaimer: I’m co-founder and CEO of openBoM developing cloud based bill of materials and inventory management tool for manufacturing companies, hardware startups and supply chain. My opinion about BOM can be unintentionally biased.



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  • Grégory Perasso

    “that was created by 3D CAD systems” agree with you .. But in most of companies where I’ve worked on CAD/PLM integration, for me, the problem is that they does not adapt CAD methodology to PLM context. We should not use CAD system in a same way by storing CAD files in a file system or a cloud based system, or when directly integrated to enterprise xBOMs. cause problem is the same , not only for eBOM … but also for mBOM, service BOM, or even process plan … where we try to leverage 3D models for dynamic work instructions , MES, quality inspection , etc …

  • beyondplm

    Gregory, thank you for your comment! I assume you mean that CAD file system is not an equivalent to eBOM. If this is what you mean, I agree 100%.

  • Loïc Mouchard

    I think PTC and Siemens PLM explains in their documentation the 2 main approaches that are used to managed PLM-CAD BOM.
    1) CAD-centric approach : you first generate the geometries and build the structure of the product. I think Siemens PLM refers to bottom-up approach.
    2) Part : you first generate the Part structure, and then “fill the geometry”. This would be also refers to a Top-Down approach.

    But you also have more and more mechatronic products (or smart product), that mixes mechanical part, electronic components and software. I could not see yet an PLM implementation that manage all those fields in a single BOM.

    System engineering should also not be forgotten, or RFLP structures (Requirement – Functional – Logical – Physical), as sold by Dassault Systemes.


  • beyondplm

    Loïc, you’re right – these are options I’ve seen as well.

    IMO, these two (top-down and bottom up) approaches are dominant. I’ve seen more bottom up approaches in engineering to order environments.

    Mechatronics (or smart and IoT products) are typically using mechanical BOM as top level assembly (TLA) and more often slide down to top down approach to manage BOM. It is not unusual, especially for smaller companies, to manage BOMs separately.

    RFLP approach is more rigid from my experience of working with DS products (but it was time ago) in terms of how data is defined and managed. I’m sure DS products improved many things since I last time touched them.

    Best, Oleg

  • Greg Bedenkof

    Great write up! Our company just purchased CADLink for Siemens PLM and it solved most of the challenges associated with managing our engineering BOM.


  • beyondplm

    Greg, for my best knowledge CADLink from QBuild Corp is an integration between CAD and ERP systems. Maybe I’m missing something, but by connecting CAD to ERP you cannot solve engineering BOM problems. You can only hide them in the translation from design BOM to manufacturing BOM. None of these systems (CAD and ERP) is good enough to manage things like configuration, modular BOM, etc. Can you share some of your best practices?