BOM: Overstructured, Understructured or Lean?

I’d like to continue discussion I started in my earlier postSeven Rules Towards Single Bill of Materials. So, what are possible collisions on the way to the single bill of materials?. So, let’s take design, engineering and manufacturing bills. When I look on opposite sidesdesign and manufacturing, the purpose, and as a result, how these bills look like. Design bill started from CAD and, obviously, take as a starting point, design structure. So, we can get very structured bill of material. As opposite, manufacturing bill of material foundation is manufacturing process. The levels of manufacturing bill are driven by manufacturing process definitions, stocking and other elements of manufacturing process. What is the role of engineering bill? Do we need it?

If I’m looking from the perspective of needs, it looks like engineering bill is not needed (wait for a moment, don’t kill me now :)). Design Bill provides information about how my product structured. Manufacturing Bill provides information how my product will be assembled (or build). However, I found distance between these structures / views is a huge, connection between them is not obvious. This is, in my view, place where product lifecycle technologies need to be focused – to step beyond pure design or manufacturing structures to engineering level and build lean engineering bill of material that will become master BOM in the organization.

What are the advantages of such approach? Master Engineering Bill will be able to connect design elements, especially those that related to custom manufacturing and will provide set of configurable modules. Master Engineering bill will support different techniques to create a conditionbased structures and many others. From Manufacturing side, engineering bill will get required information about Item Masters.  Different elementsdesign and manufacturing, will be interconnected in this engineering bill, so no more missing parts or impossible product options.

What are the disadvantages of such approach? I see two major problemsneed to build unified data structure and synchronization work between department and people. The multiple bill of material approach solves problems of people collaboration and communication. Each department has their own bill, they are working on. The problem is in the endmissing parts on the shopfloor, missed dates or high product cost. In order to support, single Engineering Master Bill of Material, we need to find right technologies that allow to people to work simultaneously on different pieces of this bill, synchronize, change, update. This collective bill of material should be supported by PLM technologies looking on how to collaborate between design and manufacturing.

Just my thoughts.
Best, Oleg


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  • Nawal

    The two BOMs – design and engineerring – may be a legacy of 2D to 3D CAD transition.

    Through out 80s, 90s, as most companies moved to 3D, they did not make the change wholesome. It was an environment of mix – 2D and 3D – coexisting.

    As some are using 2D and others are using 3D, 3D CAD can not be master engineering BOM. There was a need for process outside 3D CAD, which acts as master within engineering.

    Even though most companies have moved on to 3D, the practices have not changed. So many customers have told me that they should be making the CAD structure complete by adding all components, but they do not do it.

    I have feeling that this is more of process problem than tool problem. Even the current tools are sufficient to accomplish it. But, it is very difficult to change the habits.

  • Nawal, I’m trying not to speak about tool problem, but more about methodology. Do you want to say 3D CAD eliminates need in Engineering BOM? This is sounds strange, so I want to clarify. Does it mean you are ready to live with 3D CAD system and Manufacturing BOM? Thanks, Oleg

  • AndyF


    The answer really depends on the product being produced as well as the manufacturing process. There is no simple answer and no general case.

    We build complex consumer products with fairly large engineering BOM’s. But the final assembly is all outsourced so the engineering BOM and the mfg BOM are disconnected significantly. Not only is there the outsourcing angle that breaks the links, but the CAD BOM doesn’t include many items needed for a finished good such as the packaging, assembly lube, plastic bags, protective tape, customer documentation, etc. The CAD BOM is just a subset of the final BOM and the final BOM is owned by a different company who handles the final assembly.

    That is just one case and I’m sure you’ll find thousands of different models if you look around the industry. There might be a few places that still design and build products internally from the ground up but they are probably the exception these days.

  • Andy, Thanks! I think your simple answer finally convinced me 1/no best practices in the way you manage your BOM- design/engineering/manufacturing; 2/ there are so many implication inherited from way to you design/manufacture; 2/non of know me software can handle it today in perfect way (just my thoughts). Flexibility+Usability need to be in focus. Best, Oleg

  • Nawal


    Let me first qualify, there is no one-size-fits all BOM solution. There is too much variability in busiensses.

    But, for great many businesses, we can combine the 3D CAD BOM with Engineering BOM. The problem is 3D CAD system is being used primarily by designers. Non-geometry design stakholders, like product engineers, system engineers, exist out-side the CAD. One reason is that 3D CAD is more exensive than Excel. Hence, there is a need for existence of engineering BOM, which kind of is a super-set of CAD BOM.

    PLM tools offer the ability to author the BOM for all these engineering stakeholders. So, with tight integration of PLM and CAD as well as some process changes, all engineering stakeholders can work on the same BOM.

  • Nawal

    This is problem with blogging. You do not get time to think before commenting. 🙂

    Re-reading my two comments again, it seems that I am contradicting myself.

    The point that I want to make is, for many customers the 3D CAD BOM and Engineering BOM are different, even though there is no need for two structures to be different from functional point of view. For example, engineering BOM and manufacturing BOM are different in many case, because the way they need to be arranged.

    In most of these situations, it is different because systems used by the stakeholders do not talk to each other. It could be 2D CAD vs 3D CAD or could be CAD vs non-CAD.

  • Nawal, and this is what is good about blogging ;)… you can discuss and you can tell, I was wrong :).. At least, I see it as fun :)…

    Getting back to BOM – I thought, in many cases CAD and Engineering have the same stakeholder in organization. Do you see them as a different?
    With regards to your previous comment – most of CAD systems today have some PDM solution, but not all of them have a good engineering BOM solution. Most of BOM solutions that comes from CAD-based company is limited and can just add non-CAD items to the BOM.

    Best, Oleg

  • Nawal

    I remember a story with a friend. He was offered a job as product engineer in auto supplier. After joining, he asked why he was selected. Apperently, two folks were shortlisted. He knew how to use CAD tool, the other guy did not. All of their existing product engineers did not use CAD tool. So, they made changes out-side of CAD, and asked the designers to update the drawings/model (which in many case, desingers forgot).

    I see some variation of this, all the time. Designers work on the sub-systems. But, there are other folks who are resposible for overall systems and product. In many cases, the CAD exist only at the sub-assembly level.

  • Nawal, Great story! So, you want to say Design and EBOM stuff will be separated ;).. I believe, this is different for different size of companies. As bigger you go, the more you are right :). My question, in any case, do you think these guys can work on the same BOM? Best, Oleg

  • Nawal

    They can work on the same BOM provided CAD can support all kinds of non-geometric parts in BOM and not only piece-parts of integer quanity.

  • Nawal, what is interesting is that many times, ability to manage non-geometric parts was presented as a need for engineering bom. Do you want to say, CAD can handle too?

  • Nawal


    My point is CAD can and should be engineering BOM, provided it handles the non-geometric parts.

    The only issue remains is access to the data. There are two options for this:

    1) PLM can be give access to non-CAD folks with tight integration between CAD and PLM.

    2) CAD vendors should offer non-geometry editing license for cheap. This will give folks to edit CAD-BOM without the ability to add or modify geometry. (And, when I mean cheap, I really mean cheap – competing with Microsoft Office pricing)

  • Nawal, so you basically talk about what today PDM/PLM is doing (forget about terminology for the moment). Nobody will probably call CAD cheap license not doing with geometry – CAD… right? Best, Oleg

  • Nawal

    Yup. That is the reason, I said in first comment –

    “I have feeling that this is more of process problem than tool problem. Even the current tools are sufficient to accomplish it. But, it is very difficult to change the habits.”


    I understand the need for engineering BOM to be different than manufacturing BOM. Because, former is a functional decomposition view while the later is a process /supply chain view. But, there is a really no need for CAD BOM to be different than Engineering BOM. It is just that former is incomplete due to business process issues.

  • HervĂ© Menga

    Even if the blog is not really a good format…
    This is my point of view (very personal, sorry):
    There is only one Bill Of Materials (even if we used to say that they are many) : the list of physical components i need to get (order) to construct my product. I use this list to make my shopping, and this is exactly the same for a company.
    All the rest is just temporary lists coming from the various structures, or better said “models”, that i use in engineering (development) to perform my engineering activities:
    For example, the design model (the digital mock-up, the geometric model, however you call it) gives the so called “CAD BOM”, which is the list of CAD models got from the structure of CAD parts and assemblies (only valid for Mechanical Design)
    And the process model (the model that says how you intend to make the geometry) gives the so called “Engineering BOM” which is the list of manufacturing processes that participate to the “manufacture” the geometry of my design model nodes : Assembly processes for Mechanical Design (through any kind of fixturing processes, but also welding, glueing, painting, covering, laminating), Manufacturing processes (getting a shape from a raw material, such as molding, bending, machining), or other assembly processes of other technologies (welding components on a circuit board, cabling, piping…).
    The process model is not the routing (the list of tasks that i need to perform on a plant workstation in order to manufacture a semi-finished material).
    We usually are confused with the terminology (BOM, models, structures, parts and assembly, material) because we get a big influence coming from the available software applications (CAD, PLM, ERP, and so on…), but the world of engineering is a virtual world we only knowledge is manipulated through models (instead of documents/paper in the ancient times when softwares were not available to help). And we, humans, cannot “see” a model, we can only “see” reports on models : lists, tables,… so we have difficulties to make the difference between models and lists from the models.
    But, very personally said (sorry), a CAD designer never manipulates a list of CAD files, he manipulates the digital mock-up, i.e. the design model with his CAD system. He does not need the CAD BOM. So who does ?
    Feel free to remove this comment if you find it too bizarre, sorry again….

  • Jovan

    Without thinking, like Herve, that a CAD BOM is non necessary, I don’ think that it should be the EBOM.

    I think a point has been raised but missed in this conversation.

    The Engineering BOM is a logical view of the mind and must be process as such.
    For me an EBOM is not composed of Parts, otherwise the definition of Part is too stretched. A part is something that a someone can manipulate either physically or virtually (CAD Parts).
    The EBOM for me is composed of logical elements that I’ll call features

  • Jovan

    Without thinking, like Herve, that a CAD BOM is non necessary, I don’ think that it should be the EBOM.

    I think a point has been raised but missed in this conversation.

    The Engineering BOM is a logical view of the mind and must be process as such.
    For me an EBOM is not composed of Parts, otherwise the definition of Part is too stretched. A part is something that a someone can manipulate either physically or virtually (CAD Parts).
    The EBOM for me is composed of logical elements that I’ll call features.
    You will see this approach in most of the complex product industries (Indus Equipment, Aerospace, Ship Building, Energy,…). Nobody cares about an EBOM of parts. They care about the features that are in the end product. The part is a transitional element to go from this structure to an MBOM.
    For small assembly definition, the Part Structure is very similar to the CAD, this is right. But if it crosses several logical functions, the engineer will not design it by “Object” but by logical function.
    The success of many PLM implementation result in the understading of this statement. I have seen many failed implementation because an EBOM of Parts has been introduced and was never needed. The EBOM of Parts became some kind of monster between a functional decomposition and a Manufacturing BOM.
    The layer that the feature add will help the engineer to define their product without really care of the part that will be used, and help to chose the right design afterward. By not manipulating the same object you give the flexibility to manage different structure and reducing the interferences of managing 2 (or many) structure of the same object.

    🙂 If you remember well Oleg, I think that idea was raised in one of my first comment in your blog

    I’ll be in Lowell tomorrow and Friday, hope to see you there.

  • Nawal, Thanks for your view! Great discussion… Best, Oleg

  • Herve, I think you made excellent comment! What I like is that you emphasized very well – this is all about internal processes in the company and tools. You can call BOM- Model or report, but this is still will be the same issue with internal process in the organization to get this FINAL SHOPPING LIST right and on time!… In the past time, reports and paper lists used. Today – advanced modeling, Digital mockups, collaborative tools etc. In addition, I agree, this space is very much influenced by terminology coming from software tool (for good and for bad).
    Now, my point is how to organize BOM(s) / Model/ Reports or whatever else we call it to have efficient processes in organization.
    Best, Oleg

  • HervĂ© Menga

    I did not say that a CAD BOM was not necessary, i said that the CAD designer does not need a CAD BOM.
    So why in some companies we are speaking of the CAD BOM, and of the difficulties to “transform it” into an EBOM (same, who needs the EBOM ?), and then “at the end” to the MBOM (ah, here, we could assume that the MBOM is necessary to procurement/logistics people to be able to order the components (personnally, i think that this could be THE BOM…).
    I must admit i have some problems with the idea of an EBOM being composed of logical elements (?).
    But this idea behind that the mockup is composed of “logical elements” could be explained like the following:
    Of course, i know that before to make any mechanical design that involves geometric problems, a mechanical designer is doing some system engineering activities, i.e. is considering the product with a systemic approach (product = system), so he is first constructing the functional model of this system. Then he is allocating to each function a sub-system or a system component (this gives him a system architecture model), and for each sub-system, he must study it geometrically if this sub-system is a mechanical system. Why geometrically ? Because the function of this mechanical system is the transformation of mechanical energy by means of this mechanical system, so it involves mechanical interfaces… Of course, because the geometric model of the system is somehow the translation of the function “Transform the energy”, the geometric model is the functional response of a mechanical system to the question.
    By analogy, if you imagine that the systems technology is electronic (transformation of a signal into another electric signal), the functional model made by the designer will be an electronic diagram (electronic model), which corresponds to the geometric mock-up for a mechanical system.
    So, the list of geometrical “parts” that composes a mechanical system could be understood as the list of the functional elements of this mechanical system.
    It implies that the functional “view” of a mechanical system can be modelled as the digital mock-up of this system (including of course the GD&T information that is carried by the interfaces), which i call the “design model” of the system. What a great idea!
    But now what is the architectural “view” of this mechanical system ? I think personnally that the architectural view could be modelled as the process model of this mechanical system.
    For a “small mechanical system” as you say, Jovan, it seems quite obvious that the process model is very similar to the design model. Why ? May be because a small mechanical system involves only basic assembly operations, so the process to make an assembly of components is similar to a composition : if you want to make the full system, the process is easy : you just “add” the components. But if the process is slightly more complicated (for example, you glue two components before, and then assemble and paint afterwards), the process model is just more complicated than the simple “add” of the design model – at least because you must include in this process as “new components” the glue and the paint (which are not included in the design model)…
    Do not think that the process model must be constructed by manufacturing guys! I use to consider that the design model and the process model are two faces of the product definition : the combined answers : how the mechanical system is performing the allocated function (desig model) + how the mechanical system must be “materialized” to be able to perform the allocated function (process model).
    This “dual” behaviour of design/process models of the product definition could explain why we have problems to make the difference between the CAD BOM/EBOM.
    Sorry again for this long message, you can freely remove it if you have problems with it.

  • Jovan, I see what you mean – we may decide to have about any number of internal logical structures and processes, but finally we need to take care about “functional set of products” and “shopping list for manufacturing”…. right? The question, I’m raising is how to make these logical structures and process lean and efficient? Because if customer is ready to wait unlimited time and we have no competitors, we have all time in the world to design, plan and manufacturing :)… the optimization of internal processes starts when we need to compete and deliver on time, right? Oleg

    PS. I’m sorry. I’m not in Lowell this week, getting back to Boston on Fri only…. Best, Oleg

  • Alec Gil

    Excellent topic with outstanding contributions from everyone. I too liked Herve’s analogy of the BOM to the final shopping list. However, the question that must be answered related to Oleg’s original quandary is: well, where do you shop? That is, do you source everything from outside, build everything internally or both (most likely). If shopping externally, do you just buy standard components or outsource entire sub-systems of your products.

    All of these questions (and there are others) ultimately answer the question of how the organization manages their Bills of Materials. In an ideal case of everything being done internally, I would suggest organizations should strive toward the single BOM. Of course, there are issues of different organizational roles contributing to the BOM, and organizational ability to reconcile these contributions. I will try to expand on this topic. CAD structures are really just a useful starting point in BOM creation. Once CAD assemblies reach some defined level of maturity, the initial version of the BOM can then be extracted. I will not call this version of BOM EBOM because, philosophically, I believe it is a misnomer. It is simply initial, likely incomplete, version of the BOM. Moreover, after the initial “extraction”, people contributing to the BOM, should be able to add to or subtract from this initial version. Designers, in the meantime, if needed, must be able to continue working on the momentarily disconnected CAD structure. However and here is the key, at any point, a system (hopefully PLM or perhaps some other) must be able to reconcile these two structures on demand. In addition, that same system (PLM again) must be able to support all checks and balances that allow different organizational roles (engineering, manufacturing, purchasing, QA, etc.) to indicate to the involved stakeholders that they are done with their portion of the BOM. At the point when everyone is finished, the BOM is complete. If any changes are required in the future, a new revision must be made.

    But what about functions that are usually done in an ERP system? Well, if we are truly serious about having only one Master BOM, all of the involved business systems – at a minimum PLM and ERP – must be integrated to the point where, from the process standpoint (i.e. overall BOM creation and maintenance) they look like a single system. Let me give a few examples. If a Purchasing department needs to issue a Purchase Order in ERP for a long lead-time component, Engineering must be able to set the appropriate Item (a component in the BOM) attribute(s) in the PLM system, and their agreement to purchase will, based on some pre-defined process trigger, then be communicated to ERP. This is shopping externally. Similarly, for the job orders to be issued (internal shopping), related attributes must also be set in PLM and communicated to ERP. I agree this is difficult, but not impossible or utopian. It has been done. All that is necessary is for the PLM system to support all of the needed interactions. The more of these interactions such system supports, the easier these implementations will become.

    Lastly, what if the external BOM communications are necessary? This is one obvious place where disconnects can occur, but, if it is important for business, integrations and associated rules can be established with the involved customers or suppliers.

  • Alec, my takeaways from your great comment are as following: 1/the ultimate structure of BOM can be only defined for specific customer and rarely can be predefined; 2/Ability to synchronize between whatever we call them (BOM structures) will be the key; 3/All parties (suppliers, ERP, CAD…) need to be involved and integrated.
    Basically, you said, when all these pre-requisites done, we have ONE master bill of material in organization… I hope, I got it right… thanks, Oleg.

  • Alec Gil

    Oleg, this is exactly right. Very well summarized.

  • Vikas

    What could the possible problems be when we try to combine the bills from multiple sources to create a single bill?

    Thank you.


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