BOM 101 for Engineers

I’ve been fortunate having been given the chance to talk to many manufacturing companies ranging in size from small hardware startups to large manufacturing companies. In having done so, I’ve learned much from asking people about Bills of Materials, or BOM.  Doing so exposes much about how a company designs, manufacturers, and services its products.

As an engineer, you may have asked yourself why are BOMs such complex data structures. Or perhaps, you simply take for granted BOMs are a fact of life and deal with them best as you can. In this post, I will try to give you a greater understanding of BOMs and perhaps if you don’t already do so, appreciate them for what they are: the core of all manufacturing processes.

Bill of Materials, or BOMs, are the core of all manufacturing processes.

Engineering BOM is typical the beginning of any Bill of Materials management activity. Based on my observations, there are three aspects in which engineers are involved with engineering BOM management:

Part List. A part list is a simplest way to manage an engineering BOM. Usually done by exporting information from a CAD system and adding non-geometrical items. It’s a typical way to create a list of parts that can be used for ordering purposes and/or communicating with contractors.

Structure transformation. A CAD structure is not an engineering BOM. Restructuring is one of the most complicated processes when creating an engineering BOM. In my experience, this process can not be easy automated (if at all) demanding much human involvement. Mapping between data structures is hard and referencing between structures is even harder. However, structure transformation is absolutely important to the process of correctly creating an engineering BOM.

Configurations. Most products today demand configurations such as models, options, etc. The management of these configurations in a CAD system is complex and confusing. If you try to apply configurations to a structure transformation, chances are you will get lost. The best results can be achieved if a tool used to manage engineering BOMs is capable to model configuration. However, this is often not the case and as a result, companies end up with many complex spreadsheets.

BOM management remains a challenge in most manufacturing organizations. Let’s now try to understand the elements of a BOM that influence the engineering activities. I’m familiar with four BOM related elements that are the lifeblood of most product development processes.

BOM and Part Lists

A Bill of Materials is at heart a list of all the items required to make a product. BOMs include components, raw materials, and sub-assemblies. They may also include intermediate items identifying in-process elements to facilitate planning and other manufacturing processes. Depending on the industry people refer to BOMs differently. For example, in the process industry, it can be called a recipe or formula. A Part List is usually a term used to refer to a single level list of a specific level of an assembly or sub-assembly.

Part Number

Part Numbers is one of those terms that is very tricky to define; there are entire product development and BOM management stories and histories behind it. I’ll try to keep it simple with a short definition: a Part Number (PN) is a unique identifier that identifies a single object in a Bill of Materials. The trick in naming them, however, is defining an object and keeping it consistent with your internal processes. Assigning part numbers is often complicated and a big topic of discussion in manufacturing companies. A short list of issues often discussed around the part numbering process include the traditional definition of FFF (Form, Fit and Function), interchangeable parts, substitute items, and special parts, to name a few.

Routing

Consider a navigation system with roads between different places of interest. Now imagine part numbers. Routing is a roadmap that defines the path of part numbers across the manufacturing floor by specifying workstations and labor time associated with every station. Routing is usually applied to manufactured parts or items.

Drawings

Historically, drawing are where people put the BOM for a product, sometimes solving the problem of BOM distribution within a company.  However, a BOM in a drawing presents many disadvantages. In most situations, people don’t need a drawing, rather, they need a BOM and/or part list. Another point of confusion is the discussion about applying part numbers in drawings. In most situations, this represents the limitation of systems used for product development, e.g., PDM, PLM. Separating Part Numbers and Document Numbers is the most reasonable way to manage the confusion of BOMs in a drawing.

For the last few decades, the importance of contract manufacturing has increased significantly. It affects many engineering activities. A BOM is one of those tools that are very important and can help you optimize and streamline contract manufacturing activity; something I’m seeing more and more of. Perhaps this is something you deal with on a daily basis.

Globalization and contract manufacturing are two important trends shaping modern manufacturing. Companies are using contract manufacturers (CM) for different purposes: design, component supply, assembly, fabrication, etc. So, what are the critical elements of a BOM system capable of supporting your CM processes? Here’s what I’ve learned:

  1. Access to CAD components and libraries. Having information about components, availability, cost and other parameters such as regulation is critical. To replicate this information in your BOM system is possible, but not reliable and not scalable. Check if your BOM system can access this information and automate both the import and export of data to avoid manual data entries.
  2. Flexible and granular BOM management. You need to organize BOMs in such a way engineering and CM will be able to access them. Doing so will allow early access to all parties involved in design and manufacturing to access product information.
  3. Change management. When it comes to BOMs, change happens. All the time. It will happen to your design and manufacturing plan. Find a BOM tool that allows you to manage the traceability of changes alongside manufacturing plans.
  4. Collaboration. You need to have the right technology in place to enable your CM and subcontractors to access information in your BOM at any time. You’ll need all the other three aforementioned points to create a reliable “everyone on the same BOM” that cuts down on mistakes and errors while holding all distributed stakeholders accountable.

I’ll close this post with a few tips I’ve learned along the way of how to optimize BOMs and my thoughts on the proverbial Engineering BOM (EBOM) versus the Manufacturing BOM (MBOM). Now that you have a better understanding of BOMs, here are few ways to optimize them:

Function Oriented BOM

By definition, a BOM is not strictly functional. However, in my view, there are many BOMs in organizations which reflect their “product structure” as the main driving force behind how their BOMs are organized. As a result of this, many companies experience difficulties with operations and processes that involve these BOMs. This can be remedied if you think of the BOM from a functional standpoint. The form of a BOM follows functions. Ensure that the final form of your BOM reflects what you want the BOM to do. Your BOM tool should be sufficiently flexible to allow this.

Wide Company Usage

Very often BOMs start in the engineering department. Compartmentalized organizational logic made BOM separation natural. However, when you start planning cross functional processes, managing BOMs become a big challenge. I suggest you include the high-level business view in a BOM by structuring it around end items that capture both the product you are creating and the processes involved in manufacturing it. Stay away from silo thinking.

Part Numbers and Documentation

Don’t mess with these two main groups of identification parameters. Don’t try to combine them. Build BOM around part numbers and think about how to simplify the relationships between Parts and Drawings. The complexity of these relationships will make your future change process messy and complicated. Traditionally, BOM ends up in the drawing sheet. It was in the past. With massive adoption of 3D CAD systems and computer automation, you can re-think it.  Managing part numbers is a separate topic that I will address in another post.

Modules and Flattening

Use grouping techniques to create part of BOM that can be easily handled and replaced. Use logically combined parts that belong to specific configurations. It will help you to simplify your ordering system. Modern tools allows you to deal with hierarchies much easier. However, think twice before you introduce an additional level in BOM hierarchy. Flat BOM is much easier to handle. It is very important to create a BOM structure that allows you to run change processes as easy as possible. Analyze your change processes upfront.

EBOM vs. MBOM

From a technical standpoint, it is relatively easy to explain the difference between EBOM and MBOM. The first (EBOM) represents the way a product is designed (structure, models, functionality, configurations, etc.) The variety of characteristics depend on the type of manufacturing and processes. Manufacturing BOM (MBOM) defines how a product will be produced (including aspects of material ordering, routing, different manufacturing plants, etc.).

EBOM and MBOM are not entirely different but data structures and attributes used in both often do not overlap. Some engineering attributes and structures are not relevant for an MBOM. On the other hand, MBOM information is often irrelevant and not needed by engineers and designers.

The thing that makes everything complicated is the process between the EBOM and MBOM worlds. The “throw over the wall” manufacturing concept co-exists together with the tightly collaborative process of work on EBOM and MBOM. Engineers request information about the product (EBOM) as early as possible in the development cycle. At the same time, manufacturing planning can get back to engineering in order to finalize and optimize the product. It’s best to ensure your BOMs are optimized to increase the effectiveness of both engineering and manufacturing.

Bill of Material is an important topic and it is the lifeblood of all product development processes. Modern manufacturing trends such as globalization, contract manufacturing, mass customization, IoT, and many others are increasing product complexity and demand more sophisticated and connected tools to help engineering and manufacturing companies to work together.

This post reflects some basic aspects of BOM management for engineers. Please let me know what you think. There are plenty of other BOM related topics I didn’t get into here but would love to do so in future posts.

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