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How to Generate Bill of Materials (BOM) from a CAD Assembly (Step-by-Step Process)

How to Generate Bill of Materials (BOM) from a CAD Assembly

Introduction to BOMs

A bill of materials (BOM) is a comprehensive list of all the materials, components, and assemblies required to manufacture a product. At its essence, a BOM provides crucial manufacturing information that answers the questions:

  • What parts do I need?

  • How many of each?

  • How are they all put together?

BOMs have a number of important uses across the product lifecycle:

  • Engineering - BOMs allow engineers to define the materials and components needed to design a product. The engineering BOM (EBOM) maintains the relationship between assemblies, subassemblies, parts, and raw materials in the engineering documentation.

  • Manufacturing - The manufacturing BOM (MBOM) provides the information required for procurement, production planning, and shop floor operations. The MBOM transforms the EBOM structure into the ideal assembly sequence for manufacturing.

  • Costing - With the part quantities and manufacturing steps defined, the BOM provides the input data to accurately estimate overall costs.

  • Sourcing - The BOM can be shared with suppliers to get accurate lead times and pricing for required materials and components.

  • Quality Control - BOMs ensure the correct revisions of parts are used during manufacturing and reduce errors caused by part substitutions.

  • Maintenance - The as-built BOM makes it easy to identify replacement parts needed for maintenance and service.

In summary, the bill of materials is an essential manufacturing and product definition document with applications across engineering, production, costing, purchasing, quality, and maintenance.

Essential Elements of a BOM

A well-structured BOM includes all the information needed to manufacture and assemble a product. While the specific elements can vary based on the product, industry standards, and organizational needs, there are a few essential components that should be included in any BOM:

  • Part Numbers: Unique identifiers assigned to each component and sub-assembly. Using consistent part numbering makes it easier to track inventory and find components.

  • Part Descriptions: Clear textual descriptions of each component, answering questions like the material, color, size, specifications, etc.

  • Part Revisions: The revision or version number of each component, such as Rev 1, Rev A, etc. This allows tracking of engineering changes.

  • Quantities: How many of each component is needed to make the assembly. This drives purchasing quantities.

  • Unit of Measure: Along with quantity, the unit representing that quantity like EA (each), KG (kilogram), FT (feet), etc.

  • Levels/Tiers: A multi-level or tiered structure representing the parent-child relationships of assemblies, sub-assemblies, and components. Higher level assemblies are made up of lower level sub-assemblies and parts.

Including these essential elements ensures your engineering and manufacturing teams have all the necessary information to procure parts, plan production, and successfully build your products. A BOM lacking any of these elements can severely impact your ability to get quality products to market quickly and efficiently.

Creating BOMs Quickly and Efficiently

Whether you're creating your first BOM or your hundredth, you'll want the process to be as fast and smooth as possible. Here are some tips to generate BOMs quickly and efficiently:

  • Use BOM software that integrates with your CAD tool. Rather than manually building BOMs in Excel, using dedicated BOM software that connects directly to your CAD assembly data can save huge amounts of time. Leading options like Katana, Arena, and Odoo can import assemblies from SolidWorks, Inventor, Creo and other major CAD tools. The assembly structure and component relationships automatically become your BOM structure.

  • Start with the highest level assembly and work down. Begin by adding your top level or final assembly into the BOM software. The subassemblies and parts used in that top assembly will be brought in and structured. Then continue moving down the assembly hierarchy in the software.

  • Reuse similar BOMs. For products in the same family, you can save BOM templates to use as starting points. Tweak the structure and swap components rather than starting from scratch each time. The software will adjust quantities and levels accordingly.

Automating the process through capable BOM management software, building from the top down, and reusing previous BOMs as templates will shave hours off the time it takes to generate accurate BOMs. Your engineering and manufacturing teams will thank you!

Making the Most of Your BOMs

The bill of materials contains crucial information that goes well beyond just listing the parts needed to build a product. You can maximize the value of your BOMs by:

  • Sharing BOMs with suppliers - Send your BOM to suppliers to get accurate quotes for costs and lead times. Having the full list of parts lets suppliers understand the complete scope of work and provide reliable estimates.

  • Creating work orders, purchase orders, and production schedules - The manufacturing quantities in the BOM make it easy to break down the production plan. The BOM drives everything from work orders on the shop floor to purchase orders to suppliers to material requirements planning.

  • Updating BOMs whenever engineering changes are made to the product - Engineering changes and design revisions are a fact of life. As soon as the product design is modified, update the BOM so it always reflects the current state. This ensures the right version of parts is ordered and production has up-to-date documentation.

The BOM isn't just a static document. Use your bill of materials proactively as a source of truth for your manufacturing process. Keeping your BOM accurate and in sync with engineering changes enables smooth production scheduling and execution.

Types of BOM Structures

There are a few key ways that BOMs can be structured:

Single-Level BOM

A single-level bill of materials contains only one level of components. It lists all the parts and materials required to make the top-level or final product, but does not show the relationships between sub-assemblies and parts. Single-level BOMs provide a simple, flat list of everything needed to build the end item. They are easy to read but lack the detail to show how components are grouped into sub-assemblies.

Indented BOM

Indented bills of materials use indentation to illustrate the product structure. The top-level or final assembly is listed at the far left, with sub-assemblies indented to the right. Parts used to make each sub-assembly are further indented. This creates a visual representation of the assemblies, sub-assemblies, and components. Indented BOMs clearly show the relationships between parts. They provide more detailed information than single-level BOMs.

Modular BOM

A modular bill of materials divides a complex product into logical groups or modules. For example, a car BOM could be split into modules like engine, transmission, interior, and electronics. The modules can be broken down into sub-assemblies and parts. Modular BOMs make it easier to understand and manage BOMs for highly complex products by organizing them into functional groups. This modular structure mirrors how the end product is actually designed and assembled.

BOM Software Options

Excel is commonly used to create simple BOMs, but it has limitations for more complex assemblies. Some of the downsides of managing BOMs in Excel include:

  • Manual data entry leading to errors

  • Hard to show relationships between levels of assemblies

  • Scalability issues for large BOMs

  • No integration with engineering CAD tools

  • Lack of collaboration features to share BOMs across teams

That's why dedicated BOM management software like Katana is highly recommended for a streamlined CAD to BOM workflow. Katana provides key advantages such as:

  • Direct import of CAD assembly structures

  • Automated BOM creation from CAD models

  • Customizable data fields and templates

  • Collaboration tools to share BOMs with internal teams and suppliers

  • Integrations with ERP, MRP and PLM systems

  • Robust security and access control

With software like Katana, you can optimize your CAD to BOM process. The assembly hierarchy and component relationships established in CAD become the foundation for your BOM structure. Additional product data can be appended right within Katana to generate a complete, accurate BOM ready to meet downstream manufacturing needs.

Generating BOMs in Katana

Katana is a dedicated BOM software that integrates with CAD tools like SolidWorks to streamline the process of generating BOMs. Here's how to leverage Katana to quickly create accurate BOMs from your CAD assemblies:

Import Assemblies from CAD

The first step is to import your CAD assembly files into Katana. This maintains the product structure and component relationships from your CAD design. Katana supports common CAD formats like STEP, IGES, DXF, and SolidWorks files. Simply select your top level CAD assembly and import it into Katana.

Map CAD Structure to BOM

Once imported, the assembly structure from your CAD design automatically becomes the BOM structure in Katana. You get the component breakdown with parent-child relationships mapped from CAD into the Katana BOM.

Add Metadata

With the framework in place, you can now enrich the Katana BOM by adding crucial metadata like part numbers, descriptions, quantities, manufacturers, costs, and any other attributes required for manufacturing. Katana's bulk editing tools make it fast and easy to populate metadata across hundreds of BOM items.

Katana seamlessly converts CAD models into intelligent BOMs with all the data needed to accurately build, cost, and order the parts for your products. The automated CAD import and bulk editing features save vast amounts of time compared to manually creating BOMs from scratch.

Sample BOM

Below is an example BOM for a basic bicycle assembly with 3 levels:

![Sample Bicycle BOM](

As you can see in this sample BOM, the top level is the complete bicycle assembly. The next level shows the 4 sub-assemblies that make up the bike - the frame assembly, wheel assembly, drive train assembly, and handlebar assembly.

Within each sub-assembly, the parts are then listed. For example, the frame assembly is made up of the frame, seat post, and pedals.

The key information included for each part is:

  • Part Number

  • Description

  • Quantity

  • Unit of Measure

Having a visual representation of the BOM structure like this sample makes it easy to understand the hierarchy of components in the overall assembly.

Benefits of BOMs for Manufacturing

A comprehensive and accurate bill of materials (BOM) provides immense value for manufacturing by ensuring you have all the required parts to build a product. The BOM gives the detailed information needed to accurately estimate costs, set delivery dates, and efficiently plan production.

Ensuring Parts Availability

The BOM contains the complete list of raw materials, fabricated parts, electronic components, mechanical parts, and sub-assemblies needed to manufacture the product. By using the BOM, manufacturers can identify and source all required parts well in advance of production. This prevents unexpected shortages or delays when assembly begins.

With an up-to-date BOM, purchasing has visibility into upcoming needs. They can place orders and expedite parts that have long lead times to align with production schedules. Unexpected part shortages during manufacturing are incredibly disruptive and lead to stalled production lines and missed delivery dates. A detailed BOM helps avoid such scenarios.

Accurate Cost Estimation

The BOM provides detailed data on part quantities and relationships between parent assemblies and child components. With this information, manufacturers can accurately calculate costs for materials, labor, and production overhead.

Reliable cost estimates help set competitive yet profitable pricing for new products. As engineering changes are made, the BOM facilitates rapid cost impact assessments so prices can be adjusted if needed. Tight integration between BOMs and enterprise resource planning (ERP) software enhances cost estimation capabilities.

### Production Planning and Scheduling

With parts requirements defined in the BOM, production planners can sequence manufacturing operations, schedule work orders, set throughput targets, and establish realistic delivery timelines. The BOM drives everything from planning material purchases to optimizing assembly line configurations and staffing.

When BOMs are linked to product lifecycle management (PLM) software, changes made by engineering automatically flow through to production plans. This synchronization helps compress time-to-market for new products.

Next Steps for Ongoing BOM Management

Once you have generated your initial BOM, there are several key steps to keep it up to date:

  • Update the BOM whenever engineering changes are made. As part of your engineering change process, the BOM should be updated to reflect any changes to parts, quantities, or structure. This ensures it always matches the latest design.

  • Link the BOM data to your PLM system. Product lifecycle management software centralizes all product data in one place. Integrating your PLM system with your BOM management ensures continuity across the product lifecycle.

  • Regularly review the BOM for accuracy as the design matures. Performing routine audits reduces the chances of errors impacting downstream manufacturing processes.

  • Manage revisions and versions diligently. Use revision numbers to identify the status of a BOM. Store previous versions for traceability.

  • Get input from manufacturing teams. The engineers creating the BOM may not be aware of manufacturing challenges. Getting production input improves the BOM's accuracy.

  • Automate updates where possible. Workflows that automatically pull BOM data from CAD and push it to PLM reduce manual work and chances for human error.

Keeping your BOM synchronized with the product's current state is crucial for efficient, on-time manufacturing. Following these best practices will save you headaches down the road.


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