Manufacturers often run into a common scenario: multiple top-level assemblies share the same subassembly. For example, Assembly A and Assembly B both require Subassembly 1. Instead of rebuilding Subassembly 1 every time you manufacture either A or B, you may want to build a batch of Subassembly 1 ahead of time and draw from that stock when needed.

This guide walks through how to handle this scenario in Cetec ERP by modeling the subassembly as a semi-finished good and using it across different BOMs - without fragmenting inventory or overcomplicating work orders.

Scenario: Shared Subassembly Used in Multiple Parent Assemblies

You're building two separate assemblies (let's say Assy A and Assy B), both of which use the same subassembly (Sub 1). Your goal is to:

• Build Sub 1 separately in advance
• Treat Sub 1 as a complete, inventory-tracked unit
• Use it later when building either Assy A or B
• Avoid exploding Sub 1’s BOM on the parent work order

This is a common case in contract manufacturing, electronics, and ETO environments where shared modules or tested units are produced ahead of time and stored until final assembly.

Step-by-Step: Handling Shared Subassemblies in Cetec ERP

1. Model Subassembly 1 as a Standalone BOM

Start by creating Sub 1 as its own BOM in Cetec ERP. Define it with its components and operations just like you would for any standalone product.

In both Assy A and Assy B BOMs, insert Sub 1 as a component (just like a purchased part), rather than nesting its full structure. This simplifies the top-level BOM and treats Sub 1 as a finished item.

Tip: Think of Sub 1 as a semi-finished good, not an expansion of an internal BOM.

2. Create a Build-to-Stock Work Order for Sub 1

In Cetec ERP, create a build-to-stock work order for Sub 1. This is an internal work order that creates inventory stock of Sub 1, much like how you’d purchase inventory from a vendor.

This order:

• Is not tied to a specific customer PO
• Fulfills general demand created by your MRP
• Adds finished Sub 1 units to your inventory

This is an internal production order, separate from customer demand. It's your own initiative to build and stock a subassembly.

3. Use MRP to Estimate Sub 1 Demand

To determine how much Sub 1 to build, run the MRP - Build Report in Cetec ERP. This will show upcoming demand from both Assy A and Assy B BOMs.

You can then create a build-to-stock order for the projected total quantity needed.

4. Pick Sub 1 from Inventory on Assy A or B Work Orders

When a sales order comes in for Assy A or B, and a corresponding work order is generated, you’ll pick Sub 1 from stock as a component - just like any other purchased part.

Because Sub 1 is now an inventory item:

• It appears on the pick list
• It is tracked with full traceability
• Its cost rolls into the parent assembly properly

This approach also preserves the audit trail of Sub 1’s build, tests, and inspections.

Confirmed: Sub 1 is a BOM Component, Not an Exploded BOM

You do not need to explode Sub 1 on the Assy A/B BOMs. Instead, treat it as a single component. This keeps work orders simpler and preserves modular control over how and when you build Sub 1.

“Build to stock” for Sub 1 = supply
Assy A/B work orders = demand

Managing Changes to Shared Components Across Multiple BOMs

Shared subassemblies solve another common manufacturing problem: maintaining the same component across many different BOMs.

A motor, connector, fastener, PCB, fabricated component, or complete subassembly may be used in dozens of parent assemblies. If engineering needs to replace that part or move those BOMs to a different revision, manually opening every BOM creates unnecessary work and increases the chance that one assembly gets missed.

Cetec ERP’s BOM Use screen, also known as the Where Used report, lets you start from the component or subassembly and see the BOM revisions where it is currently used. From there, you can replace the component with another part or revision across the BOMs displayed on the screen.

For example, if Sub 1 is used by Assy A, Assy B, Assy C, and ten other products, engineering does not have to search through each parent BOM individually just to determine where Sub 1 needs to be changed.

This gives engineering a more controlled workflow:

1. Identify every BOM that uses the shared component or subassembly.

2. Review which BOM revisions should be affected.

3. Replace the component or revision across the applicable BOMs.

4. Use the ECO process when the change needs formal review and traceability.

This becomes increasingly valuable as product families grow. Instead of maintaining the same component relationship separately across dozens of BOMs, engineering can manage shared components from a central where-used view and avoid repetitive manual BOM updates.

For step-by-step instructions, see How to Use the BOM Use Screen to Replace Components.

Summary

Using build-to-stock work orders and modeling subassemblies as individual BOMs is the best practice for managing shared components across multiple products. This gives you flexibility in planning, control in production, and simplicity in execution, all while keeping your data clean.

Key Takeaways:

• Model shared subassemblies (like Sub 1) as their own BOMs
• Use build-to-stock work orders to pre-build and stock them
• Treat them as inventory parts when building top-level assemblies
• Use MRP to plan demand across all parent BOMs
• Use BOM Use / Where Used to identify where shared components and subassemblies appear
• Replace components or revisions across applicable BOMs instead of editing each BOM individually
• Use the ECO process when engineering changes require controlled review and traceability

For a related guide on managing multi-level BOMs and production control in Cetec ERP, check out: How to Create a Multi-Level BOM

Need help configuring this in your Cetec ERP system? Contact our support team, or explore more how-to videos in our knowledge base.