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Bill of Materials

Bill of Materials

A Bill of Materials (BOM) defines the list of component parts required to make an assembly, create builds and allocate inventory.

A part which can be built from other sub components is called an Assembly.

BOM Line Items

A BOM for a particular assembly is comprised of a number (zero or more) of BOM "Line Items", each of which has the following properties:

Property Description
Part A reference to another Part object which is required to build this assembly
Quantity The quantity of Part required for the assembly
Reference Optional reference field to describe the BOM Line Item, e.g. part designator
Overage Estimated losses for a build. Can be expressed as absolute values (e.g. 1, 7, etc) or as a percentage (e.g. 2%)
Consumable A boolean field which indicates whether this BOM Line Item is consumable
Inherited A boolean field which indicates whether this BOM Line Item will be "inherited" by BOMs for parts which are a variant (or sub-variant) of the part for which this BOM is defined.
Optional A boolean field which indicates if this BOM Line Item is "optional"
Note Optional note field for additional information

Consumable BOM Line Items

If a BOM line item is marked as consumable, this means that while the part and quantity information is tracked in the BOM, this line item does not get allocated to a Build Order. This may be useful for certain items that the user does not wish to track through the build process, as they may be low value, in abundant stock, or otherwise complicated to track.

In the example below, see that the Wood Screw line item is marked as consumable. It is clear that 12 screws are required for each assembled Table, but the screws will not be tracked through the build process, as this line item is marked as consumable

Consumable BOM Item Consumable BOM Item

Further, in the Build Order stock allocation table, we see that this line item cannot be allocated, as it is consumable:

Consumable Build Item Consumable Build Item

Substitute BOM Line Items

Where alternative parts can be used when building an assembly, these parts are assigned as Substitute parts in the Bill of Materials. A particular line item may have multiple substitute parts assigned to it. When allocating stock to a Build Order, stock items associated with any of the substitute parts may be allocated against the particular line item.

Available Quantity

When calculating the available quantity of a particular line item in a BOM, stock quantities associated with substitute parts are included in the calculation.

Inherited BOM Line Items

When using the InvenTree template / variant feature, it may be useful to make use of the inheritance capability of BOM Line Items.

If a BOM Line Item is designed as Inherited, it will be automatically included in the BOM of any part which is a variant (or sub-variant) of the part for which the BOM Line Item is defined.

This is particularly useful if a template part is defined with the "common" BOM items which exist for all variants of that template.

Consider the example diagram below:

Inherited BOM Line Items Inherited BOM Line Items

Template Part A has two BOM line items defined: A1 and A2.

  • A1 is inherited by all variant parts underneath Template Part A
  • A2 is not inherited, and is only included in the BOM for Template Part A

Variant B has two line items:

  • A1 is inherited from parent part A
  • B1 is defined for part B (and is also defined as an inherited BOM Line Item)

Variant C

  • A1 inherited from A
  • C1 defined for C

Variant D

  • A1 inherited from A
  • B1 inherited from B
  • D1 defined for D

Variant E

  • Well, you get the idea.

Note that inherited BOM Line Items only flow "downwards" in the variant inheritance chain. Parts which are higher up the variant chain cannot inherit BOM items from child parts.

Editing Inherited Items

When editing an inherited BOM Line Item for a template part, the changes are automatically reflected in the BOM of any variant parts.

BOM Creation

BOMs can be created manually, by adjusting individual line items, or by upload an existing BOM file.

Add BOM Item

To manually add a BOM item, navigate to the part/assembly detail page then click on the "BOM" tab. On top of the tab view, click on the icon then, after the page reloads, click on the icon.

The Create BOM Item form will be displayed:

Create BOM Item Form Create BOM Item Form

Fill-out the Quantity (required), Reference, Overage and Note (optional) fields then click on Submit to add the BOM item to this part's BOM.

Add Substitute for BOM Item

To manually add a substitute for a BOM item, click on the icon in the Actions columns.

The Edit BOM Item Substitutes form will be displayed:

Edit BOM Item Substitutes Edit BOM Item Substitutes

Select a part in the list and click on "Add Substitute" button to confirm.

Validate BOM

After adding BOM items manually or uploading a BOM file, you should see the following view:

Invalid BOM View Invalid BOM View

The first message in the red box The BOM for PCBA TEST has changed, and must be validated. points out that InvenTree BOM needs to be "validated". BOM validation is a way to ensure a BOM does not have duplicate items/parts.

To process with BOM validation, click on the icon and the Validate BOM form will be displayed. Click one the "Validate" switch then click on Submit

Valid BOM View Valid BOM View

Multi Level BOMs

Multi-level (hierarchical) BOMs are natively supported by InvenTree. A Bill of Materials (BOM) can contain sub-assemblies which themselves have a defined BOM. This can continue for an unlimited number of levels.

When viewing a BOM table, sub-assemblies are not loaded by default, but can be loaded "on demand" by pressing the icon associated with the particular subassembly:

Flat BOM Table Flat BOM Table
Expanded BOM Table Expanded BOM Table

Last update: December 15, 2023