BOM management for multi-level production: from release to dispatch

A bill of materials says what goes into one finished unit: each raw material, bought-out part and sub-assembly, with the quantity of each and the level it sits at. For a simple product with ten components, a spreadsheet works. For a factory running forty active products, each with 30 to 150 components across several levels, a spreadsheet BOM is a problem waiting to surface.

What a multi-level BOM contains

A multi-level BOM lists not only the top-level components but the sub-assemblies inside them and the materials inside those. A garment BOM has fabric by colour and weight, thread, interlining, buttons, zips and labels, and also the cut sub-assembly with the pieces per size, the sewing sub-assembly with its operations, and the finishing sub-assembly with pressing, folding and packing.

Each level corresponds to a production stage. The link between the BOM and the routing is what makes explosion possible: the calculation of every material, sub-assembly and operation needed for a work order.

Single-level, multi-level and variant BOMs

• Single-level: only the direct children of the finished item. No sub-assemblies. Fine for simple products.
• Multi-level: each node can itself be a BOM. Any depth of sub-assembly. Needed for products with intermediate stages.
• Variant: one BOM template where components or quantities change by variant, such as size, colour or material. Essential for garments, furniture and automotive sub-assemblies.

The four BOM errors in almost every factory

• Stale versions in production. Engineering updates the BOM, production runs the old one, and consumption is deducted at the wrong quantities.
• No variant handling. Twelve colours and four sizes become 48 separate BOMs. A component change has to be made 48 times and is made 30.
• No alternates. The BOM names one component. When it is short, the line stops or someone substitutes and nobody records it.
• BOM not linked to routing. The material list and the operation sequence are two documents, so nobody knows which material is consumed at which operation.

Explosion at release

When a work order is released in FleekERP, the BOM is exploded: the full tree is traversed and the material requirement for the ordered quantity is calculated, including sub-assemblies. The explosion reserves material against the order and creates the operations from the routing.

It also freezes the BOM version. The version used for this order is locked at release. If the BOM changes tomorrow, this order runs on today's. That is what keeps the cost and the trace of the order accurate.

Consumption on operation complete

As each operation completes, the material on that operation is consumed from the lots issued to the order. If the assembly operation consumes components A, B and C, those quantities move from stock to work in progress the moment the operator completes the operation. By the time the finished item reaches dispatch, stock is already right.

Shortages before the line starts

The most valuable output of a correct BOM is the shortage you see first. When the system knows what every open work order needs, it can compare that to stock and open purchase orders and show the item that is short, and the order it will stop, before the line starts.

The factories that stop losing hours to material shortage are not the ones with the best stores. They are the ones whose BOMs are correct, linked to the routing, and exploded against real stock at release.