The bill of materials of a palletising cell counts one hundred and forty lines in Inventor. The ERP holds one hundred and thirty-seven. Three lines apart, nobody knows which ones, and ordering starts next week. Sound familiar? Then somewhere in your process there is a spot where somebody retypes.
Every retyped line turns one BOM into two truths, each living a life of its own. In this article we follow the route from engineering BOM to purchasing list and ERP order: which fields must travel along, where the manual work creeps in and what getting your BOM to ERP without retyping demands from the quality of your model. Tooling such as the export tools of Thundercad plays a part, but the data flow itself comes first.
Two truths cost more than one
Retyping takes time, but that is the smallest problem. Run the numbers, with assumptions you should adjust for your own shop: one hundred and forty lines, half a minute per line for looking up, typing and checking. That is over an hour per machine, and part of it comes back with every revision.
The real costs come afterwards. Engineering releases revision B with two extra locking plates, but purchasing still orders from the revision A list. Or someone types a 4 where a 2 stood, and two spindles too few arrive. The fitter reports it, and the detective work begins: which list was right, who changed what, what else is wrong? From that moment on everyone double-checks everything, and those structural distrust costs appear in no budget anywhere.
And then there is the delay. An order that can only go out once somebody has time to type easily sits waiting for a day. On a rush order that bites immediately: the lead time of your ordering process suddenly matters as much as the supplier's delivery time.
The route in three stations
On its way from model to order, a BOM passes three stations, and at each station its shape changes:
- The engineering BOM: the structure as designed, with assemblies, subassemblies and quantities per level. This is the source, and it lives in the model.
- The purchasing list: flattened and filtered. Purchased parts with totals across the whole machine, manufactured parts listed separately, standard parts bundled.
- The ERP order: the same lines, but now tied to item numbers the ERP knows, with ordering information added.
They are three views of the same data. As long as every transition is an export or an import, there is one truth that merely changes shape. The moment a human sits in between, reading and typing, the truth splits. So the assignment is not "type faster", but to set up every transition so there is nothing left to retype.
Mind the difference between filtering and rewriting. A purchasing list may show less than the engineering BOM, but never anything different: every field someone "quickly improves" along the way is a break in the flow that resurfaces later as a difference between systems.
Which fields must travel along
Whatever the ERP needs has to be present in the model; an export cannot invent anything. These are the fields that matter in practice:
| Field | Source in your model | Why the ERP needs it |
|---|---|---|
| Item number | iProperty, filled when the part is created | The key by which lines are recognised and matched |
| Description | iProperty, built up in a fixed way | Recognisability for purchasing and the shop floor |
| Quantity | The assembly structure itself | Ordering, reserving and recalculating |
| Make or buy | Category or property per part | Decides the route: order it or produce it |
| Material | The material in the model | Buying semi-finished stock and costing |
| Unit | Pieces, metres or kilos per part | Prevents orders in the wrong unit |
The biggest pitfall is the item number. If engineering invents its own numbers, the ERP does not recognise them and the manual work starts anyway. With Article Manager you consult the articles from your ERP directly inside Inventor and place parts with the correct number and description attached. The number is then right at the source, not after a check at the end.
Want to see which fields already come through cleanly at your company, and where the manual work sits? Export a real BOM in your own column layout and put it next to your ERP order.
Try 30 days freeCutting out the manual work: the file as the interface
The simplest reliable transition is a file the receiving end can read in. First refresh the bill of materials with Update BOM, so the latest model changes are in, then export with Export BOM to Excel in your own template: columns, order and layout exactly as the import function of your ERP or your buyer expects them. No shifting columns, no pasting lines. The nice thing about this sequence is that every step is small, and every step immediately removes typing.
How to set up such a template is covered in BOMs from Inventor to Excel: always in your own template. And if you want to go beyond files, towards article integration or a direct connection, read Connecting Inventor to your ERP: where do you start?; we deliberately leave the technology of that integration aside here. For the data flow it makes no difference whether a file or an integration sits in between: the fields and the quality demands stay the same.
What this demands from your model
A BOM is only as good as the model underneath it. If you want to deliver without retyping, the modelling has to meet a few demands:
- Every part has its own unique item number; the same number for two variants is forbidden.
- The iProperties the ERP needs are filled before release, not "later at some point".
- Quantities come from the assembly structure. Parts that were only "written onto" the drawing do not exist for the ERP.
- Helper geometry and reference parts are set up so they do not count in the quantities.
- New articles are created through one agreed route, so duplicate numbers never appear.
- Changes always run through the model, never directly in an export list: the model stays the source.
Frequently asked questions
Who owns the item number: engineering or the ERP?
The ERP is the register: numbers are born there and live on there in purchasing, stock and costing. Engineering consults that register and uses the numbers in the model, for instance through Article Manager directly inside Inventor. Inventing numbers on the engineering side is the shortest route to duplicates.
What do I do with changes after the first handover?
Export the complete, refreshed BOM again and let the receiving end process the difference; never manually patch lines in a previously shared file. State the revision clearly with the list, so it is always traceable which state was ordered against.
Does this work without an ERP integration?
Yes. The route through a structured export file works with virtually any ERP that has an import function, and for many companies it stays sufficient for years. Start there: with the free trial month of Thundercad you set up your own export template and test the flow on a live order.