The shop foreman calls work preparation with a simple question: is frame 4021 in yet or not? The answer depends on what "in" means. The cut parts have been lying there for a week. The welded frame has been sitting next to the straightening table since yesterday. And the coated frame, the only one the fitter can do anything with, is still at the coating shop. The same part three times, three different answers.
If you have that conversation often, you do not have a communication problem but a structure problem. One model passes through several production stages, and as long as those stages have no place of their own in the BOM and the metadata, planning cannot schedule them and purchasing cannot order them. In this article you will read how to give semi-finished parts in your Inventor BOM an identity of their own: when a stage deserves its own part number, how to build that into your structure and how to pull per-stage lists out of it, by hand or with a toolbox like Thundercad.
To be sharp about scope: this is about stages of the same part: cut, welded, coated. The distinction between making, buying and standard parts is a different question; we covered that earlier in Make parts, buy parts and standard parts: cleanly separated in your BOM.
One model, three routes
Take that frame. It starts as a bundle of tube and plate that the sawing department cuts to size. The cut parts go to the welding bay, or to a welding shop down the road. After that, the welded frame almost always leaves the building: blasting and powder coating or galvanising is rarely done in-house. Three stages, then, each with its own lead time, its own workstation or supplier and its own cost price.
If only the end result appears in your BOM, everything before it is invisible. The planner cannot book the coater, because no article called "welded frame, uncoated" exists. Purchasing cannot place the coating order, because there is nothing to attach it to. The intermediate stock, five welded frames waiting for transport, is registered nowhere. And in the actual costing, sawing, welding and coating are one grey lump. So every stage you want to plan, order or count needs an identity of its own.
When does a stage deserve its own part number?
Not every operation should become an article; otherwise every drilled hole turns into a BOM line. A workable rule of thumb: a stage gets its own number as soon as something you want to track passes over it. In concrete terms:
- The stage crosses the company boundary: outsourced welding or coating has to be ordered, shipped and reported back.
- Stock of it can exist: welded frames on the shelf, coating only once a customer order lands.
- Planning steers it separately: the stage has its own lead time or workstation.
- You want to know the cost per step, for instance to compare outsourcing with doing it yourself.
If a step stays within one work order and one hall, it is usually just an operation on the routing and not a separate article. Cut parts are separate components with their own numbers in Inventor anyway; the question mainly concerns the welded and the coated stage. How you then build those numbers, meaningful or meaningless, is a discussion in itself; we had it in Part numbers that scale with you. Here only one thing counts: every stage has a number, and the numbers refer to each other.
How to build the stages into your structure
The shape that causes the least friction in practice: one assembly level per orderable stage. For the frame it looks like this:
| Stage | In Inventor | What it contains | Who steers it |
|---|---|---|---|
| Cut | individual parts | tube and plate parts cut to size | sawing department and material purchasing |
| Welded | assembly (or weldment) | all cut parts | welding bay or subcontractor |
| Coated | top assembly with one component | the welded frame | purchasing and final assembly |
The coated stage feels a bit bare in Inventor at first: an assembly with a single component, the welded frame, and nothing else. Yet that is exactly right. Coating is not geometry but a condition; you capture it in fields, not in features. The alternative, coating as an operation line on the routing of the welded article, is fine as long as you never stock uncoated frames or deliver them separately. Pick one line and hold on to it; a mix of both flavours is where the confusion starts.
A clear structure only pays off when the lists come out just as clear. Thundercad puts your BOM into Excel in a few clicks, in your own template, ready for purchasing and planning.
Try 30 days freeMetadata per stage: the same card for every part
Structure alone is not enough; purchasing and planning steer on fields. Three fields do most of the work: the stage itself (cut, welded, coated), the treatment (powder coating with colour code, galvanising, blasting) and whether the step is outsourced. Record them as iProperties with fixed pick values instead of free text: "powder coated", "powder coating" and "coated" are one thing to a human and three different worlds to a filter.
With the iProperty Panel you set up a dedicated data card per document type for exactly this: a part asks for different fields than an assembly, and while filling it in the engineer sees straight away which field is still empty. That turns the stage field from a good intention into a fixed part of the release.
One list per step: sawing, welder, coater
With stages in the structure and fields in order, the BOM becomes a source from which every department pulls its own extract. The cutting list is nothing more than the BOM of the welded frame: all parts with stage "cut", with material and length added. The coater gets a list of welded articles, treatment codes and quantities. Planning reads the lead time per stage instead of estimating it.
Export BOM does the manual work here: it puts the BOM, including the columns you choose, into your own Excel template in one go. Filtering by stage or treatment is then a matter of one column. The sawing department gets its list, purchasing filters the outsourced work per supplier, and nobody retypes anything.
Frequently asked questions
Does every welded frame also need a coated variant?
No. A separate article for the coated stage only pays off once that stage crosses a boundary or sits in stock: outsourced coating, intermediate stock, or uncoated frames you deliver on their own. If coating happens within the same work order, an operation line on the routing is enough. More important than the choice itself is making the same choice everywhere.
How do I keep the relationship between the stages visible?
In three places at once. The structure itself: the coated article contains the welded one, the welded one contains the cut parts, so the BOM shows the chain by itself. The description: the same base name with the stage added. And the data card: a field that points to the parent or child number, so even a loose Excel line can be traced.
Does this work without an ERP integration?
Yes. The stages, numbers and fields live entirely in Inventor; an Excel export per stage already takes purchasing and planning a long way. An integration removes the retyping afterwards, but it is not a precondition for starting. If you want to see the exports and data cards in practice, you can try Thundercad free for 30 days.