Setting up a BOM

Hi All,
I have multiple BOM’s to set up and am getting confused with the first one.
Basically the steps are as follows. I am unsure as to what to set as items and what to create BOMS for. The steps are

1 - Order sensor from supplier that comes with supplier serial number

2 - We then take the sensor and perform the following in house operations. Calibrate x 2, normalise x 2 and then glue (keeps original supplier serial number)

3 - We then send the sensor out for welding at a sub contractors. No material is required, just the sensor (keeps original suppliers serial number)

At this stage the item can be branded by engraving it with a different customers logo as in step 4. I would assume at step 4 there are multiple items as the logo makes it different so we would normally hold a stock of items at level 3 and just engrave them when we get orders

4 - We then send the sensor to a different subcontractor for engraving. At this point it gets a new serial number (ours) but must link to the original suppliers serial number

The finished item at Step 4 can then either be packed (would require extra materials when packing such as a cable etc), or can go into a further assembly

I am unsure with the above whether i take the final item as an item and create a bomb that gets it from the supplied sensor to the finished item or do I create a new item at each level and if so how do i maintain serial numbers

An example of how to do this would be great as I can then replicate it for all our other items

Thanks in advance

@stanster This seems a bit tricky.

To get it working out of the box, you should not create BOMs. Just make stock entries to and from your supplier and maintain separate warehouses for workstations to maintain your stock. You can add custom fields on the Serial No to track process status.

You can create a BOM for your final Item where both the parent and child items have separeate Serial No.

But you can try my suggestion and see if it works okay.

We can also customize so that Serial No can be transferred during a “Manufacture” operation, but that would be a new feature.

Thanks for your reply.
What would be the normal method for this with ERPNext
I was thinking I could have a BOM for the final item and that is made up of the sensor as it comes in plus all the operations including sub contract elements.
What I am not sure of with this method is how I will be able to manage the sensors at different stages of completion as we generally calibrate 50, then normalise 50, then weld 50 then engrave 50. All of these have individual serial numbers.
An example would be great for me to look at if you have one

@stanster there is no example I can show you but you should work with a combination of custom fields, Stock Entry and BOM