[Feature request] By-products for Assembly BOMs

The problem:

We stock a wide range of rigid materials in standard lengths of 3m, but we offer these for sale online in shorter lengths, e.g. 1m and 2m.

We use assembly BOMs to break down our standard stock lengths into shorter selling SKUs. For example, a 1m SKU has a BOM of 0.333 x 3m and a 2m SKU has a BOM of 0.667 x 3m.

But, an assembly BOM can only produce a single output SKU (e.g. 0.667 x 3m → 2m) and leaves a fractional portion (i.e. 0.333 x 3m) of the original standard length in stock in the system. After a few assembly jobs, you end up with enough “fractions” left to add up to a whole standard length, except you do not actually have that standard length in stock - in reality the stock is smaller fractional pieces and your stock figures in the system do not reflect the physical stock in the warehouse.

(For 1m you could use the “Quantity to Produce” setting and output 3 x 1m from a single 3m. But this does not help for e.g. creating 2m lengths from 3m stock.)

Options that don't work:

We can turn auto-assembly off on all our Assembly BOMs, and manually run stock adjustments each time we cut a product. This would be entirely manual and error prone. And with auto-assembly off, stock availability does not propagate through an Assembly BOM.

We could use production BOMs to convert our stock with more control over the outputs, but that still means (1) manually running a production order on demand for each sale which is not viable in an e-commerce business and (2) stock availability does propagate through a production order, so any produced items show as out of stock which is very bad for e-commerce.

The alternative is to plan and run production orders ahead and maintain physical stock of every possible length for each material, but this would grossly and unnecessarily increase our stock holding, also a no-no.

Feature request:

We need a way for an Assembly BOM (which can auto-assemble) to also produce a “by product”. While the current BOM only allows for a wastage % or wastage qty per product line, we could add an optional “By product" field which works in conjunction with the wastage fields. This assumes a one-to-one relationship between the input product and the by product. The wastage % or wastage qty would always produce one unit of the by product. For example:

BOM for ALU-T50-2M: Aluminum T-Profile 50mm (2m length)

Product - Qty - Wastage qty - By product
ALU-T50-3M - 0.667 - 0.333 - ALU-T50-1M

and

BOM for PVC-TRUNK-100-2M: Plastic trunking base and cover, 100mm wide (2m length)

Product - Qty - Wastage qty - By product
PVC-BASE-100-3M - 0.667 - 0.333 - PVC-BASE-100-1M
PVC-COVER-100-3M - 0.667 - 0.333 - PVC-COVER-100-1M

Note for implementation: Ideally for a sale, assembly jobs should be submitted per line and re-assessed before deciding whether the next line needs an assembly to run. e.g. If a sale includes 1x2m and 1x1m of the same product then we don't need to run two assembly jobs and use up two lengths of the input material. But this scenario is not likely to occur frequently.

A much more complex solution using Production BOMs would be to allow (1) automatic loading of a production job when a sale is created, combined with (2) an option on Production BOMs to allow stock availability to propagate though the BOM.

(For the record only: I also considered an alternative Assembly BOM solution which would allow us to define multiple “output” products for a BOM but that approach does not allow the wastage items to be kept separate if there is more than one input product in the BOM. It has to assume that all the input products are combined first, and therefore any outputs can only be a portion of the combined material. You quickly start re-inventing a Production BOM…)