Why is it that the SAP system does not allow quantity zero for components in a BOM? I have seen a number of people posting that this is a need for them in their business, but it seems that most of the consultants that respond to this request can't fathom why anybody would have a need for a zero quantity for a component in a BOM. When the various examples are explained to them, they suggest using work-arounds instead of fixing the underlying problem.
The best I've seen is that people suggest a work-around where you use a quantity of .001 in the BOM. But this doesn't fix the underlying problem that indeed there are many instances where a zero is the most accurate number you can put in the quantity field. Here at Varian Medical Systems, we currently have the .001 work-around in more than 25,000 occurrences in our BOM's. It would be nice to have the correct solution provided by SAP, which would be to allow a quantity of zero. Of course you can't divide by zero, and this confuses some programmers who argue against providing this solution, but from a user perspective, it is needed. In every case where we use a quantity of zero, the production and costing relevancy are turned off, so no MRP demand for zero is created. Apple Computer became the largest company in the world by capitalization by designing products and software that work the way most human beings think, not the way a programmer thinks. I will go even further to suggest that the quantity field in BOM's should allow for alpha and special characters in addition to numbers. Having a hard edit that forces the production and costing relevancy to be turned off in these instances would address any concerns about calculating component requirements.
Below are nine reasons why you need to allow zero as a quantity in a BOM.
Reasons Why You Need
Qty 0 in BOMs
- A/R Materials (As Required): Lubricants or Adhesives required to build a product are not rationed out by the drop, or by the bottle, but left to the assembler to determine the appropriate quantity based on SOE instructions. On the drawings, Engineers will call out A/R (as required) in the qty box (see DWG BOM 1).
- Variable qty items: Shims or trimmer balance weights are issued as one each, but cannot be determined until the assembly of the product occurs. As appropriate, differing quantities are issued to the product to fit the need for the specific machine being built (see DWG BOM 2)
- REF Materials. Quite often, assembly drawings will need to show the mating interface with other parts of the machine which are not actually part of the assembly. In this case, we would show the interface as REF on one assembly, but as quantity 1 on another assembly (see DWG BOM 3).
- Tooling: Tooling needs to be tracked and linked to the assemblies that it is used on. But it does not get consumed on a one-for-one basis with the assembly. So we want to use SAP where-used capability by linking each tool within each BOM where it is relevant, but show the quantity as 0. On the drawing tooling is called out as REF (see DWG BOM 4).
- Must-Choose Optional Choices: On assemble-to-order products, one of several different choices may be needed for various parts of the machine configuration. These must-choose options are items where the machine will not be functional without one of the available choices (such as three choices of tires on a car. The way these options are handled on the drawings is by showing them with Alpha characters in the quantity field where you must choose one of the A items, one of the B items, and one of the C items to have a fully configured, workable machine. On the BOMs, we call out all the choices as qty 0, with a note to refer to the customer sales order for which choice has been made (see DWG BOM 5).
- May Choose Optional Choices: On assemble-to-order products, in the case where an option is a may choose option you may either order or the option or not; the machine will operate fine either way. In this case the option would show on the drawing with an * in the quantity field and on the SAP BOM, you would call out quantity 0 with a note to refer to the customer sales order for which choice has been made (see DWG BOM 6).
- Acceptable Substitute Items: In some cases two interchangeable part numbers may be acceptable to use in the product. For example, two manufacturers make RF drivers that are fully compatible and work fine in our machine. But Field Service required the use of two distinct part numbers for reliability tracking, so the drawings allow for either part A or part B to be used. Depending on the current cost/reliability/availability of the two parts, we will designate one item as quantity 1 in the SAP BOM and the other item as quantity 0. On the drawing, you call out one item as quantity 1 and the other as quantity * with a note explaining the ability to substitute one item for the other as desired (see DWG BOM 7).
- JIT KIT support: In order to efficiently procure and build product, we may create documents that are sets of material that can be procured on a single PO. So we end up with one set of drawings depicting way the machine is built and resides in the field for the next X years, and another group of drawings defining sets of material in special packaging aiding in efficient build of the product. On both groups of drawings the quantity would be 1 (or whatever qty is needed on the machine) but in the SAP BOMs, only the JITKIT BOM would have a quantity >0. The manufacturing BOMs would call out the set as qty 1 but all the individual pieces of the set would be called out as qty 0. In that way when you look at the where-use of a component in one of the sets, you would be able to determine what assembly drawings the item appears on, and also which drawing is the active driver of the material (see DWG BOM 8).
- Request to move certain items to later in the build process: Assembly drawings usually show the assembly in the finished state, as the assembly will look out in the field being used by the customer. But internally in the factory we often desire the assembly to be built to an unfinished level with some pieces missing to allow for easier testing of the full product. Or we may choose not to put the final cosmetic touches on a machine until close to the shipping point in order to avoid scratching or denting of exterior surfaces. For example, a modulator assembly will be built with recyclable in-house panels and only have the finished panels swapped out for the recyclable tooling panels at the clean, pack, and ship operation. Other assemblies will have access panels omitted altogether to allow for easy access for machine tuning in final test. These missing panels would be added at clean, pack, and ship. So in the SAP BOMs, we change the quantity from 1 to 0 in the assembly BOM, and create separate BOMs showing quantity 1 with the clean, pack, and ship items that complete the assembly built days or weeks earlier (see DWG BOM 9).