So, and ERP inventory is tracking whatâs happening in reality. If you have 100 on the shelf, you say you have 100 in ERP inventory. You use 25 on the shelf, you take 25 out of erp. You now have 75 on the shelf and 75 in ERP. This is the ideal matching of how itâs âSupposedâ to work. In this case, you canât ever have negative of something in real life, so you wouldnât have negative of something in ERP land.
Now bring some real life transaction hygene into the mix and play with the timings.
You have 10 on the shelf. Erp says that you have 10. You have a job that needs 100. That morning you get a shipment of 500, but the receiving people are busy and donât get that recorded right away, because there is a stack of paper to go through is sitting on their desk. This is pretty typical. But they knew that the production guys needed it to keep going or the production guys pilfered the receiving area to see if they were there.
Now the production guys finished there 100 parts. Backflush needs to issue the 100 parts, but ERP thinks you only have 10. If ERP stops at 0, there are 90 parts that donât get issued that they physically used. Later that day, receiving does there paperwork and receives the 500. Now ERP says that you have 500, but 90 of those were actually used so in reality you really only have 410.
If you allowed negatives, the inventory would have backflushed down to -90. Then the receipt would have happened and you would be back to 410, like it should be.
without negatives
10-100 = 0
0+500 = 500
with negatives
10-100 = -90
-90+500 = 410
So negatives are necessary to allow for some flexibility. In the timing of transactions.
Also, there is basically the same scenario with material locations. If the backflush bin runs to 0, and it canât go negative, when you move material into that bin in ERP land (mirroring what you did in real life just out of order) the amount will be off.
So , negatives should definitely, absolutely be investigated and fixed (exception dashboards are great for this), but simply not allowing negatives simply covers up and creates more problems than is solves.
Even if you arenât backflushing, this will cause the same problems, because if you have not allow negatives on, and someone is trying to physically move/issue parts that they can see, but the system says âThis will result in a negativeâ, they should investigate and go to receiving and say âHey receive this so I can do my crapâ⌠But do they?
The reason Backflushing allows negatives, even when you are set up to not, is that when you are making a manual transaction, and the system stops you, a person is getting that message and has to (is supposed to anyway) do something about it. With backflushing, there is no one to send the message to, and it would lead to this error where epicor says you have more than you do.
Anyways, thatâs my soap box for the day.