Deassignment of Back to Back Work Order

Hi, 

Our current business process has us creating BTB work orders during Sales Order creation. Sometimes, the material produced from the resulting BTB work order is needed to fullfill a different, more urgent sales order. 

We were originally consulted that we could break this link using the assignment workbench, but that does not appear to be the case. We are now being told that the only way to break this link is to delete the sales order. 

We're not happy with this response. If production tracking has already occurred and QC performed, the material is going to be allocated to the original Sales Order. We can deallocate the material and reallocate it to a different order, but there will still be a link between original SO and WO. 

The overall question is - how can we break the link between a BTB WO and an SO? 

Thank you.