The criteria for combining deliveries is:
1. Same delivery date
2. Same ship to party
3. Same plant
4. Same shipping point
If you don't want deliveries been combined while create delivery note with VL10B (for example), you can change the customer master data with XD02, in the sales area view, do not check "Order combination".
Reference: Combine deliveries in VL10B with different Delivery dates | SAP Community