Hi Pradipta,
In ECC by activating DIMP you can combine the multiple planned orders to single planned order. By using MILL_OC tcode you need to select the four planned orders to be combined and define one of the selected planned order as a reference order and execute. A new planned order with combined qty of four planned orders will be created using master data of the reference order. This new order is the combined order.
Read SAP Help for more details.
Combining Production and Process Orders - SAP Mill Products - SAP Library
Thanks & Regards,
Ramagiri