Sir,
Though you have used the term sub contracting process, however the process is nothing but job work process and it is therefore advisable to follow procedure prescribed under noti no. 214/86 CE.
The above procedure is required if you are registered under central excise and also making duty payment on finished goods manufactured in your factory premises.
You may issue job work challans for issuance of raw materials and for receipt back of subassembly material from the subcontractor if you are registered under central excise, else you may use Ordinary challans books which are available in the market.