Just I want to know how to enable the search by product name in the item number look up in the purchase order and sales order screen
You'll need a modification for that as this field is only a 'display' field. The actual product name is saved in a separate table per language. You can however search directly on the search name.
Greetings, Gertjan van der Linden | Dynamics AX Solution Architect
In AX2012 R3 you can use the keyword search for this.Only available for sales orders though.