As additive manufacturing (AM) emerges as an end-of-use product manufacturing process, design for additive manufacturing (DFAM) as a new design philosophy receives more and more attention. However, current DFAM research focuses on downstream and part-level design activities such as structural optimization and design rules. Design freedom enabled by AM such as, part consolidation and function integration has not been fully investigated. These design freedom forces designers to rethink about assembly-level design so as to embrace integrated functionality. To understand how to integrate AM characteristics into design process, three questions are investigated: 1) why does conceptual design need to be redone for assembly? 2) what has changed by AM in design concept generation? 3) how to do conceptual design in AM context? Afterwards, a conceptual design framework is proposed to aid design flow management. In the end, a throttle pedal redesign case is demonstrated as verification of the proposed design framework.