Techniques and systems for computer aided design of physical structures using an object splitting design process that optimize manufacturing efficiency are described. A described technique includes splitting, by a computer program, a three dimensional model of an initial object into an up skin region and a down skin region based on an analysis of draft angles along at least one surface of the three dimensional model of the initial object. The technique further includes producing, by the computer program, first and second three dimensional models of respective first and second objects in accordance with the up skin region and the down skin region to create separate first and second physical structures using one or more computer-controlled manufacturing systems such that the first and second physical structures are combinable to form a combined physical structure.