Optimal part orientation in Rapid Manufacturing process for achieving geometric tolerances

Rapid Manufacturing (RM) processes have evolved from the Rapid Prototyping (RP) paradigm and are increasingly being used to manufacture parts, tools and dies in addition to prototypes. The advantages of RP methods to produce complex shapes without the use of specialized tooling can naturally be extended to RM processes. For RM to be accepted as a mainstream manufacturing process, parts created by RM have to consistently satisfy critical geometric tolerances specifications for various features of the part. This paper investigates the relation between cylindricity tolerance, one of the key form tolerances, and part build orientation in layered manufacturing. The effect of build orientation on cylindricity error is analyzed by three methods: first by a simple analytic method, second by simulating the manufactured surface using a CAD (Computer Aided Design) file of the part and third by using an STL (Stereolithography) file. The mathematical relationship between cylindricity error and part orientation in a RM process is modeled and critical feasible regions for cylinder build orientation are calculated. A graphical technique for calculating the optimal build orientation for a part with multiple cylindrical features is also developed and presented in this paper. This method is tested and validated with the help of a test case and the results are provided in the paper.