A Surface Texture Modeling System for Solid Freeform Fabrication

Solid Freeform Fabrication, SFF, is a set of manufacturing processes that fabricates parts as a bonded stack of individual layers. The Three Dimensional Printing process, 3DPTM process, is an SFF technology developed at MIT. It builds layers by ink jet printing binder onto the surface of a bed of powder. The bed of powder is lowered and fresh powder is spread onto the bed. As subsequent cross sections of the part are printed, the part exists, submerged in the powder bed. Access to the individual layers as they are fabricated gives access to the interior structure of the part. This approach allows the part to have high geometric complexity. In this work a designer centric Computer Aided Design system is proposed to allow the interactive creation of functional surface texture on mechanical parts. This system is structured to behave like a VLSI CAD system, which offers substantial process capabilities. The requirements for a Mechanical CAD, MCAD, system to behave like VLSI CAD are determined to be: 1. That the informational model of the unit cell of texture be separable into distinct logical subsets.2. That manipulations on either subset not violate the logical consistancy of the other subset. This thesis shows that geometric dimensions and tolerances carry the essential information of the model of a unit cell of functional texture. A variety of Unit Cell editors are evaluated according to their ability to meet the desired system criteria. A tool, Swiss Solid Geometry, SSG, for the design of unit cells of functional texture is developed, that fullfills requirement #1. SSG is an approach to MCAD modeling that combines geometric primitives in the manner of Constructive Solid Geometry, however the primitives of SSG, are different. They consist of simple objects such as lines, but includes the spatial envelope around them of a fixed offset. Also, they are used to represent both positive and negative regions of space. The placement of the individual replications is established by a mesh, that covers the intended 3D surface region. A meshing algorithm is developed that regularizes the mesh by directly utilizing the dimensional tolerances specified in the process of Unit Cell design. The geometric dimensions are instantiated as standalone geometric entities that push and pull on the nodes of the mesh in order to bring their length into dimensional tolerance. This method fullfills requirement #2, and it is implemented into a CAM software called Vari 4. The modularity of the CAM software, Vari 4, is described in detail. Thesis Supervisor: Professor Emanuel Sachs Title: Professor of Mechanical Engineering