A Parallel Slicing Algorithm for Solid Freeform Fabrication Processes

Slicing can accountfor more than 60% ofthe time to prepare apartfor building on astereolithographic apparatus. To improve the preparation time, a parallel slicing algorithm was developed. The algorithm was run on a Butterfly GP1000 using 2,4,8, 16, and 32 processors and superlinear speedup was observed due to high memory requirements. The parallel algorithm can reduce slice times by up to 92% on 16 concurrent processors as compared to a single processor. INTRODUCTION Stereolithography is one of several different Solid Freefonn Fabrication (SFF) technologies available today (Ashley, 1991). The most common stereolithography apparatus (SLA) is the SLA 250 from 3D Systems (Valencia, CA). Because of its popularity, the initial software development described in this paper was aimed at this machine; however, it is believed that the concepts can be extended to any of the technologies. The preparation of a part, detailed by 3D Systems (1989), begins in a CAD system. A solid model is created to represent the part. The part is then converted to a stereolithographic fonnat (stl) file. This file contains a set of triangles which define the surface of the part and the outward pointing nonnals to these triangles. Next, this faceted representation is preprocessed for building in the SLA. First the part is supported, and then it is sliced by another computer. Then the files containing the layers are sent to a third computer for merging, preparation, and reconstruction in the SLA. The parts are built layerby-layer from the bottom up in layers 0.0025 to 0.030 inch thick. One of the biggest complaints of the users of this technology is that the preparation time before building is too long. Slicing in particular can account for 60% or more of the time between the CAD system and the SLA. Because of this, efforts are underway to reduce the slicing time. This paper discusses techniques for improving the slicing speed by employing parallel architectures.