Stereolithography accuracy, QuickCast™ & rapid tooling

Abstract

Over the past six years Stereolithography has undergone substantial advances in speed, material properties and accuracy. As a result, the technology has evolved from a ‘curiosity’ capable of generating only rough three dimensional objects intended primarily for geometric visualization, to a practical means of rapid and economically producing accurate patterns for direct shell investment casting, and very recently, for the fabrication of ‘Rapid Tooling’. Documented accuracy advances over this period will be presented. The QuickCast™ technique for generating shell investment casting patterns without tooling, was released by 3D Systems in October 1993. Since then over 5000 QuickCast patterns involving more than 1000 different geometries have been successfully cast in twenty alloys by thirty different foundries. Numerous organizations have proceeded directly from a CAD model, to a QuickCast pattern, to a functional mental prototype within three weeks! As a consequence, users have saved substantial time and money, and the acceptance of QuickCast by industry has been remarkable. Nonetheless, QuickCast 1.0 exhibited six shortcomings. First, the removal of supporters often caused ‘pinholes’ in downfacing surfaces. Second, both up-facing and down-facing surface quality was poor. Third, drainage of uncured liquid resin was problematic for geometries such as the thin trailing edge of an airfoil. Fourth, generating ‘vents’ and ‘drains’ required manual drilling after the pattern had been built. Fifth, the void ration (i.e., fraction of the pattern volume ultimately filled with air) was limited to about 65%. And sixth, the yield of Grade C or better castings was about 80%. This presentation describes the basic ideas behind the evolution of version QuickCast™ 1.1. Specific data is presented relating to: (1) a dramatic reduction in the incidence of pinholes, (2) substantial improvements in both up-facing and down-facing surface quality, (3) enhanced resin drainage, (4) the development of software to enable user-selectable vent and drain hole locations and diameters directly into the STL file, (5) measured void ratios as high as 83%, and (6) foundry yields in excess of 95%. The impact of these advances on Rapid Tooling is discussed, with special emphasis on improvements in both pattern and casting accuracy and surface finishOver the past six years Stereolithography has undergone substantial advances in speed, material properties and accuracy. As a result, the technology has evolved from a ‘curiosity’ capable of generating only rough three dimensional objects intended primarily for geometric visualization, to a practical means of rapid and economically producing accurate patterns for direct shell investment casting, and very recently, for the fabrication of ‘Rapid Tooling’. Documented accuracy advances over this period will be presented. The QuickCast™ technique for generating shell investment casting patterns without tooling, was released by 3D Systems in October 1993. Since then over 5000 QuickCast patterns involving more than 1000 different geometries have been successfully cast in twenty alloys by thirty different foundries. Numerous organizations have proceeded directly from a CAD model, to a QuickCast pattern, to a functional mental prototype within three weeks! As a consequence, users have saved substantial time and mo...