Stereolithography Epoxy Resins SL 5170 and SL 5180: Accuracy, Dimensional Stability, and Mechanical Properties

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Pang, Thomas H.

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Stereolithography (SL) resins based on epoxy chemistry provide significantly improved overall part accuracy, dimensional stability, and mechanical properties relative to the earlier acrylate SL resins. In July, 1993, epoxy-based SL 5170 resin was introduced for use on the SLA-250 system. In March, 1994, the epoxy-based resin for the SLA-500 system, SL 5180, was also released. These epoxy resins have minima11aser-cure and post-cure shrinkage, resulting in extremely low curl and distortion. Overall dimensional accuracy has also improved. Standard User-Parts built in SL 5170 on the SLA-250, and now, SL 5180 on the SLA-500, have recently achieved the highest level of dimensional accuracy from a statistically significant number of measurements taken in the x, y, and z directions. Diagnostic test results presented in this paper show that these epoxy-based resins are now capable of producing extremely flat parts when required. SL parts built in these resins also exhibit superb dimensional stability in the lasercured state, as demonstrated by the "Green" Creep Distortion diagnostic test. Dimensional stability in the laser-cured state is critical, especially for SL parts having the characteristic quasi-hollow internal structure, generated using the QuickCast™ build style. Creep results are presented in this paper. Furthermore, the overall mechanical properties of these epoxy resins were measured according to the ASTM standards for plastics. Tensile, flexural, and impact properties for the epoxy-based and acrylatebased SL resins are presented in this paper. Mechanical properties ofthermoplastics, acrylic plastic (PMMA) and medium impact polystyrene, are also presented for comparison. The data shows that the mechanical properties of epoxy-based SL 5170 and SL 5180 are comparable to, or exceed those of acrylic plastic and medium impact polystyrene. For applications that require greater mechanical strengths than SL 5170 and SL 5180, metal parts can be obtained using QuickCast. QuickCast, made possible with the development of these epoxybased SL resins, is the key to successfully utilizing SL parts for shell investment casting applications, and the generation of precision metal components directly from SL parts. Furthermore, when a "negative" core and cavity pair of a part geometry is produced in metal using QuickCast, tooling is obtained. Prototype, and eventually, production functional parts may then be ultimately injection molded in the QuickCast tooling, using the desired engineering thermoplastic material.


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