By: Lilli Manolis Sherman

Stronger, tougher, stiffer, faster, and better-looking materials reflect the growing interest in rapid-prototyping and rapid-tooling technologies that can significantly decrease product development time and cost. Recent introductions include five stereolithography (SL) resins aimed at producing more functional prototypes. Also new are two colored resins for an inkjet-style desktop.

Stronger, Whiter SL
Moving rapid prototyping closer to direct manufacturing has been a key focus of materials development at DSM Somos, according to Montgomery. New materials aimed in this direction are Somos 9420 EP-White, a liquid epoxy-based photopolymer said to combine the mechanical properties of polypropylene with appearance similar to white injection molded materials. DSM says the resin is proving useful for functional prototypes of snap-fit parts, living hinges, and patterns. It is described as strong, resilient, and less likely to break than other SL resins when performing fit-and-function tests. Living hinges made from the material reportedly withstand repeated flexing without breaking, unlike most SL resins.

Two other new SL materials are produced with Somo's novel oxetane chemistry, first used in '01 to develop WaterShed 11120, an ABS-like SL resin. New ProtoFen 0-XT Clear and White boast even faster processing speeds, greater accuracy, and higher HDT (70 C with uv post-treatment and >100 C with heat treatment). Related to the epoxy family, oxetane chemistry reportedly produces faster photocures, higher green strength, and better resistance to moisture for higher dimensional stability.

A combination of high impact strength and elongation is touted for Huntsman Advanced Materials' new RenShape SL 7800, a clear amber epoxy acrylate photopolymer designed to produce high-accuracy models and functional prototypes. Huntsman expects the new material to allow users to build robust parts as well as QuickCast investment casting patterns from a single vat of material, eliminating the need to switch photopolymers.

SL 7800 exhibits good green strength, is easy to clean up, and is said to require minimal part finishing. Once cured, the material exhibits an 87 Shore D hardness, flexural modulus of 330,000 to 380,000 psi, elongation of 10% to 18%, notched izod impact of 0.73 to 1.1ft-lb/in., and HDT of 144 F. It is said to be the first SL resin to be formulated with significantly reduced antimony content and conforms to FDA-approved USP Class VI testing for use in medical modeling and prototyping.

Filled Composite for SL
NanoTool is the third resin in DSM Somos's line of reinforced composite materials - filled liquid epoxies - for SL. It follows the 2003 launch of ProtoTool 20L, said to offer stiffness up to 300% higher than unfilled resins plus ultra-low shrinkage and high heat resistance. And it follows the 2004 introduction of NanoForm 15120, the first nanocomposite for rapid prototyping, which offered enhanced stiffness and accuracy with the processing ease of unfilled resins.

The new composite is said to combine the best features of its two predecessors. It boasts more than 30% faster processing and ease of secondary operations, further advancing the use of SL composites in applications such as wind-tunnel testing, rapid tooling, and metal-plated structural composites.