JEC COMPOSITES MAGAZINE - Issue #36 - October 2007 - 58

KNOW-HOW Prototyping Next-generation stereolithography materials improve prototype functionality Significant advances in materials performance have the potential for expanding the use of stereolithography for the production of ultra-durable prototypes and initial parts. exposed layer solidifies, the platform drops by a single layer thickness and the next cross-section is traced. The process continues until the part is complete. It is then cleaned and post-cured in a UV oven or thermal oven (figure 1). LAURENCE MESSÉ GROUP LEADER, HUNTSMAN ADVANCED MATERIALS T he pressure to bring new part designs to market as quickly as possible continues to drive design engineers and their prototyping partners. To support the burgeoning demand for high-quality, rapid prototypes, numerous processes and materials have been introduced over the past decade. The overwhelming majority of new technologies are based on the ready availability of computer-aided design (CAD) data that is used to build threedimensional solid models and prototypes. The key rapid prototyping (RP) methods in use today are stereolithography (SL), selective laser sintering (SLS), fused deposition modelling (FDM) and 3D printing (3DP). Each process is “additive”, i.e. parts are comprised of numerous cross sections or layers of material. These additive methods feature a range of strengths and weaknesses necessitating the selection of the best technique for a project according to its specific requirements. Fig. 1: Diagram of the SL process RP technology overview In general, before choosing a rapid prototyping method, design engineers must not only consider the materials used in the process, but also the surface finish, accuracy and physical performance properties of the end parts. RenShape® SL 7800 resin is a next-generation hybrid photopolymer that combines high strength and flexibility for the production of high accuracy models and functional prototypes. Photopolymers used in the SL process include acrylates and acrylate/epoxy hybrids. Each resin exhibits its own unique set of physical properties that determine its suitability for building concept models, form-and-fit parts or functional prototypes. Photopolymers are formulated to simulate clear thermoplastics, polypropylene and opaque white ABS. The SL process is recognized for its ability to quickly build accurate models and prototypes with an excellent surface finish that requires little secondary finishing. Parts are easily primed and painted or plated. Drawbacks of conventional acrylate and first-generation acrylate/epoxy hybrid SL materials include high moisture sensitivity that can decrease dimensional stability and mechanical performance in humid environments and over extended periods of time. Selective laser sintering Like SL, SLS uses a high power laser to solidify material cross sections to form a three-dimensional part. However, in this process, the laser fuses small particles of plastic, metal or ceramics to form the solid part. The SLS process and the variety of durable SLS materials are ideal for the production of functional prototypes and parts that can withstand exposure to high heat and chemicals. Historically, SLS has been known for the ability to produce stronger parts with better mechanical strength than SL. However, the overall SLS process is slower than SL and the resulting prototypes are typically less accurate than SL parts. Because the base materials used in SLS are powders, the standard finish on prototypes is somewhat porous and not as smooth as the surface on SL parts. Stereolithography In the SL process, a metal platform is lowered into a vat of photopolymer – a liquid resin that cures after exposure to UV laser light. To build a part, the laser traces successive cross-section layers of a design onto the surface of the photopolymer. As each light- JEC Composites Magazine / No36 October - November 2007

JEC COMPOSITES MAGAZINE - Issue #36 - October 2007

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #36 - October 2007