MULTI-LAYERED COMPOSITES USING PHOTOLITHOGRAPHY

The mechanical properties of the parts made using solid freeform fabrication technologies are limited by their resins used. Previous research has shown that the mechanical properties of these parts can be enhanced substantially by using glass and fiber reinforcements. However, all of the published data is for single layered composites, which does not demonstrate its feasibility to manufacture multilayered real objects. In this paper experiments carried out to build multi-layered parts with glass fiber tow as reinforcement in a matrix of photopolymeric resin are described. These specimens are then tested in uniaxial tension and three point bending to determine their improvement in mechanical properties. The experimental data shows that the tensile strength and tensile modulus increased linearly with the volume fraction of the fiber in the composite, thus demonstrating that the trends observed in single layer composites can be also seen in multi-layered composites. Introduction In the past 10 years, solid freeform fabrication (SFF) technologies have allowed the design engineer to produce a working model of a part without the need for tooling, advance planning, and often within hours or days, instead of months. As improvements or revisions are necessary, the part can be redesigned easily before it is prototyped again, and the process can be repeated as many times over a period of days to arrive at the final design. Many of the SFF technologies utilize polymers to make their parts, either using a certain wavelength of radiation (as in photolithography) or applying localized heat of fusion (as in selective laser sintering). One of the drawbacks of these processes is the compromise in mechanical properties due to those of the pure polymers. These parts are of lower strength than those made using commercially viable processes. One way to strengthen these parts is to re-enforce the parts with high modulus glass, quartz or carbon fibers. In work done at Clemson University over the past five years [1-6], the process of photolithography has been expanded as a rapid prototyping technology by producing composite parts using glass and quartz fiber as reinforcement. The prototype is generated by reinforcing by selectively laying fibers in situ to improve the mechanical properties. These studies have shown that the strength of liquid resin based polymer parts can be increased by up to an order of magnitude. with a very small percent of addition of glass or quartz fibers. Because no real component is made up of a single layer, it is necessary to detennine the effect of multiple layers in the build process, and to use more than uniaxial testing to determine the mechanical properties of the parts. Objective The objective of this experiment was to build and test multi-layered parts to see if the single layer technology could be applied to manufacture multi-layer, real composite parts. The tensile strength, tensile modulus and modulus of toughness would be studied to measure the enhancement of mechanical properties.