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Keywords
Stereolithography, Polymers, Fabrication
Abstract
A new fabrication process for rapid prototyping is proposed in this paper. Optical and thermal effects are simultaneously used in this process to locally induce a phase change in a liquid resin. This phase change phenomena is used to 11 write" three-dimensional shapes or patterns. Such objects or patterns can involve macroscopic engineering prototypes through to nanostructures for exploitation in waveguiding and photonic crystals. Several advantages can be achieved through this new process, in terms of accuracy, cost and time.
Introduction
The most important rapid prototyping technologies currently available or under research are shown in Figure 1. Among them, stereolithography (SL) (Hull, 1986) is the most popular process. SL involves the curing or solidification of a liquid photosensitive polymer by a laser beam scanned across its surface. The laser supplies energy that induces a chemical reaction, bonding large number of small molecules and forming a highly cross-linked polymer. As the reaction proceeds, the viscosity of the resin in the direct vicinity of the light spot increases until vitrification takes place, freezing the curing process and promoting an incomplete curing reaction. The residual unreacted polymer could be the source of oxidation and degradation that may limit the durability of the models obtained.
The first layer is formed on an elevator platform, which is then lowered to allow new liquid resin to flow onto the working surface. This process is repeated, with each new layer adhering to the previous one. Once the model is finished, it undergoes a series of post-processes that makes it safe to handle. The insufficient extent of cure obtained during the building process means that it is necessary to complete the cure in an ultraviolet (UV) chamber during the so-called post-cure operation. Important consequences of insufficient polymerisation are warping due to relaxation, diffusion and evaporation of low-molecular weight components, and post-cure shrinkage due to density changes associated with the post-cure of the liquid resin trapped in the lattice structure (Flach and Chartoff, 1994; Weidemann et al., 1995).
An alternative process to SL is proposed in this research paper. This process, designated by stereo-thermal-lithography (STLG), comprises both heat and UV radiation effects, solving some of the major limitations of conventional SL process, such as efficiency,...