Laser stereolithography

Venanzi, C. A., W. J. Skawinski, and A. D. Ofsievich (1996) Molecular models by laser stereolithography. In Physical Supramolecular Chemistry, eds. L. Echegoyen and A. E. Kaifer, pp. 127-142. Dordrecht Kluwer Academic Publishers. Second version The Use of Laser Stereolithography to Produce Three-Dimensional Tactile Molecular Models for blind and Visually Impaired Scientists and Students, http //people.rit.edu/easi/itd/itdv01n4/ article6.htm (accessed December 14,2009). 

Duplication of prototype master models (made by special techniques such as laser stereolithography, laser powder sintering, LOM etc.) in polyurethane or epoxy resins by the vacuum casting process within the scope of rapid prototyping . 

FIGURE 4.134 Polymerization processes using the example of laser stereolithography... 

Laser stereolithography machines (Viper SLA, Viper Pro) and polymer printer (Invision) produce 3D Systems. Polymer printing or jetting systems (Eden Series) are from Objet, systems with DLP projectors (Perfactory) of Envsiontec. 

Methods are used to produce the more costly rapid prototypes include those that produce models within a few hours. They include photopolymerization, laser tooling, and their modifications. The laser sintering process uses powdered TP rather than chemically reactive liquid photopolymer used in stereolithography. Models are usually made from certain types of plastics. Also used in the different processes are metals (steel, hard alloys, copper-based alloys, and powdered metals). With powder metal molds, they can be used as inserts in a mold ready to produce prototype products. These systems enable having precise control over the process and constructing products with complex geometries. 

Juodkazis S, Horyama M, Miwa M, Watanabe M, Mizeikis AMV, Matsuo S, Misawa H (2002) Stereolithography and 3D micro-structuring of transparent materials by femtosecond laser irradiation. In Panchenko VY, Golubev VS (eds) Seventh international conference on laser and laser-information technologies. SPIE Proc 4644 27-38... 

Stereolithography is simple in concept and it provides great economies for the design lab as well as for the modeling process. It also provides previously unrecognized challenges for the polymer photochemist, for it is entirely a laser-initiated technology, and the polymerization reactions take place to depths below a finitely thin surface layer. 

In stereolithography the positions of polymerization x and y are controlled by a mirrored scanner which reflects the laser onto the surface of the to-be-polymerized monomer at a point x,y and the z dimension is determined by the position of the elevator, as shown in Figure 5. During the polymerization z, the depth to which reaction occurs, is held constant through the use of a UV photoinitiator that bleaches either not at all or very slowly, relative to the rate of polymerization. 

Our use of bleachable photoinitiators to carry out polymerization at depth opens the possibility of controlling the vertical dimension photochemically rather than mechanically. We have used the photoreduction of Eosin by triethanolamine to sensitize the polymerization of multifunctional acrylates to demonstrate the principle. Irradiation is carried out at 514 nm with an Ar+ laser having a beam diameter of 1.4 mm. The volume of sample irradiated is a small fraction of the total, simulating the conditions found in stereolithography. Because of bleaching of the photoinitiator, the irradiation generates... 

Microfabrication was achieved by micro-stereolithography using a CW Ar+ laser (see Figure 1.164) [3],... 

An acrylic chip was fabricated by stereolithography without an assembly process such as bonding. This fabrication method is a 3D method by solidifying a photopolymerizable resin layer-by-layer via the scanning of a UV laser beam. A special double-controlled surface method was adopted in order to produce a smooth and transparent surface for high-quality optical detection [240]. 

In a search for visible-light photoinitiators for stereolithography, the 6,8-diiodo-, 6-nitro-8-iodo-, and 6-nitro-7-methoxy-8-iodo- and T-benzyl-6-nitro-7-methoxy-8-iodoBIPS [respective Xmax (nm) and first-order half-lives for thermal fading (s) 606, 35 572, 330 568, 70 and 578, 15] were converted to their colored forms by heat or UV irradiation in solution in trimethylolpropane triacrylate containing added coinitiators. The benzyl compound with added A -phcnylglyciiie was the best initiator when irradiated with a 632-nm laser beam.114,115... 

Indirect tooling methods are many. Examples include cast aluminum, investment metal cast, cast plastics, cast kirksite, sprayed steel, spin-castings, plaster casting, electroforming, room temperature vulcanizing (RTV) silicone elastomer (Chapter 2 Silicone Elastomer), elastomer/ rubber, reaction injection, stereolithography,338 344 (Table 17.4), direct metal laser sintering, and laminate construction. 

SFF encompasses many different approaches to additive fabrication, including Stereolithography (SLA), Selective Laser Sintering (SLS), Electron Beam Melting (EBM), Laminated Object Manufacturing (LOM), Fused Deposition Modeling (FDM), and 3D Printing. 

Generally speaking, the stereolithography process works by building the prototype, layer by layer, using a laser beam that solidifies each slice of the model until it is complete. As the model is created, multiple horizontal slices are stacked on top of each other until the model is complete. Most... 

Stereolithography builds plastic parts layer by layer by passing a laser beam (guided by a three-dimensional image) on the surface of a pool of liquid photopolymer. This photopolymer quickly solidifies where the laser beam strikes the surface of the liquid. Once one layer is completely traced, the part is lowered a small distance into the pool, allowing new liquid to cover the completed layer, and then a second layer is traced on top of the first. The layers bond and eventually form a complete, three-dimensional object after many such layers have been formed. A schematic diagram of this process is shown in Figure 6.26. 

The stereolithography system is controlled by the interconnected CAD system, computer-controlled optical scanning system, control system for the platform and levelling wiper or blade for the recoating process (in between laser curing steps). 

Three-dimensional machining (or 3D photopolymerization or stereolithography) gives the possibility to make objects, even with complex forms, for prototyping applications. A laser beam is used for the excitation. Creating 3D microscale structures for microelectromechanical, microoptics and microfluidic applications requires to use high peak power laser pulses allowing a multiphoton (typically two photon) of the photoinitiator at the focal point. 

Other uses include the production of flexographic printing plates from UV-cur-able materials. An interesting application is three-dimensional modeling (stereolithography) in which a solid part is made from a vat of UV-curable liquor by the use of UV lasers controlled by computers using CAD/CAM software. 

Stereolithography " and laser ablation are also used as alternative techniques for the microfabrication for microfluidic devices. 

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