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ALEX DEN OUDEN |
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Oude techniek en werktuigbouw, industriële geschiedenis en archeologie |
Historical engineering and technology, industrial archaeology and history |
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In laser scanning stereo lithography, a liquid photopolymer resin is selectively cured using an ultraviolet beam from a laser. The laser beam is focused onto the surface of a vat of this resin. It scans the surface in parallel lines. In the moving focal point of the beam, the resin is hardened almost instantaneously. In this way, a thin (virtually 2D) layer is built of a shape corresponding to a horizontal slice of the final model. The machine's software slices the CAD model of the 3D shape to be produced into the required layers. The computer directs the laser beam by means of a set of galvanometer-controlled mirrors.
Just below the surface of the liquid photopolymer, a horizontal elevator tray supports the layer of cured resin. As soon as a layer is finished, the elevator tray is lowered one step (one layer thickness) to submerge the finished layer and fresh (liquid) resin floods onto the surface, covering it ready for the next layer. When the tray elevation step is set correctly, each layer neatly bonds to the previous layer.
In this way, the process is repeated, building layer after layer, until the complete model is finished. It is fully submerged in liquid resin and rests on the elevator tray. After the final layer is scanned, the elevator tray is slowly raised. The model emerges from the bath and can be removed for final curing and cleaning up.
Laser scanning stereo lithography machines can be operated with various ultra-violet emitting lasers depending on power requirements. This gives the possibility of exchanging lasers or upgrading the system as required. The laser output is controlled from the computer, and for the lower power option (100mW Argon) no external cooling water is required.
The laser beam is focused using a flat field lens, which enables a laser spot-size of 0.1-0.15 mm to be maintained across the entire vat. The two-dimensional galvanometer scanning system offers a vector speed of up to 10 m/s at the liquid surface, positioning accuracy ± 0.05 mm.
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