Describe the laser and laser scanning importance in liquid based RP systems.
In liquid-based rapid prototyping (RP) systems, such as Stereolithography (SLA), the laser and laser scanning system are of paramount importance. They are the core mechanisms that enable the conversion of a digital design into a physical object with exceptional precision and detail.
The Role of the Laser
The laser serves as the energy source that drives the chemical process of photopolymerization. A UV laser is used because the liquid photopolymer resins are formulated with a photoinitiator that reacts specifically to ultraviolet light.
Energy Source: The laser emits a highly focused and powerful beam of UV light. This beam has the precise energy and wavelength required to trigger the chemical reaction that solidifies the liquid resin.
Solidification: As the laser strikes the surface of the resin, it cures and hardens the material at that exact point. This allows the system to build the object layer by layer, starting with a liquid and ending with a solid.
Precision and Resolution: The laser's ability to be focused down to a very small spot size is what gives SLA its superior resolution. The fine point of the laser allows for the creation of intricate details, thin walls, and fine features that are not possible with other methods.
The Role of the Laser Scanning System
The laser scanning system is the mechanism that directs the laser beam to "draw" the shape of each layer. This is typically accomplished using a pair of computer-controlled mirrors, known as galvanometers.
Beam Steering: The galvanometer mirrors rotate with extreme precision to deflect the laser beam in the X and Y axes across the surface of the resin vat. By controlling the angle of these mirrors, the system can trace the exact cross-section of the part for the current layer.
Speed and Accuracy: The galvanometers are capable of moving at very high speeds, allowing for rapid tracing of complex shapes. The accuracy of their movement is critical for ensuring that the dimensions of the final part are faithful to the original digital model.
Drawing the Layer: The laser scanning system essentially "draws" each layer, solidifying the resin one vector at a time. The laser turns on and off as it moves to create the solid and hollow parts of the design.
Importance in the RP Process
The combination of a powerful, focused laser and a high-precision laser scanning system is the reason why SLA is known for producing parts with:
High Dimensional Accuracy: The laser's fine spot size and the precise control of the scanning mirrors allow for very tight tolerances, often less than 0.05 mm, making it ideal for functional prototypes, molds, and parts with critical fit requirements.
Exceptional Surface Finish: The point-by-point solidification process results in parts with an extremely smooth surface finish, which minimizes the need for extensive post-processing like sanding.
Intricate Details: The small spot size of the laser allows for the creation of extremely fine and delicate details that would be impossible with other methods.