The SLA process, also known as light modeling or stereolithography, works on the principle of photopolymerization of liquid photosensitive resins. The liquid material can rapidly undergo photopolymerization under the irradiation of ultraviolet light of a certain wavelength and intensity, and the molecular weight sharply increases, and the material changes from a liquid state to a solid state. The liquid tank is filled with liquid photocuring resin. Under the action of the deflection mirror, the laser beam can scan on the liquid surface. The scanning track and the presence or absence of light are controlled by the computer. When the light spot is hit, the liquid is solidified. At the beginning of the forming, the working platform is at a certain depth below the liquid level, and the focused spot is scanned point by point on the liquid surface according to the instruction of the computer, that is, solidification point by point. When a layer of scanning is completed, the unirradiated area is still a liquid resin. Then the lifting platform drives the platform down to a height, and the formed layer is covered with a layer of resin. The scraper scrapes the liquid surface of the resin with higher viscosity, and then scans the next layer, and the newly cured layer is firm. The ground is glued to the previous layer and repeated until the entire part is manufactured, resulting in a three-dimensional solid model. The SLA method is currently the most studied method in the field of rapid prototyping technology and the most mature method in technology. The parts formed by the SLA process have high precision, the processing precision can generally reach 0.1mm, and the raw material utilization rate is nearly 100%.
Molding technology features
Rapid prototyping technology has several important features:
1) It is possible to manufacture arbitrarily complex three-dimensional geometric entities. Thanks to the principle of discrete/stacking, it simplifies a very complex 3D manufacturing process into a superposition of 2D processes, enabling the machining of arbitrarily complex shaped parts. The more complex the part, the more it shows the superiority of RP technology. In addition, the RP technology is particularly suitable for parts that are difficult to manufacture or even impossible to manufacture by conventional methods such as complex cavities and complex profiles.
2) Rapidity. Design and processing information for a new part can be obtained by modifying or reorganizing a CAD model. Parts can be manufactured from a few hours to tens of hours, with outstanding features for rapid manufacturing.
3) Highly flexible. Complicate manufacturing processes, rapid manufacturing of models, prototypes or parts without the need for any special fixtures or tools.
4) Rapid prototyping technology has achieved two advanced goals pursued by the mechanical engineering discipline for many years, namely the integration of materials (gas, liquid, solid phase) process and manufacturing process integration and design (CAD) and manufacturing (CAM) integration.
5) Combine with reverse engineering (Reverse?ngineering), CAD technology, network technology, virtual reality, etc., and become a powerful tool for rapid product development.
Flow chart
The process of rapid prototyping is as follows:
1) Construction of a three-dimensional model of the product. Since the RP system is directly driven by the 3D CAD model, it is first necessary to construct a 3D CAD model of the workpiece being machined. The 3D CAD model can be directly constructed by computer-aided design software (such as Pro/E, I-DEAS, SolidWorks, UG, etc.), or the 2D pattern of the existing product can be converted to form a 3D model, or the product entity can be Laser scanning, CT tomography, point cloud data, and then use the reverse engineering method to construct a three-dimensional model.
2) SLA laser rapid prototyping
The SLA process, also known as light modeling or stereolithography, works on the principle of photopolymerization of liquid photosensitive resins. The liquid material can rapidly undergo photopolymerization under the irradiation of ultraviolet light of a certain wavelength and intensity, and the molecular weight sharply increases, and the material changes from a liquid state to a solid state. The liquid tank is filled with liquid photocuring resin. Under the action of the deflection mirror, the laser beam can scan on the liquid surface. The scanning track and the presence or absence of light are controlled by the computer. When the light spot is hit, the liquid is solidified. At the beginning of the forming, the working platform is at a certain depth below the liquid level, and the focused spot is scanned point by point on the liquid surface according to the instruction of the computer, that is, solidification point by point. When a layer of scanning is completed, the unirradiated area is still a liquid resin. Then the lifting platform drives the platform down to a height, and the formed layer is covered with a layer of resin. The scraper scrapes the liquid surface of the resin with higher viscosity, and then scans the next layer, and the newly cured layer is firm. The ground is glued to the previous layer and repeated until the entire part is manufactured, resulting in a three-dimensional solid model.
3) Post-processing of molded parts.
The molded part is taken out from the molding system, polished, polished, coated, or placed in a high-temperature furnace for post-sintering, and further enhanced in strength.
Material properties
SLA material
Photosensitive resin is a substrate that is laser-cured and rapidly formed, and its performance characteristics have a decisive influence on the quality of the molded part. Photocuring resins using SL should generally have the following properties:
1) The viscosity is low, and the low-viscosity resin is favorable for the faster leveling of the resin during molding;
2) The curing speed is fast, and the curing speed of the resin directly affects the molding efficiency, thereby affecting the economic benefits;
3) The curing shrinkage is small, and the photosensitive resin undergoes a change from liquid to solid during the curing process. This change often causes linear and volume shrinkage of the resin, and the curing shrinkage causes deformation, warpage, cracking, etc. of the part. Affecting the precision of the molded parts and reducing the shrinkage of the resin is the main goal in the development of the photosensitive resin, and the low-shrinkage resin is advantageous for molding the precision parts;
4) The degree of primary curing is high, which can reduce post-cure shrinkage, thereby reducing post-cure deformation;
5) The wet strength is high, and the high wet strength can ensure that the post-cure process does not cause deformation, expansion and interlayer peeling;
6) The swelling is small, and the swelling of the wet molded part in the liquid resin sample piece in the liquid resin causes the part size to be large;
7) The toxicity is small, which is beneficial to the health of the operator and does not cause environmental pollution.
The main application of SLA molded parts
1) Directly make various resin sample pieces or functional parts for structural verification and functional testing;
2) making fine parts;
3) manufacturing parts with transparent effects;
4) The prototype can be quickly turned into various molds, such as silicone rubber mold, metal cold spray mold, ceramic mold, electroforming mold, epoxy resin mold, lost mold, etc.;
5) Instead of the lost mold in investment casting, it is used to produce metal parts.
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