SLA is an additive manufacturing process that belongs to the reduction photopolymerization family. In SLA, objects are created by selectively curing a polymer resin layer by layer using an ultraviolet (UV) laser beam. The material used in SLA is a photosensitive thermoset polymer in liquid form. The light-curing molding process is also often called stereolithography. The English name is StereoLithography, referred to as SL, and sometimes referred to as SLA (StereoLithography Apparatus). This process was patented by Charles Hull in the United States in 1984 and is the earliest developed rapid prototyping technology. Since 3D Systems first launched the SLA commercial rapid prototyping machine in 1988, SLA has become one of the most mature and widely used RP typical technologies. It uses photosensitive resin as raw material and uses a computer-controlled ultraviolet laser to solidify it. This method can simply and fully automatically produce complex, three-dimensional shapes that have been difficult to produce with various processing methods in the past. It has epoch-making significance in the field of processing technology.
1. molding principle of SLA 3d printing technology
Filled with liquid photosensitive resin, the ultraviolet laser beam emitted by the helium-cadmium laser or argon ion laser scans the surface of the photosensitive resin point by point according to the layered cross-sectional information of the part under the control of the control system, so that the thin layer of resin in the scanned area A photopolymerization reaction occurs and solidifies to form a thin layer of the part. After one layer of curing is completed, the workbench moves down a distance of one layer thickness so that a new layer of liquid resin can be applied to the surface of the originally cured resin. The scraper will smooth the surface of the resin with a higher viscosity and then proceed. The next layer is scanned and processed, and the newly solidified layer is firmly bonded to the previous layer. This is repeated until the entire part is manufactured, and a three-dimensional solid prototype is obtained.
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2. Process of SLA 3d printing technology
The production of light-curing rapid prototypes can generally be divided into three stages: pre-processing, prototyping, and post-processing. The pre-processing stage mainly involves designing a three-dimensional solid model through CAD, converting data on the prototype, determining the orientation, applying support, using discrete programs to slice the model, and designing the scanning path. The generated data will accurately control the laser scanner and The movement of the lifting platform is actually to prepare data for prototype production; prototype production is to perform light-curing molding on a dedicated light-curing rapid prototyping equipment system. Before prototype production, the light-curing rapid prototyping equipment system needs to be started in advance so that the temperature of the resin material reaches a preset, reasonable temperature. A certain stabilization time is also required after the laser is ignited. After the equipment is running normally, start the prototype production control software, read the layer data file generated by the pre-processing, and start the stack production. The entire photocuring process of the laminate is completed automatically under the control of the software system. After all the laminates are produced, the system automatically stops. Post-processing: After the prototype stack is produced in the rapid prototyping system, subsequent processing, such as stripping, is required to remove waste materials and support structures.
3. Advantages and disadvantages of the SLA 3d printing process
Advantages of SLA Technology
1. The light-curing molding method is the earliest rapid prototyping manufacturing process. It is highly mature and has been tested over time.
2. Prototypes are made directly from CAD digital models, with fast processing speed and a short product production cycle, without the need for cutting tools and molds.
3. Can we process prototypes and molds with complex structural shapes that are difficult to form using traditional means?
4. Make CAD digital models intuitive and reduce the cost of error repair.
5. Provide samples for experiments that can verify and check the results of computer simulation calculations.
6. It can be operated online and controlled remotely, which is conducive to the automation of production.
Pitfalls of SLA technology
1. The SLA system is expensive to build, and the use and maintenance costs are too high.
2. The SLA system is precision equipment that operates on liquids and has strict requirements for the working environment.
3. Most of the molded parts are resin, with limited strength, stiffness, and heat resistance, which is not conducive to long-term storage.
4. The preprocessing software and driver software require a large number of calculations and are highly correlated with the processing effect.
5. The software system is complex to operate and difficult to get started; the file format used is not familiar to most designers.
4. Development trends and prospects of SLA
SLA technology is mainly used to manufacture a variety of molds, models, etc.; it can also be used to replace the wax pattern in investment casting with an SLA prototype mold by adding other ingredients to the raw materials. SLA technology has faster molding speed and higher precision, but due to shrinkage during the curing process of the resin, stress or deformation will inevitably occur. Therefore, it is the trend to develop photosensitive materials with small shrinkage, fast curing, and high strength. The development trend of stereolithography is high speed, energy savings, environmental protection, and miniaturization. The continuously improving processing accuracy makes it possible to make great achievements in the fields of biology, medicine, microelectronics, and other fields.
