Brief introduction to the process of three-dimensional printing rapid prototyping manufacturing
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This molding method is one of the world's deepest research, the most mature technology, and the most widely used rapid prototyping method. In 1984, the three-dimensional printing technology was still in the laboratory research stage. In 1988, the first operational manufacturing system was commercialized. In 1989, American Chryster first applied this technology in engineering practice, but it did not receive enough attention until 1992.
1) Process principle
SLA-Stereolithagraphy Apparatus, also known as stereolithography, photocuring, etc. The basic process principle (shown in Figure 4) is to use CAD to perform the 3D geometry of the required prototype, generate data files and process the surfaced model. The inner and outer surfaces of the model are discretized by small triangles, and the STL (Stereolitho- graphy) file format, which is commonly used in rapid prototyping manufacturing systems and defaults to industry standards, is obtained. The model is cut by equidistant or unequal distance processing to form a series of parallel horizontal cross-section sheets from bottom to top, that is, the surface model is cut into a series of cross sections by a computer. The optimal path including both the cross-sectional profile path and the internal scan path is generated for each slice by a scan line algorithm. At the same time, the model is positioned on the molding system to design the support structure.
The slice information and the generated path information are used as a command file (CLI file) for controlling the molding machine, and a numerical control command delivery machine of each level is programmed. The thinner the layering, the higher the precision of the resulting part, and the delamination of unequal thickness is used to speed up the forming process.
The laser beam in the laser forming machine is scanned by the numerical control command, so that the liquid photosensitive resin contained in the container is solidified and bonded together layer by layer. The curing process begins with the first layer of liquid on the working platform. When the first layer is cured, the working platform is lowered by a distance along the Z-axis (ie, layer thickness, taking into account material and process factors), so that a new layer of liquid resin is covered. On top of the cured layer, a second layer of curing is performed. Repeat this process until the final layer is cured, and a 3D prototype entity is generated. The liquid photosensitive resin contained in the liquid storage tank will solidify in a certain area at a certain wavelength (such as 325 nm) and intensity ultraviolet laser irradiation to form a solidification point. At the beginning of the forming, the working platform is at a certain depth below the liquid level, such as 0.05~0.2mm. The focused laser spot is scanned point by point on the liquid surface according to computer instructions, that is, point by point. The resin that was not irradiated with laser light after one layer of scanning was still liquid. Then the lifting frame drives the platform and then descends to a level. The newly formed layer is covered with a layer of resin and then scanned for a second layer to form a new processing layer and firmly connected with the solidified portion.
For a molding machine that scans with a laser deflection mirror, the focal length and the liquid spot size change as the laser beam is deflected, which directly affects the curing of the thin layer. In order to compensate for changes in focal length and spot size, the speed of laser beam scanning must also be adjusted in real time. In addition, the scanning speed of each thin layer must also be adjusted according to the thickness of the layer of the material to be processed (layer thickness variation).
2) System composition
Typically, a three-dimensional printing system consists of a laser, an X-Y motion device or a laser deflection scanner, a photosensitive liquid polymer, a polymer container, control software, and a lifting table.