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The application of SLA Rapid Prototyping Technology in the manufacture of RTV silicone rubber seals

rapid prototyping technology is a method of layered forming entities by UV laser scanning with liquid photosensitive polymers (epoxy resin or/and acrylic resin, etc.) as raw materials. Stereo lithography apparatus (SLA) is one of the key equipment for the rapid application of electronic and electrical forming technology with strict requirements in wear resistance, flame retardancy and antistatic properties. It has the characteristics of high manufacturing accuracy and raw material utilization, and can be used to manufacture high-precision entities with complex shapes. This work discusses the application of SLA Rapid Prototyping Technology in the manufacture of room temperature vulcanized silicone rubber (RTV silicone rubber) seals

1 technical principle

sla rapid prototyping is divided into three steps: pre-processing, layered stacking free forming and post-processing. Pre processing refers to the CAD design of finished products according to the drawings or real objects provided by users, that is, 3D modeling. If possible, optical scanning or CT scanning can also be carried out on the real objects to directly obtain the 3D model of finished products, and then output the 3D model file (triangular patch file) in STL format, On this basis, slice and support processing (with a thickness of 0.05~0.5 mm) are carried out (similar to adding processing fixtures, but the support is formed at the same time with the mold)

layered overlay free forming is the core of rapid prototyping, including slicing and slicing. Its principle is shown in Figure 1. The specific process is as follows: the UV laser scans each layered section designed by CAD point by point, so that the resin thin layer in the scanned area produces photopolymerization reaction and crosslinks and solidifies; After the thin layer is cured, the workbench moves downward, and a new liquid resin layer is placed on the surface of the just cured resin. At the same time, the scraper moves horizontally to keep the liquid level level, and then a new layer is scanned and cured; The newly cured resin layer is firmly bonded to the previous cured layer, and so on until the solid molding is completed

Figure 1 Schematic diagram of SLA layered superposition free forming principle

post processing is to take out the formed products from SLA for grinding and polishing

sla rapid prototyping technology can be used to make resin molds, which are suitable for the production of small batch and high-precision room temperature (low temperature) pouring rubber products

2. Application in the manufacture of RTV silicone rubber seals

when two kinds of rubber seals (as shown in figures 2 and 3) of the CHO1 laparoscopic surgery instrument (product of German ETM company) used in a hospital in Gansu Province are damaged, if you buy imported accessories, on the one hand, the cost is very high; On the other hand, the goods cannot be delivered in time, which affects the normal operation. Therefore, according to the requirements of the hospital, we completed the production of these two kinds of rubber seals in one working day

2.1 mold manufacturing

2.1.1 CAD design

first, use vernier caliper, inner micrometer and outer micrometer to accurately measure the size of the damaged rubber seal and the installation shaft, and determine the interference between the seal hole and the shaft to be 0.15~0.2 mm according to the elasticity and shrinkage of the rubber used

after completing the mapping of the seal, carry out the CAD design of the mold. The principle of CAD design is to use the least material to construct the mold. The CAD model of the rubber seal mold of the laparoscopic surgery instrument is shown in Figures 4 and 5 (the end face of the evenly distributed 6 pouring holes is a non assembly surface), and the wall thickness of the mold cavity is only 0.5mm

Figure 4 CAD model of rubber seal a mold

Figure 5 CAD model of rubber seal B mold

2.1.2 molding

after completing the CAD design of the mold, transfer the three-dimensional model file in STL format to SLA rapid prototyping machine (model: sps450b, liquid tank size: 450 mm x 450 mm, product of Xi'an Jiaotong University Institute of advanced manufacturing technology), Spr-3010 photosensitive resin used for molding (formula: bisphenol A epoxy resin 83, ethylene oxide hexylene glycol diacrylate vinegar 17,1,4-methyl cyclohexane divinyl ether 4.8, diaryl Hexafluoroarsenate tin salt 7.2, benzoin dimethyl ether 4.8) has good water resistance, chemical resistance, dimensional stability and toughness, high strength, wide applicable temperature and humidity range, and can be used in the production of automotive parts, aviation parts and medical devices

through rpdata data data processing software, it is determined that the mold model is placed horizontally on the workbench with the gate up, and then the three-dimensional model is sliced by layers, with a slice thickness of 0 2 mm, so that the triangular patch file is converted into the contour information of the two-dimensional slice. In order to prevent the warping deformation of the mold in the forming process and ensure the stability of the mold making, the support design of the model must also be carried out. After that, 10 uniformly distributed worktables are produced according to the two specifications of molds. Finally, run rpbuild production software, that is, turn on the laser and adjust the working liquid level to zero, carry out layer by layer laser scanning curing and superposition molding, and complete the production of the mold. The SLA rapid prototyping process parameters of this seal mold are: resin temperature 30 ℃, laser power 160 MW, but generally it is composed of two basic parts: loading and force measurement. The laser wavelength is 355 nm, the light intensity is 1.9 x 100000 CD, and the filling scanning speed is 2200 mm S-1, filling vector spacing 0 1mm。 The forming mold is washed with acetone to remove the grease and support. Finally, the forming mold is irradiated under the ultraviolet lamp for 2h to further crosslink and solidify

the rubber seal mold of laparoscopic surgery instrument manufactured by SLA rapid technology is shown in figures 6 and 7. It only takes about 3H to complete the molding of 10 molds of each of these two specifications

2. 2. Seal manufacturing

adopt two-component addition molding RTV silicone rubber pouring to form the seal of laparoscopic surgery instrument. The formula of component A is: light terminated polydimethylsiloxane 100, white carbon black 6 3. The economic level of lead oxide has increased by 12 5. Methyl silicone oil 6 3; The formula of component B is: silicic acid, which is a problem that nearly 100 third tier cities in the country are thinking about. Yiku 119, stannic dialkyl bisulfite 6 3。 After components a and B are mixed evenly in the ratio of 10:1, slowly pour the mixed liquid into the container of 20 rapid prototyping molds (in order to prevent the mixed liquid from overflowing the container during vacuum pumping, the height of the container is designed to be 3 ~-4 times the height of the mold), and the mixed liquid is injected into the mold cavity through the mold pouring hole. After that, put the container into the vacuum box with a vacuum degree of 8 Remove air and moisture bubbles from the mixture at 5 x PA. After exhausting, take out the container from the vacuum box and vulcanize it in an electric heating box at 60 ℃ for 4H. Finally, take the vulcanized product out of the oven, peel the mold thin layer on it by hand, and gently polish the convex part of the gate with sandpaper to make the end face flat and smooth, so as to obtain the finished seal (as shown in Figures 8 and 9). After testing, the performance of the seal met the requirements and was put into use immediately. The actual use shows that the service performance of the seal completely reaches the level of the original accessories

3 conclusion

sla rapid prototyping technology is suitable for the production of small batch and high-precision room temperature (low temperature) pouring rubber products. Compared with traditional technology, its production cycle is shortened by 60% - 70%, and the production cost is greatly reduced. (end)

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