Rapid Prototyping is a new multi-disciplinary integrated manufacturing technology. After the 1980s, with the application of computer aided design, product modeling and design capabilities have been greatly improved, but after the product design is completed, before mass production, samples must be made to express the design idea, to quickly obtain feedback on product design, And to assess the feasibility of product design, feasibility studies. In an increasingly competitive market today, time is effective. In order to improve the market competitiveness of products, the whole process from product development to batch production requires pressing down costs and increasing speed. The emergence of rapid prototyping technology has provided an effective way for the solution of this problem and has gained much attention both at home and abroad.
1 basic principle of rapid prototyping technology
Rapid prototyping is a generic term for product prototyping using discrete layering principles. Its principles are: 3D CAD model of the product → Layered Discrete → Stacking of raw materials layer by layer according to the discretized plane geometry information → Generate solid models.
The technology combines computer technology, laser processing technology, new materials technology in one, relying on CAD software to create a three-dimensional solid model in the computer and cut into a series of plane geometry information, in order to control the laser beam scanning direction and speed, By bonding, sintering, polymerization or chemical reaction and other means of selective processing of raw materials layer by layer, which quickly piled up to create a solid product model.
2 rapid prototyping processing characteristics
Rapid Prototyping breaks through the traditional part machining mode of "Blank → Machining → Finished Product" and pioneered the process of manufacturing parts without tools. It is an unprecedented processing method of laminating. Compared with the traditional cutting methods, rapid prototyping has the following advantages:
(1) Rapidly manufactured free-form surfaces and more complex parts, such as grooves, shoulders and hollow sections, greatly reduce development costs and development cycles for new products.
(2) It is a non-contact processing, do not need tools and fixtures necessary for machine tool cutting, no tool wear and cutting force. The company is located in:
(3) No vibration, noise and cutting waste.
(4) can be completely automated at night production.
(5) high processing efficiency, can quickly create a solid product model and mold.
The following table shows the comparison of rapid prototyping and conventional cutting methods.
Table comparison of rapid prototyping and conventional cutting methods
3 rapid prototyping technology development
Rapid prototyping concept that RP (Rapid Prototyping Technology) concept can be traced back to 1979, the Tokyo University Institute of Technology, Professor Nakagawa Wei Xiong invented the laminated model modeling method, in 1980 Xiaoyu Xiu-men also proposed the light modeling method . After the idea was put forward, Maruguchi II continued its research in 1984 and started product trial in 1987.
In 1988, 3D Systems of the United States took the lead in launching Stereo Lightgraphy Apparatus (SLA), a rapid prototyping practical device, and was sold on the world market with an annual sales growth rate of 30% -40%. In recent years, with the improvement of scanning galvanometer performance, as well as material science and computer technology, rapid prototyping technology has matured, and in 1994 officially entered the popularization stage.
According to the shape and type of materials used, rapid prototyping currently has the following four types.
3.1 The use of laser-curable resin material light modeling method
Light modeling device has been the United States 3D Systems company SLA champion, and form a monopoly market. The working principle shown in Figure 1. UV light emitted by the laser, the optical system assembled into a thin beam, the light beam under computer control, a selective scanning liquid laser scanning mirror lifting device container photosensitive resin photosensitive resin surface, the use of photosensitive resin UV solidification mechanism , Layer by layer curing photosensitive resin, each curing a layer, the table down a precise distance, and according to a new layer of surface geometry information so that the laser scanner to scan the liquid surface, so that a new layer of resin curing and sticky On the previous layer of cured resin, the process repeats until a solid model of the part is created. Laser three-dimensional modeling manufacturing accuracy up to now ± 0.1mm, mainly used to provide samples and experimental models. In addition, Japan's Teijin machine developed SOLIFORM can be directly produced injection molding and vacuum injection mold.
3.2 paper stacked modeling method
The paper laminate modeling method is currently the most widely used LOM device developed by Helisys. The device uses a special roller paper heated by the heating roller paper connection, and then cut the paper with a laser until the heated roller automatically leaves, and then the laser cut the paper into the required level shape
LOM can make some large-sized parts and thick-wall samples which are hard to be produced by the light modeling method, and the production cost is low (about 1/2 of the light modeling method) and the speed is high (about 1/5 of the woodworking production time) And easy to analyze design concepts and functions.
3.3 melting modeling method
Melt modeling method developed by the United States Stratasys FDM (Fused Deposition Modeling) the most widely used. Work, the direct control of the computer nozzle extrusion thermoplastic materials and layers of geometric information in accordance with layer by layer from the bottom up to create a solid model. FDM technology is the most prominent feature of speed (general model only a few hours to shape), non-polluting, in the prototype development and casting wax mold has been widely used.
3.4 hot plastic modeling method
Thermoplastic molding method to the DTM company developed selective laser sintering SLS (Selective Laser Sintering) more applications. The method is to use CO2 laser melting sintering resin powder sample preparation. Work, the beam emitted by the CO2 laser under computer control, according to the geometry of the cross-sectional geometry of the layers of material to scan the powder, the laser scanning of the powder melting and solidification together. Then, apply a new layer of powder, and then laser scanning sintering, so repeated until the required sample.
SLS technology modeling speed (general products, only 1 day ~ 2 days to complete), modeling accuracy (minimum thickness of each layer of powder about 0.07mm, laser dynamic accuracy up ± 0.09mm, and has automatic laser compensation) , Prototype strength (polycarbonate flexural strength of up to 34.5MPa, nylon up to 55MPa), so the prototype can be used for functional testing and assembly simulation in order to obtain the best surface and observe the situation with.
In the rapid prototyping technology development and application, the United States and Japan are at the forefront. In recent years, the rapid prototyping technology in our country has developed rapidly. Huazhong University of Science and Technology in 1994 developed two successful prototyping prototype HRP and RPS, has now entered the commodity market, widely used in automobiles, toys, aerospace, shipbuilding, military and other industries.
4 rapid prototyping technology in the mold manufacturing applications
4.1 rapid casting mold
Converting a CAD model of a part to be cast into a rapid mold shell creates a ceramic mold shell according to the geometry of the cross-section of each shell of the mold shell and then quickly molds the metal parts in a rapid investment casting method. In addition, the rapid prototyping technology can be generated prototype as a casting mold master mold, to achieve rapid casting parts, the process is as follows: Parts CAD three-dimensional design → Computational Fluid Dynamics Analysis (CFD) → LOM model manufacturing → Investment Casting Metal parts.
4.2 rapid mold making
The traditional method of mold manufacturing cycle length, high cost, a set of simple plastic injection mold its value is above 100,000 yuan. Any errors in the design reflected in the mold will cause irreparable damage. Rapid prototyping can accurately mold the mold core and cavity, can also be used directly in the injection process of plastic samples, in order to find and correct mistakes.
The Idaho National Engineering and Environmental Testing Center uses rapid solidification, the RSP technology, to achieve rapid and economical injection mold manufacturing. The method uses prototypes made by rapid prototyping as a matrix for the manufacture of molds by depositing droplets of metal or alloy sprayed onto the matrix. The process is as follows: a molten tool steel or other alloy is pressed into a nozzle to meet the high-speed flowing inert gas to form a mist drop of about 0.05mm in diameter, sprayed and deposited onto the mother substrate, and the mother sample is copied Of the surface structure of the shape, with the release agent to deposit the formation of the steel mold separated from the mother sample, you can make the required mold.
The material used for the sample depends on the alloy material on which it is sprayed. For spray tool steel, the choice of ceramic materials, similar materials and aluminum oxide powder and zirconium oxide to choose from. The method has the advantages of high production precision (minimum surface coating of 0.038mm and manufacturing accuracy of ± 0.025mm to ± 0.05mm when sprayed on tool steel), short time (normal mold can be formed within a week) and low cost (generally Traditional mold manufacturing costs 1/2 to 1/10).
4.3 rapid casting mold
Using polycarbonate as the material, the SLS is used to make the mother type quickly, and the ceramic shell is made on the surface of the mother body. After firing, aluminum or tool steel is cast in the shell to obtain the mold core and cavity. The method of making the cycle does not exceed 4 weeks, the mold can produce 250,000 plastic products.
Rapid Prototyping Technology (RP) is a new integrated technology that rapidly materializes prototypes by using material accumulation theory. It has been widely used in almost all industrial fields such as machinery, automobile, electrical appliances, aerospace, military and so on, creating a new era of rapid manufacturing of molds The development of broad prospects. 【Suzhou Mold Casting】