Application of the hottest rapid prototyping techn

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Application of rapid prototyping technology in rapid tooling manufacturing

1 introduction

rapid prototyping technology (RPM) uses discrete/stacking principles (such as solidification, bonding, welding, sintering, polymerization or other chemical reactions) to manufacture parts. Its working process is to obtain the path, limit and way of accumulation through discretization, and "stack" the materials through accumulation to form a three-dimensional entity. First, a three-dimensional CAD model is obtained in the CAD modeling system or the shape and size of the part entity are measured by measuring instruments, and it is transformed into a CAD model; Secondly, the CAD model is processed, and the CAD model is discretized along a certain direction (usually Z direction), and the plane slice is layered. Then, the discrete layered information is combined with the forming process parameter information, which is converted into the numerical control code to control the work of the forming machine. Through the special cam system, the materials are regularly and accurately superimposed (stacked) to form a three-dimensional solid part. It can be seen that from the perspective of forming, rapid prototyping technology is the "stacking forming" method. From a mathematical point of view, the working process of rapid prototyping technology can also be regarded as a process of differentiation and integration. From the perspective of material morphology change, rapid prototyping technology is a process of material decomposition and combination. Therefore, rapid prototyping technology is a new technology integrating computer-aided design, precision machinery, numerical control, laser technology and material science. It is essentially different from traditional manufacturing methods. RPM technology is also a kind of green manufacturing technology because it will not produce waste in the process of manufacturing products, and the list of CMA national quality inspection center (such as chip cooling lubricant, etc.) will cause environmental pollution. Because RPM adopts the principle of converting three-dimensional shape into two-dimensional plane layered manufacturing, the complexity of the object is formed. The rapid tooling manufacturing RT supported by rpm is also a new manufacturing technology developed in order to shorten the development cycle of new products and launch marketable, customized multi-product and small batch products to the market as soon as possible. Due to the progress of product development and manufacturing technology, as well as the continuous pursuit of novel, strange and changeable market consumption orientation, it has become an indisputable fact that the life cycle of products (especially consumer goods) is getting shorter and shorter. Therefore, industrial developed countries have taken rpm/rt as an important research topic and one of the core technologies of manufacturing industry to shorten product development time and mold manufacturing cycle, and China has also begun the research, development and application of rapid manufacturing industry

2 Introduction to typical rapid prototyping process methods

the designer converts the physical model of the part into the three-dimensional design CAD model of the part through three-dimensional CAD modeling or three-dimensional digitization, and then processes the model data, slices it with layered software, and discretizes the plane "layered" along a certain direction to obtain the cross-sectional profile of each layer. Accordingly, the forming of the rapid prototyping system is carried out according to the selected curing methods (stereolithography, powder sintering, thin-layer stacking, melt deposition and three-dimensional printing). At present, there are many kinds of RPM methods, but the most commonly used ones are rapid modeling systems based on SLA, LOM, SLS, FDM, TDP and other principles

2.1 the working principle of stereo lithography

sla is shown in Figure 1. It uses liquid photosensitive resin (such as a special epoxy resin) as modeling material and UV laser as energy: one is helium Fourier laser (wavelength 325nm, power 15~50mw), the other is ammonia ion laser (wavelength 351~365nm, power 100~500mw), and the laser beam spot size is 0.05~3mm. After the three-dimensional model is designed by CAD, the model is sliced horizontally, divided into thousands of thin layers, and the layered process information is generated. According to the trajectory determined by the computer, the scanning trajectory of the laser beam is controlled to solidify the liquid photosensitive resin in the scanned area, forming a thin solid section. After that, the lifting mechanism drives the workbench to drop one height, which is covered with another layer of liquid photosensitive resin, and then the second layer of laser scanning and solidification is carried out, The newly solidified layer is firmly adhered to the previous layer, so it is superimposed layer by layer until the whole model is made. Generally, the thickness of each thin layer is 0.07~0.4mm. After the model is taken out of the resin, it can be finally hardened and polished, electroplated, painted or colored

2.2 thin laminated forming technology

thin laminated forming technology forms parts by laser cutting and bonding raw paper. As shown in Figure 2, the process is to press and bond the paper coated with hot melt adhesive on one side together through the heating roller. At this time, the laser above it cuts a layer of paper into the internal and external contours of the parts according to the data obtained from the layered CAD model, and then a new layer of paper is superimposed on it. Through the hot pressing device, the layers that have been cut below are bonded together, and the laser cuts again. When cutting, the workbench continuously descends, and the cut paper remains in place for support and curing. The general thickness of the paper is 0.07~0.1mm. This method is characterized by high forming rate and low cost

2.3 selective laser powder sintering technology

the forming method of selective laser sintering (SLS) is. In the process of layer by layer manufacturing and layer by layer stacking, the fusible and bonded metal powder or non-metallic powder (such as paraffin, plastic, resin sand, nylon, etc.) is selectively scanned and heated by laser beam layer by layer a-constant, so that it reaches the sintering temperature and is sintered to form; When one layer is sintered, the workbench lowers the height of the next layer, paves the powder of the next layer, and then scans the second layer. The newly sintered layer is firmly bonded to the previous layer, and so on. Finally, the 3D entity corresponding to the CAD model is sintered. As shown in Figure 3. The outstanding advantage of selective laser sintering (SLS) is that it uses powder as the forming material, and the forming materials used are very extensive. Theoretically, any powder material that can form atomic connection between powder particles after being heated by laser can be used as the forming material of SLS

2.4 the basic principle of fused deposition forming technology

fdm is: under the control of the computer, the heating nozzle moves in the X-Y plane and the height Z direction according to the cross-sectional profile information. The wire (such as plastic wire, paraffin wire, etc.) is sent to the nozzle by the wire supply mechanism, heated and melted in the nozzle, and then selectively coated on the workbench. After rapid cooling, a layer of cross-sectional profile is formed, which is superimposed layer by layer and finally becomes a rapid prototype. Wax mold and master mold for precision casting can be made by this method

2.5 three dimensional printing technology (TDF)

three dimensional printing is a kind of technology that does not rely on laser rapid prototyping. The material sprayed by its nozzle is liquid, which is more like an inkjet print head to form a three-dimensional physical object. TDP method can be used in a wide range of materials, especially ceramic mold

3 rapid prototyping mold manufacturing

as the mold is a technology intensive product, its design and manufacturing involves various factors such as materials, processes, equipment and so on, so the mold making time is long. Generally, the design and manufacturing of moderately complex injection mold, die casting mold and forging mold takes 3 months or more. Therefore, as soon as RPM technology came out, it was quickly applied to rapid tooling manufacturing. Rapid tooling (RT) technology is mostly based on the solid model made by rapid prototyping, that is, the sample mold (master mold), which adopts the copy method (such as metal spraying, electroplating, composite material pouring, precision casting, etc.) to rapidly manufacture the main working parts of the mold (convex, concave mold or mold cavity, mold core). Its manufacturing cycle is generally 1//10 of the traditional NC cutting method, but the cost is only 1//5. Rapid prototyping mold manufacturing is divided into direct method and indirect method, which can be applied to the manufacturing of metal mold and non-metal mold

3.1 direct manufacturing of metal molds

the best way to manufacture parts with short construction period and small batch is rapid prototyping direct manufacturing of molds, which can complete the manufacture of very complex parts and molds in a few days, and the more complex it is, the more it shows its advantages. Using selective laser sintering to directly make the casting shell is to directly turn the designed three-dimensional solid model of the part into the inversion of the part in the computer CAD environment. After appropriate processing and designing the corresponding gating and riser system, the CAD graphics of the shell are obtained. In the SLS sintering process, the shell becomes a sintered entity, and the parts are still unsintered powder. Removing the powder inside the shell is the shell

3.1.1 directly making casting shell and infiltrating metal

the metal mold directly formed by selective laser sintering technology is often a low-density porous structure, which can directly form the metal mold after infiltrating the metal with low melting point phase

3.1.2 the strength and accuracy of parts formed by direct deposition has always been a difficult problem to be solved. With steel, steel alloy, iron nickel alloy, titanium aluminum alloy and nickel aluminum alloy as raw materials, the metal is directly deposited and formed by laser technology. The strength of the metal mold produced by this method is higher than that of the traditional method. DTM company has developed a rapid prototyping sintering material with a thin layer of polyacetic acid wrapped on the outer surface of steel powder. Its metal powder has been changed from carbon steel to stainless steel, and the infiltrated alloy has been changed from brass to bronze. Unlike the original need to infiltrate liquid polymer in the middle, its processing process is almost shortened by 1/2. After rapid sintering and forming by selective laser sintering process, metal molds can be directly manufactured, which contain steel 400. The service life of the mold is up to tens of thousands. But this method is more complicated

3.2 indirect manufacturing of metal molds

rapid prototyping can be used to indirectly manufacture molds. Indirect molding refers to making hard molds, or spraying metal to obtain contour shapes, or making master molds to copy soft molds, etc. After special treatment of the prototype surface obtained by rapid prototyping manufacturing technology, instead of wood mold, gypsum mold or ceramic mold is directly manufactured, or the prototype is transformed into gypsum mold or ceramic mold through silicone rubber mold transition, and then the metal mold is cast from gypsum mold or ceramic mold

with the improvement of forming and manufacturing technology, this indirect molding process has been basically mature, and its method varies according to the size of parts production batch. Silicone rubber mold is commonly used, with a batch of less than 50 pieces; Epoxy resin mold, less than hundreds of pieces; Less than 3000 metal cold spraying molds; Quickly make more than 5000 steel molds for EPM electrode processing

3.2.1 metal cold spray mold

taking the rapid prototyping prototype as the sample mold, the low melting point metal is fully atomized and sprayed to the sample mold surface at a certain speed to form the mold cavity surface. The back is supported by epoxy resin or silicone rubber composite filled with aluminum, and the shell is separated from the prototype to obtain a precision metal mold, also known as hard mold. This usually refers to the indirect method of manufacturing, adding gating system, cooling system and mold base to form an injection mold. It is characterized by simple process, short cycle, and the formation of fine patterns on the cavity and surface at the same time, which saves expensive and time-consuming steps such as drawing, numerical control processing and heat treatment in traditional mold processing, and does not need machining. The mold has high dimensional accuracy and low cost. The rapid solidification process is adopted by the American ADA engineering and environmental experiment center to realize the rapid and economical manufacturing of injection molds. In this method, the sample made by rapid prototyping technology is used as the master sample, and the mold is made by the deposition of metal or alloy droplets sprayed on the master sample. The technological process is that the molten tool steel or other alloys are pressed into the nozzle, which meets with the high-speed flowing inert gas to form foggy droplets, which are sprayed and deposited on the master sample to replicate the surface structure of the master sample

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