Research on the most economical rapid prototyping

2022-08-05
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Research on economical rapid prototyping system

rp technology is considered as a major breakthrough in manufacturing technology in the past 20 years, which can be comparable with NC technology in the 1960s. As soon as this advanced manufacturing technology appeared, it was highly valued by advanced industrial countries, and it was concerned and supported from the strategic height of global competition in the 21st century. China also entered this field in the early 1990s. At present, some units are close to or have developed commercialized RP systems and began to sell a small amount. However, a big problem in the popularization and application of RP technology is that its equipment is expensive, and many enterprises, especially small and medium-sized enterprises, are simply unable to purchase it. In view of this situation, the author puts forward the concept and principle of economical RP system, and discusses its system composition and application characteristics

1 basic principle

rp system is a high-tech product that integrates mechanical engineering, CAD, cam, CNC, precision servo drive, laser technology and new material technology. How to reduce the price of RP system? The author puts forward the principle of combining modularization with substitution, decouples the complex RP system into relatively independent modules, and then analyzes which modules are unique to the RP system and cannot be replaced, which modules can be replaced with other same or similar functional modules without or with little modification, and the cost of RP equipment will be significantly reduced after replacement. RP system can be divided into four parts in terms of function: modeling design module, slicing processing module, forming control module and forming device module. Which of the four modules cannot be replaced? Obviously, the function of the slice processing module is to process the CAD 3D model of a part into 2D plane data, which is unique to RP technology and cannot be replaced. The modeling design module only needs to output the file format required by the forming machine for users who already have the CAD 3D Modeling Application Foundation (software, hardware and talents), without new investment. For users without workstations or high-end microcomputers, CAD modeling software and 3D modeling ability, in order to reduce the investment cost of RP technology, they can also take advantage of the talents and computer software and hardware advantages of other units, such as colleges and universities, scientific research institutes, to realize remote communication to transmit data to the forming machine through computer networks, such as local area, wide area, or even public. Can the forming control module and the forming device module be replaced? The following is a discussion on this issue

rp technology is an advanced manufacturing technology that directly uses CAD model to drive rapid manufacturing of 3D parts with complex shapes, while CNC machining technology is a computer digital control technology, which uses digital signal to control the executive parts to complete the predetermined part forming process. The material processing dimension of LOM, SLA, FDM, SLS and other rapid prototyping process methods is n = 2, that is, the CAD 3D model of a part is discretized, the experimental conditions and results are automatically saved (reduced) into a two-dimensional plane, and then the two-dimensional plane is stacked into a physical three-dimensional entity. According to the condition of n = 2, the dimension m of the motion control system to ensure its implementation is 2.5. For CNC machine tools, if the material processing dimension n = 2, the dimension of the motion control system to ensure its realization is also M = 2.5. If n = 3, the dimension of the motion control system is m = 5 (if the free-form surface is fitted with a spatial plane, M = 3) [1, 2], so the general continuous cutting control CNC machine tools have the linkage function of more than 2.5 axes. This shows that from the perspective of information processing and motion control, the CNC system of CNC machine tool with linkage function of more than 2.5 axes (the CNC system referred to here includes CNC device, programmable controller, spindle drive and feed drive device) can complete the forming control process of LOM, SLA, FDM, SLS and other forming processes. Therefore, the forming control module of RP system can be replaced by the existing CNC machine tool control system with linkage function of more than 2.5 axes. The rapid prototyping device module refers to the moving parts that complete the forming movement of a certain rapid prototyping process. Obviously, the original moving parts of the CNC machine tool, such as the x-y-z motion unit, can also be used as a necessary part of the rapid prototyping device module. However, it is necessary to develop special parts that are organically integrated with the original moving parts of the machine tool to complete the rapid prototyping movement

to sum up, the economical RP system we proposed refers to a rapid prototyping system that is based on the existing CNC machine tool with linkage function of more than 2.5 axes, uses the existing workstation or high-end microcomputer and 3D CAD modeling software as the modeling design module, and only configures the necessary components in the slice processing module and rapid prototyping device module to complete the product forming process

2 system composition

the core of the economical RP system is to replace a large part of the functions of the RP system with the user's existing CNC machine tool system, so as to reduce the investment cost of RP equipment. In the following, the economic layered solid manufacturing (LOM) system is taken as an example to discuss the composition characteristics of this economic RP system

2.1 mechanical system

the mechanical part of the economical RP system is the forming device module mentioned above, which includes X-Y-Z motion unit (headstock, workbench), raw material storage and feeding mechanism, hot pressing mechanism, laser cutting mechanism or special tool cutting mechanism, etc. The x-y-z motion unit is an existing CNC machine tool, but the raw material storage and feeding mechanism, hot pressing mechanism, laser cutting mechanism or special tool cutting mechanism need to be specially developed. Since the RP technology came into being, its forming process has developed more than 10 kinds of control systems, such as layered solid manufacturing, light curing forming, powder sintering forming, melt deposition forming and vapor deposition forming, which are controlled by computer and combined with advanced electronic measurement and control technology. There are also many varieties of CNC machine tools. Research and analyze RP technology, various common process methods, possible combination modes and various combination modes of various CNC machine tools, How to use the moving parts of the original machine tool as much as possible to simplify the forming device module and reduce the investment cost of the economical RP system is one of the key technologies in the research and development of economical RP equipment. For example, if the economical LOM system is developed on a vertical machining center machine tool, the cutting mechanism must be fixedly connected with the spindle, while the raw material storage and feeding mechanism and hot pressing mechanism need to be installed on the machine tool workbench

2.2 control system

the contour scanning of the forming machine borrows the software and hardware resources of the CNC machine tool control system, while the motion control of the raw material storage and feeding mechanism and hot pressing mechanism needs special software and hardware, and must be coordinated with the CNC numerical control system

2.3 software system

the software system includes two parts: Geometric Modeling and information processing. The geometric modeling software has the same requirements as the general RP system. There are two kinds of slicing software: one is to process CAD 3D modeling files into STL file format, and then slice them into input data required by rapid prototyping equipment. Secondly, a series of slice profile data are cut directly from the CAD file as the input data of the forming machine. The forming control module of the economical RP system is the machine tool numerical control system, and the file format that the machine tool numerical control system can accept is NC code. Therefore, we can only use the method of CAD direct slice processing to generate accurate slice contour data for automatic programming. In addition, it should be pointed out that the NC code generated by automatic programming and post-processing must include the control signal coordinated with the single board computer that controls the movement of the raw material storage and feeding mechanism and hot pressing mechanism, so as to meet the needs of the coordinated work between the NC device of the machine tool and the single board computer

2.4 communication system

the microcomputer is used as the 3D CAD modeling and automatic programming module, and the microcomputer can directly communicate with the machine tool and forming device through r232c or r422 port; The workstation is used as the D modeling and automatic programming module of the 3D CA Figure 4 PDS System. The communication with the microcomputer can be realized through the local area, and then the communication with the machine tool and forming device can be realized through the serial port. For the machine tool with map interface, the information can be directly transmitted with the workstation; When the 3D CAD modeling and automatic programming module is separated from the NC machine tool and the forming device in a long distance, the remote communication can also be realized by means of wide area, local area and public modulation and demodulation

3 characteristics and socio-economic significance of economical RP system

the characteristics and innovation of economical RP system is that the system uses the existing NC machine tool with linkage function of more than 2.5 axes as the forming control module, and uses the moving parts of the original machine tool to form the forming device module as much as possible, so that the control accuracy is much higher than the existing rapid prototyping equipment; The CAD direct method is used to extract the driving data required by the rapid prototyping system as the basic data of the rapid prototyping system, and the programming language of the NC machine tool is used as the control language; The system can realize remote communication through computer networks such as local area, wide area, and even public, which greatly facilitates many users who do not have the supporting CNC machine tools, workstations, high-end microcomputers and other equipment and product design capabilities, and also creates conditions for the combination of factories, schools, and institutes

the research and development of this economical RP system has not been seen at home and abroad. Research institutions or developers at home and abroad research and develop complete rapid prototyping systems, but their market prices are expensive. The other is to research and develop the concept molding machine to reduce its market price. At present, there are commercialized equipment in foreign countries, but this concept molding machine achieves the purpose of reducing the cost at the cost of reducing the manufacturing accuracy of the prototype. At the same time, the process of these products is based on spray forming, spraying adhesive and spraying (extrusion) thermoplastic materials, which also greatly limits its scope of use [4]. The market price of the economical RP system we studied (taking LOM system as an example) is estimated to be 5% of that of the non economical system, which is much lower than the cost of the conceptual mold making machine. In addition, the CNC machine tool can also perform CNC machining and continue to work for 5 minutes, which improves the utilization rate of the equipment. More importantly, the development of this economical RP system will reduce the application difficulty of RP technology and greatly accelerate the popularization of RP technology, because it is identical with the working process of CNC machine tools in CAD modeling and NC automatic programming, and the share of CNC machine tools in Chinese enterprises and the popularity of CNC technology are much higher than that of RP technology. Therefore, the research and development of economical RP technology is very suitable for China's national conditions, and opens up a new way for the wide application of rapid prototyping technology in China's manufacturing enterprises. At present, with the support of Shanxi Youth Science Foundation, we are carrying out the research and development of economic layered entity manufacturing (LOM) system, and have achieved phased results. (end)

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