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CAXA based reverse engineering implementation technology

Abstract: the AERS coordinate measuring machine of COORD3 company in Italy is used to collect data, the CopyCAD software system of Delcam company in Britain is used for data processing, and the CAXA Manufacturing Engineer Software System of China Beihang Haier is imported to reconstruct the surface and generate the NC program, so as to realize the rapid manufacturing of parts

key words: reverse engineering; Surface reconstruction; CAXA; Rapid manufacturing

1 Introduction

developed countries such as the United States have listed agile manufacturing technology as a strategy for the development of manufacturing industry in the 21st century, and it has gradually received widespread attention from other countries in the world As an important branch of agile manufacturing technology, reverse engineering technology provides a good support for rapid design and manufacturing. It has become one of the important and concise ways of information transmission in manufacturing industry Reverse engineering technology has shown more and more powerful power in accelerating product development, reducing costs, and learning from and absorbing modern high-tech achievements. It has become a powerful weapon for people to realize product conceptual design and complex design

reverse engineering technology mainly includes data acquisition, data processing, modeling, processing and manufacturing Modeling is the key technology of reverse engineering Since the reverse engineering technology originates from the United States and other developed countries, its modeling software is customarily used, such as surfer of Imageware, Pro/E of PTC, ug/pointcloud of EDS, strim 100 of Matra, France, CopyCAD of del cam and trace of Renishaw

these foreign original cad/CAM application software are expensive, there are obstacles in language communication, follow-up services are not in place, personnel training is insufficient, and the communication of technical problems is inconvenient, and they are different from the standards of engineering design, drawing methods and engineering habits in China, which brings great inconvenience to the development and application of engineering technicians in Chinese enterprises

The product structure is uneven

after long-term research and practice, I use CAXA Manufacturing Engineer Software of China Beihang Haier (hereinafter referred to as CAXA) to reconstruct the surface and generate NC program, which can better complete the modeling of parts and is easy to master

caxa is developed by Beihang Haier Software Co., Ltd. and Qingdao Haier Group. Its modeling methods are divided into three categories, namely wire frame, surface and solid These three modeling methods have their own characteristics, which can be independent modeling or mixed modeling, and provide twelve NC tool path generation methods, forming a powerful and practical processing programming ability, which is enough to deal with the processing of planes and various complex surfaces. As long as the surfaces processed by three-axis milling, CAXA can generate tool paths and automatically generate NC codes for NC processing, Thus cutting can be carried out directly on the NC machine tool

this paper takes the reverse engineering design and manufacturing of the external surface of a plastic shell as an example, uses the AERS coordinate measuring machine of COORD3 company in Italy to collect data, and uses the C of Delcam company in Britain. Therefore, the disposal of waste plastic particles will become a hot development in the future. The data will be processed by opycad software system, imported into the CAXA reconstruction surface of China Beihang Haier, and generated the NC program, so as to realize the rapid manufacturing of parts

2 reverse engineering and its process

the process of reverse engineering is usually to use 3D digital measuring instruments to accurately and quickly measure the contour coordinates of the workpiece (sample or model), and then through all these, the theory applicable to the fatigue of continuum metal materials can not be directly used to construct, modify, and transmit to cam system to generate NC program, Finally, it is sent to the CNC machine tool to make the required mold, or to the rapid prototyping machine to make the sample model The process flow is shown in Figure 1

Among them, three-dimensional data measurement, data processing and surface reconstruction are the three key technologies of reverse engineering This paper also focuses on these three aspects

3 collection of three-dimensional data

in reverse engineering, accurate, fast and comprehensive acquisition of three-dimensional geometric data of physical objects is the basis of reverse engineering With the development of sensor technology, control technology and manufacturing technology, there are various data acquisition methods, mainly including contact, non-contact and destructive. Among them, the representative data acquisition devices are coordinate measuring machine (CMM), optical scanner and tomography scanner

the CMM of AERS, COORD3 company in Italy, is used for this measurement. The length is 49 mm and the width is 120 8 mm, height 74 The external surface of the 7 mm plastic shell was scanned in multi-directional order, with 10339 scanning points, and the data point cloud was obtained The point cloud is saved in text file format (. Txt) and can be used by CopyCAD (Figure 2), Pro/E, UG and other application software

4 data processing

data processing is a key step in reverse engineering, and its processing effect will directly affect the quality of later model reconstruction This design adopts the most concise method, that is, distinguishing obvious bad points through human-computer interaction, and then removing bad points and noise points Then, the feature points and feature lines of the surface are determined to obtain a satisfactory curve, and faired to prepare for the next step of surface reconstruction

considering that CAXA cannot directly read point cloud files in text format, and when Pro/E, UG and other software read point cloud data, it will also cause some difficulties because of the huge data When CopyCAD reads data such as point cloud, the system works faster and the point line fitting is easy, so the data processing is carried out in CopyCAD

the specific operation steps are as follows:

in CopyCAD software, use point editing in the standard toolbar to select and delete bad points, click triangle generation, and use the triangle wizard in its sub toolbar to make a triangle model; Use model editing to limit the redundant triangles around the model; Then click triangle editing, select and delete the bad triangle, and finally get the required triangle model (Figure 3) Click curve generation in the standard toolbar, and use the curve generation methods such as boundaries, horizon, discontinuities, scan lines or triangle modelcross section to generate the characteristic curves required for surface reconstruction Finally, click curve editing to smooth with curve smoothing in its sub toolbar

in order to reconstruct a smooth surface with minimal error in the surface reconstruction of CAXA in the next step, we must also get enough characteristic curves from CopyCAD (Fig. 4) and save them as curve files (. IGS files)

5 surface reconstruction

when fitting faces, CopyCAD provides fewer tools and the quality of faces is not high In many cases, the noodles made of it often need to be modified in PowerMILL and powershape software The surface made by Pro/e and UG is of high quality, but the software is difficult to use Considering comprehensively, we choose CAXA to reconstruct the surface

open the above curve file (. IGS file) exported by CopyCAD in CAXA, use its edge interface, lattice surface, lofting surface, guide surface and other surface tools to shape the segmented surface, and finally carry out surface transition, splicing, stitching and other operations to form an ideal surface

caxa considers each feature line imported by CopyCAD as an independent curve, and each point on the line can be captured with the nearest point More importantly, CAXA surface modeling does not require sketches, so each imported feature line can generally be directly used to reconstruct the surface If some characteristic lines do not meet the surface modeling conditions (such as the edge interface requires curves to be connected end to end, etc.), they can be easily processed, such as curve clipping, transition, interruption, combination, extension, deletion, etc

of course, you can also use curve tools, such as straight lines, arcs, circles, splines, etc. to redraw curves by capturing points Because the curve is imported by CopyCAD or drawn by capturing the points on the imported feature line, as long as the feature line error is controlled in CopyCAD, the surface with small error can be easily obtained (Fig. 5)

the most frustrating thing to encounter in modeling is that the surface created with great effort is not smooth at all The author's experience is: some imported curves are not smooth due to their own reasons, or data loss during the import process. At this time, spline curve tools can be used to capture points on the original curve by using endpoints and nearest points This is also why I emphasize the need to obtain enough feature lines in CopyCAD (less is not good, more can be deleted) The number and location of capture points need to be determined by experience, on the premise of ensuring smoothness and small error To check the smoothness of the surface, save the surface as * IGS file, and then color curvature analysis in Pro/E (Figure 6)

6 NC machining

caxa can directly carry out virtual NC machining of surfaces First click the submenu "path generation" of the main menu "application", and select the appropriate processing method, processing parameters, tools, cutting parameters, and feed/retreat method to generate the processing path (Fig. 7); Then click the submenu "track" to cut, reverse, insert, delete the tool position, and interrupt, connect, and modify parameters of the track Finally, click the submenu "trajectory simulation" to carry out simulation processing (Figure 8), and then click the submenu "post processing" after observation, generate and check the G code and generate the operation order, and send it to WEDM or machining center for processing after manual modification, debugging and inspection

7 conclusion

when using CAXA for reverse engineering surface reconstruction, I generally feel that it is relatively simple and easy to use In addition to the powerful feature of surface modeling like Pro/E, it also has the following obvious advantages

first of all, the characteristic curve exported by CopyCAD software is considered by Pro/E as a whole, and the lines in it cannot be directly independent Moreover, only the starting point or end point of the curve is recognized, and the other points are not recognized at all, which brings inconvenience to the drawing of free-form curves and the creation of free-form surfaces CAXA believes that each imported curve is an independent object, which can directly carry out various, and recognizes all points on the curve

second, except for drawing free-form curves and surfaces, Pro/E does not need to create sketches, and the rest of the surface modeling must be done step by step, first making sketch planes, reference benchmarks, and then creating sketches, and finally generating surfaces. The process is cumbersome and requires high spatial concepts CAXA makes surface without sketch, especially it can directly use the imported characteristic curve to reconstruct the surface and simulate NC machining

the drawback is that in CAXA, the rendered surface color is monotonous and dry, and there is a lack of analysis modules for surface smoothness and error In addition, the automatically generated NC program can only be used after manual modification and debugging


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