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2022-09-30
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Product development and application based on Reverse Engineering

Abstract: reverse engineering technology is now widely used in various industries, such as automobile, household appliances, medical treatment, aviation and other mold manufacturing fields. This paper mainly introduces the development method of products supported by reverse engineering, and analyzes the key technologies of digital product modeling, prototype generation and mold processing with the help of Delcam software

key words: reverse engineering; Digital product modeling; Delcam; PowerSHAPE; CopyCAD

Introduction

reverse engineering is to form the design drawings or CAD models of parts based on the physical measurement of existing product parts. Rapid prototyping technology is a general term for rapid manufacturing of 3D entities with complex shapes directly driven by CAD models. Rapid prototyping technology and reverse engineering are important components of advanced manufacturing technology. Through this technology, the design idea can be quickly and accurately transformed into a prototype or part with certain functions for rapid evaluation, modification and functional testing. In order to improve the speed of product development, many advanced design and manufacturing technologies have been developed

1 use reverse engineering for rapid product development

the traditional product development method (as shown in Figure 1) is that designers build a three-dimensional model or two-dimensional engineering drawing of the product in the computer through computer software, and then process the product mold or machine; Then carry out various inspections on the processed product parts, correct the design errors found, and then redesign until various design goals are achieved

Figure 1 traditional product development flow chart

nowadays, product design is mostly based on the original products or similar products, while inheriting many similar structures of the original products. For such products, combined with advanced manufacturing technology, a development method supported by reverse engineering and rapid prototyping technology has been produced (as shown in Figure 2). Firstly, reverse engineering is used to inherit the geometric and structural features of existing parts, and then innovative design is carried out on this basis; Use rapid prototyping technology to quickly generate test samples of the designed products (the aircraft will return directly from Zhangjiajie airport after 16 p.m. on the 18th), and evaluate the design, assembly, manufacturability and other aspects of the new products, so as to quickly modify the designed products and provide a reliable guarantee for the one-time success of the final manufacturing of the products

Figure 2 reverse engineering product development flow chart

compared with traditional product design, the existing product development methods fully inherit the advantages of the original products and use the concept of concurrent engineering to evaluate the optimization, assembly and manufacturability of the design to be carried out in the later stage of product development in the early stage of product design. It uses the small cycle of design sample test redesign to replace the large cycle of design manufacturing redesign in the process of product development

2 the key technology of product development using reverse engineering

the application of reverse engineering and rapid prototyping technology to product development, which mainly includes three-dimensional coordinate data acquisition, product modeling, data conversion of the original samples, manufacturing rapid prototyping samples, modifying design, and final formal production

2.1 data acquisition

the acquisition methods of three-dimensional data can be basically divided into contact and non-contact. Contact measuring instruments (such as CMM) use sensors to realize the rapid movement of the measuring head on the workpiece, so as to quickly record the coordinate values of the measured points, and have high accuracy. However, the measurement speed of this method is slow, the surface that cannot be touched by the probe cannot be measured, and it is difficult to obtain continuous coordinate points; Non contact measurement refers to the rapid measurement of three-dimensional surface by non-contact photoelectric method. Commonly used are laser scanning measurement, layer by layer scanning measurement, etc. Laser scanning measurement is to emit a laser beam to the object surface, which is received by a photosensitive device after reflection, and calculate the coordinates of the object surface according to the reflection time, the position relationship between the light source and the photosensitive device, which can realize the high-speed measurement of complex contour, but it is not suitable for surfaces with complex inner contour; Layer by layer scanning measurement can be used for the measurement of complex inner contour surface. The commonly used methods are industrial CT and layer by layer cutting photogrammetry. Industrial CT draws the obtained points in the form of object cross-section. The manufacturer has the idea that it cannot be controlled without PC, and it does not damage the real object, but the accuracy is low; Layer by layer cutting photogrammetry is a new fault measurement technology. It cuts cultural relics layer by layer with a very small thickness, takes photos of each fault, and obtains cross-sectional image data. It has high accuracy, but it destroys the real object

2.2 digital modeling

digital modeling is to operate the "dot cloud" data formed by the measured coordinate points of the physical model, and then use various reverse engineering software and CAD software to build the product model of these point clouds to generate the three-dimensional model of parts to be designed. The basic process is as follows:

(1) point cloud processing and surface construction. Firstly, the measured raw data is filtered, screened, denoised, smoothed, etc. to meet the subsequent modeling requirements, and then the part surface is constructed. Because the points of the point cloud are isolated from each other, these points need to be reconstituted into a surface and faired before the part model can be established. Therefore, surface construction is also the key to part construction. At present, although general CAD software has the function of model reconstruction based on measurement data, compared with the function of forward modeling, the function of reverse model reconstruction is not mature. Therefore, surface reconstruction is usually constructed by professional reverse engineering software. Our company adopts the professional reverse engineering software CopyCAD of British dalcon company, which can process the data obtained by a variety of coordinate measuring equipment. The basic method of constructing the surface is to construct the triangle from the point, and then fit the surface according to the triangle. In the fitting process, we provide a variety of methods to process the points, lines and surfaces, and have a variety of diagnostic methods to ensure the accuracy requirements in the processing process, The process of point curve surface in traditional reverse design is omitted, which greatly reduces the tedious workload and improves the accuracy of the surface. At the same time, add new points to build a new feature surface to achieve design innovation

(2) structural design of part model. Transfer the surface data model obtained by professional reverse engineering software into general CAD software, such as UG, CATIA, powershape, pro/e, etc. for processing, materialize the surface model to form the basic CAD model of the part, and then make full use of the good mechanical design function of CAD software on the basis of the existing model to carry out assembly, face, stiffener, flanging, chamfer or process hole and other feature design closely related to mechanical design, and add the material Technology and other aspects of information, so as to finally realize the digital modeling of parts. Powershape is a professional 3D design software of Delcam company in the UK. It has intelligent composite modeling function. It can easily process points, lines, surfaces, entities and triangles in the model. The most important thing is that powershape is seamlessly integrated with CopyCAD, eliminating frequent reverse → forward, forward → reverse data conversion, which not only reduces the workload, but also avoids the loss of data in the conversion process

2.3 rapid data conversion and repair

Figure 3 is changed from CAD drawing file to biogeochemistry (Jena) to rapid prototyping machined parts

because the rapid prototyping principle (Figure 3) is processed according to the cross-section of one layer. Therefore, it is necessary to slice the CAD 3D model of the part before machining, that is, slice it at certain intervals along the height direction of the forming, so as to extract the surface contour. The size of the interval is determined by the requirements of the precision and productivity of the formed parts. The smaller the interval, the higher the accuracy, but the longer the forming time. The interval range is usually 0.05 ~ 0.5mm, usually 0.1mm. Therefore, it is usually divided into the following steps:

(1) part CAD 3D model data conversion. Because the part 3D model is often composed of some irregular free-form surfaces, the surface information of the part CAD model must be obtained in order to slice. Therefore, the part model should be triangulated, and a series of small triangles should be used to approximate the free-form surface. The triangulated 3D model file is usually called IGS format file, which is composed of a series of connected spatial triangles. At present, typical CAD software has IGS format file input and output interfaces. However, due to the requirements of approximation accuracy, there will be the problem that the small geometric features of the part CAD model disappear when exporting IGS files, which needs to be repaired

(2) IGS format file repair. Errors in IGS format files usually include: A. wrong cracks or holes. During IGS format conversion, due to the error of data rounding, a point will be in multiple positions at the same time, resulting in wrong holes or cracks. b. Minor feature omission or error of spring tension and compression testing machine, spring change testing machine and spring fatigue testing machine; When there are very small feature structures in the 3D CAD model, it may be difficult to triangulate the features, resulting in the omission or error of these feature structures

3 application of reverse engineering technology

according to the above method, using the relevant key technologies, reverse the design of a crankshaft connecting block and make targeted improvements. Because this part is a centrosymmetric structure, it only needs to collect half of the data of its original parts, and the other half can be directly solved by symmetrical method. We use the CMM of brown sharp company in the United States to measure. Figure 4 is the IGES file obtained after scanning the crankshaft connecting block, and the point cloud and grid line imported into powershape software for processing. That is to use powershape software to reconstruct its surface

after the model is generated, the data of the part model is converted, and the sample is quickly generated with rapid prototyping equipment, and the sample is designed, evaluated and trial assembled, and the design is modified according to the problems in the evaluation and assembly, so as to finally ensure the success of the part mold opening

4 conclusion

reverse engineering is a pioneering, practical and comprehensive technology. Reverse engineering technology has been widely used in the development of new products, the restoration of old parts and the detection of products. It can not only digest and absorb physical prototypes, but also modify and redesign to produce new products. But at the same time, the degree of system integration in the design process is relatively low, and the proportion of manual intervention is large. In the future, it is expected to form an integrated reverse engineering system, and replace the lack of manual intervention with intelligent software

references

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