Research into the engineering application of reverse engineering technology.pdf

Journal of Materials Processing Technology 139 (2003) 472475 Research into the engineering application of reverse engineering technology Yu Zhang CIMS Application and Research Center, School of Mechanical and Automation Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, PR China Abstract Based on previous research on reverse engineering (RE) technology, the engineering application of RE is explored in this paper. The application environment of RE is built with coordinate measurement machine (CMM) and CAD/CAM software. Taking a core die of the inlet of a diesel engine as an example, this paper describes the processes of RE, from object digitization, CAD model reconstruction to NC machining. Measurement data are acquired by scanning the physical object using a three-dimensional CMM. Through processing of measurement data, the authors succeed in creating a CAD model of the die and machining the die, gaining a good result. 2003 Elsevier Science B.V. All rights reserved. Keywords: Reverse engineering; Product development; CAD/CAM 1. Introduction Nowadays, competitive pressure has reached the point, where rapid product design and optimization need to be embraced within the product development cycle. A short lead-time in product development is strongly demanded to satisfy needs, resulting from the globalization of manufac- turing activities and the changes in market requirements. In engineering areas such as aerospace, automotives, shipbuild- ing and medicine, it is diffi cult to create a CAD model of an existing product that has a free-form surface or a sculp- tured surface. In these cases, reverse engineering (RE) is an effi cient approach to signifi cantly reduce the product devel- opment cycle. RE refers to the processes in which designers acquire a design concept of a product from digitization of a physi- cal model, and create the CAD model to realize approx- imation to the physical model: the model created can be reused, modifi ed and optimized 5. By RE technology, the geometric shape of an existing part or product is measured. Based on this measurement data a complete and complex CAD model is created. RE has two key technologies, i.e. digitization of a physical model and creation of its CAD model. E-mail address: (Y. Zhang). 2. Working processes of RE Differing from the traditional design idea and method, RE technology enables one to start a design from an existing productmodelbycombiningcomputertechnology,measure- ment technology and CAD/CAM technology. RE has been of interest in many different branches such as automotives, shipbuilding, electronics, and medicine. It is often used in cases such as the following 3: (i) Where a prototype of the fi nal product has been mod- eled manually and therefore no CAD model of the prototype exists, e.g. clay model in automotive in- dustry. (ii) Where a CAD is introduced in a company and all exist- ing products must be modeled in order to have a fully digital archive. Particularly, the CAD model of a com- plex shaped part is modeled because it is diffi cult to create its CAD model directly. (iii) Where complex shaped parts must be inspected and therefore the RE model created will be compared to an existing CAD model. The RE process can principally be seen as a process chain that is composed of three main operations as follows 5: (i) Digitization of the object: The three-dimensional shape of the product is acquired by any appropriate measure- ment method. 0924-0136/03/$ see front matter 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0924-0136(03)00513-2 Y. Zhang/Journal of Materials Processing Technology 139 (2003) 472475473 Fig. 1. Working processes of RE. (ii) Processing of measured data: The three-dimensional data acquired is processed in order to fulfi ll the require- ments of the following operation. (iii) Creation of a CAD model: A complete CAD model of the product must be built in order to represent all relevant data of the product. Fig. 1 shows the working processes of RE. The whole process of RE should be computer aided. 3. Engineering application of RE Based on principle of RE technology mentioned above, the authors applied RE technology in the design and manu- facturing of the die of a diesel engine. Taking the core die of the inlet of a diesel engine as an example, this paper describes the RE processes, from object digitization, CAD model reconstruction to NC machining. The inlet is the key part in a diesel engine. It infl uences the characteristic of the diesel engine to a great extent. Because the inlet has very complex shape (see Fig. 2), it is diffi cult to create a digital model of the inlet, as well as to manufacture the core die of the inlet. The authors have therefore taken it as an example to research the engineering application of RE technology. Fig. 2. The 3D model of the inlet. 3.1. Environment of RE The environment of RE is a local area network (LAN), which is built with two work-stations, two NT work-stations, three sets of PC, a coordinate measurement machine (CMM) and three NC machines. The hardware platform uses level disposition of work-stations and PCs. The main application software utilized is the Unigraphics CAD/CAE/CAM inte- grated system and KUM measurement software provided by the zess company. The operating systems utilized are HP-UX 10.2 on work-stations and Windows NT on PCs. Fig. 3 shows the environment of RE. With computer net- work, the RE processes, i.e. object digitization, processing of measurement data, creation of a CAD model, and NC machining, are realized in a integrated environment on com- puters. Fig. 3. Environment of RE. 474Y. Zhang/Journal of Materials Processing Technology 139 (2003) 472475 Fig. 4. NC measurement and surface reconstruction of the core die of the inlet. 3.2. Digitization of the die Generally,themethodsofmeasurementofthree- dimensional geometry product data are divided into two classes, i.e. tactile measurement and optical measurement. The CMM is a general tactile measurement device, and is being widely used in industrial enterprises 1,2. The au- thors measure the geometric shape of the die and acquire measurement data using CMM and KUM measurement software with a linear scan mode. The physical model of the die is scanned on CMM using a 5mm diameter probe with a step-over across the model of 5mm in the fi rst area and 1mm in the complex area (see Fig. 4a). The number of measurement points is automatically determined by CMM according to the curvature change of the surface measured on the tactile point. In order to avoid track slip, the probe starts to measure the surface at 4mm away from the bound- ary of the surface being measured. On average, there are about 1600 measurement points acquired for each scan curve. 3.3. Processing of measurement data The result of a mechanical tracing process is a structured point sequences with a large number of points and a line structure 4. The output data of the CMM are coordinate values of the center of the probe and normal vectors in the X, Y and Z direction at the position of the tactile point. Addi- tionally, the output format of the measurement data does not accord with the demands of the creation of a CAD model. Thus one must process the measurement data. The author have self-developed a program to realize the transformation of the format of the measurement data. First, the format of the measurement data output must be transformed into a format that can be accepted by Unigraph- ics software. Then the measurement data out of the control tolerance must be fi ltered out and interactively processed in a visualized way. The data processed can be used directly for the creation of a CAD model of the die. 3.4. Creation of a CAD model of die The CAD model is created directly from measurement data using Unigraphics CAD/CAE/CAM software after pro- cessing of measurement data and transforming of the data format. There are two ways in the creation of the CAD model from measurement data using free-form feature modeling. One is called the curve mode. In this way, the construction curves are generated from measurement data fi rst, and then the surface can be created through the construction curve mesh generated. Another one is called the surface mode, the surface is generated directly from measurement data 2. Because the measurement data output are the coordinate values of the center of the probe, the surface generated from measurement data is a surface offset for distance, which equals the radius of the probe, away from actual surface measured. Thus one has to offset this surface. The surface generated is analyzed through a shading sur- face and surface analysis function in order to check its con- tinuity and smoothness, as well as the errors between the surface generated and the measurement points. The maxi- mum error is 0.2mm, which is acceptable. 3.5. NC machining of the die After the CAD model of the die is created completely, one can determine the NC machining process planning and generate the cutter location for a manufacturing applica- tion. Further machining codes are generated through NC post-processing. Finally, the die is machined by an NC ma- chine tool using its CAD model created. Fig. 4 shows the results of NC measurement and surface reconstructionofthecoredieoftheinlet,whilstFig.5shows the generated CAD model of the core die of the inlet. Fig. 5. The generated CAD model of the core die of the inlet. Y. Zhang/Journal of Materials Processing Technology 139 (2003) 472475475 4. Conclusion Based on previous research on RE technology, the authors have explored the engineering application of RE technol- ogy in the design and manufacturing of a complex product. Taking a die of the inlet of a diesel engine as an example, they have described the whole processes, from object digi- tization, CAD model reconstruction to NC machining, and have gained a good result. RE is an effi cient approach to signifi cantly reduce the product development cycle and en- sure product quality kin the design and manufacturing of a