PRODUCT QUALITY CONTROL BY USING REVERSE ENGINEERING



PRODUCT QUALITY CONTROL BY USING REVERSE ENGINEERINGJelena MICEVSKA, Zoran SPIROSKI, Jasmina ?ALOSKA, Atanas KO?OVFaculty of Mechanical Engineering, Karpos II bb, Skopje, R.Macedoniajelena@cirko-; zspiroski@;jasmina.chaloska@mf.edu.mk; atanas.kochov@mf.edu.mkAbstract: In the production process of every product, engineers are faced with different kind of problems. Most of these problems are caused by external factors which cannot be taken in consideration during the design, construction and production process. The produced part often differs from the CAD model, designed by the engineer. In this paper, technology of reverse engineering is used in order to control the quality of the final product produced by injection molding. Measurements and scans are made by using the optical device from the producer Gom, ATOS II. The necessary corrections of the die are made as a result of comparative analysis of the CAD models.Key words: reverse engineering, die design, injection moldingINTRODUCTIONReverse Engineering is a technology that is used for transformation of the produced physical models into 3D CAD models. This technology has vast use in the field of mechanical engineering, but at the same time in many different fields as medicine, architecture, art, cultural inheritance. Purpose of the reverse engineering is not just simple scanning on the models and making their copies in computer environment, but it is much more. With the help of this technology we can get any physical model that we want in computer environment, and after that make changes and analysis directly on the model or include it in any part of the CAD/CAM/CAE system.One of the many uses of this technology in the mechanical engineering is conduction of dimensional comparison between two models, where one is the actual scanned data from the physical model and the other one is designed CAD model. The dimensional comparison of the scanned model is done by receiving point cloud, which has to be segmented aligned. This way the surfaces are identical with the produced part and can be compared with the given CAD model for determination of the deviations. Reverse enginering in the tooling is used for reconstruction or reparation of the parts, tools and dies (Figure 1-1; 1-2). Fig. 1-1. Tool reparation Fig. 1-2. Part reparation(a – damaged part, b – point cloud, c – STL model, d – CAD model)Softwers that are used in the reverse engineering have the possibility to compare the scanned model with the CAD model. Usually the CAD model is imported as STL or IGES model, and is placed in the same coordinated system as the scanned model and the comparison is run (Figure 1-3). Fig. 1-3. Comparison of scanned and CAD modelUSE OF THE REVESE ENINEERING FOR QUALITY CONTROL OF TOOL Reverse enginering enables fast control of the dimensions, as well as the surfaces of the produced model with the technology of injection molding of polymer material. Some of the dimensions (diameters of holes, lengths, widths etc.) can be controlled with classical measuring instruments but everything gets complicated when it should be controlled and determent if the quality of the surfaces is in the defined tolerance range. In cases like this, the technology of the RE is irreplaceable. Description of the product – housing for starThe product – housing for star is compound of the ridge switch – type BS (Figure 2-1), made from – ULTRAMID B3S. This product has very risponsable role in the hole assembly since it is used as a switcher of the electromotors, transformer stations, welding aparatures, resistors, heaters. The product has also high built-in power, long electric durability and safety from contact voltage. The characteristics of this product are completely regulated with the international standard IEC 60947-3. Fig. 2-1. Ridge switch - type BSHousing of this product has to satisfy many requirements. At the same time it has to be made from a certain material and has to have certain precision of the functional and built-in dimensions, given in the technical documentation (Figure 2-2). Fig. 2-2. 2D drawing of the part- housing for starRidge switchs typical are produced in many different sizes. In this case the process of the reverse engineering is used for quality control of the tool, or more precise for determination of the deviations of the produced model from its 3D model. The control is conducted with the 3D model (design in Solid Works 2010, figure 2-3), created from the 2D technical documentation (fig. 2-2), and 3D scan (made with ATOS II) of the produced model (figure 2-4). After creating CAD models of the two models they are joined in same virtual environment and comparative analysis is conducted.Fig. 2-3. 3D model made in SolidWorks 2010 Fig. 2-4. Produced modelProcess of creating 3D scanned data with Atos IIATOS II (Figure 2-5) is 3D scanner that is characterized with high precision, fast work and mobility. It has light source – projector (pos. 2, figure 2-5) and two photosensible devices – cameras (pos. 1 and 3, figure 2-5). The possession of two cameras puts this 3D scanner in advantage before the competition. Fig. 2-5. ATOS II – contact-less device for collecting dataATOS II works on the same principal as the human eyes. Same way as the human register only the information seen by the both eyes, the camera collects the data that is seen by the both cameras (Figure 2-6).Fig. 2-6. Working principal of the ATOS IIATOS II can scan models with vast volume range from 35x28x20 mm to 1700x1360x1360 mm. It has digital camera that is working with 1.300.000 pixels. Time needed for one scan is 0,7 seconds. Distance of the points in the cloud point is from 0,08 to 1 mm. Accuracy of the 3D scanner is 0,002 mm, which makes it optical measuring device.Phases of the process of scanning:1st phase – preparation of the 3D scanner and the modelBefore the scanning is started, the volume of the model needs to be calculated. This is important step because according to the volume of the part the 3D scanner is prepared. This means that the adequate size of the lenses is chosen and put on the two cameras and the projector. Next step is calibration of the equipment, step very important for the accuracy of the final results. During the calibration, except setup of the optics, setup of the temperature and the humidity is made.Also according to the volume of the model, the size of the referent points is chosen. These referent points are important because they are the link between the model and the 3D scanner. The 3D scanner captures the surface of the model through these points and also merges all of the scanned data through them.2nd phase – process of scanningScanning is the process in which the data collected with the 3D scanner is transfer into the computer. The scanning of the whole model is done scan by scan (Figure 2-7), which are well merged through the referent points. Fig. 2-7. Scanning processThe process of 3D scanning should be conducted in highly controlled conditions (temperature, lighting, movement) since the precision of the device is very high and with only a slight change of the conditions there is a possibility of incorrect results. When the whole process of collecting data is finished, in the software we have one point cloud (Figure 2-8) which resemble of the model that is scanned but it is useless for many operations and has to be finished adequate, depending of the purpose of the scanning.This process of scanning the model is done in Project mode which is finished with the process of polygonization. Fig. 2-8. Housing for star – point cloud3rd phase – poligonizationThis is the phase in which from point cloud we get polygon model (Figure 2-9). The poligoznization is automatically run, but there are some aspects of it that can be controlled, as precision and size of the polygons. Fig. 2-9. Housing for star – polygon modelThese modifications are controlled manually because they depend on the precision of the finishing surface that we need.After the poligonization, we automatically enter into new mode in the software, called Evaluation mode. In this mode slight changes can be made on the geometry of the model. First thing, that is necessary to be done is to remove the places were markers used to be because of the irregular finishing. These surfaces are cut off, and then are replaced with new ones. If the whole surface is a little bit noisy, smoothing can be applied. In this mode, model can be presented with sections by the desired axis and the desired distance between the sections. In this mode also comparisons between scans or models can be PARATIVE ANALYSIS The comparative analysis in condactued in the software Atos v5.1.1. CAD model from the 2D drawings is drawn in Solid Works 2010 and it is exported as STL file, so it can be imported in this software for the analysis. The imported model is set as a reference, which means that the analysis is going to be according to it. The poligonized model from the scans is also imported in the software in the same window as the CAD model. When the both models are imported, they are overlapped by the coordinate systems. The overlapping of the model is very important because the validity of the whole analysis is in risk. So before importing the models we assure that the coordinate systems of the both models are identical actually that the both models are set identically in the space. The analysis of the deviation is run automatically but the analyzed degree of the deviation is set manually by the operator. This means that we can determent how precise should be the analysis depending on what is our final goal. Since we wanted to see if the deviations of the dimensions and surfaces are higher than 104 mm, we set the scale that way, so the deviations less than 104 mm will not be shown on the screen. The results of the analysis can be seen on the figure 3-1.Fig. 3-1. Analysis of the deviationsDISCUSSION From the comparison between the two models it is clear that there are some deviations in the geometry, bigger that the permitted ones. Deviations can be caused by two groups of problems: Deviations from the shape,Deviations from the tolerance dimensions. Fig. 4-1. Deviation from the shapeUnformed places of the model, shown on the figure 4-1 with red colour (position 1) are as a result of traped air in the tool. Crack, shown on the figure 4-1, with yellow colour, (position 2) is a result of so called “cold joint” which is caused by early hardening of the melted polymer. Deviations of the surface are cause of the uneven cooling.Coorection of these imperfections can be made by changing the techological parametars in the process of injection molding or by changing the tool. Bigger devations that the ones permitted by the constructor can be solved only by correction of the segments of the tool. 30.25 mm Deviation is 0.2 mm.Measured dimension is 30.25mmTolerance dimension is 30±0.05mmFig. 4-2. Deviation from the dimensionsCONCLUSIONUnlike the use of classic coordinate measuring machines, here, with only one quick session of scanning, we can detect and define all the deviations and irregularities of the produced part:Of the all free and tolerant dimension,Geometric tolerances of the shape and form etc,Irregularity of the complex surfaces indicates on incorrect values of the technological parameters. With their change and by re-scanning and re-comparing produced part with 3D model, we shall determine the optimal values ??of technological parameters. This way we perform optimization of production process, to obtain correct product.It is important to notice that this is not just simple measurement of one part but it is much more. Use of the reverse engineering is part from a whole process of development and adaptation of a technology for serial production of a certain part. Through analysis of the dimensions and the form of one product produced with the technology of the injection molding of polymer materials, we can make conclusions not only for the tool itself but also for the technological parameters within the process. This results in increasing the quality of the overall process of production.Apart from the scanning of the part it is good to scan the tool/mold, which in this case it is not done. By conducting analysis on the tool itself we can get additional information, which can be used for better optimization of the whole process.The whole system ATOS II is adequate for transportation and change of the working environment.REFERENCESTraining Tutorial ATOS v5.1.1Vesna Mandic,: Virtuelni inzenering, Masinski fakultet u kragujevcu, Centar za virtuelnu proizvodnju, 2008W. Dealey: The magic, art and science, Modern mold&tooling, Vol.3 No.3 2001Kim G. J. Designing Virtual Reality Systems, Springer, London, 2005Lee K., Principles of CAD/CAM/CAE Systems, Addison-Wesley Longman 1999Kalpakjian S., Manufacturing Processes for Engineering Materials, Pearson Education Inc, New Jersey 2003 ................
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