CAD API based tool path control for novel incremen

文件名称: CAD API based tool path control for novel incremental sheet forming .pdf

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详细说明：基于CAD技术的API自动控制算法开发，以实现一种新型的渐进成形工艺CAD API BASED TOOL PATIL CONTROL FOR SILEET FORMINO 83 PkM with Linear actuators Master tool with slave tool Fig. 2. Prototype of a PKM-based DSF machine The prototype has an industrial fagOr 8070 control. It can handle simultaneously interpolated 28 axes and the execution channels allow four different machining operations to run in synchronization. For the dsf process six axes are enough, three for the forming(master)tool and three for the supporting(slave) tool 2.1. Tool path calculations and forming strategies The master tool path is processed with the CATIA CAM post-processor for surface milling. This CAM program supports Z-level calculations for 5 axis milling machines so the normal vector at cach contact point can be used to calculate the slave tool path This is done by a home made offline path calculator based on the master tool path Forming tests were carried out after several simulations with two forming strategies (strategy 'Aand 'B with constant step depth) on a truncated cone with different wall angles. At strategy 'A,, the slave tool supports the sheet on the backside, by moving ly along the our, constantly on the flat zone of the part (on the first forming level) as shown in Fig. 3 MASTERTOOL Fig. 3. Section view of a truncated cone showing forming strategy ' A At strategy 'B'(see Fig. 4)the slave tool moves synchronously along the outer contour right on the opposite side of the sheet and supports the master tool Pollack periodic 5. 2010. 2 L. PANITI MASTER TOOL SLAVE TOOL 4. Section view of a truncated cone showing forming strategy B The master tool needs a support at least on the first Z-level(strategy 'A)with a predefined offset to avoid unwanted deformations. Fig. 5 shows the master-slave configuration and the tool paths for strategy 'B(on the left-hand side) and 'A'(on the right-hand side) thickness t surface normal master tool path laster Tool path tool radius, Rr 区2 Level n) Slave Tool Path z-Level n, tool cen:er pcint Fig. 5. Master-slave tool configuration, strategy B and'A Using the notations given in Fig. 5, the tool center point of the slave tool can be calculated for strategy ' B'(1)and'A'(2)respectively by the following formulas TCPS= TCPM+(2R T (1) TCP TCP X", TCPVM/R TCP, where TCP is given by the coordinates. The volume constancy leads to the relationship (3) between the initial (to) and the actual (t1) sheet thickness by a given wall angle a. where t is calculated with the formula so-called t1=t0 3) Pollack Periodico 5. 2010. 2 CAD API BASED TOOL PATIL CONTROL FOR SILEET FORMINO 2.2. Results of Tool Path calculations and forming The tool path calculation time depends on the computer resources(CPU, memory etc. ) the complexity of the part and the number of the contact points. The CATIa CAM program is using linear spline interpolation; so the sum of the points can be a huge number in some cases. Fig. 6 shows the result of a simple truncated cone's tool path calculation with strategy 'B 日.上P民线国巴只 Fig. 6. Tool Paths in CATIA, strategy ' B DSF increased the flexibility of the conventional ISF and with multistage forming [15], where the final shape is created with more than one NC programs, higher formability can be realized. Fig. 7 shows a part manufactured incrementally with multistage DSF. The results can be easily achieved by applying a higher wall angle Fig. 7. DSF with multistage forming(second NC program) 2.3. The problem of the commercial post-processor In some cases the post-processor's master tool path generation cannot be used with strategy 'A because the result of the linear interpolation is not sufficient in connection Pollack periodica 5. 2010.2 L. PANITI with accuracy and control. The number of contact points decreases with the increase of the forming depth, more precisely with the decrease of the circumference. This means at the first Z-level that the number of generated points is always higher than it is on the last 7-level. In most of the cases this leads to asynchronous movement of the two forming tools and to unwanted sheet deformation One solution is to use other post-processors. The other solution is to increase the contact points with a 'controlled 3D model 3. CAD API for parameterized 3D model building The Application Programming Inter face of commercial CAD programs gives the ability, to every user, to develop their own applications. These are highly capable of enhancing certain parts of the work with the software, its level of customization, and efficiency of usage, without a deep programming know ledge. Solid Works is a user- friendly CAD application in this field and it is also a product of Dassault Sytemes like CATIA. Moreover the necessary program the Visual Basic for Applications can be found in the install package. These were some of the main reasons why the Solid Works API was chosen to overcome the problem mentioned in Paragraph 2.3 A novel method was presented by Hussain and gao([161-l17D to test the thinning limits of sheet metals in negative incremental forming. The CAD APl is able to build predefined parameterized models mentioned by Hussain and Gao [16]. lig. 8 shows the graphical user interface of the CAD API and a circular generatrix'(a geometric element that generates a geometric figure, especially a spline that generates a surface by moving the spline in a specified fashion) Arisk Those Y saw rodels sane nae seve fader osher ig. 8. Graphical user interface of the CAD API The program was designed to create approximations of parts with circular cross section in order to test the thinning limits in DSF. The picture in /ig. 8 is showing the Pollack Periodico 5. 2010. 2 CAD API BASED TOOL PATIL CONTROL FOR SILEET FORMINO required parameters, which are to be given in the fields on the left-hand side. The accuracy of the approximation can be controlled via the number of sides, which means, that a polygon with the umber of sides is used instead of the cross sectional circle. The approximation of the generatrix' is based on the curve length, in such a way that the relative difference between the length of chain of lines and of the length of the curve is minimum the same as the relative difference in the cross section the thickness of the sheet can also be given. By clicking the generate button the generation of the model starts and the CAd api closes itself. The models can be saved in step format but Solid Works API supports other formats as well 3.1. Accuracy of the generated 3D models The models produced by the API have a good approximate accuracy(see Fig. 2), which can be improved by the increase of sides. Inumber of sides Fig. 9. Approximation error(in %)of the cross section as a function of sides 3.2. Results of the CAD API model building The CAD API uses the 'lolt' command (one of the 3D feature commands in Solid Works)to build the models. On the lell-hand side in Fig. 10 a predefined parameterized model can be found with a circular generatrix created with the ' revolve feature command and on the right-hand side the same model is shown with the discussed approximation. The sides for the approximation are also visualized. For rea time visualization of complex parts the possibility of using GPUs(graphics processing units)with high performance computing [18 can be taken into consideration pplying a master tool path generation on a regular model(left-hand side of /ig. 10)processed with the CatIA CAM post-processor for surface milling using 7-level the positions of the tool center points are showing a high degree of irregularity (see Fig. 77) Pollack periodica 5. 2010.2 L. PANITI pplying the same master tool path generation on a model created with the CAD APl (right-hand side of lig. 10)the positions of the tool center points are showing an increased degree of regularity (see Fig. 12) 7P制当于曰国以图 Fig. 10. Model building result without and with approximation 国山兰多画鱼即熟区中1(回 Fig. 11. Result of the master tool path generation on a regular model 4. Conclusions In this paper a new concept of a milling machine-based Dieless Incremental Shee Forming Dsf) process, a tool path calculation special for this new technique and the CAD Application Programming Interface (for basic parts to overcome some problems of a commercial post-processor was introduced. The main objective was to create a Pollack Periodico 5. 2010. 2 CAD API BASED TOOL PATIL CONTROL FOR SILEET FORMINO CAD application that is able to create parameterized models(with approximation)in order to eliminate the errors of tool path generation and to improve the degree of regularity of the tool center point positions. The test showed significant changes in the tool center point positions but the application have to be improved in the future with generation of stL files to bypass the use of additional commercial post-processors 三〓像中 Fig 12. Result of the master tool path generation on a model created with the CAD API Acknowledgement The manufacturing of the parts was achieved in the frames of a European research (R&D) project, with CULPTOR(NMP2-CT-2 014026). The work of graduate student Z. Illes during the investigation is greatly acknowledged References [1 Leszak E. Patent US3342051A1, published 1967-09-19, Apparatus and Process for Incremental Dieless Forming [2] Maidagan E, Zettler J, Bambach M, Rodriguez P P, Hirt G. A new incremental sheet forming process based on flexible supporting the system, Key engineering Materials, Vo.344,2007,pp.607614 [3] Hirt G, Ames J, Bambach M, Kopp R. Modeling and experimental evaluation of the incremental CNC sheet metal forming process, C/RP Annals-Manuyfacturing Technology, Vol.53,No.1,2004,pp.203-206 Pollack periodica 5. 2010.2 9 L. PANITI [4 Callcgari M. Amodio D, Ccrctti E, Giardini C. Shcct incremental forming: advantages of robotised cells Vs. CNC machines, Industrial Robotics, Programming, Simulation and Applications, ARS/PLV, Gcrmany, Dcccmbcr 2006, pp. 493-514 Schafer T, Schraft R. D. Incremental sheet metal forming by industrial robots using a mering tool, Rapid Prototy ping Journal Vol. 11, No 5, 2005, pp. 278-286 [6 Vihtonen L, Puzik A, Katajarinne T Comparing two robot assisted incremental forming methods: incremental forming by pressing and incremental hammering, Inlernalionul ournal of Material Forming, Vol 1, 2008, pp. 1207-1210 [7 Jie L, Jianhua M, Shuhuai H. Sheet metal dieless forming and its tool path generation based on Stl tiles, Int. /Adv. Manuf. Technol. vol. 23, 2004, pp. 696-699 [8] Tekkaya A E. Shankar R, Sebastiani G. Homberg w, Kleiner M. Surface reconstruction for incremental forming, Prod. Eng. Res. Devel. Vol. 1, 2007, pp. 71-78 [9 Skjoedt M, Hancock M. H, Bay N Creating helical tool paths for single point incremental forming, Key Engineering Malerials, Vol. 344, 2007, pp. 583-590 forming, Journal of Materials Processing Technology, Vol. 177, 2006, pp 4094/2Cmcntal [10] Attanasio A, Ccrctti E, Giardini C. Optimization of tool path in two points incre [11 Attanasio A, Ceretti E, Giardini C, Mazzoni L. Asymmetric two points incremental forming, improving surface quality and geometric accuracy by tool path optimization, Journal of Materials Processing Technology Vol. 197, 2008, pp. 59-6 [12] Rauch M, Hascoet J. Y, Hamann J. C, Plenel Y Tool path programming optimization for incremental sheet forming applications. Compuler-Aidledl Design Vol. 41, No. 12, 2009, pp. 8 [13] Meier H, Dewald O, Zhang J. A new robot-based sheet metal forming process, Proc. of 11 th International Conference on Sheet Metal SHEMET, 2005, Erlangen, Germany, Apr 5-8,2005,pp.465-470 simulation, Proc. of 7th ICTP International Conference on Techno on and process [14] Hirt G, Junk S, Witulski n. Incremental sheet forming: quality evaluat gy of plasticity Yokohama, Japan, October 27-November 1, 2002, paper no 343 [15 Kitazawa K, Nakajima A. Cylindrical incremental drawing of shect metals by CNC incremental forming process, Proc. of 6th ITCP, International Conference on Technology of Plasticity, 1999, pp. 1495-1500 [16 Hussain G, Gao L. a novel method to test the thinning limits of sheet metals in negati incremental forming, International ournal of Machine Tools and Manufacture Vol 47 No.3-4,2007,pp.4l9-435 [171 Hussain G, Gao L,, Dar N. U. An experimental study on some formability evaluation methods in negative incremental forming,. ournal of Materials Processing Technology, Vol.186,No.1-3,2007,pp.45-53. [18] Tukora B, Szalay T. High performance computing on graphics processing units, Pollack Periodica, vol 3, No. 2, 2008, pp. 27-34 Pollack Periodico 5. 2010. 2

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