Opracowano system komputerowego wspomagania projektowania procesów głębokiego tłoczenia blach. System zapewnia niespotykaną dotychczas dokładność wymiarowo-kształtową projektowanych wytłoczek, z jednoczesnym zapewnieniem pewności prowadzenia operacji tłoczenia. Bazuje on na metodzie elementów skończonych oraz wprowadzonym do niej systemie oceny tłoczności blach opartym na wykresach naprężeń granicznych. System umożliwia również korekcję kształtu narzędzi, kompensującą sprężynowanie powrotne wytłoczki w operacjach obejmujących głębokie tłoczenie oraz okrawanie i wykrawanie. W tym celu zastosowano algorytm obliczeniowy wykorzystujący siły działające na narzędzia w trakcie tłoczenia w celu korekcji kształtu narzędzi. Korekcja taka pozwala na uzyskanie dużej dokładności wymiarowo-kształtowej wytłoczek. W celu zapewnienia stałej, wysokiej jakości wyrobów opracowano system kontroli i diagnozowania procesu tłoczenia. W systemie tym zastosowano do określania momentu utraty stateczności materiału metodę wykorzystującą pomiar pola magnetycznego generowanego w trakcie procesu tłoczenia przez wytłoczkę. System wspomagania projektowania procesów tłoczenia blach ma możliwość stosowania jako wstępniaków blach spawanych laserowo. Opracowany system zweryfikowano doświadczalnie dla różnego rodzaju blach oraz kształtów wytłoczek.
This monograph deals with the problems related to a computer-aided sheet-metal deep drawing process design system. The system is based on the finite element method supplemented with a sheet metal drawability criterion and a computing algorithm which minimizes the shape error caused by drawpiece springback . The computer-aided design system ensures that drawpieces without material-stability-loss faults and with high dimensional-shape accuracy are obtained. A new method of diagnosis of sheet-metal forming process for drawpiece manufacturing has been developed. The system ensures exceptionally high dimensional-shape accuracy of designed draw-pieces and reliability of the press-forming operation. The system allows one to design the press forming of complex-shaped drawpieces using only computer techniques with no recourse to the expensive and time-consuming trial-and-error method. This is particularly important for the motor vehicle industry where final product shape accuracy is crucial. A wide use of the system will contribute to substantial savings and an improvement in the accuracy of manufactured drawpieces. If no computer-aided design of press-forming processes is used, the costs of the tools and those of the design process are extremely high, while the time of product implementation is long. The computer-aided sheet-metal forming process design system has the form of a software package running on workstations with considerable computing power. The system enables the analysis of design correctness for any complex three-dimensional drawpiece. It is based on the finite element method with a drawability assessment system based on forming limit stress diagrams (FLSD) incorporated in it. If for the assumed drawpiece shape a danger of exceeding the limit stress occurs, the process conditions and the kind of sheet material can be changed or the drawpiece shape can be modified and an analysis of the process can be performed again. Or, when the shaping conditions unchanged, one can determine the maximum drawpiece depth. The press-forming tool shape compensation model (Chap. 8) makes it possible to compensate spring-back in complex sheet-metal forming operations, including deep drawing and drawpiece trimming and die shearing, whereby the assumed high drawpiece dimensional accuracy can be obtained. Owing to the use of theoretical FLSDs in sheet-metal forming process design, a wide range of industrial press-forming processes characterized by a highly nonlinear deformation path can be analysed. The forming-limit-strain-diagram drawability criterion used so far is correct only for simple deformation paths. The radically modified modern perturbation method, employing a complex material work-hardening curve and a plasticity function (Sect. 4.1), has been applied to determine FLSDs. It differs from the commonly used theoretical limit-strain method - the Marciniak-Kuczynski theory - in the fact that no initial material inhomogeneity, a parameter difficult to determine in practice, is introduced. Instead a small perturbation is introduced into the homogeneous solution of the problem and on this basis inferences about the possibility of loss of material stability are made (Sect. 4.2). An original method of springback compensation for complex sheet-metal forming operations, including deep drawing and drawpiece trimming and die shearing, has been developed (Sect. 8.2). This combination of sheet-metal forming operations is most common in industry. The method of press-forming tool shape compensation consists in creating virtual tools on the basis of typical results of the computer simulation of the press-forming process. In this way, by taking into account the shape error caused by draw-piece material springback, the proper shape of the tools can be determined. In the manufacture of drawpieces, high quality of the press-formed products must be continuously assured. The function of the press-forming process control and diagnosis system is to provide complex information about the quality of the drawpieces (Chap. 11). An original method of controlling and diagnosing the press-forming process based on measurements of the drawpiece's magnetic field (Sect. 11.1) is proposed. The method exploits the magnetomechanical effect, which consists in generation of a magnetic field by a ferromagnetic body subjected to a mechanical load. The method's advantage over other methods of determining the moment of material stability loss is its accurate imaging of all the phenomena that occur during press forming. The employed state-of-the-art magnetic field sensors and the magnetovision camera make possible point measurements of drawpieces and 3-D analyses. A system of remote monitoring of the press-forming process, which communicates with the Control Centre via the Internet, has been developed (Sect. 11.2). The computer-aided sheet-metal forming process design system can handle tailored blanks (Sect. 11.3). In order to produce them, different kinds of sheets, whose geometrical and physical features are matched on the basis of a structural-economic analysis of the press-formed products, must be joined together by laser welding. The magnetic measurement method is used to determine the material model of the laser-welded sheets. The computer-aided sheet-metal forming process design system allows one to properly analyse a wide range of press-forming processes. It has proved to be effective for different materials used in press forming, such as: deep-drawing of steel, aluminium, brass, stainless steel and titanium steel. The experimental verification of the whole system has proved its usefulness for sheet-metal forming design. The following conclusions can be drawn from the research: 1. Owing to the incorporation of the drawability assessment system, based on forming limit stress diagrams determined by the perturbation method, into finite element method computations, a computer-aided sheet-metal forming process design system ensuring correct results could be built. 2. By applying the perturbation theory to the determination of FLDs good agreement between theoretical FLDs and experimental results for biaxial tension for different materials was obtained (this has always been a problem in the case of the Marciniak-Kuczynski theory). The experimental verification of the perturbation theory, carried out for different drawpiece shapes, proved this theory to be useful as the criterion of sheet metal drawability. 3. A computing diagram which exploits the forces acting on the tools during press forming to correct their shape has been developed. The algorithm makes it possible to build a system which assures high quality of the products for both simple and complex press forming operations, including deep drawing, drawpiece trimming and die shearing. 4. In order to obtain accurate results, a description of the material's elastic properties used in FEM simulations should take into account a change in Young's modulus with plastic strain since the plastic strains which arise in the drawpieces change the elastic action of the sheet metal during springback. Neglecting this phenomenon results in substantial differences between the results of sheet metal springback simulation and the experimental results. 5. In order to take full advantage of the tool shape correction system's capabilities, one should use full stamping dies. 6. An original method of controlling and diagnosing press forming processes on the basis of measurements of the magnetic field around the drawpiece has been developed. The method is based on the magnetic effect, which consists in the generation of a magnetic field by a ferromagnetic body subjected to a mechanical load. 7. Magnetic field point measurements or a magnetovision camera allow one to precisely determine the moment of material stability loss. A method of automatic material stability loss determination consisting of the analysis of the magnetic field strength signal during the sheet-metal forming process has been developed. 8. The sheet-metal forming process control and diagnosis system allows one to monitor several industrial plants from one control position via the Internet. 9. The computer-aided sheet-metal forming design system also handles tailored blanks. 10. A method employing magnetic measurements of sheets was used to create a material model of the weld area and the heat-affected zones.