COMPENSATION OF SPRINGBACK EFFECT IN DESIGNING NEW PRESSING TECHNOLOGIES

Transcription

1 Abstract COMPENSATION OF SPRINGBACK EFFECT IN DESIGNING NEW PRESSING TECHNOLOGIES Maciej Nowosielski 1, Krzysztof Żaba 1, Paweł Kita 1, Michał Kwiatkowski 1 1 AGH University of Science and Technology, Faculty of Non-Ferrous Metals, al. A. Mickiewicza 30, Kraków, mnowosie@agh.edu.pl This paper presents the issues related to analyze and avoid springback effect during metal forming process. Stamping process simulations were performed using the eta/dynaform. FEM-based simulations let to better understand how to design tools and forming process parameters affect the final quality of components and productivity. The mathematical model of pressing process takes into account a springing plate and three core tools: punch, die and punch, which are given modifications to compensate the springback effect. Tools are rigid elements with the selected kinematic and load conditions. The simulations take into account the friction coefficient, which is an important factor in the process of formation. Blank material model should take into account large elastic-plastic deformation as well as the effects of plastic anisotropy properties. The influence of numerical parameters on the accuracy and efficiency of numerical calculations were determined. This allowed to determine the optimal numerical model and gave satisfactorily results accurate with not very long calculations time. Determined through simulations tool shape correction allows for improvement in the quality of the resulting product. Verification of the numerical calculations were technological tests for sheets made of nickel superalloy. Tests were performed on samples of varying degrees of deformation at room temperature. The results will be used to build a database of materials. At each stage of deformation were determined fields of displacement and changes in the distribution of thickness. Keywords: springback, sheets, nickel alloys, tools 1. INTRODUCTION Competition at market, affects the companies to introducing new products and technologies of its producing at higher quality. Pressing processes are among others highly demanding. There are a lot of parameters as force, friction, lubricants, temperature which can influence at quality of final product. Problem of springback effect is also very important for thin sheets used in forming structures with complex surface. One of the main methods used to simulate the pressing processes is FEM. It allows specifying the spring angle and in addition fields of deformation, stress, local risk of cracks in material [1]. The biggest advantage of this approach is that FEM method is cheaper in comparison with method of trial and error. So far, traditional designing and manufacturing based on experience of designers, who correlated their earlier research with errors during their work. That approach entails high cost. Modern metal forming methods must be based on CAD/CAM capabilities. It allows to short time of process, and save the money. Factor affecting the quality of the stampings is accuracy of form and dimensions and it is strongly associated with spring of material [2]. The paper presents the results of springback effect simulation and experiments on samples made of the heat-resistant nickel superalloys, INCONEL 625 and INCONEL 718, designed for the manufacturing of innovative products. Extremely negative relationship between susceptibility to the springing and the shape of the product justifies the need for a new practical knowledge that is necessary in the process of creating the desired shape of the product with the required supplies. For materials made of nickel superalloys INCONEL

2 625 and INCONEL 718 which are characterized by big springback effect preferably is to firstly simulate process, and next perform at industrial conditions [3]. LS-DYNA is widely used software to study analysis, and compensation of springback effect during the metal forming processes. Basic parameters are being mostly chosen to give efficient and accurate simulation results [4-6]. During the simulation, and compensation of springback effect it is recommended using proper material model the same at each stage. 2. EXPERIMENTAL SETUP Samples were prepared as shown in Fig. 1 of sheet made of INCONEL 625 and INCONEL 718, 0,6 mm thick. Springback effect was measured by the method of bending at 90 angle, in the specially constructed single-angle bending device schematically presented at Fig. 2a. To bending was used universal testing machine of the Zwick Company. Spring angle was measured on non-deformed samples, and samples after deformation 30, 45 and 60% by rolling. Investigations were realized in room temperature. Fig. 1. Sample for bending Simulations were realized using eta/dynaform 5.8.1and its solver LS-DYNA. For process of simulation was used material model for forming and springback simulation, material model 37, which is mostly used. All tools should use shell elements and the rigid material. Set of tools from software is presented at Fig. 2b. Analysis of spring angle was made using software GOM Inspect V7.5 SR1. Mechanical properties of sheets were obtained during standard technological tests. Fig. 2. Bending at angle 90 device a) real, b) meshed model from preprocessor

3 3. RESULTS Parameters necessary for modeling, characteristic for material model implemented to eta/dynaform are presented in Table 1. Table 1. Parameters characteristic for material model for INCONEL 718 Mass density [g/cm 3 ] Young s Modulus [GPa] Poisson s Ratio [-] 8, ,29 Lankford Parameter R00 [-] Lankford Parameter R45 [-] Lankford Parameter R90 [-] 0,69 1,24 2,14 During technological tests for material INCONEL 625 obtained spring angle 0,67 8; 14; 22 n case of INCONEL 718-0,51 2; 11; 18 with deformation relatively 0, 30, 45 and 60%. With an increase of deformation increase of spring angle was observed. Results indicate a greater risk of changes in the shape after deformation for INCONEL 625. Results of measuring spring angle depending on the strips deformation of INCONEL 625 and 718 are shown in Fig. 3. Fig. 3. Spring angle for INCONEL 625 and INCONEL 718 after deformation Hardening curves for both materials are presented in Fig. 4. Fig. 4.Hardening curves achieved in experiments a) INCONEL 625, b) INCONEL718

4 Results of spring angle achieved at simulation and in technological test are presented at Fig. 5. c) d) Fig.5.Deformed samples achieved at simulation process in comparison to technological tests a) results from simulation (INCONEL 625), b) result from experiment (INCONEL 625) c) results from simulation (INCONEL 718), d) result from experiment (INCONEL 718) Deviation between angle 90 and sample after springback for INCONEL 625 and INCONEL 718 achieved during simulation used eta/dynaform with solver LS-DYNA, module SCP is presented in Fig. 6. Fig.6.Deviation between angle 90 and sample after springback a) sample of INCONEL 625, b) sample of INCONEL 718

5 4. SUMMARY To achieve highest accuracy of modeling it is necessary to provide very accurate data about material, boundary conditions and process conditions. Simulations performed on a single processor workstation sustained about 14 hours. Were performed simulations for non-deformed samples, an achieved compatibility at the level of 90%.Deviations in shape are similar at both samples. It is worth emphasizing, that results from computer simulations and from experiments are compatible for all stages of process. The next stage will be modeling of processes at deformed samples, according to technological tests, and use of tool eta/dynaform with solver LS-DYNA, especially with use module Springback Compensation Process. This will be applied to compensate shape of tools at product with complex shape. REFERENCES [1] HOJNY M.: Application of an integrated CAD/CAM/CAE/IBC system in the stamping process of a bathtub 1200 S, Archives of Metallurgy and Materials, 2010, vol. 55(3), s [2] PAĆKO M., DUKAT M., ŚLEBODA T., HOJNY M.: The analysis of multistage deep drawing of AA5754 aluminum alloy, Archives of Metallurgy and Materials, 2010, vol. 55(4), s [3] ŻABA K., NOWOSIELSKI M., KWIATKOWSKI M., HOJNY M.: Deformability of nickel superalloys intended for shell elements of aircrafts, Conference Proceedings, COMAT 2012, Plzen, Czech Republic [4] MAKER B. N., ZHU X.: Input parameters for springback simulation using LS-DYNA, Livermore Software Technology Corporation, June 2001 [5] HOJNY M., GLOWACKI M.: Computer modeling of deformation of steel samples with mushy zone, Steel Research Int., 79 (2008), [6] MAKER B.N., ZHU X.: Input Parameters for Metal Forming Simulation Using LS-DYNA, April 2000