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노학곤,이경훈,강범수,김정 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.11
Electromagnetic forming (EMF) processes require no more than about 300 μs to complete. Given the high speeds involved (150 m/s to 250 m/s), it is almost impossible to determine the flow stress through the application of a mechanical property test. In this study, the flow stress of Al 1100-O at high speeds was predicted by inverse parameter estimation. The constitutive equation of flow stress is given by the Cowper–Symonds model. Firstly, a practical experiment process is set up with a spiral coil for the EMF-free bulge test. To compare the results of our experiments with the numerical results, an EMF simulation was prepared and the X- and Zdisplacements of the sheet on the center line were measured to compare them with the results of experiments as obtained using 2- D scanning. To find the optimal properties for the EMF process, a reduced-order model (ROM) with the Kirging method was adopted to form the basis. From this model, an inverse parameter estimation was conducted using the nonlinear least squares method with a genetic algorithm. By comparing the results of the experiments with the ROM results, the validity of the flow stress obtained by an inverse estimation was validated.
노학곤,송우진,강범수,김정 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.8
Electromagnetic forming (EMF) is a high strain rate forming process that uses Lorentz force. In this study, electromagnetic formingwith a rectangular block shape in the center of the forming die was examined to determine the possibility and applicability of EMF. However, the high speed of the process in the absence of a medium between the coil and the workpiece results in bouncing of the workpiece,which may result in poor forming. So, in this study, the use of a cushion plate is proposed as a means of reducing the degree ofbounce in an EMF process. A 3D electromagnetic numerical model using a spiral forming coil was considered. An RLC circuit, coupledwith the spiral coil, was numerically simulated to determine the deformation behavior and design parameters, such as the input currentand the magnetic forces. A cushion plate was used between the forming coil and the sheet to be deformed to reduce the extent of bounce. In the numerical simulation, the sheet was found to be well fitted to the objective die with the cushion plate. The simulation resultsshowed that the extent of bounce was drastically reduced because of the velocity direction of the workpiece and the cushion plate. Theexperiment was performed using 24 kJ to deform Al 1100 with a thickness of 1.27 mm, based on the simulation results. The deformedsheet was well formed, and closely fitted the objective die with a minimum of wrinkling, relative to the results obtained without a cushionplate. As a result, an EMF process with a middle-block die was successfully established both numerically and experimentally to reducethe bouncing.
Experimental and Numerical Study on Patterned Emboss Forming Using Electromagnetic Forces
노학곤,안우진,송우진,강범수,김정 한국정밀공학회 2015 International Journal of Precision Engineering and Vol.16 No.7
In this paper, we propose the use of electromagnetic forming to produce emboss pattern shapes using one forming coil and a single die punch with electromagnetic forces. Considering the noncontact characteristic of the process, the formation of the patterns could be attributed to its high speed. The high impact on the sheet workpiece at a speed of 150-250 m/s produces significant coining pressure, which acts over an area larger than that of conventional forming. In this study, four different patterns were produced on AL 1100-O sheets of area 40 mm × 40 mm and thickness 1.27 mm. The four types of emboss patterns were created by deformation using only one spiral coil. Using the simulation results, an experimental spiral coil with 10 turns was fabricated. Four different patterns were successfully produced on the metal sheet in the experiment. The length and depth of the patterns were measured by three-dimensional scanning relative to the die shape and good agreement was observed. This confirmed that emboss pattern forming by EMF using a single die can be used to replace the costly process of the conventional method.
유한요소해석을 통한 전자기 성형장비 공정변수의 성형력에 미치는 영향
노학곤(Hak Gon Noh),박형규(Hyeong Gyu Park),송우진(Woo Jin Song),강범수(Beom Soo Kang),김정(Jeong Kim) Korean Society for Precision Engineering 2013 한국정밀공학회지 Vol.30 No.7
The high-velocity electromagnetic forming (EMF) process is based on the Lorentz force and the energy of the magnetic field. The advantages of EMF include improved formability, wrinkle reduction, and non-contact forming. In this study, numerical simulations were conducted to determine the practical parameters for the EMF process. A 2-D axis-symmetric electromagnetic model was used, based on a spiral-type forming coil. In the numerical simulation, an RLC circuit was coupled to the spiral coil to measure various design parameters, such as the system input current and the electromagnetic force. The simulation results show that even though the input peak current levels were at the same level in each case, the forming condition varied due to differences in the frequency of the input current. Thus, the electromagnetic forming force was affected by the input current frequency, which in turn, determined the magnitude of the current density and the magnetic flux density.
노학곤(Hakgon Noh),윤준석(Junseok Yoon),송우진(Woojin Song),강범수(Beomsoo Kang),김정(Jeong Kim) 한국자동차공학회 2012 한국자동차공학회 학술대회 및 전시회 Vol.2012 No.11
Electromagnetic forming(EMF) is an impulse or high-speed forming technology using pulsed magnetic field to apply Lorentz forces to workpiece. Generally, EMF have better formability characteristic due to its high-speed forming condition. in this paper, numerical simulation were performed to investigate formability enhancement of EMF. Gurson-Tergaard-Needleman(GTN) plasticity material model was used to verify the effect of the tool-sheet interaction which is main reason of formability enhancement. A free bulging and a conical forming die with 0.7T AL1050sheet was used to predict damage evolution based on GTN model. The impact between the tool and sheet results in combined stress states such as compressive hydrostatic stresses. In conclusion, the damage reduction because of the tool-sheet interaction can be the main factor increasing formability in EMF process.