To carry out the simultaneous forming and perforating of the plate, a feasibility study was carried out on electromagnetic forming and perforating of the plate. By conducting electromagnetic forming and perforating experiments of the plate, the optimal energy required to perform the operation was obtained.
Metal Forming
Conventional Metal Forming
Lightweight design is one way to reduce vehicle emissions and increase fuel efficiency. In the search for new technologies to improve aluminum formability, electromagnetic forming is considered in the present work.
High Strain Rate Forming
The magnetic field of the workpiece is of opposite nature to that produced by the coil. Due to the opposite nature of magnetic fields, repulsive force between the coil and workpiece leads to the formation of the workpiece.
Motivation
There is little literature reported on current pulse impedance and its effect on workpiece deformation during electromagnetic forming. Also, there is no information in the literature about the simultaneous forming and perforating of the sheet.
Objectives of the Research Work
In the present study, the effect of crow blocking during electromagnetic deformation is analyzed by considering the maximum deformation of the plate to find out the effective current pulse responsible for the formation. In the present study, a feasibility study is carried out on electromagnetic forming and perforating the sheet to obtain an optimal energy to carry out the process.
Contributions of the Work
Organization of the Thesis
It also presents the finite element modeling and simulation of electromagnetic forming and perforation of the plate. In the following sections, electromagnetic tube forming and electromagnetic plate forming are discussed both experimentally and numerically.
History
The latest developments and trends in electromagnetic imaging are discussed in the review by Psyk et al. The two factors responsible for the temperature increase during electromagnetic forming are plastic deformation and Joule heating.
Equipment and Material
- Capacitor Bank
- Forming Coil
- Field Shaper
- Workpiece
The surface of the field shaper near the workpiece acts as a shaper coil and produces its own magnetic field. Due to the opposite nature of the magnetic field, a repulsive force is created, which causes the workpiece to be shaped [27].
Electromagnetic Tube Forming
Another problem with using the die for electromagnetic forming is sparking between the die and the workpiece. The upper limit of workpiece thickness depends on the energy capacity of the electromagnetic forming machine and the strength of the coil.
Electromagnetic Sheet Forming
The electromagnetic force during electromagnetic forming decreases as the distance between the coil and the workpiece increases. 45] concluded that formability is not increased by electromagnetic forming, as shown in the forming limit diagram.
Advantages of Electromagnetic Forming
Electromagnetic forming can lead to high productivity if automated, as the operating time is around 200 µs. Since the electromagnetic forming reduces springback, close dimensional tolerances can be given to the product.
Limitations of Electromagnetic Forming
Introduction
Experimental Setup
An ignition switch is used to discharge the high voltage energy from the capacitor bank to the coil. The Rogowski coil voltage is proportional to the rate of change of current through the conductor. The induced voltage in the Rogowski coil is proportional to the change in the speed of the current, but to make the voltage proportional to the current an integrator is needed.
Tube Expansion
Where, σ is the conductivity, J~s is the current density in the tube, µ is the permeability, Γ represents the surface area of the coil and the tube, Γ represents the region where the coil is connected to the external current supply. Where M represents the structural mass matrix, C is the structural damping matrix, u is the nodal displacement vector, K is the structure stiffness matrix, and F is the load vector. The spiral was modeled as rigid. 3.14) where σy and ¯ε are the equivalent plastic stress and plastic strain, ˙¯ε is the relative rate of plastic strain and TR and Tm are the room and melting temperatures of the material.
Results and Discussion
Effect of Coil Length
For coil C2 (relative magnitude equal to 1), the magnetic pressure distribution is fairly uniform along the axis of the tube. In the case of coil C3 (relative magnitude greater than 1), the magnetic pressure distribution becomes non-uniform with maximum at the tube ends. The non-uniform distribution of the magnetic pressure is due to the relative size of the tube coil system.
Effect of Current Frequency
The strain increases rapidly up to 10 kHz, then the strain increases slowly and reaches a maximum value, which can be explained by Figure 3.15. When the displacement reaches a maximum value corresponding to the thickness-dependent frequency, the displacement begins to slowly decrease, which can be explained by Fig. 3.16, which shows that the phase shift of the eddy current increases with thickness. The phase shift (θ) is the phase shift between the surface eddy current and the eddy current at a given depth as we move through the thickness of the tube, as shown in Figure 3.17.
Formability Analysis
Initial circle diameter (Di) (3.17) The stress values were measured in two regions as close to the pipe failure and far from the pipe failure region. Stress values at points close to pipe failure are considered unsafe while stress values at points far from failure are considered safe. The stress values obtained for the spiral tube length ratio less than one are shown in Figure 3.21.
Summary
The effect of current frequency on electromagnetic tube expansion is analyzed using finite element simulation. As the frequency is increased beyond the optimum value, the tube distortion decreases due to induced current becoming out of phase as we move through the tube thickness. Effect of frequency on deformation is more prominent for thin tubes. Therefore the effect of frequency can be neglected for thick tubes provided available magnetic pressure can deform the tube.
Dual Electromagnetic Sheet Forming
Finite Element Modelling of Electromagnetic Form- inging
The use of the BEM for the sky allows to deal with complex 3D geometries with multiple connected conductors and movement of the conductors. The variable of the BEM is a surface current which allows the coupling of the model to external current sources through simple Dirichlet constraints. The R-L-C parameters used are the resistance of 10.5 mΩ, the inductance of 359 mH and the capacitance of 426 µF.
Results and Discussion
Therefore, in the case of single plate forming, the bottom layer of the coil hinders the deformation of the workpiece. The Lorentz force obtained in forming double plates is greater than that of forming single plates. The deformation obtained in two-sheet electromagnetic forming is equal to or greater than that of single-sheet electromagnetic forming.
Crow-barring effect during Electromagnetic Sheet FormingSheet Forming
Figure 4.16 shows the deformation in the center of the workpiece using a portion of the current pulse. From Figure 4.16 it is clear that the maximum deformation occurs at 1.5 part of the current pulse which is equal to the deformation obtained without crow bar. From Figure 4.18 it is clear that the maximum deformation occurs at 1.25 part of the current pulse, which is equal to the deformation obtained without crow bar.
Summary
Electromagnetic forming and perforating is a new method to perform the simultaneous forming and perforating of the plate. Since no information was found in the literature about simultaneous forming and perforation of the plate, a feasibility study was first carried out. In the current research work, the feasibility study for simultaneous EM forming and perforation of plates with detailed analysis of the effect of process parameters has been carried out.
EMFP Die Design
The overall size of the die used was 250 mm square with a height of 60 mm. The pattern required to create the die cavity was fabricated in thermocarbon material as shown in Figure 5.3. Further reduction of friction can be achieved by mirror finish and lapping of the die.
Punch for EMFP
Coil
Top and bottom FRP sheets protect the coil from contact with the sheet or other experimental equipment. End plugs were used to connect the coil to the high voltage terminals from the capacitor bank.
EMFP Setup
Results and Discussion
It was observed that the discharge energy of 3.1 kJ was insufficient to deform the sample and drill all the holes in the sheet. As we have discussed, AA 1050 requires 5.2 kJ of energy to perform a successful EMFP operation, but in the case of AA 5052, the 5.2 kJ discharge energy was insufficient to pierce all of them. The maximum dome height of 21 mm was obtained in the case of AA 1050 with a discharge energy of 7.5 kJ.
FEM Analysis of EMFP
The finite element model created to study the electromagnetic formation and perforation of plate is shown in Figure 5.18. The first bracket expression represents the dependence of the fracture on pressure and explains the decrease in stress to fracture as the hydrostatic stress (σm) increases. The first bracket expression represents the dependence of the fracture on pressure and explains the decrease in stress to fracture as the hydrostatic stress (σm) increases.
Results of EMFP Simulations
The impact velocity was 185.06 m/s, which is the minimum velocity required for the plate to perforate according to the die shape. Assuming the plate comes to rest after perforation, the minimum velocity required to perforate the holes is given by This shows that the minimum velocity required to punch holes increases as the number of holes to punch increases.
Summary
First, the electromagnetic pressure is calculated, which serves as input to the forming and perforation model. Second, the magnetic pressure obtained from the electromagnetic model is given as input to the forming and perforation model to calculate the stress, strain distribution and velocity of the plate.
Conclusions
Electromagnetic plate forming and perforating have been done using two types of punches namely pointed and concave. During electromagnetic forming and perforating of a plate, perforated holes are elongated in the radial direction due to simultaneous forming and perforating of the plate. For AA 1050 sheet, the optimum value of discharge energy to perform electromagnetic forming and perforating is found to be 5.2 kJ.
Scope of Future Work
Li, Effect of field shaper on magnetic pressure in electromagnetic forming, Journal of Materials Processing Technology. Li, Analysis and reduction of coil temperature rise in electromagnetic forming, Journal of Materials Processing Technology. Li, Analysis and reduction of coil temperature rise in electromagnetic forming, Journal of Materials Processing Technology 225 (Supplement C.
