Design of a Warm/Hot Electromagnetic Forming System for the Forming Brittle Sheet Metals
Program Name: ARDEB 1005 | Project Code: 215M929
Forming of brittle sheet metals has become increasingly important over the past decades. Especially, the use of materials with limited ductility such as high strength steel, aluminum and magnesium as sheet metals in automobile industry, in addition to the use of titanium and aluminum alloys in the modern applications of defense technologies, have strongly promoted the research and development activities on forming of brittle sheet metals. In forming of brittle sheet metals, two major problems stand out: the difficulty of forming at room temperature and the tearing due to the progressive contact between the sheet and the die (especially in thin sheet materials used in defense industry). The main reason why alternative forming methods (such as hydroforming and stretch forming) are used in the defense industry (especially in aircraft construction) is to overcome the above mentioned problems. Electromagnetic forming is a type of high velocity forming technology which is particularly used in the forming of sheet metals and walled pipes. This technology bases on the idea that a high intensity pulsed magnetic fields induce a current within a nearby conductor generating sufficient Lorentz forces which eventually causes the work-piece deform plastically. As can be understood from the above explanations, electromagnetic forming does not necessitates any mechanical means like molding. By virtue of this feature, the main cause of the rupture problem is naturally eliminated. Furthermore, the electromagnetic field may not be used only for forming, with induction heating methods, metals can also be heated to very high temperatures which provides a great advantage in terms of forming brittle sheet metals. In this project, an electromagnetic forming system will be designed and constructed and also the effectiveness of the system will be evaluated. To ensure the formability of sheet metal, pre-heating will be applied by the electromagnetic induction method, then the material reaching a certain temperature will be shaped by means of passing a high frequency current. Moreover, in the project, the design of an appropriate die and a coil will be studied in the light of novel numerical methods and analysis techniques. In this project, aluminum 7XXX series, a material widely used especially in the defense industry, is selected as the brittle material to be formed, however this choice is an application requirement and the method to be developed will be applicable to other brittle materials like Armox armor steel and magnesium. The main objective of the project is to enable the electromagnetic forming system to reach the capacity to form brittle materials at mild and hot temperatures by means of continuous redesigning and updating the system. For this aim, the system will be expanded as it is able to heat the work-piece by induction and AL 7XXX alloys will be the subject material. Finally, the efficiency and the performance characteristics of the system will be measured by forming 1 mm and 1.5 mm thick sheets.
Induction Furnace Design
The design of a certain induction furnace for a certain application depends mostly on empirical formulas and experience. The purpose of this project is to perform an electromagnetic-thermal coupled analysis for designed coil with certain billet and observing its performance during the heating period. This will lead to the ability of expecting the required coil current and its frequency, to heat certain part of a certain billet to a certain temperature at the predetermined time. Then, the simulation results can be used to build the coil and leads to design the power supply for the induction furnace. It is already known that the design of the induction furnace depends mainly on general calculations and on the experience. Induction Heating (IH) systems using electromagnetic induction are developed in many industrial Applications. induction heating is composed of four parts. They are rectifier, filter, high frequency inverter, and resonant load. The rectifier module is considered as full-bridge rectifier. The second portion of the system is a capacitive filter. The ripple components are minimized by this filter. The third is a high frequency converter to convert the constant DC to high frequency AC by switching the devices alternately. In our project Insulated Gate Bipolar Transistor (IGBT) will be used as a power source, and can be driven by PWM signals of driver circuit. In the resonant load, the power consumption is about 10000W. The following figure shows bridge topology of for induction heater.
This system has High efficiency and is suitable for commercial heating and the power is 3 to 30 kW. To control the entire induction heating system C2000 MCU is needed. The C2000 MCU controls the whole process and communications and drives the fan and the relay, and generates the PWM signal to drive the IGBTs. C2000 MCU starts the first procedure to detect the pot. The system returns to standby mode if there is no pot or the pot is not appropriate. Power Supply: The main power supply is obtained directly from the grid or AC source, 220VAC 50 Hz. The AC power is filtered and is not applied directly to the power diode bridge. In this project a 500VDC, power supply is used. The output current of this device is 50 A. Here is a simulation circuit of this project. This circuit is designed in simpower simplorer envirement and the load is R-L-C series resonance and the inverter is valtage fed. According to this simulation C=40 uF L=27uH R=0.1 And the resonance frequency is about 5000 Hz.
The output waveforms of this simulation are given below:
As mentioned above The Micro Controller Unit type used in this project belongs to C2000 series of Texas Instrument Company (TMS320F335,) Digital Signal controller. This Digital Signal Processor is capable of controlling IGBT switched by generating PWM signal and driving them in a controlled position. PWM Generation by these micro controllers can be done by computer programming.