electromagnetic forming - hani aziz ameen

Electromagnetic forming Dr. Hani Aziz Ameen

Technical College – Baghdad – Iraq- Dies and Tools Eng. Dept.

((Electromagnetic)) forming

Dr. Hani Aziz Ameen

Asst. Prof. in Mechanical Engineering

Technical College - Baghdad

Dies and Tools Engineering Department

E-mail: [email protected]

mailto:[email protected]



Chapter

One



INTRODUCTION High Velocity Forming:- High velocity forming can be defined simply as moving a work piece at high rates (over 200 m/sec) and transforming the associated kinetic energy into plastic deformation as the work piece contacts the die surface. High velocity forming only uses a one sided die to produce parts, so the issues associated with tolerances, machining and alignment as discussed earlier with traditional stamping [1] are significantly reduced. High velocity forming methods can provide improved formability, more uniform strain distribution in a single operation, and lightweight tooling equipment [1]. With more uniform strain distribution, strain hardened alloys can be more readily shaped with reduced intermediate annealing operations. As stated previously, there are several methods that can be considered for high velocity forming; among these are explosive forming, electromagnetic forming, and electro hydraulic forming [2]. Figure (1) shows the methods available through high velocity forming [2]. High velocity forming uses several different methods for exerting force on the sheet stock including; explosive, electromagnetic and electro-hydraulic. Each only requires a one sided die, which significantly reduces several of the problems associated with the traditional stamping method.



Figure (1) Methods of high velocity forming [2]

Figure (2) typical configuration of electromagnetic apparatus forming



Figure (3) types of electromagnetic forming.

Electromagnetic forming EMF:- The EMF technique was first used in this country in the 1950’s and 60’s, due to its advantages in enabling the fabrication of many complex geometry parts and enhancing the formability of low ductility materials. Numerous applications of EMF have been implemented in industrial production; among the more spectacular applications are engine nacelles made in a single piece, electromagnetic riveting guns and hammers (developed by NASA in the mid 1980s) used in the assembly of aircraft skins, and dent pullers1. Recent advances in electronics and energy storage make EMF technology ripe for mass



Figure (4) a 316L stainless steel sample formed electromagnetically using a uniform[3]

Pressure actuator production and plans are well under way for the large scale manufacturing of fuel cell plates and tubular frames for the automotive industry. One of the most promising recent applications is the manufacturing of fuel cell plates (Figures 2 and 3), where conventional stamping methods have failed and only the EMF technique can deliver the final shape without wrinkling or tearing deeper channels[3].



Figure (5) Schematic of a uniform pressure actuator. The primary coil has many

turns going into the plane of the figure [3] Electromagnetic Forming procedure:- Electromagnetic forming has only been around since the 1960s, but it is the most common method of high-energy rate forming (HERF). In this process, electrical energy is converted to mechanical energy with the use of a magnetic field. When an electrical current is rapidly introduced through a conductor (wire), a magnetic field is created around the wire. The sudden introduction of a magnetic field creates eddy currents that flow in opposite direction in any conductor nearby. The eddy currents develop their own magnetic field and cause a repelling force. The repelling force is then used as a means of forming sheet metal into different shapes. Figure (6) a schematic showing an electrical circuit, two magnetic fields, and a compression coil. When the capacitor is charged by the power supply, the second switch is closed causing the capacitor to discharge and send a sudden surge of current through the conductor. This is the process used to create the first magnetic field. The magnetic field creates eddy currents in the nearby conductor which creates an opposing magnetic field as well. The part to be formed is then placed between the two magnetic fields where it will be forced to take shape due to the repulsive force from the two opposing magnetic fields (see Figure (7). The two types of coils used in this process are called compression and expansion coils. These coils are capable of withstanding up to 60,000 psi and 15,000 psi respectively (see Figure 6). The advantage of electromagnetic forming is that the magnitude of the fields can be controlled with extreme accuracy. The process has a high repetition rate with exact consistency. Forming dies are relatively inexpensive and most applications only require a single die because the magnetic force replaces the punch portion of a die



Figure (6) Schematic Diagram for electromagnetic forming.

Figure (7). A magnetic field between the conductor and part produces magnetic

Pressure that deforms the part to the desired shape [4].



Figure (8) three basic electromagnetic forming coils: (a) compression coil, (b) expansion coil, and (c) flat coil[4][5][6]

The tooling quality is extremely important for this process. Only one side of the tooling is used to fabricate parts, which causes tooling marks to show up on one side of the part. When a die is made up of metal, induced current can create electrical arcing between the die halves. Using dies made from nonconductive and impact-resistant plastics can eliminate electrical arcing EMF Advantage:- As the experience in introducing this method has indicated, the electromagnetic metal forming has the following advantages compared to other metal forming techniques:- 1. A significant amount of energy (usually between 5 and 200 kJ,) is stored in a large capacitor, or bank of capacitors, by charging to a high voltage (usually between 3,000 and 30,000 volts).[7] 2. Easy to use, the process is easy to implement and require no special operator skill. 3. Improved strain distribution and repeatability from work piece to work piece. 4. The great technological flexibility of the process. The same inductor can be used to form the work pieces of different configurations. 5. Simplicity of the technological equipment. Only one die or plunger is used.



6. Absence of a transfer medium during forming process. This feature allows forming the metallic work pieces through insulating coatings or the wall of a vacuum chamber. 7. The modern EMF equipment operates noiselessly. The tool and the assemblies of the electromagnetic equipment don’t need lubrication. There is no aggressive environment. 8. The improvement of the characteristics of the formed materials. The majority of aluminum alloys formed electromagnetically show an increased ductility when compared to the static deformation. 9. EMF is a desirable process because the dynamic nature of the deformation results in benefits which include increased forming limits and reduced spring back [8].

Table (1) Comparison of traditional stamping to electromagnetically formed methods [9].

EMF disadvantages:- 1. It is difficult to obtain parts with deep drawing by using electromagnetic forming procedure. In order to obtain deep drawings it is necessary to form the work piece by various inductors. 2. Not all metals and alloys can be formed using EMF. Low-conductive materials require high-conductive "drivers" to be formed. 3. Not any shape is suitable for forming electromagnetically. The forming forces are created as a result of the interaction of the current induced in the work piece with the magnetic field of the inductor. 4. Not all the geometries of the work piece are suitable for EMF. There are some restrictions with respect to thickness and diameter of the tubular work pieces.



5. The low mechanical strength of the inductors in the case of deformation of steel work pieces. The mechanical and electrical characteristics of the modern inductors permit multiple repetition of technological operations without destruction of the inductor during metal forming of relatively light metals and their alloys (aluminum, copper and magnetic alloys). 6-wear, friction as well as fretting due to high normal contact forces combined with tangential movement of the work piece [8]. Applications & Examples OF EMF:- 1- EMF Forming and Piercing:- Figure (9) shows an example of how versatile the process is and how with some ingenuity, very simple forming operations can be developed to form complex parts. The tubular part shown in Figure (9) was produced in one EMF operation using an expansion coil to form, flange and pierce a length of tubing against a single-piece die. The work piece was a 100 mm length of 6061-0 tubing with an 83 mm outside diameter and 0.89 wall thickness. The die was turned from 4340 steel tubing with a 12.7 mm wall thickness. Two drilled holes are used for the piercing operation. The formed part was removed from the die by means of a simple ejector. The parts used a 6kJ impulse for forming and production rates of 240 pieces per hour could be achieved using only manual loading and unloading[7].

Figure (9) Forming and Piercing of a tubular part in one operation [7].



2- EM Forming of axi-Symmetric Work pieces:-

EM forming of axisymmetric work pieces has been a niche manufacturing technique for many years. This process uses solenoid coils, which produce a nearly uniform magnetic field. The uniform magnetic field, combined with an axi-symmetric work piece, makes the process relatively easy to design and implement. Tubes can either be expanded or contracted, depending on the location of the coil, as shown on Figure (10).

Figure (10) Tube contraction and expansion EM operations [6].

The tubes are generally considered to be of fixed length and long enough to neglect any edge effects on the EM field. Tube contraction uses the same principles to contract a tube. It is mainly used in industry to produce mechanical joints (crimping), since uniform pressure distributions given by the coils produce better crimp joints than those made with mechanical presses [8]. 3- EM Forming OF Sheet Metal:-

EMF of sheet has never gained as much acceptance as tube forming in commercial applications. EMF can be used to form parts from flat sheet, or to sharpen features of pre-formed work pieces (Figure11) in so-called hybrid operations. Sheet metal work pieces do not deform uniformly, as do tubes, leading to additional complications in the design and implementation of the process.



Figure(11)Two types of EMF a) flat sheet forming and b) feature

sharpening[10].

Flat or “pancake” coils are generally needed to form parts from sheet metal (Figure 12). These coils do not produce uniform magnetic fields and often have dead spots where the magnetic field, and thus the induced pressure are zero [6]. The magnetic field is cancelled out for adjacent coils for which current flow occurs in opposing directions.

Figure (12)Types of flat or pancake coils with approximate resulting pressure

distributions along indicated sections [10].

EMF of sheet has become the focus of numerous investigations due to the possibility of increasing the formability of aluminum alloys. Several studies have indicated that the formability of aluminum increases when it is formed using high-speed processes like EMF or electro hydraulic forming.



Simplified Analysis of EM Forming Processes:-

A simplified analysis of the EM forming process is presented here to familiarize the reader with the basic principles of the process and how the forming pressures are generated. The circuit used in EM forming can be simplified as an RLCcircuit, to perform a first order analysis. Figure (13) shows the simplified circuit [10].

Figure (13) schematic illustration of an EM forming system, b) simplified EM forming circuit[10].

The current discharged through the coil in this circuit can be described by the following differential equation.

1 2 3



Where I = current in Amperes, t= time in seconds, R = resistance in Ohms, C = capacitance in Farads and f= frequency in Hertz.

Where L = inductance in Henrys.

Figure(14)Current versus time profile given by the solution equation[10].

In an actual EMF process, the current profile would be quite different, as shown in Figure(14). The process only lasts for a few microseconds and the current is prevented from becoming negative by adding a diode to the circuit to avoid damage to the capacitors, which do not react well to changes in the sign of the applied current.

4 5



Figure (15) Current versus time profile for an actual EM forming coil [10].

The simplified analysis does not take into account the changes in the magnetic field caused by the deformation of the work piece.

Magnetic Pressure Distribution:-

The magnetic field in the coil and the magnetic field induced in the sheet repel each other resulting in a body force on the sheet that is typically referred to as the magnetic pressure. Analyzing the interactions between a varying magnetic field and a deforming work piece is not a trivial matter. The magnetic pressure is given by:

Where:- P = pressure in Pascals, μ= permeability of free space and H = electromagnetic intensity. The electromagnetic intensity varies with time, location, applied current and geometry, and is very hard to determine. Electromagnetic intensity distributions for idealized spiral coils have been analytically determined, but no general analytical solutions exist for sheet metal forming operations with flat coils. Despite the complexities of the problem, Plum [10] reports an empirical formula that can be used to determine the magnetic pressure required to form a part from a tube. The relationship is given by:

6



Where YS = yield strength, t = wall thickness, OD = outer diameter, Py = pressure to yield the hoop, Pm = magnetic pressure, N = a correction factor that ranges from 2 to10. The correction factor N accounts for inertial effects, high strain rate effects and the geometry of the part [10].

Magnetic Pressure Distribution on a Sheet Caused by an Idealized Spiral Coil:-

Theoretical magnetic pressure distributions caused by different coils on flat conductive plates determined can be determined. Several simple geometries were analyzed which led to an expression for the magnetic field intensity and the pressure distribution caused by a spiral coil. The equations for the magnetic field intensity, H, and pressure distribution, P, are;

Where I= current in Amperes, N = number of turns in the coil, g = distance from the coil to the work piece in meters, a1 = distance from the centre of the coil to the first wind of the coil meters, a2= distance from the centre of the coil to the last wind meters and r = radius in meters. The theoretical predictions were compared with experimental results. A comparison between the analytical predictions and experimental results for a spiral coil is shown in Figure (16), which shows reasonably good agreement between the theoretical and measured values.

10

9

7 8



Figure (16) Normalized predicted (solid line) and measured (dashed line and

points) magnetic intensity (and pressure) distribution versus radial position for a spiral coil[10]



Chapter

Two



Review of New Work In EMF 1- Formability and Damage in Electromagnetically Formed AA5754 and AA6111. ((J.M. Imbert1, S.L. Winkler1, M.J. Worswick, S.Golovashchenko))/2004 Abstract: This paper presents the results of experiments carried out to determine the formability of AA5754 and AA6111 using electromagnetic forming (EMF), and the effect of the tool/sheet interaction on damage evolution and failure. The experiments consisted of forming 1mm sheets into conical dies of 40° and 45° side angle, using a spiral coil. The experiments showed that both alloys could successfully be formed into the 40° die, with strains above the conventional forming limit diagram (FLD) of both alloys. Forming into the higher 45° cone resulted in failure for both materials. Metallographic analysis indicated that damage is suppressed during the forming process. The failure modes are different for each material; with the AA5754 parts failing by necking and fracture, with significant thinning at the fracture tip. The AA6111 exhibited a saw tooth pattern fractures, a crosshatch pattern of shear bands in the lower half of the part, and tears in the area close to the tip. Both areas showed evidence of shear fracture. This experimental study indicates that there is increased formability for AA5754 and AA6111 when these alloys are formed using EMF. Experimental Procedure:- The experiments consisted of forming 1mm sheet into conical dies of 40° and 45° side angle, using a spiral coil. A Magnepress system with a maximum storage capacity of 22.5 kJ at 15 kV, capacitance of 200 μF and inductance of 230 nH was used. The conical cavity dies were made from tool steel hardened to 50 Rc. A vacuum port was provided to evacuate the air before each part was formed. Figure (17) shows a schematic of the experimental apparatus. The material was cut into 165x165 mm (6.5”x 6.5”) squares. The AA5754 was provided with a solid film lubricant which was removed. No lubrication was used in the experiments. Circle grids were used to measure the engineering strains. Grids with a nominal diameter of 2.5 mm were applied using electrochemical etching. The strains were measured in the rolling direction using a digital grid measurement system.



Figure (17) schematic of the experimental apparatus. Result and conclusions:- Safe parts were produced from both alloys with the 40º cone, with charge voltages of 8.0 kV for the AA5754 and 9.0 kV for the AA6111. All the parts formed with the 45º cone failed at charge voltages of 9.0 and 10.0 kV for AA5754 and AA6111, respectively. Figure (18) show AA5754 parts formed with the 400. Buckling was observed in all of the formed parts. In the AA5754 samples the buckling is localized in the area of the vacuum hole (Figure19), whereas for AA6111 it was more evenly distributed Figure (20).

Figure (18) AA5754 cone formed with the 40° die (8.0 kV)



Figure (19) AA5754 cone formed with the 45° die (9.0 kV). View (I show a neck in

the area under the step and fracture near the tip. An incipient neck is shown in the inset. View (II) shows buckling in the area of the vacuum hole.

Figure(20)AA6111 cone formed with the 40° die (9.0 kV). No tip impact was

observe the AA6111 parts.

Figure (21) show some defect during



the experimental Conclusions:-

Aluminum alloys AA5754 and AA6111 exhibit increased formability when formed using EMF. The damage measurements obtained support the theory that this increase is due to the suppression of damage caused by the tool/sheet interaction. The materials do not fail in pure ductile failure; rather, the failure modes seem to be a combination of plastic collapse, ductile failure, and shear localization. 2- Aspects of Die Design for the Electromagnetic Sheet Metal Forming Process. ((D. Risch1, E. Vogli2, I. Baumann2, A. Brosius1, C. Beerwald1,W. Tillmann2, M. Kleiner1))/2006 Abstract:- Within the electromagnetic sheet metal forming process, work piece velocities of more than 300m/s can occur, causing typical effects when forming into a die, which will be described and discussed in the present paper. These effects make numerous demands regarding the die design. In order to analyze these requirements, experimental as well as numerical investigations have been carried out. Thereby, special focus is put on the possibilities to accomplish these requirements, which are discussed in the following. Experimental setups: The experimental setup for the analysis regarding the geometrical inserts (case A), shown in Figure(22), consists of a spirally wound tool coil, a sheet work piece, a drawing ring, a cover plate as well as different forming elements which can be adapted to the cover plate. Due to the modular die system an easy change of the forming elements is possible. A vacuum port is attached to the cover plate as well as to the inserts to ensure a vacuum inside the die and to avoid pressurized air which acts against the magnetic pressure. The used work piece material was aluminum (Al 99.5) with a thickness of 1.5 mm, which was formed with a charging energy of 1,260 J.



Figure (22) Experimental setups

In order to enhance the wear resistance of the cover plate against the impact and to reduce the friction between the aluminum work piece and the cover plate, three different types of layer systems have been deposited. In this context, hard layers (DLC with and without H-doping), soft layers (MoS2) and multilayer systems (Ti / TiAlN, TiAl / TiAlN) containing six individual layers have been deposited. Summary & outlook;- Two promising die concepts for the electromagnetic sheet metal forming process are pointed out in the present paper. One possibility regarding the die design is the target oriented modification of local stiffness realized in the present investigation by use of geometrical inserts. It could be observed that the occurring geometrical deviations are reduced by increasing the stiffness of the work piece. The second possibility presented in this paper is the use of coated cover plates in order to increase the lifetime of the stressed parts of the die as well as to prevent the use of lubricants by the electromagnetic forming, which could cause geometrical deviations of the work piece. For this purpose the different coating systems have been characterized. Based on this, two layers, namely the DLC-layer and the MoS2-layer, have been chosen for further investigation regarding to their behavior during the electromagnetic sheet metal forming. Although the work piece was not lubricated during the experiment, no fretting between aluminum work piece and the coated cover plate could be observed. Moreover, all coated cover plates have shown a better wear and friction resistance compared with the uncoated ones. Further layer optimization will be associated with a significant decline of the wear and impact resistance for high speed forming conditions which are present during electromagnetic forming.



3- Forming limits for electromagnetically expanded aluminum alloy tubes: Theory and experiment. ((J.D. Thomas a, M. Seth b, G.S. Daehn b, J.R. Bradley c, Triantafyllidis ))/2007 Abstract:- In recent work has extended the concept of forming limit diagrams (FLD) to model the ductility of electromagnetically formed sheets. This general theory is hereby applied to study the ductility of freely expanding electromagnetically loaded aluminum tubes. Necking strains are measured in tubes of various geometries which are loaded by different coils and currents. The experimental results are plotted in principal strain space and show reasonable agreement with the corresponding theoretical FLD predictions, which indicate a 2- to 3-fold increase in the forming limits with respect to the quasistatic case.

Figure (23) Schematic representation of the experimental set-up for electromagnetic expansion of tubes.



Figure (24) shows. (a) The bare 4-turn coil. (b) Sample-actuator configuration. The 31.7 mm tall aluminum tube sample is shown fitted around the urethane-

coated 4- turn coil.

Figure (25) Final configuration showing localized necking of tubes deformed using the experimental EMF setup. (a) 31.7 mm tube deformed with 4-turn coil, (b) 31.7 mm tube deformed with 10-turn coil, (c) 85.1 mm tube deformed with 4-

turn coil and (d) 85.1 mm tube deformed with 10-turn coil



4- Effects of coil length on tube compression in electromagnetic forming. ((YU Hai-ping, LI Chun-feng))/2007 Abstract:- The effects of the length of solenoid coil on tube compression in electromagnetic forming were investigated either by theory analysis or through sequential coupling numerical simulation. The details of the electromagnetic and the mechanical models in the simulation were described. The results show that the amplitude of coil current waveform and the current frequency decrease with the increase of the coil length. And the peak value of magnetic pressure is inversely proportional to the coil length. The distribution of the magnetic force acting on the tube is inhomogeneous while the tube is longer than the coil. The shortened coil length causes the increases of the maximum deformation and energy efficiency. The numerically calculated result and the experimental one of the final tube profile are in good agreement. Experimental Work:- The dimensions and shape of the electromagnetic tube compression system are shown in Figure (26). The EMF machine used in the experiments is EMF-30 (total capacitance 70.2 μF/kV).

Figure (26) System model for electromagnetic tube compression



A pulse of current through the coil is the load in EMF, which is easily measured by experiment. The first period of the current pulse is considered to be responsible for the tube compression. Aluminum alloy (A3003) tubes were prepared to carry out the tube compression tests. The radial displacement of the deformed tube was measured to estimate the effect of coil length on the moderate deformation before buckling.



Figure (27) Effect of coil length on radial displacement: (a) C1; (b) C2; (c) C3 Conclusions: 1) The amplitude of coil current waveform and the frequency of the current decrease with the increase of the coil length. And the peak value of magnetic pressure is inversely proportional to coil length 2) The distribution of the magnetic force acting on tube is inhomogeneous while tube length is larger than coil length. And the tube length outside the coil increases with the decrease of the coil length, which strongly restricts the penetration of magnetic field, so the corresponding magnetic force opposite to coil C3 end is damped slowly. 3) The shortened coil length causes the increase of the maximum deformation, forming velocity and energy efficiency. The numerically calculated result and the experimental one of the final tube profile are in good agreement. 5- Novel Layers for Dies Used in Electromagnetic Sheet Metal Forming Processes. ((E. Vogli1, F. Hoffmann1, J. Nebel1, D. Risch2, A. Brosius2, W. Tillmann1, A. E. Tekkaya))/2008 Abstract:- Due to the high forming velocities during electromagnetic sheet metal forming processes, a high impact force acts between work piece and die. Here, the die surface sustains high damages shown by high wear and galling of the work piece on the die surface. To enhance the die lifetime, a novel coating concept based on the PVD (physical vapor deposition) process was developed. In doing so, the hardness and the toughness of the designed layers were varied and adjusted to the demands of AlMg-sheet forming process.



Figure (28) draft of the experimental setup and exemplary cover plate.

Experimental setups: In order to enhance the resistance of the forming tool employed by EMF against wear and impact as well as to extend the lifetime of the die, an innovative concept concerning the die surface modification has been developed and will be presented in this research work. In this context, different PVD layer systems have been designed and deposited, in which the hardness and toughness of the layers have been adjusted related to the soft aluminum sheets and high forming velocity. Additionally, a finite element simulation was carried out in order to estimate the occurring contact forces between the work piece and the forming tool. Based on these results, accompanying electromagnetic forming experiments have been performed to establish the correlations between developed layers and real forming conditions. Summary & outlook: In this research work an approach to enhance the galling resistance of dies employed by electromagnetic forming processes was presented. Two different kinds of coatings – low friction DLC layer and Ti/TiAlN multilayer’s - were studied and adapted to the EMF process demands. It was detected that the DLC layers feature lower friction coefficients at high hardness and lower Young’s modulus than the Ti/TiAlN multilayer’s, while the hardness of the multilayer’s increases when reducing the Ti monolayer thickness by a constant steady- state Young’s modulus. Based on the level of Young’s modulus, DLC layers have a higher ductility than Ti/TiAlN multilayer. Consequently, the hardest DLC layer and Ti/TiAlN multilayer with the thinnest Ti monolayer (10 nm) were chosen for further investigation in the EMF process. Coated dies show no galling after forming Al sheet, while after forming AlMg3 sheets a slight material transfer was observed. However, the galling resistance for both coated dies was enhanced compared to the uncoated ones. The wear resistance of DLC coated dies was higher than the Ti/TiAlN coated dies independently of the materials to be formed. 6- Electromagnetic blank restrainer in sheet metal forming processes. ((Y.R. Seo))/2008 Abstract:- Electromagnetic blank restrainer (EMBR) is a new technology that was recently developed to control material movement in sheet metal forming processes. Magnetic attraction on the ferrous sheet metal is the intrinsic property of EMBR. The 3D finite element analysis (FEA) of an electromagnetic system is conducted to determine the distribution of magnetic flux density on contacting surfaces of the sheet metal. The distribution is then used to estimate the magnetic force. Experiments have been conducted to measure the magnetic force and compare



with results from the FEA. In order to evaluate the quality of forming with each method, an experimental die has been built. The die forms a channel in a single stroke and provides a direct indication of how each restraining method controls blank movement in the die. Experiments:- An experimental die has been built to prove the feasibility of EMBR in the sheet metal forming process. (Figure.29a) shows the schematic of the die that forms a channel in a single stroke. The die is designed such that the restraining force can be applied by blank holder, draw bead, and EMBR. (Figure.29b) shows electromagnets that are assembled in the die flanges. The blank is made of 1mm CRDQ 1008 steel sheet metal and its size is 102_406 mm. It has been electro-etched with 5mm circle grids, of which the deformations can be measured for plastic strains after forming. Nitrogen gas springs are assembled in the blank holders to generate 9000N for BHF and draw bead clamping force. Fig. 30(a) and (b) shows channels formed with EMBR and the draw bead, respectively. EMBR did not show any sign of forming deficiency or problem while the draw bead left scratches on the blank surface.

. Figure 29 (a) Schematic of channel forming die, (b) EMBR assembly in the die.



Figure (30) A channel formed with (a) EMBR and (b) draw bead. Conclusions: We have proved the feasibility of EMBR in sheet metal forming processes by conducting various experiments and die tryouts. Many technical and economical advantages of EMBR over the draw bead are also discussed in the present paper. In this way, we can reduce the blank size with EMBR and generate substantial cost savings in production. Second, the flexibility and controllability of EMBR can create unprecedented opportunities to optimize the sheet metal forming process. EMBR can be made in any size and installed in any location in a die to meet specific forming requirements and achieve a high forming quality. 7- Warm Electromagnetic Forming of AZ31B Magnesium Alloy Sheet. ((Ulacia1, A. Arroyo2, I. Eguia2, I. Hurtado1 and M.A. Gutiérrez))/2010 Abstract:- In the current contribution electromagnetic forming experiments are performed for rolled AZ31B magnesium alloy sheet at different temperatures up to 250ºC. Two forming operations are studied in this paper, i.e. drawing and bending operations. The final deformations achieved for the different conditions were measured and the effect of both temperature and discharged energy on deformation is shown. In one hand, increasing the forming temperature the yield strength of the material decreases while on the other hand, the electrical conductivity and thus the induced forces are also decreased. It is observed that increasing the forming temperature, for a given discharged energy, the maximum height of the deformed part is decreased. However, increasing the discharged energy at warm temperatures, higher deformation values are achieved without failure. Additionally, bending experiments show that spring back effect is also decreased at warm conditions. Equipment and tooling:- The experiments were conducted using a commercial Maxwell Magneform capacitor bank with a maximum stored energy of 60 kJ. The energy is stored in 30 capacitors, each of them with a capacitance of 60 μF, divided in four independent banks in order to adjust the discharging parameters.



Figure (31) show experimental work Experimental Results and Discussion:-

A- Drawing operation:-

Figure (32) shows the influence of the forming temperature and discharged energy. It can be noticed that the maximum height achieved in EMF experiments is decreased when forming temperature is increased for a given discharged energy. The effect of energy on the maximum height achieved is obvious, increasing discharged energy, the height increases for all the studied temperatures. Moreover, it should be remarked that at warm temperatures, a higher energy could be discharged without failure of the work piece, obtaining better final results.



Figure (32) Effect of the forming temperature and discharged energy on the maximum height.

Figure (33) Deformed parts obtained by EMF at different conditions: (a)

100ºC –9 kJ, (b) 100ºC – 12.6 kJ and (c) 250ºC – 15 kJ.

B- Bending operation:- Figure (34) shows the final results of the bending operation experiments for the different discharged energies and temperatures. When analyzing the results, it must firstly be remarked that the deformation achieved was not homogeneous in the whole flange due to the coil geometry and the induced forces for all the temperatures. In the experiments the die radius and the thickness of the sheet were kept constant. Meanwhile, increasing the forming temperature the yield strength is decreased and therefore the decrease of the spring back can be explained.



Figure (34) Effect of the forming temperature and discharged energy on the bending experiments: (a) different temperatures at 4.5 kJ, (c) different

temperatures at 6 kJ (e) room temperature at different energies, (b) measured angle, (d) final angle vs. temperature and (f) final angle vs. discharged energy.



8- Proposal for a Test Bench for Electromagnetic Forming of Thin Metal Sheets. ((M. Geier1, E. Paese1, J. L. Pacheco1, R. P. Homrich2, J. C. S. Ortiz1))/2010 Abstract:- This paper presents a proposal to build a test bench for electromagnetic forming processes. The project considers the analysis of the electrical circuit and forces involved in the system for selection of low voltage capacitors, resistors, buses, main discharge switch and material choice for actuator’s insulation and rigidity, considering also the manufacturing process of actuators and dies. Among the aspects considered for the design, energy efficiency has been prioritized by the use of non-conducting material to the dies. Free bulging experiments were performed with aluminum AA1100 plates for a system configured with a flat coil actuator. Test measurements of electric currents in the coil actuator with and without the work piece as the secondary circuit were performed, as well as an evaluation of wear and functionality of the system. Actuator Coil and Dies; For this project, a flat spiral coil actuator was selected (Figure 35). The coil was modeled on CAD and then machined on a CNC machine from a 150 x 150 x 15 mm copper plate. A cavity in the shape of the coil was machined with a 0.1 mm gap in a polyacetal block providing rigidity and insulation. The upper die has a circular cavity.

Figure (35) Machined flat spiral coil of electrolytic copper (a) and a sectioned view of the Dies (b).



Results and Discussion:-

Figure (36) Electromagnetic forming results for AA1100 sheets with 0.8 (0,9 kV)

and 0.3 mm (1 kv). The paper presents a proposal of a test bench for electromagnetic forming of thin metal sheets for laboratorial experiments. The presented design solutions are simple, functional and feasible. Aluminum sheet plates of up to 3 mm thick were successfully deformed by the presented EMF machine confirming that this concept serves as test bench and also as a reference for the construction of more powerful and robust machines and with higher degree of automation. 9- MATHEMATICAL MODELING OF AN ELECTROMAGNETIC FORMING SYSTEM WITH FLAT SPIRAL COILS AS ACTUATOR. ((E. Paese1, M. Geier1, J. L. Pacheco1, R. P. Homrich2, J. C. S. Ortiz1))/2010 Abstract:- This study presents mathematical modeling and calculation procedure for problems of electromagnetic forming of thin circular metal sheets using flat spiral coil as actuator. The method focuses specifically on the calculation of the electromagnetic field generated by the flat coil and analysis of the circuit that models the electromagnetic forming system. The flat coil is approximated by concentric circles carrying the current discharge from the capacitors. The calculation of electromagnetic force and magnetic couplings between the coil and metal sheet are made to the initial time, before the plastic deformation of the sheet. The method is based on the Biot-Savart law, and the solution of magnetic induction integral equations is performed by numerical methods specifically with the use of Matlab commercial software. A routine calculation, which models the problem as a set of differential equations was implemented in the Matlab, this provides important information that serves as feedback for system design. Free bulging experiments were performed to demonstrate a good relationship with the



mathematical model predictions for electrical discharge current in the coil and induced currents in the metal sheet, behavior of the transient electromagnetic force between coil and work piece and, distribution of magnetic field and electromagnetic density force along the coil. Also, achieved results showed that there is a strong dependence of the back electromagnetic force with respect to plate thickness for the system analyzed. The difference phase between the current induced in the coil and work piece with higher negative peaks generate the back electromagnetic force. Parameters of the Electromagnetic Forming System; With the aid of preliminary analysis using mathematical model, a system of electromagnetic forming was developed for deep drawing of thin circular metal sheets by using a flat spiral coil. More information about the characteristics of the system is shown in Figure 37.

Figure (37) Die of electromagnetic forming device.



Table (2) System parameters and working conditions.

Thickness 0.3mm Thickness 0.5mm Thickness 1mm

Figure (38) Experimental results for different thicknesses. Conclusions; This work developed a numerical method which can simulate the electromagnetic forming of metal sheets in initial time before plastic deformation. This algorithm was implemented in software Matlab. This mathematic model showed satisfactory results when compared with experiments, validating it and the method of numerical solution. This mathematical modeling was used as a basis for designing an experimental machine for electromagnetic forming.



Chapter Three



Theory of magnetic forming:- In order to calculate the deformation to expect from a magnetic forming system it is necessary to know the energy and voltage of the capacitor bank and the half of the ringing discharge. Together these factors determine the coil current and therefore the B filed and the pressure exerted on the work piece. The capacitor bank energy and voltage determine the capacitance in the series L C and the charge (Q) on the capacitor. This amount of charge flows off the capacitor as it is being discharged to zero-volts during the current rise time. The charge and the rise time determine the average current flowing out of the capacitor and through the coil. For a ringing or un damped discharge the rise time is equal to one-half period or one-fourth of a complete sin wave cycle. T0 =T/2 = 1/4 *2π/ω ------------11 Where: T0 = current rise period T = half period During the first half cycle of the discharge, the current rises from zero to a maximum and returns to zero in a sinusoidal fashion. The voltage goes from a maximum to zero and then almost to full reverse voltage. During this time the charge (Q) is removed from the plates as the voltage goes to zero and then a charge of almost (Q) is placed on the capacitor in the reverse direction. Since the discharge is a sin wave, the peak current will be (π/2) times the average current. The average current is found by dividing the capacitor charge by the rise time E = 1/2*CV2 -------------12 and C = 2E/V2 -------------13 Q = CV -------------14 I avg = Q/T0 = 2Q/T -------------15 I peak = π/2*I avg = π/2 * 2Q/T = πQ/T -------------16 Where: E = capacitor energy (Joules) C = capacitance(Farads) V = voltage (volts) Q = charge (Colombes) TO

2 = current rise time = T/2 T = half period or pulse width If the discharge half period is not known but the system inductance can be measured or estimated then the half period can be estimated for the L-C circuit and the current be arrived at from the half period.



T = √LC -----------------17 Where L= system inductance (henries) C = system capacitance (farads) From the peak current and coil geometry it is easy to calculate the peak B field to expect as follows:- Where; I = NI/2b (amp/cm) ------------------18 Cos θ = a / a2 + b2)1/2 ------------------19 B max = 4π/10 * I * COS θ ------------------20 I = is the current per unit length for the coil and, COS θ= is a geometry dependent factor determined by how long and slender the coil is. θ = is the angle between the coil mid-plane and the diagonal across the bore of the coil. Once the peak field has been determined, it is to arrive at the peak pressure exerted on the work piece if the shielding is complete since the pressure is proportional to B2 and a field of 100Kgauss is equivalent to a pressure of 5800 psi (6000 = 4*1O7 nt/m2). If the shielding is not complete, then this pressure must be multiplied by a factor of (1-K2) where K is the ratio of the field inside the work piece to the field outside. P= B2 outside - B2 inside *5800 pdi = (1- K2 ) B2 * 4*105 nt/m2 ------------------21 B Field=1 tesla The peak is a function of B2 or I2 ,and the current is a sine wave, the pressure is a sin2 function and when integrated over a half cycle, the average pressure in one half of the peak pressure. The impulse or momentum to this work piece per unit area can be calculated as follows: I/area =∫Fdt/A =1/2*P T0 ------------------22 Where: T = halfperiod (second) P = pressure (nt/m2) I = impulse or moment (Kg.m/s) Unit area = m2

1/2 comes from integrating sin2



Example 1:- For the single turn coil used with the 9K joule bank the magnetic field per unit current can be calculated: θ = 450, cos θ = 1/√2 I = NI/2b =1*I/1.27cm = 100KA/1.27cm B= 4/10 * 100KA/1.27cm * 1/√2 = 70 gauss per 100 KA For every 100k amps of peak current from the capacitor bank this coil will produce a peak field of 70k gauss. For each of the five capacitor banks constructed during this experiment these calculations area as follows: Bank (1):- V= 20KV E= 3K Joules T = 2.2 μs E = 1/2 * CV2

C = 2E/V = 2(3KJ) / (20KV)2 = 15 μ farads Q = CV = (15 μf)*(20KV) = 3 coulombs Iavg =2Q/T = 2*0.3 coulombs/2.2 μs =273 KAMPS Ipeak= 1.57(273 kamp) = 428 kamp Bmax= 428 kamp *(70k gauss/1001 amp =300k gauss Pmax = (300)2 * 6000 psi/ (100kg)2 = 54000 psi = 37,2*107nt/m2

Iimpulse/m2 = 1/2*PT = 0.5(37.2 * 107)*2,2 μs = 409 Example 2:- Bank (2):- E = 7.5 Kgauss, V = 5KV, T= 85 μs, C= 600 μ farads Solve:- Q =CV = (600μf)*(5KV) = 3 coulombs I = 2Q/T = 2(3)/85 μs = 70KAMP Ipeak =π/2*(Iamp) = (1.57)*(70Kamp) = 110Kamp Bmax = 110Kamp = 70gauss/100KAMP = 77Kgauss Pmax = (77Kgauss)2 * 6000psi/(100Kgauss)2 = 3600psi = 2.5*107 nt/m2

Impulse/m2 = 1/2*PT =1/2 (2.5 * 107 nt/m2) * 85 μs = 1060 nt*s/m2



Reference

[1]- Daehn, G.S., ((High Velocity Metal Forming)), in ASM Handbook. 2006, ASM International. p. 405-418. [2]- Kamal, M., ((A Uniform Pressure Electromagnetic Actuator for Forming Flat Sheets)), in Materials Science and Engineering. 2005, the Ohio State University: Columbus. p. 261. [3] – Jesse D. Thomas((THEORETICAL FORMULATION AND NUMERICAL IMPLEMENTATION OF ELECTROMAGNETIC AND THERMOMECHANICAL LOADING PROCESSES IN SOLIDS)), ((thesis))/2008. [4]- ((Sheet Metal Fabrication)) By: Matthew Cloutier/2008. [5]- R,Ernst,P.Gillon((Finite element modeling of electromagnetic sheet metal forming))/2003. [6]- ((ELECTROFORMING)),Published by the EPRI Center for Materials Fabrication,Tech Commentary/vol,3/No,5,1986. [7]- Glenn S. Daehn ((High Velocity Metal Forming)) ASM Handbook, Volume 14B, Metalworking: Sheet Forming, Published 2006, ASM International,pp. 405-418. [8]- Richard W.Davies ((Electromagnetic Forming of Aluminum Sheet Automotive Lightweighting Materials))/2006. [9]- Kristin E.Banik,B.S ((FACTORS EFFECTING ELECTROMAGNETIC FLAT SHEET FORMING USING THE UNIFORM PRESSURE COIL))/thesis/ 2008. [10-] José Miguel Segundo Imbert Boyd ((Increased Formability and the Effects of the Tool/Sheet Interaction in Electromagnetic Forming of Aluminum Alloy Sheet))/thesis/2005. [11]-J.M.Imbert1,S.L.Winkler1,M.J.Worswick,S.Golovashchenko ((Formability and Damage in Electromagnetically Formed AA5754 and AA6111))/ 2004. [12]- D. Risch1, E. Vogli2, I. Baumann2, A. Brosius1, C. Beerwald1,W. Tillmann2, M.Kleiner1 ((Aspects of Die Design for the Electromagnetic Sheet Metal Forming Process))/ 2006.



[13]J.D.Thomasa,M.Sethb,G.S.Daehnb,J.R.Bradleyc,Triantafyllidis((Forming limits for electromagnetically expanded aluminum alloy tubes: Theory and experiment))/ 2007 . [14]- YU Hai-ping, LI Chun-feng((Effects of coil length on tube compression in electromagnetic forming))/ 2007. [15]-E.Vogli1, F. Hoffmann1, J. Nebel1, D. Risch2, A. Brosius2, W. Tillmann1, A. E. Tekkaya ((Novel Layers for Dies Used in Electromagnetic Sheet Metal Forming Processes)) /2008. [16]- Y.R. Seo((Electromagnetic blank restrainer in sheet metal forming processes))/ 2008. [17]- Ulacia1, A. Arroyo2, I. Eguia2, I. Hurtado1 and M.A. Gutiérrez(Warm Electromagnetic Forming of AZ31B Magnesium Alloy Sheet)/2010 [18]- M. Geier1, E. Paese1, J. L. Pacheco1, R. P. Homrich2, J. C. S. Ortiz1((Proposal for a Test Bench for Electromagnetic Forming of Thin Metal Sheets))/2010. [19]- E. Paese1, M. Geier1, J. L. Pacheco1, R. P. Homrich2, J. C. S.(( MATHEMATICAL MODELING OF AN ELECTROMAGNETIC FORMING SYSTEM WITH FLAT SPIRAL COILS AS ACTUATOR))/2010.



The Author

Dr. Hani Aziz Ameen , Birth date 1971 in Baghdad- Iraq, has Ph.D. in

Mechanical Engineering – Applied Mechanics – from the University of

Technology –Iraq in 1998. He has more than 50 published papers and he is

an expert in the ANSYS software and finite element analysis and in the field

of plasticity and metal forming process.

Working in several universities and colleges (Technology University-

AlNahreen University- Tikrit University – Technical College AlMusaib)

And now he is Asst. Professor in the Technical College – Baghdad –Dies

and Tools Engineering Department.

E-mail: [email protected]

www.mediafire.com/haniazizameen

mailto:[email protected]

http://www.mediafire.com/haniazizameen