Design and Development of 4kJ Electromagnetic Forming Machine

Electromagnetic forming is a type of high-velocity, cold forming process for electrically conductive metals, most commonly copper and 

Project Title

Design and Development of 4kJ Electromagnetic Forming Machine

Project Area of Specialization

Mechanical Engineering

Project Summary

Electromagnetic forming is a type of high-velocity, cold forming process for electrically conductive metals, most commonly copper and aluminium. The work piece is reshaped by high-intensity pulsed magnetic fields that induce a current in the work piece and a corresponding repulsive magnetic field, rapidly repelling portions of the work piece. The work piece can be reshaped without any contact from a tool, although in some instances the piece may be pressed against a die or former. The technique is sometimes called high-velocity forming or electromagnetic pulse technology.

A special coil is placed near the metallic work piece, replacing the pusher in traditional forming. When the system releases its intense magnetic pulse, the coil generates a magnetic field, which in turn accelerates the work piece to hyper speed and onto the die. The magnetic pulse and the extreme deformation speed transforms the metal into a visco-plastic state, increasing formability without affecting the native strength of the material. 

A rapidly changing magnetic field induces a circulating electric current within a nearby conductor through electromagnetic induction. The induced current creates a corresponding magnetic field around the conductor. Because of Lenz's Law, the magnetic fields created within the conductor and work coil strongly repel each other.

Electromagnetic forming has a number of advantages and disadvantages compared to conventional mechanical forming techniques.

Some of the advantages are:

• Improved formability (the amount of stretch available without tearing)
• Wrinkling can be greatly suppressed
• Forming can be combined with joining and assembling with dissimilar components including glass, plastic, composites and other metals.
• Close tolerances are possible as springback can be significantly reduced.
• Single-sided dies are sufficient, which can reduce tooling costs
• Lubricants are reduced or are unnecessary, so forming can be used in clean-room conditions
• Mechanical contact with the work piece is not required. This avoids surface contamination and tooling marks. As a result, a surface finish can be applied to the work piece before forming.

The principle disadvantages are:

• Non-conductive materials cannot be formed directly, but can be formed using a conductive drive plate
• The high voltages and currents involved require careful safety considerations

The die used in the electromagnetic process should be made of low electrical conductivity to minimize the magnetic cushion effect. Dies are generally made of steel or epoxy resin.

The machine and the work coils required in EMF process can be viewed as general-purpose tooling. Therefore it can be said that the tooling for this process is inexpensive.

Project Objectives

1. Analysis of Electrical circuit (RLC Circuit) for 4KJ.
2. Calculations for Capacitor bank (resistor, inductor, capacitors), High voltage switches and Power supply.
3. Assembly and fabrication of Circuitry and Frame of the machine.
4. Machining of spiral copper coil for sheet metal forming.
5. Testing of machine on various energy levels.
6. The workpiece material will be aluminum ranging from 0.4mm to 1mm.

Project Implementation Method

The metal work piece to be fabricated is placed in proximity of a heavily constructed coil of wire. A huge pulse of current is forced through the work coil by rapidly discharging a high-voltage capacitor bank using a switch. This creates a rapidly oscillating, electromagnetic field around the work coil.

The high work coil current creates ultra-strong magnetic forces that easily overcome the yield strength of the metal work piece, causing permanent deformation. The metal forming process occurs extremely quickly (typically tens of microseconds) and because of the large forces, portions of the work piece undergo high acceleration reaching velocities of up to 300 m/s.

When the switch is closed, electrical energy stored in the capacitor bank is discharged through the forming coil producing a rapidly changing magnetic field, which induces a current to flow in the metallic work piece. The current flowing in the work piece produces a corresponding opposite magnetic field, which rapidly repels the work piece from the forming coil, reshaping the work piece.

In the electromagnetic forming process, the conductivity of the metal and the eddy currents, which makes contact with magnetic field, creates a net pressure on the surface of the metal. Then the metal surface moves inward due to the effect of this pressure, this mainly occurs due to the transfer of energy from the magnetic field to the metal.

In the electromagnetic forming process, the metal absorbs energy from the magnetic field to be deformed. To utilize most of this energy in the forming operation, and to reduce the energy loss due to resistance heating, the forming pulse is kept short for better optimization of energy produced by the magnetic field. In general, pulse has duration of between 10 and 100 second.

The electromagnetic forming method uses a capacitor and forming coil to create intense magnetic field. The efficiency of the magnetic pulse mainly depends on the resistivity of the material being formed. For better output, the resistivity of the material must be less than 15 micro-ohm-centimeters.

In most of the forming processes, tool contacts with the specimen to get the desired output. However, in the case of electromagnetic forming, the magnetic field is used to apply the pressure on the surface of a metal, which normally does not require any kind of lubrication. In addition, it leaves no tool marks on the metal surface.

In the electromagnetic forming process, the metal is loaded and achieve plastic region, which results in plastic or permanent deformation, so that the spring-back associated with the mechanical forming process is completely eliminated because no mechanical contact is present during the process of metal forming.

Benefits of the Project

The forming process is most often used to shrink or expand cylindrical tubing, but it can also form sheet metal by repelling the work piece onto a shaped die at a high velocity. High-quality joints can be formed, either by electromagnetic pulse crimping with a mechanical interlock or by electromagnetic pulse welding with a true metallurgical weld. The process works best with good electrical conductors such as copper or aluminum, but it can be adapted to work with poorer conductors such as steel. 

Advantages of magnetic pulse forming:

• Reproducibility: The electric energy in the coils can be controlled very precisely, the reproducibility is very high.
• Without contact: In contrast to traditional deformation techniques, the magnetic fields generate the forces. No lubrication is necessary and since this technique operates without contact, the damage, which can be caused by a former in the conventional method, can be avoided.
• Low Energy Consumption: Although very high electrical current is required to generate the high intensity electromagnetic field, the duration of the current is only approximately 50 to 100 microseconds. Since there are no electric motors or mechanical moving members, there is no heat or friction losses.
• Highly Repetitive: Once the system is set up, it is highly repetitive and requires no periodic adjustments as is customary in mechanical processes.
• Minimal Equipment Maintenance: It is highly reliable and needs no adjusting as is customary with mechanical machinery.
• Assembling of Dissimilar Metals: The material to be formed needs to be an electrical conductor such as mild steel, or aluminum. However, the mating part does not have to be an electrical conductor, it can be steel, cast iron, aluminum or, it can even be fiberglass, plastic etc.
• Spring-back: The material is deformed plastically, resulting in a permanent plastic deformation, where spring-back of the deformed material is avoided.
• The process ensures a higher formability of the work pieces due to the lower internal stress and friction, in comparison with other mechanical forming processes. Work pieces which must be stress-relieved in conventional forming processes, can be formed with magnetic pulse forming in a single step.

Uses of Electromagnetic Metal Sheet Forming Machine,

Automotive Industry:

• Drive shafts
• Components of air conditioning
• Fuel filters
• Closing caps of cylindrical components
• Coatings of exhaust systems
• Simultaneously forming and perforating aluminium tubes (e.g. for car seats)

Electrical Sector:

• Electric fuses
• Components of electric motors
• Cable ducts

HVAC - Industry: Heating, Ventilating, and air Conditioning:

• Components of cooling units, air conditioning, cooling tubes (as a replacement of e.g. brazing or mechanical joining techniques)

Aerospace Industry:

• Components of planes : drive shafts, lining of ammunition, control rods
• Components of fuel pumps

Technical Details of Final Deliverable

Our project of 4kJ of Electromagnetic Forming machine is capable to deform the metal sheet  of around 0.4-1 mm to required shape. This machine increases the formability of the sheet and also deform sheet more efficiently in comparison to other forming processes as it reduces the spring-back and wrinkling effect. On large scale industrial production this process has high productivity rate and thus reduces the per unit cost. This process can be used for multiple applications like compress or expand hollow profiles, flat and three dimensional sheet metal can be shaped, joined and cut. Operations such as punching, blanking, bending and flanging can also be done.

Final Deliverable of the Project

Hardware System

Core Industry

Manufacturing

Other Industries

Core Technology

Others

Other Technologies

Sustainable Development Goals

Industry, Innovation and Infrastructure

Required Resources

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