Magnetic pulse forming sheet metal,an american haunting movie summary,local community resources for emergency preparedness 2014,disaster preparedness meaning in hindi - PDF 2016

Magnetic pulse forming is a technology that has gained interest in the last decades – thanks to the increased formability it offers for high-resistance-low weight ratio materials such as aluminum and magnesium alloys. EHF can form hollow shapes with much ease and at less cost compared to other forming techniques. EHF is more adaptable to automatic production compared to other high energy rate forming techniques.
EHF can produce small – to intermediate sized parts that don't have excessive energy requirements. It is also a solid-state welding process, which means that the materials do not melt during the creation of a bond, which provides the opportunity to join dissimilar materials.
With this process, it is possible to join tubular products as well as sheet materials, depending on the coil which is used. Joining of conventionally non-weldable materials, in a quick and cost-effective manner, such as dissimilar material joints. Development of complex workpieces or new products, which were previously not possible with the conventional joining processes. Contact-free: no marks of forming tools and processing of coated or sensitive materials is possible. There is no heat, radiation, gas or smoke, shielding gas, which is less harmful for the operator. In hostile environments machines can perform the joining operation, avoiding supplementary investments in operator safety. It is possible to improve the work conditions of the welder or operator, since the technology is environmentally clean.
One workpiece has to withstand the impact of the other, so it is possible that a mandrel or support is required to prevent deformation. The Belgian Welding Institute has acquired large experience with the electromagnetic pulse welding process.
If there is sufficient industrial interest, BWI wants to further investigate this very innovative welding process and to demonstrate its potential benefits for the industry. One major complexity of the process lies in the design and study at the work piece level and the interaction between the several physical aspects involved: the electromagnetic waves as source of energy, the thermo-mechanics controlling the strain and stress evolution, as well as the study of fracture and damage under high-speed loading conditions. Many metals tend to deform more readily under extra – fast application of load which make these processes useful to form large size parts out of most metals including those which are otherwise difficult – to – form. There are several advantages of using these forming processes, like die costs are low, easy maintenance of tolerances, possibility of forming most metals, and material does not show spring-back effect.
The explosives used are generally high – explosive chemicals, gaseous mixtures, or propellants. The sheet metal work piece blank is clamped over a die and the assembly is lowered into a tank filled with water.

The process is versatile – a large variety of shapes can be formed, there is virtually no limit to the size of the work piece, and it is suitable for low – quantity production as well. Explosive forming is mainly used in the aerospace industries but has also found successful applications in the production of automotive related components.
Since the repelling force acts on the coil as well the work, the coil itself and the insulation on it must be capable of withstanding the force, or else they will be destroyed.
When a tube – like part x is to fit over another part y (shown as insert in Fig 9.3(i)), coil is designed to surround x so that when energized, would force the material of x tightly around y to obtain necessary fit. From energy considerations, the ideal pressure pulse should be of just enough magnitude that accelerates the part material to some maximum velocity and then let the part come to zero velocity by the time it covers the full fly distance.
It has found extensive applications in the fabrication of hollow, non – circular, or asymmetrical shapes from tubular stock. A bank of capacitors is first charged to a high voltage and then discharged across a gap between two electrodes, causing explosions inside the hollow work piece, which is filled with some suitable medium, generally water.
With the modern equipment, it is now possible to precisely control the energy within specified limits, therefore the primary factor is the dimensional accuracy of the die. All materials that can be formed by conventional forming processes can be formed by EHF also. This joining technology makes use of electromagnetic forces for deformation and joining of workpieces.
The discharge current induces a strong transient magnetic field in the coil, which generates a magnetic pressure, which causes one workpiece to impact with another workpiece. The explosive deformation force is however created in a safe way, by using electromagnetic forces generated by an induction coil. From the point of view of the potential applications, which are mostly factory-made parts, this is not necessarily a disadvantage.
The previous projects were focused on the application of the process for joining tubular applications. This work is dedicated to the development of a predictive model and computational tool able to deal with the interaction between the electromagnetism and the thermo-mechanics in a 3D finite elements frame work.
There are two techniques of high – explosive forming: stand – off technique and the contact technique. The process has the greatest potential in limited – production prototype forming and for forming large size components for which conventional tooling costs are prohibitively high. The work coils needed for different applications vary although the same power source may be used.
A high charging voltage is supplied for a short time to a bank of capacitors connected in parallel. The expandable coils are less costly and are also preferred when high energy level is needed.

The magnetic coil is placed inside the tube – like part, so that when energized would expand the material of the part into the collar. All forming coils fail, expendable coils fail sooner than durable coils, and because extremely high voltages and currents are involved, it is essential that proper safety precautions are observed by the production and maintenance personnel. The compression applications involve swaging to produce compression, tensile, and torque joints or sealed pressure joints, and swaging to apply compression bands or shrink rings for fastening components together. These explosions produce shock waves that travel radially in all directions at high velocity until they meet some obstruction. These materials are aluminum alloys, nickel alloys, stainless steels, titanium, and Inconel 718. This process also offers the possibility to join dissimilar materials, which are difficult to weld using the conventional welding processes.
This means that after welding, parts can immediately be unloaded and further processed with standard equipment. Electromagnetic pulse welding of sheet materials, which currently receives more and more attention, is considered as quite promising, due to the many advantages this process offers.
We introduce the computational aspects of the electromagnetism, from the selected approach to include the geometry of the parts down to the coupling with the electric machinery behind the process. The explosive charge is placed at some predetermined distance from the work piece, see Fig 9.1. Flat coils have been used on flat sheets to produce stretch (internal) and shrink (external) flanges on ring and disc – shaped work pieces. This is followed by the computational techniques needed to couple the electromagnetic computation to the thermo-mechanical one with a special focus on the problem of tracking the displacement of the deformable part within the electromagnetic module. When the charging is complete, which takes very little time, a high voltage switch triggers the stored electrical energy through the coil. The deformation can be controlled by applying external restraints in the form of die or by varying the amount of energy released, Fig 9.4. We also introduce some aspects more related to the physics of the process such as the phenomena of elastic spring-back elimination and surface bonding (welding). A high – intensity magnetic field is established which induces eddy currents into the conductive work piece, resulting in the establishment of another magnetic field. The forces produced by the two magnetic fields oppose each other with the consequence that there is a repelling force between the coil and the tubular work piece that causes permanent deformation of the work piece. A methodology for identification of the electric parameters defining the machinery and needed to perform the simulation is introduced.

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Comments to “Magnetic pulse forming sheet metal”

  1. jhn writes:
    For the water needs the medical doctor is warranted beneath the seal. Clear on what we are aluminium.
  2. Reg1stoR writes:
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