01-08-2012, 04:40 PM
Electromagnetic Forming
[attachment=29944]
Introduction
Electromagnetic metal forming (EMF) is the use of electromagnetic forces to form metal. There
are two very broad implementations.
· Radial forming, in which a round part such as a tube or ring is compressed or expanded.
The forming can be done either onto a die to give the tube a more complex shape, or onto
a smaller tube to swage the two tubes together.
· Sheet forming, in which a metal sheet is formed against a die to give it a more complex
shape.
Briefly, EMF works by the magnetic induction effect. When a coil or solenoid is placed near a
metallic conductor and pulsed via an energy store like a capacitor bank, a magnetic field is
generated between the coil and the workpiece. If done quickly enough, the magnetic field is
excluded from penetrating into the workpiece for a short period of time. During this time, a
pressure is generated on the workpiece that is proportional to the magnetic flux density squared.
This "magnetic" pressure is what provides the forming energy.
The energy is usually supplied to the workpiece in the form of kinetic energy. The magnetic
pressure pulse accelerates the workpiece up to a certain velocity (such as 200-300 m/s). This
kinetic energy drives the material into the die, causing forming on impact.
TECHNOLOGICAL OPPORTUNITIES OF ELECTROMAGNETIC
FORMING
GENERAL REMARKS
As the experience in introducing this method has indicated, the electromagnetic metal forming
has the following advantages compared to other metal forming techniques:
1. High efficiency of the technological process. The major factor limiting the
efficiency increase is the very significant time spent on the process preparation
(installation of the workpiece, adjustment and taking out the finished part). If
necessary electromagnetic equipment can be designed with an output capacity of
3600 operations per hour or even more.
2. The technological process can be easily automated and mechanized. It is possible
to control the equipment remotely. The tool (inductor), creating the magnetic
field, is not connected to the workpiece mechanically. The forming energy can be
dosed precisely up to 1% and with the remote control.
3. The great technological flexibility of the process. The same inductor can be used
to form the workpieces of different configurations.
4. Simplicity of the technological equipment. Only one die or plunger is used.
5. Absence of a transfer medium during forming process. This feature allows to
form the metallic workpieces through insulating coatings or the wall of a vacuum
chamber.
6. The possibility of obtaining high specific pressures. Nowadays the pressures of up
to 108 H/m2 can be obtained without destroying the inductor and pressures of up
to 109 H/m2 can be obtained with the disposal inductors.
7. High culture of production and simplicity of equipment maintenance. The modern
EMF equipment operates noiselessly. The tool and the assemblies of the
electromagnetic equipment donít need lubrication. There is no aggressive
environment. The equipment is completely automated. The monitoring and
control of the operation can be performed by single worker.
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. The microstructure of the alloys with the
same amount of strain has fewer distortions while formed by EMF if compared to
the static deformation.
9. It is possible to perform EMF in hard-to-reach areas. The tool (inductor) can be
connected to the capacitor bank by a flexible bus bar, which allows to perform the
technological operations far away from the capacitor bank (expanding the long
tubes in the central section, corrugation and punching holes in large area metal
sheets).
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 workpiece
by various inductors. Each subsequent operation must be performed by the
inductor, the shape of which repeats the shape of the formed workpiece.
By: Irvin De La Paz, Joan Mojica and Marlene Pujols
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 workpiece with
the magnetic field of the inductor. In order to obtain the induced current the
defined conditions must be met.
4. Not all the geometries of the workpiece are suitable for EMF. There are some
restrictions with respect to thickness and diameter of the tubular workpieces.
5. The low mechanical strength of the inductors in the case of deformation of steel
workpieces. 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). On metal forming of the steel
workpieces the strength of the inductor decreases significantly.
The presented advantages and disadvantages must be considered when introducing EMF.
Considering all those features, it is necessary to remember that the application of EMF is not
always economically justified. The significant cost benefits can be obtained in the case where the
workpiece is especially designed as applied to the new technique so all the possible advantages
can be used.
REQUIREMENTS IMPOSED ON THE SHAPES OF THE WORKPIECES
Since EMF is performed due to interaction of the magnetic field with the induced current in the
forming workpiece, it is necessary that the shape of the workpiece provide for continuity of the
path of the induced current. Fig. 20 shows the admissible and the inadmissible versions of the
initial workpieces for all types of possible technological operations. It shows that when a
cylindrical workpiece is formed with cylindrical inductor, currents leak along its periphery. If the
cylindrical workpiece has a through slit along the generatrix of the cylinder or a large number of
through openings, the forces acting on the workpiece are weakened and forming is low-effective.
Due to low duration of the pressure pulse, it does not appear possible to use EMF for forming of
solid metal workpieces.
[attachment=29944]
Introduction
Electromagnetic metal forming (EMF) is the use of electromagnetic forces to form metal. There
are two very broad implementations.
· Radial forming, in which a round part such as a tube or ring is compressed or expanded.
The forming can be done either onto a die to give the tube a more complex shape, or onto
a smaller tube to swage the two tubes together.
· Sheet forming, in which a metal sheet is formed against a die to give it a more complex
shape.
Briefly, EMF works by the magnetic induction effect. When a coil or solenoid is placed near a
metallic conductor and pulsed via an energy store like a capacitor bank, a magnetic field is
generated between the coil and the workpiece. If done quickly enough, the magnetic field is
excluded from penetrating into the workpiece for a short period of time. During this time, a
pressure is generated on the workpiece that is proportional to the magnetic flux density squared.
This "magnetic" pressure is what provides the forming energy.
The energy is usually supplied to the workpiece in the form of kinetic energy. The magnetic
pressure pulse accelerates the workpiece up to a certain velocity (such as 200-300 m/s). This
kinetic energy drives the material into the die, causing forming on impact.
TECHNOLOGICAL OPPORTUNITIES OF ELECTROMAGNETIC
FORMING
GENERAL REMARKS
As the experience in introducing this method has indicated, the electromagnetic metal forming
has the following advantages compared to other metal forming techniques:
1. High efficiency of the technological process. The major factor limiting the
efficiency increase is the very significant time spent on the process preparation
(installation of the workpiece, adjustment and taking out the finished part). If
necessary electromagnetic equipment can be designed with an output capacity of
3600 operations per hour or even more.
2. The technological process can be easily automated and mechanized. It is possible
to control the equipment remotely. The tool (inductor), creating the magnetic
field, is not connected to the workpiece mechanically. The forming energy can be
dosed precisely up to 1% and with the remote control.
3. The great technological flexibility of the process. The same inductor can be used
to form the workpieces of different configurations.
4. Simplicity of the technological equipment. Only one die or plunger is used.
5. Absence of a transfer medium during forming process. This feature allows to
form the metallic workpieces through insulating coatings or the wall of a vacuum
chamber.
6. The possibility of obtaining high specific pressures. Nowadays the pressures of up
to 108 H/m2 can be obtained without destroying the inductor and pressures of up
to 109 H/m2 can be obtained with the disposal inductors.
7. High culture of production and simplicity of equipment maintenance. The modern
EMF equipment operates noiselessly. The tool and the assemblies of the
electromagnetic equipment donít need lubrication. There is no aggressive
environment. The equipment is completely automated. The monitoring and
control of the operation can be performed by single worker.
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. The microstructure of the alloys with the
same amount of strain has fewer distortions while formed by EMF if compared to
the static deformation.
9. It is possible to perform EMF in hard-to-reach areas. The tool (inductor) can be
connected to the capacitor bank by a flexible bus bar, which allows to perform the
technological operations far away from the capacitor bank (expanding the long
tubes in the central section, corrugation and punching holes in large area metal
sheets).
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 workpiece
by various inductors. Each subsequent operation must be performed by the
inductor, the shape of which repeats the shape of the formed workpiece.
By: Irvin De La Paz, Joan Mojica and Marlene Pujols
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 workpiece with
the magnetic field of the inductor. In order to obtain the induced current the
defined conditions must be met.
4. Not all the geometries of the workpiece are suitable for EMF. There are some
restrictions with respect to thickness and diameter of the tubular workpieces.
5. The low mechanical strength of the inductors in the case of deformation of steel
workpieces. 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). On metal forming of the steel
workpieces the strength of the inductor decreases significantly.
The presented advantages and disadvantages must be considered when introducing EMF.
Considering all those features, it is necessary to remember that the application of EMF is not
always economically justified. The significant cost benefits can be obtained in the case where the
workpiece is especially designed as applied to the new technique so all the possible advantages
can be used.
REQUIREMENTS IMPOSED ON THE SHAPES OF THE WORKPIECES
Since EMF is performed due to interaction of the magnetic field with the induced current in the
forming workpiece, it is necessary that the shape of the workpiece provide for continuity of the
path of the induced current. Fig. 20 shows the admissible and the inadmissible versions of the
initial workpieces for all types of possible technological operations. It shows that when a
cylindrical workpiece is formed with cylindrical inductor, currents leak along its periphery. If the
cylindrical workpiece has a through slit along the generatrix of the cylinder or a large number of
through openings, the forces acting on the workpiece are weakened and forming is low-effective.
Due to low duration of the pressure pulse, it does not appear possible to use EMF for forming of
solid metal workpieces.