Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROMAGNETIC JOINING OR WELDING
OF METAL OBJECTS
FIELD OF THE INVENTION
The present invention is generally in the field of metal works and
relates to a method and apparatus far working of metallic workpieces. The
present invention relates particularly to such method and apparatus for
working of metallic workpieces by a pulsed magnetic energy.
BACKGROUND OF THE INVENTION AND PRIOR ART
Pulsed magnetic forming (PMF) is a process in which a metal
workpiece or a portion thereof is put into a rapid motion by a pulsed
magnetic field which causes the workpiece to deform. One advantage of the
PMF process is in that energy Ioss in this process is minimal and conse-
quently there is no or very little heating of the workpiece. In addition, this
process does not have the disadvantage of leaving tool marks, as is the case
in a variety of other techniques (see M. Cenanovic, Magnetic Metal Forming
1~ by Reverse Electromagnetic Forces. In Proceedings of the Fourth IEEE
Pulse Power Conference, Institute of Electrical and Electronic Engineering,
1983).
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The PMF process uses a discharge capacitor or a bank of
capacitors, a forming coil and often a field shaper, for creating an intense
magnetic field. The very intense magnetic field required for the PMF
process is a result of a very rapid discharge of electric energy, stored in
the
capacitor, into the forming coil. The resulting eddy currents that are
induced in the workpiece yield magnetic repulsion between the workpiece
and the forming coil, and this causes the workpiece to deform.
As the wflrkpiece surface moves under the influence of the
repulsion force, it absorbs energy from the magnetic field. In order to apply
- most of the available energy to forming and reduce energy losses due to
permeation of energy into the workpiece material (which cause energy waste
by resistance heating), the forming magnetic pulse is made to be very short.
In most PMF applications, the pulses have a duration between about IO to
about 2~0 ,u sec. (duration of the first wave of the discharging current).
i~ _ Background on prior art apparatuses and methods for working of
metal workpieces by the PI~fF process can be found in the following U.S.
Patents: 3,64,787 (Brower), 3,961,739 (Leftheris), 4,170,887 {Baranov),
4,31,393 (Weir), 4,807,31 (Berg et al.), ~,3~3,617 (Cherian et al.) and
x,442,846 (Snaper).
GENERAL DESCRIPTION OF THE INVENTION
In the following text, with the aim of streamlining the description
and facilitate better understanding of the invention, use will at times be
made with the following terms:
Workpiece: A metal object which is deformed, in accordance with the
invention, by work applied on surfaces thereof. ,
Moving surface: A surface of a workpiece which is put into an abrupt
.. and rapid motion by a pulsed magnetic force. In accordance with the
invention the moving surface is a solid made to impact another surface
(which may be stationary, or which may be a moving surface moving in an
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opposite direction) with a kinetic energy which causes the two surfaces to
become joined or welded (regarding 'joining" and "welding" - see below).
Working: A process which is a result of work applied on a workpiece
S or on a portion thereof which causes the workpiece or portion to deform.
Working in accordance with the invention is by means of PMF and in
addition to giving rise to a change in shape of the workpiece, brings to
joining of a surface of a worked on workpiece or portion, to another surface.
Joining: Working of an object or portion thereof so as to cause a surface
thereof to come into very tight contact with another surface. 3oining, for
example, may be an act of crimping of an essentially tubular workpiece
against another cylindrical object within the workpiece's interior so as to
very strongly and essentially permanently force opposite surfaces of the two
1~ objects against one another. The purpose of joining may, for example, be
to ensure tight electrical contact, i.e. with minimal electrical resistance,
between two objects.
Welding: Forming of a first workpiece in a manner such that the two
initially separated, opposite surfaces become integrated with one another.
In welding such two surfaces are in fact melted and then solidify together
to become integral.
Worked on portion: Part or portion of a workpiece which is being
2~ worked, i.e., being put into a rapid motion by a PMF force, for joining or
welding to another portion of a workpiece. For example, in the case of a
cable lug or a connector, the worked on portion will consist of the portion
which comprises a hollow receptacle which receives the cable and which is
' then crimped by the PMF force to join or weld with the cable contained
therein. The worked on portion is made of an electrically conductive
material or has at least a surface coated by an electrically conductive
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_q._
material. The electrically conductive material may, for example, be made
of metal or an electrically conductive polymer.
Counter portion: A portion of a workpiece which is being joined or
welded to the worked on portion. The counter portion may be included in
a different workpiece to that comprising the worked on portion {e.g. in the
case of joining the cable in a cable lug, the worked on portion will be the
portion comprising the receptacle of the cable lug, as noted above, and the
counter portion will be the portion of the cable containing the receptacle
- which becomes joined or welded to the worked on portion), although at
times the counter portion may be included in the same workpiece as the
worked on portion (e.g. welding two flanges of a workpiece to one another,
crimping a tube for joining or welding its wails one to the other so as to
seal
the end of a tube, etc.). The counter portion may at times also be a worked
_ on portion, this being the case, for example, where two portions are put in
rapid motion one against the other to bring them to join or weld to one
another (e.g. this is the case in crimping walls of a tube to seal a tube
end).
First workpieee: A workpiece which comprises the worked on portion
which has to be joined or welded to a counter portion in another, second
work~iece (see below).
Second workpieee: A workpiece comprising the counter portion in the case
where the worked on metal portion is in another workpiece.
?5 The present invention concerns the employment of the PMF
process for joining or welding surfaces of workpieces or portions of
n
workpieces to one another. In accordance with the present invention this is
achieved by causing at least one workpiece or a portion of a workpieee
_ comprising one of the surfaces to be joined or welded {the worked on '
portion) to move rapidly towards another workpiece or a portion of a
workpiece comprising the other surface to be joined or welded (the counter
portion). The rapid movement results from a PFM force applied on the
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_ j _
worked on portion which is either made of an electrically conductive
material or has at least one surface which is coated by an electrically
conductive material. The conditions of the PMF force are controlled such
that after the two surfaces impact one against the other they become joined
a
or welded to one another. The control of PMF force is typically such that
the speed of the moving surface will impart a kinetic energy to the worked
on portion, prior to impact, which is larger than the sum of the plastic
deformation of the worked on portion and of the elastic deformation of the
counter portion.
The invention provides a novel process for joining or welding of
objects one to another, as well as structures obtained by such joining or
welding. The process of the invention allows the manufacture of some
objects or structures which are novel per se, e.g. a joint between a cable and
a connector such as a cable lug in which the filaments or wires are
1~ compacted almost to maximum with very little void space (being close to
zero), i.e. the filaments or wires fill essentially the entire lumen in which
they are contained; or a super conductor cable having filament embedded in
a cable sheath or matrix with very little vaid space; joints between two super
conductor cables; a novel grounding cable or pole; etc. Such novel objects
or structures, regardless of the manner in which they are produced, also
form an aspect of the invention.
The invention thus provides a method of joining or welding of at
least two solid portions one to another, comprising inducing movement in
at least one of the solid portions, which is either made of an electrically
2~ conductive material or has at least one surface coated by an electrically
conductive material, by means of a pulsed magnetic forming force so as to
impact at least one other solid portion, the movement imparting a kinetic
energy on the at least one solid portion to cause the at least two solid
portions to join or weld to one another.
The two solid portions to be joined or welded may be made both
of the same material or may be made both of a different material. For
example, both may be made of steel, of stainless steel, of brass, of copper,
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etc. Alternatively, one may be made of one such exemplary alloys or of an
electrically conductive polymer and the other may be made of another
material such as metal, electrically non-conductive material, etc. '
In accordance with a preferred embodiment, the invention
P
provides . a method for joining or welding of at least two solid portions
comprising forcing the solid portions one against the other by inducing rapid
movement in at least one of the solid portions so as to cause at least one
surface thereof to impact the other solid portions, said at least one of the
solid portions being made of or comprising at least one surface made of an
10electrically conductive material, and the movement being induced by a
pulsed magnetic forming force which is being at a magnitude such that the
initial kinetic energy of the at least one of the solid portions prior to
impact
is equal to or larger than the combined plastic deformation energy of the at
least one of the solid portions and the elastic deformation energy of the at
I5 least two solid portions after impact, whereby the at least two solid
portions
become joined or welded to one another.
The two solid portions which are to be joined or welded to one
another, a priori facing one another or are placed so that opposing surfaces
either touch or are proximal to one another. The PMF force is then applied
20 from a forming coil situated proximal to a surface of the worked on portion
other than that which is opposite a corresponding surface in tile counter
portion, and thus brings to movement of the worked an portion. (It should
be noted that even where the two portions touch one another, there is
sufficient spacing between the two surfaces on a microscopic level to allow
25 acceleration and build-up of kinetic energy by the worked on portion).
As already pointed out above, the worked on portion and the
counter portion may be both on the same workpiece. This may, for
example, be the case of crimping an end of a tube, e.g. a metal tube, to join
or weld internal walls one to another so as to seal the tube. Alternatively,
30as also already pointed out above, the worked on portion may be on one
object and tile counter portion may be on another object: for example, as in
the case of joining a connector to an electric cable. In most cases, one of
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_7_
the solid portions to be joined or welded will be stationary and the other
will be a worked on portion which is put into rapid motion by a PMF farce.
However, in some cases, both solid portions will be put into a motion one
. against the other, this being the case, for example, in sealing of an end of
a metal tube, already noted above. In the latter case where all solid portions
to be joined or welded are forced into rapid movement, both will in effect
be worked on portions as well as counter portions.
In accordance with one embodiment of the invention, the two
solid portions to be joined or welded, each on separate object (a first and a
second workpiece) are both independently, an elongated portion. In
accordance with this embodiment, at least the worked on solid portion is a
hollow elongated member, and the dimensions of the two portions being
initially such that they can fit one into the other. The method according to
this embodiment comprises:
1~ (a) inserting one of the two portions into a hollow interior of the
other;
(b) causing surfaces of a first elongated worked on portion of a first
workpiece to move towards opposite surfaces of the other
elongated counter portion of a second workpiece by means of a
pulsed magnetic force, so as to cause the surfaces of the worked
on portion to impact the opposite surfaces of the counter portion
at a velocity such that the kinetic energy of the moving worked
on portion of the first workpiece prior to the impact will be
larger than a combination of the plastic deformation energy of the
moving portion and the elastic deformation energy of the counter
portion after the impact; whereby the two portions become joined
or welded to one another.
Examples of the embodiment is the joining of an electric cable
. with a cylindrical workpiece or a portion of the workpiece, e.g. joining of
a cable with a cable lug or with another type of connection device; joining
or welding of two elongated objects, e.g. two electric cables or two rods, by
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means of a tubular joining member; welding of two tubes to one another;
etc.
In accordance with another embodiment of the invention, the two
portions to be joined or welded are essentially planar. Examples of this
S embodiment are the joining or welding of one metal board, panel or foil to
another, welding of an end of one metal band or foil to the end of another
metal band or foil, etc.
A further .embodiment of the invention is concerned with the
production of super conductor cables or wires. Such cables have a matrix,
envelope or jacket made from one alloy, e.g. aluminum or copper, and have
filaments, which are contained within lumens or longitudinal bores in the
cable, and which are made from another alloy, e.g. niobium or titanium -
niobium alloys. In accordance with the invention, such a composite cable
or wire is prepared by inserting filaments within longitudinal bores or
1S hollow lumen of a cable or wire which is then constricted by means of a
PMF process. As a result, a very tight composite cable or fiber is obtained
with very little, almost zero void space. At times, the filaments are by
themselves a composite structure, and may also be prepared by a PMF
process in accordance with the invention.
A still further embodiment of the invention concerns the
production of a ground lead or cable, particularly such having an internal
metal core sheathed by an insulating material, at times encased within
another metal sheath.
An additional embodiment is concerned With the crimping and
2S welding of walls of a metal tube so as to form a gas tight seal.
A further embodiment is concerned with the crimping of a tube
made of metal or of an electrically conductive polymer, onto an object made ,
of an electrically non-conductive material so as to bring to joining of the
tube with said object. -
The PMF process of the invention may also be used, in accor-
dance with other embodiments, for joining or welding of a first, planar
workpiece, to a second, spherical workpiece.
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As will be appreciated, the above embodiments are only some
examples of myriad of embodiments ail being within the scope of the
invention as def ned herein.
The invention also provides a device useful in the above method.
The device of the invention comprises a power source, one or more
capacitors (which can store large electrical energy), a current control
circuitry and a forming coil.
The overall form and dimensions of the farming coil in the device
of the invention will determine the worked-on metal portion which joins or
10welds to the counter metal portion as well as, at times, the final shape of
the
worked-on portion. For example, in case of joining or welding of two
planar workpieces, the size and shape. of the planar forming coil will
determine the size and shape of the portion of the first workpiece which is
being worked and which then welds to the counter portion in the second
workpiece. In case of joining or welding of two elongated portions, the
length of the coil will determine the length of the worked on portion which
welds to or joins with the counter portion. Furthermore, the shape of the
forming coil, i.e. the shape of the path traced by the coil, will be a factor
influencing the final cross-sectional shape of the worked on portion after
working thereof. For example, in joining together of two tubular objects,
a forming coil has a hexagonal shape, may yield a final hexagonal shape of
the worked on portion.
Generally, by employing the knowledge available to him, and
additional knowledge gained in accordance with the invention, the artisan
will have no difficulties of designing a forming coil to meet desired
specifications.
The manner of performance of the invention will now be
illustrated further by reference to a specific embodiment of the invention
concerned with the joining or welding together of two essentially cylindrical
objects.
The worked on (first) portion according to the above specific
embodiment is preferably cylindrical, although it may also be prismatic, may
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have an elliptical or oval cross-sectional shape, etc. The counter (second)
portion is also preferably cylindrical, but similarly as the first portion it
can
also have a variety of cross-sectional shapes other than circular. The second
'
portion may have a cross-sectional shape similar to the first workpiece, i.e.
both will have a circular cross-sectional shape, both will have a hexagonal
cross-sectional shape, etc. However, the first and second portions may also
have different cross=sectional shapes, e.g. the first portion will be
cylindrical
and the second portion will be prismatic, etc.
In each case, the respective dimensions of the two portions should
. be such to allow either insertion of the second portion into the lumen of
the
first portion or the insertion of the first portion into the lumen of the
second
portion.
The first portion is induced into a rapid movement by a pulsed
magnetic force generated by a coil proximal to one of its surfaces other than
15_ the surface which welds or joins to the opposite surface in the second
portion. In one embodiment of the invention, the second portion is inserted
within the first portion and the first portion is then crimped onto the second
portion, by means of a magnetic forming coil surrounding its external
surface. In accordance with another embodiment, the first portion is inserted
into a lumen of the second portion and then expanded by a magnetic force
from a coil adjacent its interior surface so as to cause it to impact into and
then join with the walls of the surrounding second portion.
Edges of a prismatic hollow object, are somewhat more resistant
to crimping than other parts of the walls of the prismatic object. Thus, in
the case of a prismatic object, the PMF force may have to be adjusted
somewhat to account for this additional resistance. The resistance towards
crimping at the object's edges decreases with increase in the associated
angle, which is correlated with the increase in the number of sides of the
prismatic object. Accordingly, edges of octagonal objects are less resistant
3!0 to crimping forces than edges of a hexagonal object (assuming the same
wall
thickness and the same metal alloy in both cases), and edges of hexagonal
objects are in turn less resistant to crimping than those of a pentagonal or
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a rectangular object. It is clear that when the number of sides of the
prismatic hollow object is increased, the PMF force required for crimping
approaches that of a cylindrical object. The extra force required in case of
a prismatic hollow object (as compared to a hollow cylindrical object) can
S also be reduced by rounding the edges. The artisan should be able, without
undue difficulties, to design a PMF device with a forming coil to meet a
certain desired specif cation.
In the folls~wing, the invention will be described with reference
to a preferred embodiment in which both the first and the second portions
are cylindrical. At the moment of impact of the rapidly moving first portion
with the second portion, the kinetic energy of the first portion is at least
equal to the sum of the plastic deformation energy of the moving first
portion after the impact and the elastic deformation energy of the second,
still portion. This may be represented by the following approximate
1~ Equation (1):
U z (A1 +A2)/mi
wherein U is the velocity of the moving surface of the first
portion, prior to the impact,
ml is the mass of the first portion, and
A1 and A., are the plastic deformation energy of the first
portion, and the elastic deformation energy of the
second portion, respectively, which may be
calculated according to the following approxi-
mate Equations (2) and (3):
2J
A - Q V e~tz/cl+a,l> T ~r -1) (2)
i - i i ~(oi 1
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Az - 6z yz e~°~riy+szl~ /~roz ~ rz -1~
wherein rol and roz, are, respectively, the radii of the first and second
portions
prior to the deformation,
r1 and r2 are, respectively, the radii of the first and second portions
after deformation,
Ql and QZ are the tensile strength of the alloys of which the first and
second portions are made,
Vl and V2 are, respectively, the volumes enclosed within the first
and within the second portions after the deformation, and
8~ and 82 are the relative extension of the first and the second
portions, respectively, calculated according to the
following Equations (4) and (5):
SI = ~ ro1- rr I (4)
Y01
Sz-~ roz-rz
roz
Based on the above energy requirements (A1 and A2), the
working voltage (V) may be calculated by the following Equations (6)
and (7):
W - km ~ U 2 lL
4~z ,uo rol h
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_ 2W
C
where W is the energy stored in the capacitor battery,
k is a coefficient which depends on the parameters of the
PMF device (including capacitance and own inductance)
and parameters of working coil,
1 is the length of the working coil (and also the length of
the deforming section of the workpiece),
is the magnetic permeance in vacuum,
h is the thickness of the space between the working coil
and the workpiece,
L is the total inductance of the electric discharge circuirt
(the coil, pulse generating switch and capacitor battery);
U, m and rol are as defined above.
Where the object is other than cylindrical, it may at times be
necessary to utilize somewhat altered parameters of the pulsed magnetic
energy. For such objects it is necessary to define AI and AZ and thereafter
the
velocity and the voltage can be determined using Equations (6) and (7).
For example, where a prismatic hollow object is crimped onto a cylindrical
object in its interior, typically a somewhat stronger magnetic force will be
required in view of the increased resistance of the edges to deformation. In
addition, as will be appreciated, the above equations are applicable for a
situation where the length of the portion which is being deformed is larger
than the tube's diameter; where the portion is smaller than the tube's
diameter,
some corrections in view of resistance towards deformations at one or both
ends of the deformed portion should be taken into account.
The kinetic energy which will be imparted on the first portion,
will determine whether the first and the second workpiece will join or weld
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to one another. Generally, larger kinetic energy will result in welding and
smaller in joining. Typically, where the moving speed of the surfaces of the
first workpiece are less than 300 meters/second, the first and second
workpieces will be joined to one another. Where the moving speed of the
surfaces of the first workpiece is more than 300 meters/second, the surfaces
of
the first and second workpieces which come into contact, may become
welded to one another. For welding, it is usually preferred to maintain some
small separation between the opposite surfaces of the first and the second
workpiece to allow said surface of the first workpiece to accelerate and
achieve the desired velocity for welding. For welding it is at times desired
for
the non-moving, second workpiece to be firmly immobilized so as to
stay essentially motionless at the time of impact of the first workpiece
therewith.
At times it may be desired to induce movement of the worked
on portion by several magnetic pulses one after the other rather than by a
single magnetic pulse. This may be achieved, for example, in a device having
a plurality of current discharge circuits, each of which being activated at
different times. Such a device is novel and also forms an aspect of the
invention.
In the following, the invention will be exemplified by non-limiting
specific embodiments, with occasional reference being made to the annexed
drawings. The exemplified embodiments are concerned primarily with the
working of portions of metal workpieces. However, it will be appreciated that
the invention in general and many of the described embodiments in particular
is also applicable, mutatis mutandis, to the working of portions made of an
electrically conductive material other than metal, e.g. a conductive polymer.
For example, a tube made of an electrically conductive polymer may be
worked in a similar manner as illustrated in Figs. 1-5 or 16. In addition,
rather
than being made wholly of electrically conductive material, the worked on
portion of the exemplified embodiments may have one or more surfaces
which are coated by a conductive material. The artisan, based on the teaching
CA 02240769 2005-11-10
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of this invention, will have no difficulties in carrying out the invention
with
worked on portions made of electrically conductive material other than metal
or such comprising only one or more surfaces made of electrically conductive
material.
BRIEF DESCRIPTION OF THE DRAWINGS
Figs. 1-5 show a sequence of joining together of a multi-fiber cable
and a cable lug:
Fig. 1 is a perspective view of an assembly consisting of a cable and a
cable lug a$er insertion of the end of the cable into the lumen of the cable
lug;
Fig. 2 is an upper, partially cross-sectional view of the assembly of
Fig. 1;
Fig. 3 is a cross-section through lines 3-3 in Fig. 2;
Fig. 4 is an upper, partially cross-sectional view of the assembly after
constriction of the cylindrical portion of the cable lug and the formation of
a
firm joint between the cable and the cable lug;
Fig. 5 is a cross-section through lines 5-S in Fig. 4;
Fig. 6A is an isometric view of a PMF device in accordance with an
embodiment of the invention useful, inter alia, for the preparation of a joint
between a cable and a cable lug as shown in Figs. 1-5;
Fig. 6B is a side view of a PMF coil in accordance with another
embodiment of the invention;
Fig. 7 shows a device in accordance with another embodiment of the
invention;
Fig. 8 shows a joint between a cylindrical object and a tube manufac-
fared in accordance with the invention using a device such as that shown in
Fig. 7;
Fig. 9 is a schematic representation of the manner of joining of two
poles, in accordance with an embodiment of the invention;
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Fig. 10 is a schematic representation of the manner of joining of two
super conductor cables to one another, in accordance with an embodiment of
the invention;
Fig. 11 is a schematic representation of another embodiment in
accordance with the invention for joining of two super conductor cables;
Fig. 12 is a schematic cross-sectional representation of the manner of
production of a grounding cable according to an embodiment of the invention;
Fig. 13 is a schematic cross-sectional representation of the manner of
producing a super conductor cable in accordance with the invention;
Fig. 14 shows a heating coil where the coil and an electric pin are
joined or welded together by means of a metal sleeve constricted onto the coil
by a PMF process in accordance with the invention:
Fig.14A is a side view of this device;
Fig. 14B shows a cross-section through lines 14b-14b in Fig. 14a;
Fig. 15 shows a device in accordance with an embodiment of the
invention:
Fig. 15A shows one manner of use of the device for joining or welding
two hollow cylindrical objects, employing an insert or a proper positioning of
the two objects and supporting the walls;
Fig. 15B shows another manner of using the device for joining or
welding two hollow cylindrical objects, without the use of such an insert;
Fig. 15C shows a longitudinal cross-section through a joint between
two pipes of different diameter, welded together by the device of Figs. 15A or
1 SB;
Fig. 16 shows the manner of crimping and welding to one another
walls of a metal tube to achieve an airtight seal, in accordance with an
embodiment of the invention;
Fig. 17 shows the set-up for welding of two planar metal objects;
Fig. 18 is a cross-section through lines 18-18 in Fig. 16;
CA 02240769 2005-11-10
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Figs. 19 and 20 show two embodiments for welding of an initially
planar metal workpieces to a spherical metal workpiece;
Fig. 21 is a schematic representation of the magnetic conductor circuit
operating in a device according to an embodiment of the invention; and
Fig. 22 shows the magnetic conductor circuit in a device in accordance
with another embodiment of the invention.
DESCRIPTION OF SPECIFIC EMBODIMENTS
Reference is first being made to Figs. 1-S which show the
manner of joining of a cable to a cable lug in accordance with an embodiment
of the invention. Cable lug 22 comprises an attachment base 24 for
attachment to another body, and an essentially tubular portion 25 with a
lumen 26. Cable 28 comprises a plurality of conductor fibers 30 each having
an essentially cylindrical cross-section.
Cable 28 and cable lug 22 are combined by inserting end
portion 32 of the cable into lumen 26 of the cable lug as can be seen in
Figs. 1-3. The cylindrical tubular portion 25 has an original radius rol and
the
cable has an original radius roe.
In order to join the cable with the cable lug, a pulsed magnetic
force is applied onto the tubular portion 25 and consequently, the tubular
portion 25 is crimped whereby the inner faces thereof become joined with the
end portion 32 of cable 28, as can be seen in Fig. 4.
As a result of this crimping, as shown in Fig. 5, fibers 30 are
compressed to become hexagonal. After crimping the tubular portion 25, has
a radius r1 and the cable has a radius r2. Following crimping, there is some
thickening of the walls of the constricted tubular portion 25'.
In a typical cable, fibers fill up about 65% of its internal space.
After full compression, whereby the fibers become hexagonal, the fibers come
to fill essentially 100% of the internal space of the cable. This means that'
the cable after full compression constricts to about 80% of its original
diameter.
CA 02240769 2005-11-10
r
-18-
Accordingly, by knowing roe, r2 may be calculated as being
equal to about 80% of roe. r2 is equal to the internal radius of portion 25
after
constriction, and by knowing the original wall's thickness of portion 25, the
wall thickness after constriction may be calculated and from there r~ (the
radius of cylindrical portion 25 (after constriction) may be derived. Then, by
employing the above Equations 1-5, the magnetic parameters required for this
process may be calculated.
Joining of a cable with a cable lug is an example for the joining
of a cable with a cylindrical workpiece. Other examples are connecting two
cables one to another by the use of an elongated connector with two hollow
receptacles at both its ends or by the use of a hollow tube, etc.
Reference is now being made to Fig. 6A showing, in a semi-
schematical manner, a device suitable for carrying out the process as
described in Figs. 1-5. The device generally designated 40 comprises a
control module 42 which can provide a rapid intense current discharge,
electric leads 43 and 44 for the transfer of the current, and a forming coil
46.
Electric leads 43 and 44 are electrically linked to coil 46 by means of connec-
tors 47 and 47a and 48 and 48a. Typically, the forming coil 46 protrudes
from a surface, e.g. a working table, represented here by a dotted-lined
surface
49, with the rest of the device constituents being hidden behind the surface.
Forming coil 46 has a lumen 50 to which a workpiece to be constricted is
inserted. The internal walls of coil 46 are typically lined by insulating
lining
material 51.
In this specific embodiment, device 40 is used for producing of
a joint between a cable and a cable lug shown in Figs. 1-5. As will be
appreciated, the device can also be used for a variety of other purposes, e:g.
production of a grounding cable, a super conductor cable, joining of two super
conductor cables, and a variety of other purposes some of which are described
below. The width of coil 46 determines the length of the portion which will
be crimped when current is discharged through coil 46.
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In this specific example, an assembly 52 which comprises a
cable lug 53 and a cable 54, which are in loose association with one another,
is inserted into lumen 50 in a manner that the cylindrical portion 55 of cable
lug 53 is essentially entirely within lumen 50. Then, a strong current is
rapidly discharged through coil 46 and the PMF force which arises in
consequence thereto, brings to crimping of the walls of cylindrical portion 55
onto the end of cable 54, whereby the two become firmly joined to one
another.
Fig. 6B shows a forming coil generally designated 56 which
may serve a similar purpose to the coil shown in Fig. 6A. For ease of descrip-
tion, elements with a similar function to those of the embodiment of Fig. 6A
have been given like reference numerals with a prime indication and the
reader is referred to the description above for explanations of their
function.
As can be seen, the main difference of coil 56 from coil 46 in Fig. 6A is in
that it has a rib-like structure. The advantage in such a structure is that on
the
one hand the current is restricted to a narrower space and it thus more
effective in forming, and on the other hand, the ribs provide the strength
required from such a coil.
Fig. 7 shows a device in accordance with another embodiment
of the invention which in this specific example is used for welding or joining
of a tube onto a rod. Similarly as in the embodiment shown in Fig. 6, it is
clear that this device may also be used for a variety of other purposes. The
device, generally designated 57 comprises a forming coil 58 having a plurality
of winds (7 in this specific example) around a tube 59 which is made of
insulating material such as plastic. The device further comprises a power
supply 60 connected in parallel to a capacitor battery 61 and a switch 62. The
power generator 60 charges capacitor 61 and following actuation by means of
switch 62 a current is discharged through forming coil 58.
The two workpieces to be joined together which consist, in this
example, of a metal tube 63 and a metal rod 64 are inserted within lumen 65
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of insulating tube 59. In order to weld the two workpieces to one another,
there should preferably be some clearance 66 between the two workpieces,
typically about 5-20% of the internal diameter of tube 63.
As can be appreciated, upon discharge of capacitor 61, there is
a rapid and intense current flow through coil 58 which causes eddy currents in
tube 63 and the resulting magnetic pressure then causes it to rapidly crimp
onto and welds with rod 64. The length of the portion of tube 63 which is
being crimped corresponds to the length of coil 58.
Fig. 8 shows a joint 69 between a tube 67 and a rod 68 prepared
in a manner described with reference to Fig. 7. Depending on the intensity of
the magnetic pressure used to create the joint, and consequently the speed of
movement of the cylinder prior to impact with the rod, there will either be
welding between the two workpieces or only tightly joining.
Fig. 9 shows manner of joining together of two ends of
elongated metal objects in accordance with an embodiment of the invention.
The ends 70 and 71 of elongated objects 72 and 73, respectively, is cut or
beveled so as to produce two complementary oblique surfaces with a
relatively obtuse angle versus the longitudinal axis of the body. The two
objects are placed so that their beveled or cut ends touch one another with
their axis being slightly out of line with respect to one another. Then,
following the application of a strong pulsed magnetic force, as shown
schematically by the arrows in Fig. 9A, the two end segments 70 and 71
impart one another and become welded, i.e. integral, with one another.
Fig. 10 shows a manner of joining ends of two super conductor
cables in accordance with an embodiment of the invention. Two super
conductor cables 76 and 77, of which only the end portion is shown,
comprise each a metal matrix 78 made from only metal alloy and fila-
ments 79 made of another metal alloy. In order to have proper electrical
continuity, it is necessary to join two ends so that the filaments will be co-
extensive. For this purpose, the ends 76 and 77 of the two cables are cut
diagonally similarly as in the case of the rods in Fig. 8 and are brought into
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contact with one another within lumen 80 of cylindrical workpiece 82
(Fig. 10B). Then by the application of a pulsed magnetic force, represented
schematically by the arrows in Fig. 10B, the cylindrical workpiece 82 is
constricted onto the super conductor cable and consequently the tight joint
between the two cables is obtained as shown in Fig. l OC.
The manner of joining of two super conductor cables in
accordance with another embodiment of the invention is shown in Fig. 11.
The end faces 84 and 85 of cables 86 and 87 respectively, are bored to obtain
a plurality of bores 88, each corresponding to a filament 89 of the super
conductor cable, as can be seen in Fig. 11B. A joining member 90
comprising projections 92 which correspond to bores 88 is combined with the
two ends of the super conductor cables, as shown in Fig. 11 C, and then a
cylinder 94 is placed over this assembly. Then magnetic force is applied, as
shown schematically by the arrows in Fig. 10C, and consequently cylinder 94
is constricted onto the cable and as a result a firm join is obtained, as
shown in
Fig. 11D.
The manner of preparation of a ground cable or lead in accor-
dance with an embodiment of the invention is shown in Fig. 12. A conduc-
tor 100 shown in Fig. 12A consists of a core 102 made of one alloy,
e.g. iron, and a clad 104 made of another alloy, e.g. copper. The conduc-
tor 100 may be prepared as explained in relation to Figs. 7 and 8. A cylinder
or envelope made of insulating material such as polyethylene, a ceramic
material, etc. is placed over the conductor, the cylinder or envelope being
overlaid by a metal, e.g. a copper cylinder, as can be seen in Fig. 12B.
Following application of a magnetic force, as represented schematically by
the arrows in Fig. 12B, the metal cylinder 108 is constricted, which causes
also constriction of insulator 106 so as to achieve the tight structure shown
in
Fig. 12C.
Reference is now being made to Fig. 13 showing the schematic
representation of the manner of producing a super conductor cable in
accordance with an embodiment of the invention. A longitudinal matrix 110
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which is made of one alloy, e.g. copper, comprises a plurality of longitudinal
bores 112, and filaments 114 made from another alloy are introduced into
each of the bores, as shown in Fig. 13A. Following the application of a
pulsed magnetic force, as represented by the arrows in Fig. 13A, the entire
cable is constricted and consequently the walls of each of the bores joins
with
the filaments to yield a super conductor cable with practically no void space,
as can be seen in Fig. 13B.
Reference is now being made to Fig. 14 illustrating a heating
element 115 consisting of a coil 116 and a pin assembly 117. Coil 116 is
helical and extends between the two pins. Pin assemblies 117 consists of an
insulating member 118, made of plastic, a ceramic substance, etc., and an
electric pin 119 which extends through insulating member 118 and ends at a
portion 120 which is in contact with the end portion of coil 116.
The element further comprises two metal sleeves 121
enveloping the ends of coil 116 overlapping portion 120 of pin 119. Sleeve
121, is constricted onto the structure consisting of portion 120 and coil 116
and brings to tight joining of the two elements to one another which ensures
high quality electric contact which is highly resistant towards erosion which
can occur during continued operation.
A device in accordance with an embodiment of the invention,
for use in joining or welding of elongated objects to one another, is shown in
Fig. 15 (in longitudinal cross-sections). The device generally designated 122
comprises a forming coil 123 consisting of a plurality of windings, separated
from one another by an insulating material 124. The device also comprises a
field shaper 126.
As a result of application of the pulsed magnetic force, a strong
magnetic pressure will result in the lumen 128 of the field shaper and as a
result, a cylindrical object within the lumen will be constricted.
Fig. 15A shows two examples on the manner of using the
device for joining together two hollow tubular workpieces which consists of a
first tubular workpiece 130, of a relatively wider diameter, and a second
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tubular workpiece 132 of a narrower diameter. These two workpieces have
respectively a portion 134 and 136 which are to be welded to one another. A
problem in such welding is first to properly position the two workpieces so
that they will be coaxial, and furthermore, it is necessary to provide
conditions
so that upon impact between two workpieces, the portion 136 of second
workpiece 132 will remain essentially motionless and thus welded to portion
134 of the first workpiece. In the example shown in Fig. 15A both these feats
are achieved by the use of insert 138 which has the first portion 140 with a
diameter equal to the internal diameter of the tubular workpiece 132, and has
a second portion 142 which has a diameter equal to the internal diameter of
tubular workpiece 132. The two portions 140 and 142 are coaxial and
accordingly, the first workpiece 130 and the second workpiece 132 are also
coaxial. Furthermore, portion 142 of insert 138 supports portion 136 thus
upon application of a magnetic force, portion 134 moves rapidly towards
portion 136, which remains essentially motionless during impact, thus the two
portions become welded to one another.
Support of the internal walls of a tubular workpiece during
impact by an external tubular workpiece may also be achieved by a variety of
other means. These include, for example, filling the entire cylinder with a
non-compressible liquid such as water; introducing into the tube a magnetic
liquid such as mercury, oil with suspended metal particles, etc., and then
applying a constant magnetic field prior to the PMF so as to concentrate the
magnetic liquid at a portion where the support is required; by means of ice
frozen at a respective portion; etc. Such solutions of support are required,
for
example, where the internal cylinder is long and it is thus not possible to
introduce an insert such as that shown in Fig. 15A.
Fig. 15B shows the manner of using the same device without
employing an insert. In Fig. 1 SB, the two workpieces are made to be coaxial
by the use of two annular members 143 and 144. These two annular
members may be made from the same alloy as workpieces 130 and 132, or be
made of a different alloy. These two annular members assist somewhat in
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shaping the magnetic field and also serve to improve the quality of the weld:
upon application of the PMF force, the rapid internal movement of portion
134, the two annular members 143 and 144 blend with portions 134 and 136.
In order to ensure optimal conditions, i.e., that there will be no
constriction of
portion 136 upon impact, the PMF must be applied in a very short pulse,
typically for a time which equals about or slightly above T/4 (T = 2~ LC ) .
The following Equation 8 provides an example of an approximate relation
between the various parameters which allow it to meet the necessary
requirement:
m,U212 __~c C
2 fc W n' 2
0
where 1 is the length of working coil
n is the number of winds of working coil,
L is the total inductance of discharge circuit.
A joint between two tubular workpieces at a different diameter
is shown in Fig. 15C.
Reference is now being made to Fig. 16 showing an
embodiment of the invention concerned with the crimping of walls of a metal
tube and welding internal surfaces one to another. An example of use of this
embodiment is in sealing of metal tubes containing a coolant gas used in
refi-igeration or heating systems, e.g. in refrigerators or airconditioner
systems,
or sealing of tubes containing flammable gas (e.g. cooking gas etc.).
Fig. 16A is a longitudinal schematic cross section showing a
metal tube 145 a portion of which 146 being surrounded by a metal
coil 147. Upon rapid discharge of current through coil 147, as shown in
Fig. 16B, the pulse magnetic forms crimps the walls of portion 146 and
brings to welding of the internal walls of this portion one to the other. As
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can be seen in Fig. 16B, after crimping, there is thickening of the walls of
portion 146. Portion 146 may then be cut in its middle thus yielding a sealed
end 148, preventing outflow of gas from within the tube, (represented by the
arrows).
A set-up for welding of two planar metal workpieces is shown
in a perspective view in Fig. 17 and in a cross-section in Fig. 18 (in Fig.
17,
the support structure of the coil has been removed for the purpose of ease of
illustration). In order to join two planar workpieces, an essentially planar
coil
is used. Planar coil 150 shown in Fig. 17 has an overall shape and size
substantially the same as the shape and size of the area of the first
workpiece
152 which is to be joined with the second workpiece 154. As can be seen in
Fig. 18, the coil windings 156 are held in place by support wall 158 which is
anchored ~ onto a working stage by means of anchoring member 160. Upon
passing of a pulsed current in coil 150, planar workpiece 152 will move
rapidly downwards and if it will impact, workpiece 154 sufficiently rapidly,
e.g. at a speed above 300 M/sec, the two metal workpieces will be welded to
one another. For that purpose, a magnetic force is applied from the direction
as represented by the arrows in these figures.
Reference is now being made to Figs. 19 and 20 showing,
schematically, the welding of planar workpieces 162 and 162' onto objects
164 and 164', which are respectively a cylindrical and a prismatic object
(shown in cross-section).
Reference is now being made to Fig. 21 showing a block
diagram of the electric circuit for the provision of pulsed magnetic force in
a
device in accordance with an embodiment of the invention. The device
comprises a power generator 170, which may be mufti-channel as in the
depicted embodiment, and one or a plurality of current circuits 174 (three are
shown in this embodiment) and a field shaper 182. Each such circuits 174
comprises a capacitor battery 176, a forming coil 178 and a pulsed discharge
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switch 180. Each of switches 180 is under the control of a multi-channel
triggering generator 172.
Electric power, which is provided by power supply 170,
accumulates in a capacitor or bank or capacitors 176 and following a trigger
provided by generator 172, the accumulated potential discharges through
coil 180. A device comprises a plurality of magnetic forming circuits is
uniquely provided by the invention. The advantage of such a device is that by
proper timing of the triggers to each of the switches 180, a series of pulsed
magnetic forces may be applied which may be advantageous for a number of
applications.
A block diagram of a circuitry in accordance with another
embodiment of the invention is shown in Fig. 22. In Fig. 22, like elements to
those of Fig. 21 have been given like numbers with a prime indication. This
embodiment is particularly useful for providing very intense energies. The
device comprises a transformer 184 for each of circuits 174' which comprises
a primary coil 186 having a plurality of windings and a secondary coil 188
having a single wind. All the secondary coils 188 are connected in parallel to
forming coil 190.
