Electric heating – Inductive heating – Metal working
Reexamination Certificate
1999-07-16
2001-05-08
Donovan, Lincoln (Department: 2832)
Electric heating
Inductive heating
Metal working
C072S056000
Reexamination Certificate
active
06229125
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally in the field of forming of metal objects by means of pulse magnetic force (PMF) forming. PMF forming are processes where a short duration magnetic pulse is used to change the form of a metal workpiece. Change in form may be an object by itself whereby the workpiece assumes a different form. At times, however, the change in form results in the forced and rapid pressing of one workpiece against another which eventually results in either joining two workpieces together or welding both pieces, one to another. (Joining is a process whereby the surfaces of two workpieces come into close association with one another, without a molecular interaction between the two surfaces, while welding is the process where the surfaces of the two workpieces in fact merge with one another, there being an interaction on the molecular level between the two surfaces). The term “forming” or “PMF forming” as used herein, will denote all such processes.
BACKGROUND OF THE INVENTION
PMF forming processes, particularly of cylindrical objects have hitherto been disclosed. See for example U.S. Pat. Nos. 3,654,787, 3,832,509, 4,143,532, 4,170,887, 4,531,393 and 4,442,846 and DE-4,436,615. In such PMF processes, a forming coil, particularly a single wind coil, is placed around the tubular workpiece to be formed. The passing of a short duration high intensity electric current through the coil, gives rise to eddy currents in the metal workpiece, this in turn creating a magnetic pressure, resulting from the repulsive forces between the forming coil and the metal workpiece. This magnetic pressure then brings to shrinkage of the tubular workpiece. The end result, whether there will be only forming, or whether the tubular workpiece will join or weld to another workpiece, depends on the exact circumstances of the process. For effective PMF forming high intensity magnetic fields are required and in order to achieve that, it is at times useful to use a field shaper, which is in fact a secondary coil, surrounded by several windings of a primary coil connected to an electrical energy source, typically a discharge capacitor.
An effective PMF forming process, requires that there be a close proximity between the forming coil (whether a primary coil connected to an energy source or a secondary coil—the field shaper) and the metal workpiece. This however may create technical difficulties in a number of cases. For example, in the case of joining of long steel pipes by a bridging sleeve, such as that described in U.S. Pat. No. 5,442,846, it is necessary to be able to open the coil to allow the sideways withdrawal of the pipes with the joining sleeve after joining (otherwise, it would have been necessary to extract the pipe by pulling it lengthwise, which is very often practically impossible).
Another example is the joining of cable lugs to an electric cable. Cable lugs are objects which have a tubular portion, adapted to receive an end of an electric cable and another portion, generally planar, having a hole which allows passage therethrough of a screw for tight attachment to another cable lug, to an electric power source or to a ground lead. In order to ensure tight contact between an electric cable and the cable lug, after insertion of an end of a cable into the tubular portion, the walls of this tubular portion are shrunk and tightly pressed onto the end portion of the cable contained therein. This has hitherto been achieved primarily by mechanical means.
The tight joining of a tubular portion of a cable lug and a cable end can also be achieved by means of PMF forming. However, the problem is that the planar portion of the lug is of a wider dimension than the diameter of the tubular portion and accordingly, if the forming coil would have been a standard fixed coil, it would have been practically impossible to extract the cable after forming. Apparatuses specifically designed for joining of a tubular workpiece to another tubular or cylindrical workpiece, are disclosed in U.S. Pat. Nos. 3,654,787, 4,531,393 and 5,442,846. However, the apparatuses disclosed in these U.S. patents are bulky and are not suitable for field use which is where the joining of the cable end and the cable lug takes place.
The forming apparatuses disclosed in these three patents, have all a common feature in that the two halves which are clamped together so as to define a PMF forming region around the workpiece to be formed, are each connected to a different pole of the electric discharge source. The problem is that the electric contact with the source has to be a very low resistance contact, and accordingly a bulky arrangement is required to ensure the maintenance of such a contact notwithstanding the fact that at least one of the two halves of the forming coil has to be displacable.
GENERAL DESCRIPTION OF THE INVENTION
It is an object of the invention to provide a new apparatus for PMF forming. It is particularly an object to provide such an apparatus for use in joining of cable lugs to an end of an electrical cable, adapted for field use.
There are several aspects of the invention. In accordance with some aspects, the apparatus comprises a forming coil in direct contact with the electric discharge circuitry. In other aspects, the forming coil is in fact a secondary coil where current is induced by a primary coil which is in turn in direct electrical contact with an electrical discharge circuitry. The common feature in the apparatuses in accordance with all aspects of the invention is the fact that there is on the one hand, permanent electrical contact between the forming coil or the primary coil, as the case may be, and on the other hand, means are provided for easy placement of the tubular object to be formed in a forming space of the forming coil and extraction of the workpiece after forming.
In accordance with a first aspect of the invention there is provided an apparatus for pulse magnetic forming of a tubular workpiece having a coil assembly comprising:
a single wind first coil member having two ends each of which being in electrical contact with one pole of an electrical discharge mechanism; a second coil member being a complete closed loop and having a shape and size such that it traces a path parallel to that traced by said first coil; the members being detachably attached to one another such that they are positioned parallel and adjacent one another, there being an electrically insulating layer between them; said coil member having a first recess or band and said ring member having a second recess or band, the two recesses or bands being juxtaposed to one another and defining together a forming space adapted to receive said workpiece.
In accordance with a second aspect of the invention there is provided an apparatus for pulse magnetic forming of a tubular workpiece comprising:
at least one primary coil electrically connected to an electrical discharge mechanism; two removable inserts defining together a loop with an outer surface within and adjacent said at least one primary coil and an inner surface defining a cylindrical forming space adapted to receive said workpiece, each insert having two end portions adjacent the end portions of the other insert, the arrangement being such that there is no electrical contact between the end portions of the two inserts; each of said inserts defining a current flow path comprising the outer and inner surfaces of the inserts and upon discharge of current in the primary coil which gives rise to current flow in the primary coil in a first circular direction, current in the outer surface of the insert flows in a second direction opposite the first and current in the inner surface flows in said first direction, whereby the current flowing in the two inner surfaces of the two inserts form together a loop of current around the forming space.
In accordance with a third aspect of the invention, there is provided an apparatus for pulse magnetic forming of a tubular workpiece comprising:
a single wind coil consisting of three coil sections having inner faces d
Gafri Oren
Livshiz Yuri
Browdy and Neimark
Donovan Lincoln
Pulsar Welding Ltd.
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