Abstract:
An energy storage system for use in a magnetic pulse welding and forming apparatus includes a bank of capacitors and a very-low inductance conductive bus system interconnecting the capacitors. The bus system provides the ability to generate a very high frequency, short duration impulse which is needed for welding. The bus system includes first, second and third flat bus panels disposed in closely spaced overlying relation. The second, or middle, bus panel is the “hot” bus and is electrically insulated from the first (lower) and third (upper) bus panels by sheets of electrically insulating material. The first and third bus panels are connected together cooperatively form a ground bus. The bus system overlies the upper ends of the capacitors wherein the second bus panel is electrically interconnected to the respective hot contacts of the capacitors, and further wherein the ground bus is electrically interconnected with the respective ground contacts of the plurality of capacitors. The energy storage system further includes an energy source connected to the capacitors, a discharge device, a charging control device, and a discharge control device for selectively initiating discharge of energy stored in the capacitors. The bus system further includes removable connector elements that are selectively removable for controlling the total number capacitors utilized in the energy storage bank.

Description:
BACKGROUND OF THE INVENTION 
     The instant invention relates generally to magnetic pulse welding and forming, and more particularly to an energy storage apparatus for storing and supplying a high-frequency working impulse to a magnetic pulse inductor. 
     In the automotive industry, there are many tubular parts that need to be coaxially joined and/or end fittings that need to be joined to tubular components. Magnetic pulse forming devices have been used in the past to accomplish this purpose. However, the results achieved in the prior art devices have not always been of high quality and thus not acceptable in many applications. 
     Magnetic pulse devices store energy within a bank of capacitors and release the energy through an inductor coil (welding tool) that creates a magnetic force strong enough to collapse the components positioned within the inductor coil. In this regard, tubular components are pre-assembled and positioned within the center of the inductor. The energy released through the inductor coil generates an magnetic field strong enough to collapse the outer tube inwardly into engagement with the inner tube. When used to connect an end fitting, the outer tube is collapsed onto the outer surface of the end fitting. If the energy stored in the bank of capacitors is enough, the inward collapsing velocity will be sufficient to cause the metal of the outer component to penetrate the metal of the inner component forming a full metallurgical bond between the components in what is referred to as “cold stage welding”. 
     Methods and apparatus for Magnetic Pulse Welding are described in “Handbook of Magnetic Pulse Treatment of Metals”, by Kharkov, Kharkov State University, 1977 (Translated into English and edited by Ohio State University in 1996 by M. Altynova, and Glenn S. Daehn), and in the book “Magnetic Pulse Welding of Metals”, by A. A. Dudin, Moscow Metallurgy, 1979. 
     Other methods and apparatus for this process have been described in the following articles: “Magnetic-Pulse Welding: Unique Concept for Tubing Components”, by D. Dudko, V. Chudakov, L. Kistersky and T. Barber,  Proceedings of the Eleventh Annual World Tube Congress , Rosemont, Ill., Oct. 9-11, 1995; “Welding Process Turns out Tubular Joints Fast”, by L. Kistersky,  American Machinist , April 1996; and “Magnetic Pulse Welding of Tubing”, by D. Dudko, V. Chudakov, L. Kistersky and T. Barber,  The Fabricator , September 1996. The U.S. Pat. No. 3,520,049 to Lysenko et al also describes similar subject matter. 
     The prior inventors of magnetic pulse welding apparatus generally did not pay attention to the fact that the quality of the welding joint is dependent, not only on the velocity of the impact and so on the amount of the energy released, but also more importantly, on the duration of the impulse current realizing this energy. In this regard, the same volume of energy released in impulses of different duration will cause different types of metallurgical joints in the same parts. Longer duration (lower frequency) impulses will cause only a simple deformation, whereas a very short duration (high frequency) impulses will cause a full metallurgical weld. 
     It is now desirable to be able to use this method to obtain welding of tubular components that are made of stronger materials, and that have thicker walls. However, the existing magnetic pulse welding devices have generally not been able to provide a full metallurgical weld between such components. This problem has resulted from the fact that virtually all of the known apparatus for magnetic pulse welding and forming have included generally the same construction and configuration. The key factor for improving the weld in high strength materials and across thick materials has not yet been fully identified in the prior art. Some work has been focused on releasing more energy and on changing the pre-assembled configuration of the parts to achieve better welding. For example, see the U.S. Pat. No. 5,981,921 to Yablochnikov. This patent deals with a method of assembling an end fitting with a tube for a driveshaft. The specification clearly points out that the quality of the metallurgical joint for the material was independent from the Magnetic Pulse unit (column 2, lines 30-35), and the physical reason why a strong metallurgical joint between the components could not be obtained using the known magnetic pulse units was “not known yet”. 
     SUMMARY OF THE INVENTION 
     The instant invention seeks to provide an answer to the problem. According to the present invention, the quality of the metallurgical joint produced via magnetic pulse welding is a combined function of the velocity of collapsing of the component, and the duration of the initial current impulse. The velocity of the collapsing is derived from the force of repelling (density of the magnetic filed), weight of the portion to be collapsed, mechanical strength of the metal to be collapsed, the distance (gap) between the collapsing end of the outer tubular component and the surface of the inner component. Usually, this factor is figured out experimentally by finding of a range of proper gaps between components to be welded for a defined pair of materials using a predetermined level of initial impulse current through a chosen inductor. The proper combination of a gap, impulse current and inductor design usually is a result of an experimental program. A more controlled quality of the magnetic-pulse welded joint can be achieved when a definite collapsing angle is provided. This collapsing angle is a dynamically created angle at the point of touching of the inner component surface by the collapsing portion of outer component. It is known from another method of welding via impulse pressure, i.e. explosion welding, that for a given pair of metals, a fully developed weld joint will occur only when the correct collapsing angle is provided. (“Explosion Welding in Metallurgy”, 168 pgs., Kudinov, Koroteev, Moscow, “Metallurgy”, Series “New Processes of Welding via Pressure”, 1978). For explosion welding, this angle is derived from the force developed during the explosion of the explosive material. For magnetic-pulse welding, the collapsing angle is dependent on the duration of initial impulse. To be able to vary and to control the velocity of collapsing produced by the magnetic pulse welding apparatus, the level of maximum voltage is controlled, as well as reliability of discharger to produce a current impulse at the predetermined moment, and the gap between the components to be welded. Further control of the collapsing velocity can be achieved by developing a special geometry of pre-assembled components (pre-weld design). In particular, the a fixed angle between the outer component and the surface of inner component is maintained. Research has proved experimentally that a better quality of joint is obtained when using a definite fixed angle. But the most important factor that determines the collapsing angle is the duration of initial impulse, and more specifically, the duration of the first quarter of the initial current impulse. 
     To be able to vary the above mentioned collapsing angle widely and to find an optimum collapsing angle for the defined pair of metals and alloys to be welded, the frequency of initial impulse should be variable and adjustable. This frequency is dependent on several factors: (1) the self inductance of the apparatus (La), which is constant for each design and each geometry of devices included the apparatus along with their connections; (2) the capacity of the battery of capacitors (C 1−N ), which is usually constant for every magnetic pulse welding unit, and which usually cannot be changed in practice beside of total reconfiguration of unit; (3) the inductance of inductor (Li), which is higher for multi-coil inductors and lower for one coil inductors; and (4) finally is dependent on the resulting L, C and R (active resistance) of the combined system. 
     None of the known prior art apparatuses for magnetic-pulse welding are capable of changing the frequency of the initial impulse. Moreover, the frequency of most of the existing devices is not optimal for use with the types of metals currently utilized in industry. This is especially true for automotive applications, where aluminum alloys having high mechanical strength are to be joined with steel fittings. These types of applications require high frequency impulses with extremely short duration (about 10 microseconds or less). Almost all of the known magnetic-pulse welding apparatus, especially those equipped with multi-coil inductors having high self inductance, function outside of the optimal duration of the initial impulse. Still further, these existing apparatus use relatively low voltage capacitors having a high self-inductance. In this regard, to increase the energy of the impulse and the velocity of collapsing these devices have to use a large battery of capacitors which leads to a decrease of frequency of the initial impulse. This is the reason why these apparatus do not provide a high strength weld even though they do release a high energy level to increase the velocity of collapsing. 
     There is therefore a need to provide a magnetic-pulse welding apparatus capable of varying and controlling the above described critical parameters. Such an apparatus will be able to optimize the velocity of collapsing and the collapsing angle by providing a controlled adjustable initial impulse current of required amplitude and duration. Part of this functionality is provided by an energy storage system that utilizes high-voltage, low inductance capacitors, and a very-low inductance conductive bus system directly interconnecting the capacitors, a discharger and an inductor. The bus system provides the ability to generate a very high frequency, short duration impulse which is needed for high quality welding of high strength metals. The bus system includes first, second and third flat bus panels disposed in closely spaced overlying relation. The second, or middle, bus panel is the “high voltage” or “hot” bus and is electrically insulated from the first (lower) and third (upper) bus panels (ground bus panel) by sheets of electrically insulative material. The first and third bus panels are connected together cooperatively form a unitary ground bus. The bus system overlies the upper ends of the capacitors wherein the second bus panel is electrically interconnected to the respective hot contacts of the capacitors, and further wherein the ground bus is electrically interconnected with the respective ground contacts of the plurality of capacitors. The energy storage system further includes an energy source connected to the capacitors, a discharge device, a charging control device, and a discharge control device for selectively initiating discharge of energy stored in the capacitors. The bus system further includes removable connector elements that are selectively removable for controlling the total number capacitors utilized in the energy storage bank, thus being able to control the total voltage and also the duration of the initial impulse. 
     Accordingly, among the objects of the instant invention are the provision of an energy storage system for a magnetic pulse unit wherein the energy storage system utilizes a low inductance bus system for creating a high frequency, short duration impulse. 
     Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
     FIG. 1 is a perspective view of the energy storage apparatus of the present invention; 
     FIG. 2 is a cross-sectional view thereof; 
     FIG. 3 is an enlarged cross-sectional view of the connector elements for selectively connecting the capacitors to the bus system; 
     FIG. 4 is an enlarged cross-sectional view of the discharger; 
     FIG. 5 is a cross-sectional view of the central electrode; 
     FIG. 6 is a perspective view of a split inductor for use with the energy storage system; 
     FIG. 7 is a fragmentary perspective view of one type of end fitting for the split inductor; and 
     FIG. 8 is a fragmentary perspective view of another type of end fitting. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, a magnetic pulse welding apparatus in accordance with the teachings of the instant invention is illustrated and generally indicated at  100  in FIGS. 1-8. 
     The apparatus  100  includes a ground  101 , a frame generally indicated at  102  connected to the ground  101 , a connective bus system generally indicated at  104 , and a bank of high voltage capacitors with low self inductance, generally indicated at  106 . The system further comprises a discharger, indicated generally at  200 , an inductor tool generally indicated at  300 , a high voltage power source generally indicated at  400 , and a control system generally indicated at  500 . 
     The high voltage capacitors  106  are of the type that can provide a high voltage charge/discharge of 5 kV or more. The capacitors  106  have a “high voltage” or “hot” contact  128  and a ground contact  124 . The term “hot” is utilized for the contact  128  because the polarity of the contact could be either positive or negative. Capacitors  106  of the type contemplated are commercially available from power supply vendors. 
     The high voltage source of energy  400  comprises a high voltage transformer-rectifier that is designed to charge the bank of power capacitors  106  in a short time period and is further designed so that it does not require disconnection during the discharge cycle. The transformer-rectifier  400  is supplied with power from an external power source  401  through cable  402 . Transformer-rectifiers  400  of the type contemplated are commercially available from various power supply vendors. 
     The control system indicated generally at  500 , is responsible for controlling charging of the capacitors and release of the current impulse at a predetermined moment. 
     The inductor tool  300  comprises a removable inductor coil, i.e. welding tool, which is generally a one-coil inductor, solid or split, depending on the components to be welded. 
     Referring to the drawings in FIGS. 2,  2 A and  3 , the connective bus system  104  and means for selectively connecting and disconnecting the capacitors  106  is illustrated. The bus system  104  consists of the three bus panels: a bottom bus panel  108 , a middle bus panel  110 , and an upper bus panel  112 . The middle bus panel  110  is isolated from the top and bottom bus panels  108  and  112  by sheets of multilayer electrically insulative material  114 . More specifically, the multilayer isolative sheets  114  are placed on top of the bus panel  108  and under bus panel  112  respectively to electrically isolate “hot” middle bus panel  110  from the surrounding components. The top bus panel  112  is covered with exterior electrically isolative plate  116 . 
     The bus system  104  is designed to conduct a high current and high frequency working impulse of a predetermined duration directly from the battery of capacitors  106  to the inductor tool  300  at the moment of initiation of a working impulse by the discharger  200 . The bus system  104  is believed to define a new element according to the current invention. The bus system  104  is designed to have a minimal active resistance and inductive resistance, so that energy from the battery of capacitors  106  will be directly transferred to the working tool with minimal loses. Also bus system  104  shortens the total physical distance between the inductor tool  300  and the discharger  200  and minimizes the geometrical dimensions of the connective buses. The bus system further provides the ability to control the duration of the working impulse via connection or disconnection of desirable quantity of capacitors  106  depending on the components to be welded. For the above mentioned purposes the top bus  112  and the bottom bus  108  are made of highly conductive materials, for example aluminum or copper, and they have a sufficient thickness and mechanical strength to support the bus system  104 . The upper and lower pus panels  108  and  112  are connected to each other using connective metal strips  118 , which extend along the frame  102  of the unit  100 . These strips  118  electrically interconnect the upper and lower bus panels  108  and  112  together to collectively form a ground bus, which is in turn connected to ground  101  through the frame  102 . The bottom bus panel  108  includes a plurality of openings  119  that are arranged in corresponding relation to the contacts at the upper ends of each capacitor  106 . The middle bus panel  110  also includes a plurality of openings  121  in the same arrangement. 
     The ground bus panels  108  and  112  are grounded to the capacitors  106  by grounding rings (connectors)  120  which are bolted to the bottom bus panel  108  (bolt  122 ) and to a ground panel  124  (bolt  126 ) on the upper end surface of capacitors  106  simultaneously. The rings  120  surround the openings  119 . 
     Referring to CAPACITOR  106 A of FIG. 3, the central—high voltage—contact  128  of the capacitor  106 A is connected to the “hot” bus panel  110  by tapered connector cup  130 , which is seated in the opening  121  in the middle “hot” bus  110 . The connector cup  130  has a bottom wall  130   a  and a continuous side wall  130   b . The peripheral lip  130   c  of the cup  130  is tapered and engages with the tapered sidewalls of the openings  121 . The cups  130  extend through the openings  119  in the bottom bus panel  108  and through openings in the insulator materials  114 . A nut  133  threads onto the contact  128  and forces the lip  130   c  of the cup  130  downwardly into engagement with the sidewalls of the openings  121  in the bus panel  110 . Insulator rings  132  are seated within the top of each capacitor  106  to center the openings of isolative sheets  114  and to prevent accidental discharge, including corona discharge over the surfaces of the parts of the capacitors, between the high voltage contacts  128  of the capacitors  106  and the connector cups  130  and ground plates of the capacitors. Plastic fasteners  135   a  and  135   b  are fitted into openings in the ground panel  112  to fill the openings. All capacitors  106  which are to be utilized for charging are connected in this manner. 
     Referring to CAPACITOR  106 B of FIG. 3, there is provided a grounding mechanism for selectively grounding individual capacitors  106  so that they are not charged by the system. In this regard, the connector cup  130  is replaced by a metal bolt  134  that is threaded downwardly through an opening in the upper bus panel  112  and into engagement with the hot contact  128  of the capacitor to ground the capacitor. The threaded bolt  134  is surrounded by tube  136 . This arrangement selectively isolates the capacitor  106 B and allows the operator to selectively control the voltage, current and frequency of the current impulse released. 
     The discharge device  200  is illustrated in FIGS. 4 and 5. According to the current invention, the discharger  200  comprises a central electrode  201  placed coaxially inside of ring electrode  202  with an adjustable concentric gap in between. The discharger  200  further includes an ignition electrode  203  designed as a coaxial ring surrounding central electrode  201 . The ignition electrode  203  can be moved up and down with respect to the central electrode  201  and placed in a definite position by means of an adjusting bolts  204 . The ignition electrode  203  is connected to an independent source of igniting impulses  198  (see FIG. 2) by an ignition cable  205  (See FIGS.  2  and  5 ). The ignition source  198  is also connected to the external power source  401  through a cable  404 . The ignition electrode  203  is electrically isolated from the ring electrode  202  with the help of a dielectric sleeve  206  and from the central electrode  201  with the help of dielectric sleeve  207 . Central electrode  201  has opening  201   a  for the input of compressed air which is passed through to tangential jets  201   b  for organizing air flow through the discharge gap. Discharge electrode  203  includes radial openings  203   a  for further organizing air flow. 
     Ring electrode  202  is mounted to the middle bus  110  and the central electrode  201  is connected to one leg  301  of the inductor tool  300 . The other leg  302  of the inductor tool  300  is connected to the top bus panel  112  by means of a connective ring  209 . A discharge enclosure  210  is mounted on the bottom bus  108 . The enclosure  210  has a hermetic joint with the bottom bus  112  and an outlet  211  for exhausted air containing the ozone and drops of the electrode&#39;s metal after the working cycles. 
     In use, the apparatus functions as follows: at the moment of connecting “Start” button (“S”  501  in FIG. 2) transformer-rectifier  400  is switched to connect with the middle “hot” bus  110  through cables  402  and  403  and thus to the battery of capacitors  106  to start charging the capacitors  106 . The voltage on the ring electrode  202  thus rises respectively. Controlled discharge according to the present invention works as follows: as soon as the voltage on the battery of capacitors  106  reaches a chosen level, discharge will be ready to occur between the central electrode  201  and the ring electrode  202 . The discharge gap between these electrodes should be adjusted so that the working voltage cannot automatically generate a direct arc between these electrodes. Instead the ignition electrode  203  is positioned in between the working electrodes  201  and  202  in such a way that the distance between it&#39;s edge and one of the working electrodes  201  or  202  is much less than the discharge gap. For example, discharge gap for a working voltage of 15 kV should be not less then 5 mm (having in mind that direct arc through an air gap about 1 mm long occurs for voltage 3 kV). The distance between the ignition electrode&#39;s edge and one of the working electrodes  201  or  202  can be chosen to be 2-3 times less, or 1.5-2 mm. Ignition of the between the ring and central electrode is created by generating a separate discharge through the ignition electrode  203 . In other word, the ignition electrode  203  provides a spark to jump the discharge gap. Ignition voltage from the independent source of ignition impulse  198  (see FIG. 2) is about 25-30 kV. Accordingly, the ignition impulse will develop an arc between the electrodes  201  and  202  and a respective plasma jet  212  will be formed. 
     To provide a high quality discharge of energy from one electrode to the other electrode the plasma jet  212  must be controlled. In this regard, a tangential air jet from the central electrode&#39;s openings  201   b  forces air flow towards the discharge gap and creates favorable conditions for an instant working discharge  213  and for developing a powerful working impulse current through the inductor coil  300 . The main distinctive features of the discharger according to the present invention are the follows: the prior art spark dischargers have the working electrodes  201  and  202  and the ignition electrode  203  placed relatively close to each other in such a way that at the moment the working discharge is released, the plasma jet moves towards ignition electrode (See, for example U.S. Pat. No. 4,990,732). 
     According to electrodynamics law, the plasma jet  212  will normally stray out of the desired current contour. This problem leads to overheating of the ignition electrode  203 , intensive erosion and distortion of ignition electrode  203  and, finally, leads to an uncontrolled working discharge  213 . The new design of the discharger device  200  arranges the phenomenon of plasma jet  212  in such a way that the ignition electrode  203  is placed inside of the current contour and such that it will never be in the path of the plasma flow, and so will never be overheated or bombarded by the plasma jet  212 . In this case, the ignition electrode  203  is not eroded, and thus maintains it&#39;s exact geometry and it is not required to adjust the ignition electrode  203  with respect to the working electrodes  201 ,  202 , nor is it necessary to replace the ignition electrode  203  as often. Accordingly, the life time of ignition electrode  203 , as measured by the quantity of working cycles before it&#39;s replacement, should be significantly increased. 
     As indicted above, the current design organizes the flow of cooling air in the area of working discharge. This design feature is not believed to be shown in any of the known prior art. The invention accomplishes this by providing two types of openings; (1) tangential openings  201   b  in the central electrode  201  (See FIG.  5 ); and (2) radial openings  203   a  in the ignition electrode  203 . These openings  201   b  and  203   a  organize the air flow in such a way that two distinct air flows occur: (1) the first is between the ignition electrode  203  and the central electrode  201 ; and (2) the second is between the ignition electrode  203  and the ring electrode  202 . The optimal parameters for both flows are reached by changing the gaps between these electrodes. Both gaps facilitate the working discharge by forcing the plasma jet impulse  212  towards the gap between working electrodes  201  and  202 . 
     As soon as the main working current impulse is created, a powerful pulse current—about 500,000 Amps or more—travels from the battery of capacitors  106  through the low inductance current bus  110 , through the inductor coil  300  and buses  108 ,  112  to the ground  101 . The respective inductive current, in the opposite direction, is produced in the outer tubular components, placed within the magnetic field of the inductor  300 . The interaction of the initial current impulse and the secondary inductive current impulse causes a massive repulsive force and a resulting inward impact of the outer components into the inner components with a high velocity. If the velocity and a collapsing angle are optimal for the chosen pair of metals, the metal of outer component penetrates the metal of the inner component thus creating a full metallurgical bond at the molecular level. 
     The above described working cycle can be repeated every second, or every few seconds, depending on the time needed for cooling of the discharger  200 . This timing is very critical for the productivity of MPW apparatus  100 . Dependent on the application, different types of inductor tools  300  could be connected to the MPW apparatus  100 . For example, a solid coil inductor for components having a maximum outside diameter less than the inductor opening, or a split coil inductor for complicated shape components which can not be removed out of inductor after welding (for example for drive shafts with end yokes having an outer diameter more than the tube OD), or a multi-coil inductor with a long working zone for forming applications. 
     Referring now to FIG. 6, the above described MPW apparatus  100  is particularly suitable for use with a split inductor  300 . The split inductor  300  generally includes two quarter-coils  303 ,  304  each having connective legs  301 ,  302  and one semi-coil  305 . The general construction of the inductor coil is known in the art. The coils  303 ,  304 ,  305  are interfittingly engaged and aligned together with special mechanical contacts  306 . The quarter-coils  303 ,  304  are connected through feet  301  and  302 , to the apparatus  100  constantly, and the semi-coil  305  is a movable, or removable, part, which is selectively connected to and disconnected from the respective ends of quarter-coils  303 ,  304  during each working cycle. The semi-coil  305  can be articulated by using a variety of different mechanical means, such as air pressure cylinders, or manual bolts dependent on productivity requirements for loading and unloading operations. Design of the electrical contacts  306  on the respective interface ends of coils  303 ,  304 ,  305  is critically important for effective work of split inductor  300 . The most important criteria are geometry of electrical contact and average of pressure on contact surface. Referring to FIGS. 7 and 8, to reach an optimal quality of electrical contact, the quarter-coils  303 ,  304  are designed with contact inserts  307 , and  308  respectively. Referring to FIG. 7, a cylindrical insert  307  is shown, and referring to FIG. 8, a wedge insert  308  is shown. 
     For industrial inductors that need to work at a high productivity rate during extended periods of time, the inductor can alternatively be provided with channels (not shown) for circulation of cooling water or cold air. 
     EXAMPLE 
     The following represents an example of a successful application of the apparatus  100  for Magnetic-Pulse Welding of a metallurgical joint between a mild steel end fitting (driveshaft yoke) with an aluminum tube grade Al 6061, T-6 (driveshaft tube). 
     The components to be welded have the following characteristics. The annular locating ring (width “W”) on the cylindrical neck of the fitting (driveshaft yoke) was sized so that an interference fit exists between the outer surface of the locating ring and the inner surface of the tube ( driveshaft tube). The tube stop was located a distance “L” and it was sized so that, when a trimmed, the orthogonal tube end is placed fully in contact with tube stop, and a closed cavity between the inner surface of the tube and the outer surface of the fitting was created. The depth of the cavity was chosen experimentally for the said metals to be welded and depended on the predetermined initial angle “a” of a generally tapered bottom of the cavity. The initial distance “I” between the bottom of the cavity and the inner surface of the tube on the very end may be varied depending on critical parameters of the predetermined cavity shape “L”. 
     The critical parameters of the predetermined cavity shape for the above pair of components in case of having standard Al tube OD1 3.5″ (or 88.9 mm+0.1 mm) wall thickness T=2.2 mm+/−0.1 mm and a pre-machined steel end fitting with the annular locating ring OD2=84.5+/−0.1 mm. For this pair of metals with above initial shape of components to be welded: L=12 mm+/−1 mm; and a=7°+/−0.5° . The width of the annular locating ring was generally W=10 mm. The initial distance between the bottom of the cavity and the inner surface of the tube on the very end was varied: I=0-0.5 mm. The radius R=2 mm; and the chamfer C 1 =2 mm. 
     The chosen configuration of the apparatus  100  provided a bank of 12 capacitors in parallel, each having a capacitance of 12 uF for a total capacitance of 144 uF. The voltage from the discharger on a single-turn coil split inductor was 16,800 V, which was allowed to energize the split inductor with the short impulse of current about 500,000 amps. The pre-assembled components as described above were placed in position within the working zone of the split inductor  300  connected to the apparatus  100 . The second half of the split inductor was closed over the assembly and the impulse of current was discharged through the inductor. The current impulse was sufficient to cause a high velocity collapse of the outer tube onto the end fitting and cause material of the outer tube to penetrate the metal of the steel end fitting to create a full metallurgical joint at the molecular level. The resulting components were tested for mechanical strength and fatigue cycles and were proven to be within the limits acceptable for practical application for automotive industry. 
     It can therefore be seen that present energy storage system provides the unique ability to generate a high frequency short duration impulse for superior welding quality. The storage system further provides the ability to selectively disconnect capacitors to control voltage, frequency and duration of the impulse. For these reasons, the instant invention is believed to represent a significant advancement in the art which has substantial commercial merit. 
     While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.