Electric heating – Inductive heating – Metal working
Reexamination Certificate
2001-01-23
2003-04-15
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
Metal working
C219S603000, C219S635000, C219S672000
Reexamination Certificate
active
06548791
ABSTRACT:
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 a 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 field), 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., Kuclinov, 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, 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 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
Dudko Danylo
Kistersky Ludmilla
Sadokhin Viktor
Shevchenko Viacheslav
Barlow Josephs & Holmes, Ltd.
Inli, LLC
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