WO2008011148A2

WO2008011148A2 - Conductive heat resistance deformation welding method

Info

Publication number: WO2008011148A2
Application number: PCT/US2007/016462
Authority: WO
Inventors: Menachem Kimchi; Jonathon Jennings
Original assignee: Edison Welding Institute Inc
Current assignee: Edison Welding Institute Inc
Priority date: 2006-07-21
Filing date: 2007-07-20
Publication date: 2008-01-24
Anticipated expiration: 2009-01-21
Also published as: WO2008011148A3

Abstract

A conductive heat resistance deformation welding method for joining work pieces (100, 200) in a work assembly (1000). At least one cover sheet (300, 400), having a higher melting temperature and electrical resistance greater than either work pieces (100, 200) is applied. Passing an electrical current between a primary (500) and a secondary electrode (600) through the cover sheet (300, 400) causes the cover sheet n(300, 400) temperature to exceed the melting point of the work pieces (100, 200). Further heating and moving at least a portion of the work assembly (1000) sufficient to ensure physical contact between the work pieces (100,200) creates a weld pool including a portion of both work pieces (100,200). Solidification creates a weld joining the work pieces (100, 200).

Description

TITLE

CONDUCTIVE HEAT RESISTANCE DEFORMATION WELDING METHOD CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application 60/832,391; filed on July 21, 2006 all of which is incorporated by reference as if completely written herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR

DEVELOPMENT This invention was not made as part of a federally sponsored research or development project.

TECHNICAL FIELD

The present invention relates to the field of materials joining; particularly, to a conductive heat method of electric resistance welding for deformation welding applications and projection welding applications, welding arrangements for such method, and equipment for such method.

SUMMARY OF THE INVENTION

The invention includes a conductive heat resistance deformation welding method for joining a primary work piece and a secondary work piece. The process is initiated by placing the work pieces in weldable proximity with each other to form a work assembly.

At least one cover sheet, having a higher melting temperature than both of the work pieces is placed in contact with a portion of the work. The electrical resistance of the cover sheet is also greater than the electrical resistance of either of the work piece. A primary electrode and a secondary electrode are placed in electrical communication with a portion of the cover sheet. Resistively heating the cover sheet by passing an electrical current between the primary electrode and the secondary electrode causes the cover sheet temperature to become greater than the melting point of the work pieces.

The method continues with conductively heating, and causing relative movement to, a portion of work assembly sufficient to ensure physical contact between the primary work piece and the secondary work piece. The work assembly is conductively heated from the cover sheet, thereby creating a molten weld pool including a portion of the primary work piece and a portion of the secondary work piece. The method continues with cooling the weld pool to solidification to create a solidified weld joining the primary work piece and the secondary work piece. In additional embodiments, a primary cover sheet and a secondary cover sheet may be utilized. The primary work piece may have a primary work piece conduction initiation surface, and the secondary work piece may have a secondary work piece conduction initiation surface. In such an embodiment, the primary work piece may be conductively heated from the primary work piece conduction initiation surface and the secondary work piece may be conductively heated from the secondary work piece conduction initiation surface.

Fn an alternate embodiment, more than one electrode may be placed on the same cover sheet. The primary and secondary work pieces may take many forms, including by way of example only, tube and sheet forms. Various projections, rims, and other structures on the work pieces may aid in proper work piece orientation. A cover sheet may be a composite cover sheet having at least one insulator portion and at least one conductive portion, allowing the formation of a temperature gradient between the insulator portion and conductive portion. Similarly, the conductive portion may have at least one low resistance section and at least one high resistance section, to allow the formation of a temperature gradient between the low resistance section and the high resistance section.

A cover sheet may be shaped so that the step of causing relative movement to a portion of work assembly sufficient to ensure physical contact between the primary work piece and the secondary work piece induces an application of force to the work assembly in at least two non-parallel directions, and sometimes well more than two directions.

The cover sheets and the electrodes need not be separately formed. In one embodiment, the cover sheet is integrally formed with at least one primary electrode, so that the step of placing a cover sheet in contact with a portion of the work assembly further includes the step of placing a primary electrode in electrical communication with a portion of the cover sheet.

The primary work piece and the secondary work piece need not be in direct electrical communication. In one embodiment, the primary cover sheet is in electrical communication with the secondary cover sheet by means of a low-resistance shunt, and therefore the step of resistively heating the cover sheet further includes the step of inducing current flow through the low-resistance shunt.

These variations, modifications, alternatives, and alterations of the various preferred embodiments, processes, and methods may be used alone or in combination with one another as will become more readily apparent to those with skill in the art with reference to the following detailed description of the preferred embodiments and the accompanying figures and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Without limiting the scope of the present invention as claimed below and referring now to the drawings and figures:

FIG. 1 is a partial cross-sectional view of two work pieces of one embodiment of the present invention, not to scale;

FIG. 2a is a partial cross-sectional view of two work pieces of one embodiment of the present invention, not to scale;

FIG. 2b is a partial cross-sectional view of two work pieces of one embodiment of the present invention, not to scale; FIG. 3 is a partial cross-sectional view of two work pieces and cover sheets of one embodiment of the present invention, not to scale;

FIG. 4 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale;

FIG. 4a is a partial cross-sectional view of two work pieces, cover sheets, electrodes, and low-resistance electrical shunt, of one embodiment of the present invention, not to scale;

FIG. 5 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale;

FIG. 6 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale; FIG. 7 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale;

FIG. 8 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale; FIG. 9 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale;

FIG. 10 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale; FIG. 1 1 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale;

FIG. 12 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale;

FIG. 13 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale;

FIG. 14 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale;

FIG. 15 is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale; FIG. 16a is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale;

FIG. 16b is a partial cross-sectional view of two work pieces, cover sheets, and electrodes of one embodiment of the present invention, not to scale;

FlG. 17 is a partial cross-sectional view of two work pieces, a single cover sheet, and two electrodes of one embodiment of the present invention, not to scale;

FIG. 18 is a cross-sectional view of an embodiment of a composite cover sheet, not to scale; and

FIG. 19 is a cross-sectional view of an embodiment of a composite cover sheet, not to scale. These drawings are provided to assist in the understanding of the exemplary embodiments of the invention as described in more detail below and should not be construed as unduly limiting the invention. In particular, the relative spacing, positioning, sizing and dimensions of the various elements illustrated in the drawings are not drawn to scale and may have been exaggerated, reduced or otherwise modified for the purpose of improved clarity. Those of ordinary skill in the art will also appreciate that a range of alternative configurations have been omitted simply to improve the clarity and reduce the number of drawings.

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a conductive heat resistance deformation welding method, a conductive heat resistance projection welding method, the welded product produced therefrom, the welding set-up and configuration of the work pieces, and various welding components. The invention enables a significant advance in the state of the art. The preferred embodiments of the apparatus accomplish this by new and novel methods that are configured in unique and novel ways and which demonstrate previously unavailable but preferred and desirable capabilities. The description set forth below in connection with the drawings is intended merely as a description of the presently preferred embodiments of the invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention. A conductive heat resistance deformation welding method of the present invention joins a primary work piece (100) and a secondary work piece (200). With reference to FIG. 1, in one embodiment the primary work piece (100) has a primary work piece interface surface (102) and a primary work piece conduction initiation surface (104). Similarly, the secondary work piece (200) has a secondary work piece interface surface (202) and a secondary work piece conduction initiation surface (204).

The primary work piece (100) and the secondary work piece (200) are generally described herein as being in tube form or sheet form, however one with skill in the art will appreciate that virtually any work piece geometry desired to be joined by welding may be considered as a tube or a sheet. Therefore, the present invention is not limited to traditional tube and sheet shapes and configurations. The term "primary work piece" is abbreviated "PWP" throughout when describing articles or elements of the primary work piece. Similarly, the term "secondary work piece" is abbreviated "SWP" throughout when describing articles or elements of the primary work piece. Further, the term "tube form" is abbreviated "TF" throughout when describing articles or elements of the tube form of the primary or secondary work pieces. Likewise, the term "sheet form" is abbreviated "SF" throughout when describing articles or elements of the sheet form of the primary or secondary work pieces.

The interface surfaces (102, 202) are the surfaces in which a portion of each touches the other during the joining process of the present invention, and therefore may appear differently in the various embodiments. For example in FIG. 1 the work pieces (100, 200) appear as tubes with joining projections (120, 220), thus the interface surfaces (102, 202) are actually a portion of the joining projections (120, 220). However, as seen in FIG. 2a, in several embodiments work pieces (100, 200) may be more similar to a sheet of material than a tube. Thus, in this particular embodiment, the secondary work piece (200) is in sheet form (260) and therefore the interface surface (202) is simply that surface which comes in contact with the primary work piece (100). Additionally, as seen in FIG. 2b, the primary work piece (100) may have a proximal end orientation projection (113) below the proximal end (112) that is received by the secondary work piece (200). Such cooperation helps ensure accurate alignment of the work pieces (100, 200).

With reference now to FIG. 3, the conduction initiation surfaces (104, 204) are the surfaces that come in contact with cover sheets of a temperature greater than the melting temperature of the work pieces (100, 200). More specifically, a portion of the PWP conduction initiation surface (104) is in contact with a primary cover sheet (300), and a portion of the SWP conduction initiation surface (204) is in contact with a secondary cover sheet (400). The electrical resistance of the primary cover sheet (300) is greater than the electrical resistance of the primary work piece (100) and the electrical resistance of the secondary cover sheet (400) is greater than the electrical resistance of the secondary work piece (200). The electrical resistance of the cover sheets (300, 400) allow them to be resistively heated upon the passage of electrical current through the cover sheets (300, 400) to a point at which the temperature of the cover sheets (300, 400) is higher than the melting point of the work pieces. Since the cover sheets (300, 400) are in contact with the conduction initiation surfaces (104, 204), the heat generated in the cover sheets (300, 400) is conductively transferred to the work pieces (100, 200) from the initiation surfaces (104, 204) to the interface surfaces (102, 202). The conductive heating results in a molten weld pool including a portion of the primary work piece (100) and a portion of the secondary work piece (200).

An embodiment of a joining configuration is seen in FIG. 4, showing a primary electrode (500) and a secondary electrode (600). The primary electrode (500) is placed in electrical communication with a portion of the primary cover sheet (300). Similarly, the secondary electrode (600) is placed in electrical communication with a portion of the secondary cover sheet (400). Electrical current is passed between the electrodes (500, 600) thereby resistively heating the primary cover sheet (300) and the secondary cover sheet (400). In the process of traveling between the electrodes (500, 600), in one embodiment, the current passes through a portion of the primary work piece (100) and/or the secondary work piece (200). However, in certain configurations, the current need not pass through both work pieces (100, 200). The work pieces (100, 200) are composed of material generally thought of as electrically conductive and therefore there is no significant resistance heating of the work pieces (100, 200).

With continued reference to FIG.4, as current is passed between the electrodes (500, 600), or during the conductive heating of the work pieces (100, 200), relative movement between the work pieces (100, 200) is initiated. Such relative movement may be caused by a number of external forces acting on one, or both, of the work pieces (100, 200). In one particular embodiment, the relative movement is caused by force applied to one, or both, of the work pieces (100, 200) by at least one of the electrodes (500, 600). In an alternative embodiment, the relative motion force is applied by at least one of the cover sheets (300, 400). In still a further embodiment, the relative motion force is applied directly to at least one of the work pieces (100, 200). The relative motion will result in deformation of a portion of at least one of the work pieces (100, 200).

In some embodiments the desired deformation may be engineered into the configuration of the work pieces (100, 200) through the use of joining projections (120, 220), which may include, but is not limited to, folds including air gaps, folds without air gaps, and axial projections, some of which may be seen, by way of example only, in FIGS. 6-9. In such

10 embodiments, the conductive heat substantially melts, or softens, a portion of the fold, or projection, such that relative movement occurs as a weld pool is created. Specifically, in an embodiment having a fold that includes an air gap, the conductive heat softens the fold such that the air gap is substantially eliminated and a weld pool is formed thereby joining the work pieces (100, 200), as seen well in FIG. 17.

Further, the shape of the cover sheets (300, 400), and/or the shape of the electrodes (500, 600) may impart the relative movement of the work pieces (100, 200). For instance, the cover sheets (300, 400) or electrodes (500, 600) may be formed to result in sliding motion between, or at, the interface of the work pieces (100, 200). Additionally, in other embodiments the joining projections (120, 220) and/or the cover sheets (300, 400) may be configured to shape, and/or constrain, the weld pool. Finally, the weld pool is cooled to solidification to create a solidified weld joining the primary work piece (100) and the secondary work piece (200).

With reference now to FIGS. 4-19, the present welding method may be used with work pieces (100, 200) of virtually any shape or size. For instance, FIG. 4 illustrates an embodiment in which the primary work piece (100) is a PWP tube form and the secondary work piece (200) is also a SWP tube form. While the work pieces (100, 200) of FIG. 4 are both tube forms, the ends of the work pieces (100, 200) nearest the interface surfaces (102, 202) are configured differently. By configuring the ends in various configurations, the size, shape, and orientation of the final weld may be controlled. For instance, the embodiment of FlG. 5 incorporates a PWP tube form (1 10) having a PWPTF joining projection (120) near the distal end (1 14), and thus between the PWP interface surface (102) and the PWP conduction initiation surface (104). In this embodiment the PWP tube form (110) is being joined to a SWP sheet form (260). It is clear to one skilled in the art where the relative motion

1 1 will occur in this embodiment, namely a portion of the PWPTF joining projection (120) will soften, deform, and join a portion of the SWP sheet form (260) in the weld pool.

In an alternative embodiment, illustrated in FIG. 6, the PWP tube form (110) is configured to be joined to a SWP tube form (210), with each tube form (1 10, 210) having a joining projection (120, 220). In a further embodiment illustrated in FIG. 7, the PWP tube form (1 10) is configured to be joined to a SWP sheet form (260) with the PWP tube form (1 10) physically passing through an opening in the SWP sheet form (260).

The tube form joining projections (120, 220) may be shaped in a number of ways. For example, the PWP tube form (1 10) of FIG. 2 illustrates a semi-circular transverse bulge shaped PWPTF joining projection (120), whereas the joining projection, not labeled, of the secondary work piece (200) in FIG. 1, is more of a traditional flange. Further, the embodiment of FIG. 6 illustrates two semi-circular transverse bulge shaped joining projections (120, 220). An alternative to the semi-circular transverse bulge shaped joining projections (120, 220); the embodiment of FIG. 8 illustrates rolled-edge joining projections (120, 220). In such a configuration the area of the work pieces (100, 200) in contact with the cover sheets (300, 400) is significantly reduced when compared to the semi-circular transverse bulge shaped joining projections (120, 220). Further, the traditional flange of FIG. 1 may be a smoother radius flange, similar to the SWPTF flange (235) of FIGS. 8 and 9.

Yet another tube form joining projection (120, 220) is seen in FIG. 11 and is a PWPTF outward transverse folded end form (150). In the embodiments of FIGS. 10 and 11 , the PWP tube form (1 10) is configured to be joined to a SWPSF cap (280), more specifically a rolled-edge cap.

One skilled in the art will appreciate that the work pieces (100, 200) may be formed into desirable shapes after they are brought into close proximity to one another, but before

12 they are welded. For instance, FIG. 12 illustrates an embodiment in which the SWPSF cap (280) was placed adjacent to the PWP tube form (1 10) prior to the SWPSF cap (280) being formed into the illustrated shape. The cover sheets (300, 400) may be used to form the work pieces (100, 200). For example, the primary cover sheet (300) of FIG. 12 may be used to apply the forces necessary to bend the SWPSF cap (280) into the shape illustrated.

An attribute of the embodiment of FIG. 12 is that neither of the cover sheets (300, 400) actually contacts the PWP tube form (110). Thus, in this embodiment, the PWPTF flange (135) is conductively heated by the secondary work piece (200), rather than by contact with a cover sheet (300, 400). In yet another embodiment, seen in FIG. 13, a portion of the SWP tube form (210) resides inside the PWP tube form (1 10). In this particular embodiment the SWP tube form (210) is formed with a SWPTF fold (230) and the PWP tube form (110) has a PWPTF flange (135). Even further embodiments are illustrated in FIGS. 14, 15, 16a and 16b. The embodiment of FTG. 16a includes a PWPTF axial projection (140). In this embodiment the size and position of the weld or welds are determined by the design of the PWPTF axial projection (140). The PWPTF axial projection (140) controls the conductive heat transfer between the work pieces (100, 200). A further PWPTF axial projection (140) embodiment is seen in FIG. 16b. The PWPTF axial projection (140) may be a continuous projection thereby creating a seal between the work pieces (100, 200), or it may be one or more point, or spot, projections. In these embodiments the collapse of a portion of the projection (140) results in the relative movement of the work pieces (100, 200).

Still another embodiment, seen in FIG. 17, illustrates that the method of the present invention is not limited to the use of a multiple cover sheets. In fact, the use of a single primary cover sheet (300) may be preferred in some joining configurations. Here, the primary

13 cover sheet (300) is formed to bend the work pieces (100, 200) into the desired welding configuration. Thus, the cover sheets (300, 400) may be engineered to produce desirable welding configurations. As such, in some embodiments in which the primary cover sheet (300) is used in bending, or positioning, one or more of the work pieces (100, 200) it may be preferable to use a composite cover sheet (310), seen in FIG. 18. The composite cover sheet (310) may be designed to have one, or more, specifically placed insulator portions (320) and electrically conductive portions (330). The insulator portions (320) may be electrical, and/or thermal, insulators.

Incorporating at least one insulator portion (320) and conductive portion (330) allows for very precise conductive transfer of heat, and thus, a very precise weld. For instance, the conductive portion (330) of FIG. 18 does not extend to both lower corners of the of the composite cover sheet (310), thus the lower left corner of the composite cover sheet (310) is the insulator portion (320) and will not be resistively heated. In many embodiments this feature is useful because that lower left corner of the composite cover sheet (310) may be important to shaping the joint, and/or applying the force that results in the relative movement among the work pieces (100, 200), yet it may be desirable to keep the weld away from that corner. Further, as seen in FIG. 19, the conductive portion (330) may include both a low electrical resistance section (332) and a high electrical resistance section (334). The low resistance section (332) is designed to transfer the current from one of the electrodes (500, 600) to the high resistance section (334) that is resistively heated by the passage of current and conductively transfers the developed heat to the work pieces (100, 200).

As one skilled in the art will appreciate, the cover sheets (300, 400) need not be a single piece, but may be composed of multiple individual sections. Further, the cover sheets (300, 400) may be virtually any shape. For instance, the primary cover sheet (300) of FIGS.

14 10 and 11 is shaped to cooperate with the curve of the PWP tube form (110). Similarly, while the disclosure herein refers to the primary electrode (500) and the secondary electrode (600), one skilled in the art will appreciate that the invention is not limited to two electrodes but merely the flow of electrical current from a first location to a second location. The present invention may be used to join aluminum, lead, copper, brass, and other alloys; provided that the material to be joined has a lower melting point than the cover sheets (100, 200). The cover sheets (100, 200) are typically steel, but can include various other cover materials including cobalt, nickel, and stainless steel that melt at temperatures greater than the work pieces (100, 200). This invention is particularly useful with materials, such as aluminum, that are extremely difficult to resistively heat due to their high level of conductivity. Further, the method greatly reduces the porosity and cracking that is typically associated with resistively welded aluminum, particularly aluminum spot welds. Further, the present invention reverses the direction of solidification of the weld pool (800) when compared to welds completed using resistance welding. The cover sheets (300, 400) may be integral to the electrodes (500, 600), thus simplifying the welding process, reducing part count, and eliminating a source of variability. In such an embodiment, electrodes (500, 600) are more resistive than those that would be normally selected for proper resistance welding. By substituting a more resistive electrode material such as a Resistance Welding Manufactures Association (RWMA) Class 10, 11, 12, 13, 14, or other similar material, in place of the typical RWMA Class 1, 2, and 3 materials, it is possible to eliminate the need for the separate cover sheets (400, 500) when joining highly electrically conductive work pieces such as aluminum alloys, copper, and brass.

The electrodes (500, 600) may be any resistance welding electrode. Further, the electrodes (500, 600) may be configured to transmit current at a particular point, along a

15 specifically defined shape, and may be roller-type electrodes to create a seam weld. As one skilled in the art will appreciate, when joining small work pieces the electrodes may be formed as a complete ring that encircles the work piece. Alternatively, large work pieces may require the use of a seam welding electrode. One skilled in the art will appreciate that any of the end configurations of the primary work piece (100) may be joined to any of the end configurations of the secondary work piece (200), and thus the invention is not limited to those embodiments illustrated herein. Further, while the illustrations typically show the primary work piece (100) and the secondary work piece (200) having a very close cooperative fit with one another, this is not required as the relative movement, or deformation, brings the work pieces (100, 200) into the proximity required to achieve the desired weld. Thus, upon fit-up of the work pieces (100, 200), it is often desirable to have as much clearance between the work pieces (100, 200) as possible to accommodate various manufacturing irregularities.

Further, while most embodiments provide for at least a portion of the primary work piece (100) being in electrical communication with a portion of the secondary work piece (200), this is not required. For instance, the cover sheets (300, 400) may be in electrical communication with each other via a low-resistance shunt, as will be understood by one skilled in the art, and as seen in FIG. 4a.

One with skill in the art will appreciate that "relative movement" and/or "relatively moving" a portion of the primary work piece and a portion of the secondary work piece only require a change in position between a portion of the work pieces. In other words, it is understood that such does not require a physical change in the position of both work pieces, but rather a relative change of position among portions of the work pieces.

16 The conductive heat resistance deformation welding process of the present invention is a process that can be used for many applications, such as joining aluminum alloys work pieces. The process utilizes resistance heating of one or more cover sheets (300, 400) with subsequent conductive heating of the aluminum work pieces (100, 200). Although this process is termed "conductive heat resistance deformation welding," it is important to realize that this process is significantly different than standard resistance deformation welding. With the conductive heat resistance deformation welding process of the present invention, formation of the joint is similar to a continuous casting process. As such, this process incorporates both the fundamental aspects of heat generation through resistive heating and joint formation through casting.

Heat generation with traditional resistance deformation welding, as with all resistance welding processes, is based upon l²rt heating, where I is electrical current, r is electrical resistance, t is time. The traditional process effects of material bulk resistance, interface resistance, material stack-up, etc. are well understood. When considering the conductive heat resistance projection welding process of the present invention, many of the same process effects are present; however, their influences on the process may be quite different.

With the conductive heat resistance deformation welding process, heat generation is the result of resistive heating. Heat generation occurs due to the respective bulk resistances of the cover sheets (300, 400) (e.g., steel) and material of the work pieces (100, 200) (e.g., aluminum), along with all of the interface resistances. Those factors which promote resistive heating of the steel (i.e., bulk resistive heating) and decreased interface resistances (i.e., interface heating), improve the conductive heat resistance deformation welding process. This is attributable to (1) the somewhat narrow temperature range between through thickness melting of the work pieces (100, 200) and that which allows for the part to bond to the cover

17 sheets (300, 400), and (2) the consistency of the applied heat. Some of the factors which influence the above include cover sheet thickness, weld force, part material surface coatings, e.g., aluminum oxide, etc.

The generation of heat in conventional resistance deformation welding is based upon the reaction of current with the work piece resistance. Formation of the joint is dependent upon achieving sufficient heating to promote melting of the parts. During this process of the present invention, constraint is provided by the welding electrodes acting under a force as such force is applied to the outer surface of the cover sheets.

The formation of the weld with the conductive heat resistance deformation welding method of the present invention can be compared to a casting process. The resistive heating produces heat conduction to the work pieces. The heat conduction provides the energy required for the solid to liquid transformation in the weld region. The cover sheets (300, 400), along with the surrounding work piece material, generally solid aluminum, comprise the die which encases the molten portion of the work pieces. In all welding processes there is a range over which "acceptable" welds are achieved.

Typically with conventional resistance deformation welding, this range has a lower applied heat (i.e., current) level which produces a weld of adequate width and spot overlap and an upper applied heat level which results in expulsion. Similarly with the conductive heat resistance deformation welding process of the present invention, a lower and upper "applied heat" level exists. The lower level is defined as that which results in complete through thickness melting of the work pieces. The upper level is defined as that applied heat level where the molten portions of the work pieces bond with the cover sheet(s).

A number of process factors affect the conductive heat resistance deformation welding process. Similar to all welding processes, these factors are not entirely free-standing,

18 but rather, they interact with one another. As such, control of the conductive heat resistance deformation welding process is a matter of balancing various aspects of the process and the process factors so as to achieve a satisfactory joint.

Similar to the formation of a hermetic joint using resistance seam welding, the conductive heat resistance deformation welding process involves localized melting and re- sol idϊfication of the parent material. For the conductive heat resistance deformation welding process, the effect of current is similar to that of any resistance welding process. The applied current is the source of energy which allows generation of heat. The optimal amount of current corresponds to production of sufficient heat to promote full thickness melting of the material to be joined, e.g., aluminum, without subsequent bonding of the work pieces to the cover sheets.

The effect of weld force on the conductive heat resistance deformation welding process is first associated with its effect on interface resistance. High interface resistances (i.e., low weld forces) promote rapid heat generation and increased fluctuations in temperature. Such conditions decrease the ability to achieve a satisfactory joint. Second, the welding force, translated through the cover sheets, provides constraint to the weld process. In this way, higher forces allow larger welds to form.

Continuous power, along with a number of various pulsation weld schedules, can be used. With regard to the type of power utilized, satisfactory joints may be achieved with both AC and DC power. The most significant difference between the two types of power is the differential heating associated with direct current. This differential heating is identical to that which exists with all DC resistance welding processes. For the conductive heat resistance deformation welding process, compensation for differential heating is achieved by utilizing a thicker steel cover sheet. The present invention may also be practiced using fluxing or filler

19 materials added as plating on the faying surfaces, or in other forms, to facilitate completing the weld.

What is claimed then, is a conductive heat resistance deformation welding method for joining a primary work piece (100) and a secondary work piece (200), seen in FIG. 1. The primary work piece (100) has a primary work piece interface surface (102), and the secondary work piece (200) has a secondary work piece interface surface (202). In one embodiment, the steps of the method include first placing a portion of the primary work piece interface surface (102) in weldable proximity with a portion of the secondary work piece interface surface (202) to form a work assembly (1000). Next, a least one cover sheet (300), seen well in FIG. 3, is placed in contact with a portion of the work assembly (1000), where the at least one cover sheet (300) melting temperature is higher than the primary work piece (100) melting temperature and higher than the secondary work piece (200) melting temperature. The electrical resistance of the at least one cover sheet (300) is greater than the electrical resistance of the primary work piece (100) and greater than the electrical resistance of the secondary work piece (200).

Then, as seen well in FIG. 4, a primary electrode (500) is placed in electrical communication with a portion of the at least one cover sheet (300) and a secondary electrode (600) is placed in electrical communication with a portion of the at least one cover sheet (300). Resistively heating the at least one cover sheet (300) by passing an electrical current between the primary electrode (500) and the secondary electrode (600), causes the at least one cover sheet (300) temperature to become greater than the melting point of the primary work piece (100) and greater than the melting point of the primary work piece (100).

The method continues with conductively heating, and causing relative movement to, a portion of work assembly (1000), sufficient to ensure physical contact between the primary

20 work piece (100) and the secondary work piece (200), where the work assembly (1000) is conductively heated from the at least one cover sheet (300), thereby creating a molten weld pool (800) including a portion of the primary work piece (100) and a portion of the secondary work piece (200). The method continues with cooling the weld pool (800) to solidification to create a solidified weld (900) joining the primary work piece (100) and the secondary work piece (200).

In an additional embodiment, seen well in FIG. 3, the step of placing at least one cover sheet (300) in contact with a portion of the work assembly (1000) further includes the steps of placing a primary cover sheet (300) in contact with a portion of a primary work piece conduction initiation surface (104), where the primary cover sheet (300) melting temperature is higher than the primary work piece (100) melting temperature and the electrical resistance of the primary cover sheet (300) is greater than the electrical resistance of the primary work piece (100); and also placing a secondary cover sheet (400) in contact with a portion of a secondary work piece conduction initiation surface (204), wherein the secondary cover sheet (400) melting temperature is higher than the secondary work piece (200) melting temperature and the electrical resistance of the secondary cover sheet (400) is greater than the electrical resistance of the secondary work piece (200).

In yet another embodiment, seen in FIGS. 1 and 4, the primary work piece has a primary work piece conduction initiation surface (104), and the secondary work piece (200) has a secondary work piece conduction initiation surface (204). In such an embodiment, the method may include conductively heating, and causing relative movement to, a portion of the primary work piece (100) and a portion of the secondary work piece (200), wherein the primary work piece (100) is conductively heated from the primary work piece conduction initiation surface (104) toward the primary work piece interface surface (102) and the

21 secondary work piece (200) is conductively heated from the secondary work piece conduction initiation surface (204) toward the secondary work piece interface surface (202).

In an alternate embodiment, seen by way of example in FIG. 12, the step of placing the primary electrode (500) in electrical communication with a portion of the at least one cover sheet (300) and the placing the secondary electrode (600) in electrical communication with a portion of the at least one cover sheet (300) further includes placing the primary electrode (500) and the secondary electrode (600) on the same at least one cover sheet (300).

In additional embodiments, the primary work piece (100) may have at least one primary work piece axial projection (140), seen in FIGS 16a and 16b, where the step of placing a portion the primary work piece interface surface (102) in weldable proximity with a portion of the secondary work piece interface surface (202) to form a work assembly (1000) further includes causing a fixed predetermined spacing between the primary work piece interface surface (102) and the secondary work piece interface surface (202). The primary work piece axial projection (140) may be at least partially subsumed in the weld pool (800). The primary and secondary work pieces may take many forms, as described above.

The primary work piece (100) may a primary work piece tube form (110) and the secondary work piece (200) may be a secondary work piece tube form (210), as seen in FIGS. 1, 3, and 4. Additionally, the primary work piece (100) may a primary work piece tube form (1 10) and the secondary work piece (200) may be a secondary work piece sheet form (260), as seen in FIGS. 2a, 2b, and 5.

In an additional embodiment, and as seen well in FIG. 2b, the primary work piece (100) has a proximal end orientation projection (1 13) cooperating with the secondary work piece (200). The step of placing a portion the primary work piece interface surface (102) in weldable proximity with a portion of the secondary work piece interface surface (202) to

22 form a work assembly (1000) may then include the step of orienting the work assembly (1000) in a predetermined position by means of said cooperation.

Similarly, in terms of orientation purposes, the primary work piece (100) may have a transversely projecting annular rim (125), as seen in FIG. 15, cooperating with the secondary work piece (200). The step of placing a portion the primary work piece interface surface (102) in weldable proximity with a portion of the secondary work piece interface surface (202) to form a work assembly (1000) in such an embodiment may further include the step of orienting the work assembly (1000) in a predetermined position by means of said cooperation. As seen in FIGS. 18 and 19, in some embodiments, at least one of the at least one cover sheets (300) may be a composite cover sheet (310) having of at least one insulator portion (320) and at least one conductive portion (330), wherein the step of conductive Iy heating further includes the step of forming a temperature gradient between the at least one insulator portion (320) and at least one conductive portion (330). As seen in FIG. 19, at least one conductive portion (330) may have at least one low resistance section (332) and at least one high resistance section (334), such that the step of conductively heating further includes the step of forming a temperature gradient between the at least one low resistance section (332) and the at least one high resistance section (334).

In an embodiment seen in FIG. 17, the at least one cover sheet (300) may be shaped so that the step of causing relative movement to a portion of work assembly ( 1000), sufficient to ensure physical contact between the primary work piece (100) and the secondary work piece (200), further includes the step of inducing an application of force to the work assembly (1000) in at least two non-parallel directions. As seen in FIG. 17, movement directed in the direction of the arrow will provide such force to the work assembly (1000). Similarly, the

23 application of force to the work assembly (1000) may take place in more than two non- parallel directions.

The cover sheets (300, 400) and the electrodes (500, 600) need not be separately formed. In one embodiment, the at least one cover sheet (300) is integrally formed with at least one primary electrode (500), so that the step of placing at least one cover sheet (300) in contact with a portion of the work assembly (1000) further includes the step of placing a primary electrode (500) in electrical communication with a portion of the at least one cover sheet (300).

The primary work piece (100) and the secondary work piece (200) need not be in direct electrical communication. In one embodiment, seen in FIG.4a, the at least one primary cover sheet (300) is in electrical communication with the secondary cover sheet (400) by means of a low-resistance shunt (700), and therefore the step of resistively heating the at least one cover sheet (300) further includes the step of inducing current flow through the low- resistance shunt (700). Numerous alterations, modifications, and variations of the preferred embodiments disclosed herein will be apparent to those skilled in the art and they are all anticipated and contemplated to be within the spirit and scope of the instant invention. For example, although specific embodiments have been described in detail, those with skill in the art will understand that the preceding embodiments and variations can be modified to incorporate various types of substitute and or additional or alternative materials, relative arrangement of elements, and dimensional configurations. Accordingly, even though only few variations of the present invention are described herein, it is to be understood that the practice of such additional modifications and variations and the equivalents thereof, are within the spirit and scope of the invention as defined in the following claims. The corresponding structures, materials, acts,

24 and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or acts for performing the functions in combination with other claimed elements as specifically claimed.

INDUSTRIAL APPLICABILITY

The art has long sought an improvement in the ability to weld difficult to join work pieces. The method of the instant invention allows resistance heating applied to at least one cover sheet, along with relative motion between the work pieces during the welding process, to allow the secure and economical joining of a wide variety of types and shapes of material, particularly including materials that are difficult to weld utilizing traditional resistance welding methods.

25

Claims

WE CLAIM:

1. A conductive heat resistance deformation welding method for joining a primary work piece (100) and a secondary work piece (200), wherein the primary work piece (100) has a primary work piece interface surface (102), and the secondary work piece (200) has a secondary work piece interface surface (202), the method comprising: a) placing a portion of the primary work piece interface surface (102) in weldable proximity with a portion of the secondary work piece interface surface (202) to form a work assembly (1000); b) placing at least one cover sheet (300) in contact with a portion of the work assembly (1000), wherein the at least one cover sheet (300) melting temperature is higher than the primary work piece (100) melting temperature and higher than the secondary work piece (200) melting temperature, and the electrical resistance of the at least one cover sheet (300) is greater than the electrical resistance of the primary work piece (100) and greater than the electrical resistance of the secondary work piece (200); c) placing a primary electrode (500) in electrical communication with a portion of the at least one cover sheet (300); e) placing a secondary electrode (600) in electrical communication with a portion of the at least one cover sheet (300); f) resistively heating the at least one cover sheet (300) by passing an electrical current between the primary electrode (500) and the secondary electrode (600), wherein the at least one cover sheet (300) temperature becomes greater than the melting point of the primary work piece (100) and greater than the melting point of the primary work piece (100);

26 g) conductively heating, and causing relative movement to, a portion of work assembly (1000), sufficient to ensure physical contact between the primary work piece (100) and the secondary work piece (200), wherein the work assembly (1000) is conductively heated from the at least one cover sheet (300), thereby creating a molten weld pool (800) including a portion of the primary work piece (100) and a portion of the secondary work piece (200); and h) cooling the weld pool (800) to solidification to create a solidified weld (900) joining the primary work piece (100) and the secondary work piece (200).

2. The method according to claim 1, wherein the step of placing at least one cover sheet (300) in contact with a portion of the work assembly (1000) further comprises the steps of: a) placing a primary cover sheet (300) in contact with a portion of a primary work piece conduction initiation surface (104), wherein the primary cover sheet (300) melting temperature is higher than the primary work piece (100) melting temperature and the electrical resistance of the primary cover sheet (300) is greater than the electrical resistance of the primary work piece (100); and b) placing a secondary cover sheet (400) in contact with a portion of a secondary work piece conduction initiation surface (204)_f wherein the secondary cover sheet (400) melting temperature is higher than the secondary work piece (200) melting temperature and the electrical resistance of the secondary cover sheet (400) is greater than the electrical resistance of the secondary work piece (200).

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3. The method according to claim 1 , wherein the primary work piece has a primary work piece conduction initiation surface (104), and the secondary work piece (200) has a secondary work piece conduction initiation surface (204), the method further comprising: conductively heating, and causing relative movement to, a portion of the primary work piece (100) and a portion of the secondary work piece (200), wherein the primary work piece (100) is conductively heated from the primary work piece conduction initiation surface (104) toward the primary work piece interface surface (102) and the secondary work piece (200) is conductively heated from the secondary work piece conduction initiation surface (204) toward the secondary work piece interface surface (202).

4. The method according to claim 1 , wherein the step of placing the primary electrode (500) in electrical communication with a portion of the at least one cover sheet (300) and the placing the secondary electrode (600) in electrical communication with a portion of the at least one cover sheet (300) further comprises placing the primary electrode (500) and the secondary electrode (600) on the same at least one cover sheet (300).

5. The method according to claim 1 , wherein the primary work piece (100) has at least one primary work piece axial projection (140), wherein the step of placing a portion the primary work piece interface surface (102) in weldable proximity with a portion of the secondary work piece interface surface (202) to form a work assembly (1000) further comprises causing a fixed predetermined spacing between the primary work piece interface surface (102) and the secondary work piece interface surface (202).

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6. The method according to claim 5, wherein the step of creating a molten weld pool (800) further comprises the step of subsuming the primary work piece axial projection (140) in the weld pool (800).

7. The method according to claim 1 , wherein the primary work piece (100) is a primary work piece tube form (110) and the secondary work piece (200) is a secondary work piece tube form (210).

8. The method according to claim 1, wherein the primary work piece (100) is a primary work piece tube form (110) and the secondary work piece (200) is a secondary work piece sheet form (260).

9. The method according to claim 1, wherein the primary work piece (100) has a proximal end orientation projection (113) cooperating with the secondary work piece (200), and wherein the step of placing a portion the primary work piece interface surface (102) in weldable proximity with a portion of the secondary work piece interface surface (202) to form a work assembly (1000) further comprises the step of orienting the work assembly (1000) in a predetermined position by means of said cooperation.

10. The method according to claim 1 , wherein the primary work piece (100) has a transversely projecting annular rim (125) cooperating with the secondary work piece (200), wherein the step of placing a portion the primary work piece interface surface (102) in weldable proximity with a portion of the secondary work piece interface surface (202) to

29 form a work assembly (1000) further comprises the step of orienting the work assembly (1000) in a predetermined position by means of said cooperation.

1 1. The method according to claim 1 , wherein at least one of the at least one cover sheets (300) is a composite cover sheet (310) having of at least one insulator portion (320) and at least one conductive portion (330), wherein the step of conductively heating further comprises the step of forming a temperature gradient between the at least one insulator portion (320) and at least one conductive portion (330),

12. The method according to claim 11 , wherein the at least one conductive portion (330) has at least one low resistance section (332) and at least one high resistance section (334), wherein the step of conductively heating further comprises the step of forming a temperature gradient between the at least one low resistance section (332) and the at least one high resistance section (334).

13. The method according to claim 4, wherein the at least one cover sheet (300) is shaped so that the step of causing relative movement to a portion of work assembly (1000), sufficient to ensure physical contact between the primary work piece (100) and the secondary work piece (200), further comprises the step of inducing an application of force to the work assembly (1000) in at least two non-parallel directions.

14. The method according to claim 13, wherein the at least one cover sheet (300) is shaped so that the step of causing relative movement to a portion of work assembly (1000), sufficient to ensure physical contact between the primary work piece (100) and the secondary

30 work piece (200), further comprises the step of inducing an application of force to the work assembly (1000) in more than two non-parallel directions.

15. The method according to claim 1, wherein the at least one cover sheet (300) is integrally formed with at least one primary electrode (500), wherein the step of placing at least one cover sheet (300) in contact with a portion of the work assembly (1000) further comprises the step of placing a primary electrode (500) in electrical communication with a portion of the at least one cover sheet (300).

16. The method according to claim 1 , wherein the at least one primary cover sheet (300) is in electrical communication with the secondary cover sheet (400) by means of a low- resistance shunt (700), and wherein the step of resistively heating the at least one cover sheet (300) further comprises the step of inducing current flow through the low-resistance shunt (700) .

17. A conductive heat resistance deformation welding method for joining a primary work piece (100) and a secondary work piece (200), wherein the primary work piece (100) has a primary work piece interface surface (102) and a primary work piece conduction initiation surface (104), and the secondary work piece (200) has a secondary work piece interface surface (202) and a secondary work piece conduction initiation surface (204), the method comprising: a) placing a portion of the primary work piece interface surface (102) in weldable proximity with a portion of the secondary work piece interface surface (202);

31 b) placing a primary cover sheet (300) in contact with a portion of the primary work piece conduction initiation surface (104), wherein the primary cover sheet (300) melting temperature is higher than the primary work piece (100) melting temperature and the electrical resistance of the primary cover sheet (300) is greater than the electrical resistance of the primary work piece (100); c) placing a secondary cover sheet (400) in contact with a portion of the secondary work piece conduction initiation surface (204), wherein the secondary cover sheet (400) melting temperature is higher than the secondary work piece (200) melting temperature and the electrical resistance of the secondary cover sheet (400) is greater than the electrical resistance of the secondary work piece (200); d) placing a primary electrode (500) in electrical communication with a portion of the primary cover sheet (300); e) placing a secondary electrode (600) in electrical communication with a portion of the secondary cover sheet (400); f) resistively heating the primary cover sheet (300) and the secondary cover sheet

(400) by passing an electrical current between the primary electrode (500) and the secondary electrode (600), wherein the primary cover sheet (300) temperature becomes greater than the melting point of the primary work piece (100) and the secondary cover sheet (400) temperature becomes greater than the melting point of the secondary work piece (200); g) conductively heating, and causing relative movement to, a portion of the primary work piece (100) and a portion of the secondary work piece (200), wherein the primary work piece (100) is conductively heated from the primary work piece conduction initiation surface (104) and the secondary work piece (200) is conductively heated from the secondary work piece conduction initiation surface (204), thereby creating a molten weld pool (800) including

32 a portion of the primary work piece (100) and a portion of the secondary work piece (200); and h) cooling the weld pool (800) to solidification to create a solidified weld (900) joining the primary work piece (100) and the secondary work piece (200).

18. The method according to claim 17, wherein the step of placing a portion of the primary work piece interface surface (102) in weldable proximity with a portion of the secondary work piece interface surface (202) further comprises the step of placing a portion of the primary work piece interface surface (102) in contact with a portion of the secondary work piece interface surface (202).

19. The method according to claim 17, wherein the at least one cover sheet (300) is shaped so that the step of causing relative movement to a portion of work assembly (1000), sufficient to ensure physical contact between the primary work piece (100) and the secondary work piece (200), further comprises the step of inducing an application of force to the work assembly (1000) in at least two non-parallel directions.

20. A conductive heat resistance deformation welding method for joining a primary work piece (100) and a secondary work piece (200), wherein the primary work piece (100) has a • primary work piece interface surface (102), and the secondary work piece (200) has a secondary work piece interface surface (202), the method comprising: a) placing a portion of the primary work piece interface surface (102) in weldable proximity with a portion of the secondary work piece interface surface (202) to form a work assembly (1000);

33 b) placing at least one cover sheet (300) in contact with a portion of the work assembly (1000), wherein the at least one cover sheet (300) melting temperature is higher than the primary work piece (100) melting temperature and higher than the secondary work piece (200) melting temperature, and the electrical resistance of the at least one cover sheet (300) is greater than the electrical resistance of the primary work piece (100) and greater than the electrical resistance of the secondary work piece (200); c) placing a primary electrode (500) in electrical communication with a portion of the at least one cover sheet (300); e) placing a secondary electrode (600) in electrical communication with a portion of the same at least one cover sheet (300); f) resistively heating the at least one cover sheet (300) by passing an electrical current between the primary electrode (500) and the secondary electrode (600), wherein the at least one cover sheet (300) temperature becomes greater than the melting point of the primary work piece (100) and greater than the melting point of the primary work piece (100); g) conductively heating, and causing relative movement further comprises the step of inducing an application of force to the work assembly (1000) in at least two non-parallel directions to a portion of work assembly (1000), sufficient to ensure physical contact between the primary work piece (100) and the secondary work piece (200), wherein the work assembly (1000) is conductively heated from the at least one cover sheet (300), thereby creating a molten weld pool (800) including a portion of the primary work piece (100) and a portion of the secondary work piece (200); and h) cooling the weld pool (800) to solidification to create a solidified weld (900) joining the primary work piece (100) and the secondary work piece (200).

34