WELDING HEAD FOR MAGNETIC PULSE WELDING OF TUBULAR PROFILES TO A CYLINDRICAL INNER MEMBER

Abstract

The invention relates to a welding head for magnetic pulse welding of hollow thin-walled profile to an inner member having a complementary outer form to said hollow thin-walled profile. The weld head comprises two movable weld head halves (10a,10b) forming said weld head wherein each half has at least one individual induction coil (12a,12b) connected to a power source independently from the other weld head half, with coils wound in a kidney-shape. The work piece is clamped between shapers (15a,15b) integrated with each half. With this weld head could for example work pieces such as tubular thin-walled profiles be welded, even if they are integrated in a closed tubular design, as the weld head could be closed quickly over the welding position and opened for release of the work piece without experiencing arching in clamping area.

Claims

1. A welding head for magnetic pulse welding of hollow thin-walled profiles to an inner member having a complementary outer form to said hollow thin-walled profiles, said welding head comprising: two movable weld head halves forming said welding head wherein each of said weld head halves includes at least one individual induction coil connected to a power source independently from the other weld head half; and where said at least one individual induction coil in each weld head half is wound in a kidney-shape having a concave coil surface facing in a first direction towards a corresponding concave coil surface of the other of said weld head halves, and a convex coil surface facing in a direction opposite to said first direction, and at least two coil housings wherein each of said induction coils is integrated in one of said at least two coil housings; each of said weld head halves including a shaper attached to one of said at least two housings at the center of the concave coil surface, wherein the shaper has an opening corresponding to half of the outer surface of the hollow thin-walled profile to be welded, and when the weld head halves are moved together around the hollow thin-walled profile to be welded the shapers totally enclose the hollow thin-walled profile at the location for the weld.

2. A welding head as claimed in claim 1, wherein at least one of the shapers includes an electrically insulating material at least in the contact surface between the shapers.

3. A welding head as claimed in claim 2, wherein the shapers includes an electrically insulating material between said shaper and the outer surface of the hollow thin-walled profile.

4. A welding head as claimed in claim 1, wherein each induction coil winding, when the two moveable welding halves are brought together for welding, is lying within a circular sector having its center at the center of the hollow thin-walled profile, with a central angle (α) of said circular sector lying in the range of 130-160°, and between an outer arc length (L.sub.1) and an inner arc length (L.sub.2) of said circular sector, said outer arc length being located radially outside of and adjacent to the convex coil surface and the inner arc length being located radially inside of and adjacent to the concave coil surface.

5. A welding head as claimed in claim 4, wherein the central angle (α) is less than 140° of said circular sector.

6. A welding head as claimed in claim 4, wherein each induction coil winding has a first part of the coil winding lying furthest away from the shaper and located closest to the convex coil surface being wound such that the entire part of the coil winding width extends over a distance X.sub.1 and preferably that this part of the coil winding lies in one and the same plane (P1), and wherein each induction coil winding has a second part of the coil winding lying closest to the shaper and located closest to the concave coil surface being wound such that entire part of the coil winding width extends over a distance X.sub.2, wherein the distance X.sub.2 is less than 80% of the distance X.sub.1.

7. A welding head as claimed in claim 6, wherein each induction coil winding has less than ten coil turns.

8. A welding head as claimed in claim 7, wherein each induction coil winding has a coil thread with a cross section area exceeding 0.5 cm.sup.2.

9. A welding head as claimed in claim 6, wherein the second part of the coil winding lies in at least two planes such that coil winding turns are partly overlapping in the second part of the coil winding.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0031] In the following a preferred embodiment of the invention will be described with reference to the attached drawing, in which

[0032] FIG. 1 show a welding head in a perspective view according the invention, having two weld head halves 10a and 10b;

[0033] FIG. 2 show a principle flat view of the weld head according to the invention;

[0034] FIG. 3 showing the weld head with a work piece clamped between weld head halves;

[0035] FIGS. 4a-4c showing different workpieces clamped between weld head halves;

[0036] FIG. 5 showing a sectional view seen in II-II in FIG. 2 of upper weld head half.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0037] As seen in FIG. 1 is the weld head for magnetic pulse welding made as two independent weld head halves 10a and 10b, each half including at least one uninterrupted coil winding 12a and 12b respectively. The halves are brought together via abutting contacting surfaces 14, which encircles a work piece receiving zone 16. Each coil winding 12a and 12b is connected to an independent power source PSa and PSb, such that each coil winding could be controlled independently of the other coil winding.

[0038] Similar parts in upper and lower weld head half in figure are numbered with same numbers but with appendix “a” if located in upper half and with appendix “b” if located in lower half.

[0039] The design with two independent weld head halves enable the weld head to be moved into and out of contact with the welding position of the work piece located in the work piece receiving zone 16. Each weld head half includes at least one coil winding 12a/12b, which have ends 20a,22a/20b,22b connected to an electrical power source PSa/PSb.

[0040] In the figure the coil windings are located in a coil housing 13a and 13b respectively that have a kidney-shaped form corresponding to the same kidney-shaped form of the coil windings 12a and 12b respectively. The coil windings are preferably made with a coil wire of substantial cross section and with as low electrical resistance as possible, and in this case with as few coil turns as 5-10, or as shown in figure with only 6 coil turns. As the induction coil should be activated very quickly and develop high current, the electrical inductance as well as resistance should be kept low. Each coil winding 12a/12b is made by a highly conductive metal such as aluminum or copper, enclosing a coil cavity within the coil housing 13a and 13b. The entire coil housing 13a/13b could be molded or casted in one piece, by a resinous- epoxy- or other polymeric material, forming the kidney-shaped outer contour. The coil cavity and interspaces between coil windings could also be filled with an iron core in either solid or laminated structure (not shown in figures).

[0041] The abutting contacting surfaces 14 is preferably provided with an electrically insulating coating applied in any appropriate manner. This coating may also be provided in the contact surface between the work piece and the weld head half.

[0042] Such an insulating interface in contact surfaces 14 reduces the opportunity for creating arching and thus erosion/wear of the contact surfaces, as well as mechanical load on coils when sudden arching occurs. An insulating layer is applied to at least one of the contact surfaces.

[0043] In FIG. 1 is the work piece receiving zone 16 encircled by shapers in form of semi circular members, i.e. one upper semi circular member 15a in upper weld head half 10a, and another lower semicircular member 15b integrated in the lower weld head half 10b. This is the preferred form if the tubular profile to be welded is a thin walled circular tube. However, these members 15a/15b could have alternative forms being complementary surfaces to the form of the tubular profile to be welded, i.e. may have a triangular shape, a square shape, pentagonal shape, hexagonal shape or other shape than strictly circular. The shaper could as indicated above have a coating of an insulating material, or may alternatively be made in its entirety by an insulating material.

[0044] The shaper is integrated with a connecting member 17a/17b that permanently connects the shaper with the associated weld head housing. The upper weld head half 10a thus consist of the kidney-shaped coil housing 13a, the connecting member 17a and the shaper 15a. The power source PSa is preferably connected to the upper weld head connections 22a and 20a via any suitable flexible electrical conductors. The connecting member 17a/17b may preferably be made in a low resistance conductive material such as copper, aluminum or steel.

[0045] In FIG. 2 is shown the principle layout of the weld head design as seen in a flat view. The induction coils are integrated in the kidney-shaped coil housing 13a and 13b respectively. The coil housing thus has one concave surface 32a facing a concave coil surface 32b of the other half, and a convex coil surface 31a or 31b facing in the opposite direction. Each weld head half has a shaper 15a, 15b located in the housing and in the center of the concave coil surface, wherein the shaper has semi-circular opening corresponding to the outer surface of the tubular profile 30 to be welded. In FIG. 2 are 5 tubular profiles 30 shown located in the same plane.

[0046] When welding head halves are brought together for welding, as shown in FIG. 2, the kidney-shaped coil housing 13a and 13b is lying within a circular sector having its center at the center of the tubular profile 30, with a central angle a less than 160° of said circular sector. The central angle a could preferably lie in the range 130-160° of said circular sector, and as could be realized from figure are lower order of angle in this range preferred if the tubular profiles are located closer together in the product to be assembled.

[0047] The kidney-shaped coil housing 13a and 13b is further located between an outer arc length L.sub.1 and an inner arc length L.sub.2 of said circular sector, said outer arc length being located radially outside of and adjacent to the convex coil surfaces 31a, 31b and the inner arc length being located radially inside of and adjacent to the concave coil surfaces 32a,32b.

[0048] By this design could access be made possible to both closed tubular structures as well as tubular profiles located closely together.

[0049] In FIG. 3 is disclosed a work piece in form of tubular heat exchangers. Such heat exchangers typically has one header HE at one end and with a multitude of tubular pipes 30 connected to the header HE, and another header (not shown) in the other end of the tubular pipes 30, thus forming a closed tubular structure.

[0050] In FIGS. 4a-4c are shown different forms of work pieces to be welded by the welding head. First, in FIG. 4a is shown a work piece in form of an outer thin-walled tubular or cylindrical member 30′ which to be welded together with an inner member 31′ having a complementary outer form, i.e. also with a cylindrical outer form. This inner member 31′ may as shown here be tubular as well, or may also alternatively be a solid rod. Each shaper half 15a and 15b has thus a semi-circular form corresponding to half of the circumferential distance of the hollow thin-walled profile 30″.

[0051] Alternatively, as shown in FIG. 4b, the work piece has an outer thin-walled hexagonal member 30″ which to be welded together with an inner member 31″ having a complementary outer form, i.e. also with a hexagonal outer form. Each shaper half 15a and 15b has thus a form corresponding to half of the surface of the hollow thin-walled profile 30″.

[0052] In yet another embodiment, as shown in FIG. 4c, the work piece has an outer thin-walled triangular member 30′″ which to be welded together with an inner member 31′″ having a complementary outer form, i.e. also with a triangular outer form. In this embodiment the inner member is solid. Each shaper half 15a and 15b has thus a form corresponding to half of the circumferential distance of the hollow thin-walled profile 30′″.

[0053] In FIG. 5 is shown a cross sectional view seen in II-II in FIG. 2 of upper weld head half 10a. The housing 13 has the coil winding 12a encapsulated in any suitable resin material in solid state fashion. The connecting member 17a is an integral part of the housing and connects the hosing with the shaper 15, and an insulating material is suitably applied on the contact surface 14 as indicated in figure. In this embodiment is the part of the coil winding lying closest to the convex surface 31a wound in one single plane P1, while the part of the coil winding lying closest to the concave surface 32a wound in two planes P2 and P3, such that coil windings are partly overlapping. Thus, as shown in FIG. 5 is a welding head obtained, wherein each induction coil winding 12a has a first part of the coil winding, lying furthest away from the shaper 15a and located closest to the convex coil surface 31a, which is wound such that entire part of the coil winding width extends over a distance X.sub.1 and preferably that this part of the coil winding lies in one and the same plane P1. Each induction coil winding 12a has also a second part of the coil winding lying closest to the shaper 15a/and located closest to the concave coil surface 32a which is wound such that entire part of the coil winding width extends over a distance X.sub.2, wherein the distance X.sub.2 is less than 80% of the distance X.sub.1 and preferably that this second part of the coil winding lies in at least two planes P2,P3 such that coil winding turns are partly overlapping in this second part of the coil winding. By this design of the coil winding is the electromagnetic pulse directed towards the center of the shaper 15a, with coil winding wound within an angle β as shown in FIG. 5.

[0054] However, the type of coil winding and if a solid or laminated iron core is used is a matter of optimization of the electromagnetic field as directed towards the shaper, and may thus be modified in a number of ways.

[0055] It is to be understood that the above description and the related figures are only intended to illustrate the present solution. Thus, the solution is not restricted only to the embodiment described above and defined in the claims, but many different variations and modifications, which are possible within the scope of the idea defined in the attached claims, will be obvious to a person skilled in the art.