Heat exchanger plates and methods for manufacturing heat exchanger plates

A method for forming heat exchanger plates (10) comprises formation of a fluid flow channel (28) along the edges (22) of a sheet metal strip or blank, and formation of a pair of raised end bosses. The raised end bosses (32) are elongated in the longitudinal dimension and are formed within the final width dimension of the plate so as to avoid the need for trimming of excess material along the edges of the plate. The method generates less scrap than prior art processes using progressive stamping, and also permits variation of the plate lengths.

This application is the national stage application of, and claims priority to, International Application No. PCT/CA2004/000291 filed Feb. 27, 2004, the entire disclosure of which is incorporated herein by reference. The International Application was published in the English language on Sep. 10, 2004 as International Publication No. WO 2004/76093 A1 and itself claims the benefit of Canadian Patent Application No. 2,420,273, filed on Feb. 27, 2003, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to methods for manufacturing plates for heat exchangers, particularly to methods in which generation of scrap is reduced, and to heat exchanger plates made by these methods.

BACKGROUND OF THE INVENTION

Heat exchangers are commonly made from multiple stacked plate pairs which define coolant flow passages extending between a pair of headers. As shown in FIG. 1 of U.S. Pat. No. 6,273,183 issued on Aug. 14, 2001 to So et al., the plates of each pair are arranged in back-to-back relation and are joined together at their peripheral edges. The plates have raised central portions which define a flow passage therebetween and in which turbulizers may be located. Raised bosses are provided at the ends of the plates, and are apertured to provide inlet and outlet openings. When the heat exchanger is assembled, the bosses are aligned and in communication with one another thereby forming a pair of headers. Expanded metal fins may then be located between the plate pairs to allow another fluid, such as air, to flow transversely through the plate pairs. The raised end bosses also serve to create spaces between the plate pairs for insertion of the fins.

The individual plates making up such a heat exchanger are usually formed by a process known as “progressive stamping” in which the plates are progressively formed by successive stamping operations performed on a coil of sheet metal. As explained above, the end bosses must be of a sufficient height to allow insertion of cooling fins. The bosses must also be of a specific diameter or area to allow sufficient coolant flow through the headers. Thus, the strip width required for each plate is generally determined by the width of strip material required for formation of the bosses.

In many cases, the width of strip material required to form the bosses is greater than a desired width of the plate pairs. This results in the need to trim excess material along the edges of the plates, particularly between the end portions in which the bosses are formed. The amount of scrap material generated by conventional progressive stamping of heat exchanger plates can be as high as 35 percent.

Thus, there is a need for improved methods of forming heat exchanger plates in which generation of scrap is reduced or eliminated, and in which plates of varying lengths may be produced without excessive tooling costs.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a method for forming a plate for a heat exchanger, the plate having a length and a width, the length defining a longitudinal axis, the method comprising: (a) providing a flat, sheet metal strip having elongate, longitudinally extending side edges, the strip having a width substantially the same as the width of the plate; (b) forming a fluid flow channel extending along the side edges of the strip, the fluid flow channel being raised relative to the side edges; and (c) forming a pair of raised bosses in the strip, the bosses being raised relative to the side edges and the fluid flow channels, wherein a longitudinal dimension of the bosses is greater than a transverse dimension of the bosses.

In another aspect, the present invention provides a heat exchanger plate, comprising: (a) a central portion defining an elongate fluid flow channel; (b) a pair of end portions separated by the central portion; (c) a raised boss provided in each of the end portions, each raised boss having an interior and an upper surface provided with a fluid flow aperture, wherein the interiors of the bosses are in communication with the fluid flow channel; (d) a planar flange extending continuously about an entire periphery of the plate and surrounding the fluid flow channel and the raised bosses; and (e) a plurality of tabs, each of which is integrally formed with the flange and extends from the flange, each of the tabs being located in one of the end portions of the plate.

In yet another aspect, the present invention provides A heat exchanger, comprising a plurality of plate pairs formed from the heat exchanger plates according to the invention, each of the plate pairs being formed by sealing the flanges of the plates together with the interiors of the bosses of one plate communicating with the interiors of the bosses of the other plate and so that the central portions of the plates combine to form a fluid passage in communication with the interiors of the bosses, the plate pairs being stacked with the apertures of the bosses in registry, the bosses of the plate pairs forming a pair of headers.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 to 3illustrate a preferred heat exchanger plate10according to the present invention. The plate10has an elongate central portion12located between a pair of end portions14. Dotted lines16shown inFIGS. 1 to 3indicate the approximate boundaries between the central portion12and the end portions14.

The plate10has an upper surface18and an opposed lower surface20, with elongate side edges22extending along the entire length of plate10and terminating at end edges24. Extending along the side edges22of plate10are a pair of shoulders26, these shoulders26defining a longitudinally extending fluid flow channel28extending along the lower surface20of plate10. The fluid flow channel28preferably extends along substantially the entire central portion12of plate10, and may preferably extend beyond dotted lines16into the end portions14of plate10. The shoulders26are spaced from the side edges22so as to form flat peripheral side flanges30between the side edges22and the shoulders26. The side flanges30extend longitudinally along the side edges22between the end portions14.

Located in the end portions14of plate10are a pair of raised bosses32. The bosses32are raised relative to the side edges22and relative to the fluid flow channel28, having a height sufficient such that when a heat exchanger is formed by stacking plate pairs formed from plates10, each plate pair formed by joining a pair of plates10with their lower surfaces facing one another, sufficient space exists between the plate pairs for insertion of cooling fins.

The bosses32can be of any desired shape, including circular. Preferably, the bosses32each have a major diameter extending in the longitudinal direction which is greater than a minor diameter extending in the transverse direction. Most preferably, the bosses are of an oval shape. As used herein, the term “oval” refers to any non-circular shape having a generally smoothly curving periphery, such as an ellipse, a rectangle with rounded corners, or other oblong or egg shape. In the preferred embodiment shown in the drawings, the bosses32are oval in plan view, having substantially straight longitudinally extending sides34extending between smoothly curved ends, a proximal end36located at or near the dotted line16between the central portion12and end portions14, and a distal end38located proximate the end edge24of the plate10.

As shown inFIG. 2, the sides34of bosses32are spaced inwardly from the side edges22and the distal ends38of bosses32are spaced inwardly from the end edges24, thereby forming peripheral end flanges40extending around the end portions14of plate10. The side flanges30and peripheral end flanges40combine to form a continuous flange about the entire periphery of the plate10. The continuous flange provides a surface along which a pair of plates10can be joined, for example by brazing, in back-to-back relation (with lower surfaces20facing one another) to form a plate pair.

In order to provide fluid communication through the headers after assembly of the heat exchanger, the upper surface44of each boss32is provided with an aperture42. The area of the aperture42is sufficiently large to provide adequate fluid flow throughout the header, while maintaining an annular sealing surface46on the upper surface44. During assembly of the heat exchanger, adjacent plate pairs are joined to one another, for example by brazing, along the annular sealing flanges46. As shown in the preferred plate10, the aperture42may preferably be centred on upper surface44and may generally follow the shape of the raised bosses32, although this is not essential.

As best seen in the bottom plan view ofFIG. 3, the side flanges30become broader and curve inwardly toward one another as they approach the bosses32, such that the side flanges30intersect the bosses32at points50which are located proximate the intersection between the sides34and the proximal ends36of the bosses32. Thus, each peripheral end flange40substantially extends only around the sides34and distal end38of a boss32, leaving an area49(substantially coextensive with proximal end36) at which the fluid flow channel28is in flow communication with the interior of the boss32.

As mentioned above, the plate pairs formed from plates10may be provided with turbulizers such as the expanded metal turbulizers disclosed in the above-mentioned patent to So et al., which is incorporated by reference herein in its entirety. The turbulizers are preferably rectangular in shape and are received between the plates10of the plate pairs, preferably extending throughout substantially the entire central portions12of the plates10. As well as enhancing heat transfer, turbulizers provide support for the central portions12of plates10, preventing collapse or narrowing of the fluid flow channels28. In a heat exchanger constructed from pairs of plates10, the ends of the turbulizers preferably overlap the proximal curved ends36of the bosses32, so that the turbulizers provide support along the entire length of the fluid flow channels28. The inward tapering of the side flanges30functions as an integral turbulizer stop so as to prevent longitudinal sliding of the turbulizer between the plate pairs. A preferred position of the end of a turbulizer (not shown) is indicated by dotted line51inFIG. 3.

Having now described the preferred heat exchanger plate10according to the invention, the following is a description of preferred methods for manufacturing a heat exchanger plate10according to the invention.

One preferred method of the invention begins by providing a sheet metal strip52, preferably comprised of a brazeable material, which is preferably selected from the group comprising aluminum, an aluminum alloy, and aluminum or aluminum alloy clad with an aluminum brazing alloy. The strip52as defined herein is of indefinite length, having longitudinally extending side edges54, an upper surface and an opposed lower surface (not shown). The width of strip52, measured in the transverse direction, is substantially the same as the width of the plate10described above.

A plurality of strips52may be formed by longitudinally slitting a coil of sheet metal (having a width greater than the width of strip52) at one or more points across its width, with the longitudinal direction of the strip52being parallel to the direction of slitting. Alternatively, strips52may be formed by dividing a coil into sheets which are then slit longitudinally or transversely into strips52.

During the method of the invention, the strip52is severed in the transverse direction at one or more points to form a plurality of blanks53, each of which has a length, measured in the longitudinal direction, which is substantially the same as the length of plate10.

Another preferred method of the invention begins by providing a sheet metal blank53having a width the same as that of strip52and having a length which is substantially the same as that of plate10. The blanks53may preferably be formed as described above by transversely severing strips52of indefinite length. Where the length of the blank10is the same as the width of the sheet metal coil, the blanks53may be formed by cutting transversely across the width of the coil. Where the length of the blank53is somewhat greater than the width of the coil, the blanks53may be formed by slitting the coil diagonally, that is with the side edges54of the strip52being angled relative to the transverse direction of the coil.

Except as otherwise indicated, the method now described below begins with a blank53having a length and a width which are substantially the same as the length and width of the plate10. However, to indicate that the method may begin with the provision of either a strip52or a blank53,FIG. 4illustrates (in dotted lines) portions of strip52extending beyond the end edges56of blank53. In addition,FIGS. 4 and 5show the central portions12, end portions14and the dotted lines16separating the central and end portions12and14.

The next step in the method comprises the formation of the fluid flow channel28, preferably by formation of shoulders26along the side edges54of the blank53. Preferably, as shown inFIG. 5, the shoulders26terminate so as not to substantially extend into the end portions14. As shown inFIG. 5, it may be preferred to terminate the shoulders26at or near the line16dividing the central portion12from the end portions14. The termination of shoulders26is preferred so that the shoulders do not interfere with formation of a flat end flange40in the end portion of plate10.

It will be appreciated that the formation of shoulders26provides each plate10with a single, longitudinally extending flow channel28, with side flanges30extending along either side of the flow channel28. The plates10may, however, be of more complex configuration and may be formed with more than one flow channel, although all configurations would be formed with flanges adjacent the side edges54, and a raised central portion forming the flow channel(s).

As mentioned above, the width of strip52or blank53is substantially the same as the width of plate10. As used herein with reference to the width of plate10, the term “substantially the same” is intended to mean that the width of strip52or blank53, measured transversely across the central portion12thereof, after formation of flow channel28, is the same as the width of the plate10, measured transversely across the central portion12thereof, such that no edge trimming of the plate10is required. It will be appreciated that the width of the strip52or blank53, prior to formation of the flow channel28, will be slightly greater than the width of plate10since the material required for formation of the shoulders26will be drawn from the width of the strip52or blank53.

It will be appreciated that, where the method begins by provision of a strip52of indefinite length, the shoulders26may be roll-formed prior to severing the strip52into individual blanks53. Of course, the shoulders26may also be formed by stamping the strips52or blank53with an appropriate die.

The next step in the method comprises formation of the raised bosses32in each of the end portions14of strip52or blank53. The bosses32are formed by a plurality of successive stamping or drawing operations, with the degree of boss formation in each successive stamping operation being illustrated inFIGS. 6 to 9. As can be seen from the drawings, some of the material from which the bosses32are formed is drawn from the surrounding material of the strip52or blanks53. This results in material of the end portions14becoming drawn inwardly toward the bosses32. This is apparent fromFIGS. 6 to 9which show the side edges54of the strip52or blank53converging inwardly toward one another along the sides34of the bosses32.

In the most preferred embodiments according to the invention, it is preferred that the strips52are severed into blanks53prior to formation of bosses32, and that the bosses32are formed by successive stamping operations by pairs of dies. The dies are preferably mounted in an apparatus in such a manner that the distance between the dies can be adjusted, thereby permitting the formation of plates having various lengths, which is not possible in progressive stamping dies.

It will be appreciated that the length, width and height of the bosses32are selected such that the heat exchanger formed by pairs of plates10will have a desired flow through its headers, such that a desired spacing will be maintained between the plate pairs to allow insertion of cooling fins, and such that the bosses32may be formed within the width dimension of the strip52or blank53, thereby avoiding the need to trim excess material from the edges of the plate10.

After formation of the bosses32, the next step in the method comprises the formation of apertures42in bosses32, for example using a cutting die.

As shown inFIG. 9, there may be some excess material located between the distal end38of the bosses32and the end edges24of the plate10. Although not essential, some of this material may be removed by trimming, for example to provide smoothly rounded edges62as shown inFIG. 10, while maintaining an end flange40of sufficient dimensions to allow leak-free formation of the plate pairs, for example by brazing.

As mentioned above, the length of the blank53is substantially the same as the length of plate10. As used herein with reference to the length of plate10, the term “substantially the same” is intended to mean that the total length of blank53, measured longitudinally between end edges56, after formation of bosses32, is the same as the total length of plate10, before end trimming as described in relation toFIG. 10. It will be appreciated that the length of the blank53, prior to formation of the bosses32, will be slightly greater than the length of plate10, before end trimming, since the formation of bosses32will somewhat reduce the length of the blank53.

As can be seen fromFIGS. 6 to 9, the end flanges40of plate10reach their narrowest points adjacent the edges34of bosses32, due to the fact that much of the material from which the bosses32are formed is drawn inwardly from the surrounding portions of the strip52or blank53. Excessive narrowing of the flange40in these regions results in narrowing of the surfaces along which the plate pairs are formed, possibly affecting the reliability of joint formation in this area, and limiting the width dimensions of the bosses32. To avoid excessive narrowing of flange40in this region, the strips52or blanks53may preferably be provided with apertures64in the end portions14. These apertures64are centrally located in the areas of end portions14which will be cut out to form the flow apertures42of bosses32. During formation of bosses32, some of the material required for formation of the bosses32will be drawn outwardly from apertures64in the direction of the arrows inFIG. 11, thereby reducing the amount of material which is drawn from the area surrounding the bosses32.

In the preferred embodiment of the invention, in which the bosses32and apertures42are oval in shape, the apertures64are preferably also elongated in the longitudinal direction. In the particularly preferred embodiment shown inFIG. 11, the apertures64may be dumbbell-shaped, comprising a pair of circular apertures66joined by a longitudinal slit68.

Rather than trimming the end flange40as shown inFIG. 10, the flanges40may be bent along lines70shown inFIG. 9to form tabs72. The lines70are parallel to the longitudinal axis and are substantially tangential with the curve defined by the inwardly curved portion of flange40, which is located proximate the sides34of bosses32. As shown inFIG. 12, the tabs72preferably extend at right angles to the remainder of flange40, and are preferably both bent upwardly. Thus, when the plates10are combined to form plate pairs, the ends of the plate pair have an H-shaped cross section, having tabs72extending both upwardly and downwardly from flanges40. The configuration of the tabs72in a plate pair74is also illustrated inFIG. 12, with a second plate10being illustrated in dashed lines.

When the plate pairs74are stacked to form a heat exchanger, the tabs72will extend into the space between the plates10. In some preferred embodiments, the tabs72of adjacent plate pairs74are of sufficient height to abut one another, and may become connected to one another during brazing of the heat exchanger, thus providing an additional brazed connection between the plates10. In other preferred embodiments, the tabs are of lesser height, such that the tabs72of adjacent plate pairs do not contact one another. Where the tabs72of adjacent plate pairs do not engage one another, they serve to provide a plurality of surfaces to which a heat exchanger mounting bracket may be secured. Of course, a mounting bracket can also be secured to the tabs72in the embodiment where the tabs of adjacent plate pairs74abut one another.

FIG. 13is a side view showing one end of a preferred plate pair74which is formed by joining a pair of plates10in back-to-back relation, such that the flanges30and40of the plates10engage one another and are joined in a leak-free manner, such as by brazing.

Although the method according to the invention has been described as including formation of the flow channel prior to formation of the bosses, it is to be appreciated that this sequence of steps is preferred, but not essential. In other preferred embodiments, the bosses may be formed prior to formation of the flow channel. However, it may be preferred to form the flow channel first since the channel form improves the rigidity of the blank, thereby reducing its tendency to bend or twist, and possibly resulting in improved accuracy of the boss stamping operation.

In some preferred methods of the invention, the channel28of plate10is formed by stamping the strip52or blank53with a single channel-forming die which is of fixed length and which is stationary relative to the longitudinal axis of strip52or blank53. The bosses32are then formed by a plurality of dies which may preferably be movable relative to the longitudinal axis. This type of arrangement may permit a limited amount of variation in the length of plate10(as further described below with reference toFIGS. 23 to 32). However, where it is necessary to accommodate large variations in the length of plate10, replacement of the channel-forming die by another die of different length would be required. The relative positions of the boss-forming dies would then be adjusted for compatibility with the new channel length.

In order to minimize tooling costs, the present invention provides methods which allow the channel length to be easily varied without replacement of the channel-forming die. A preferred embodiment of such a method is described below with reference toFIGS. 14 to 22, which illustrates a method in which the channel28is formed by one or more stamping operations involving the use of a channel-forming die80which is movable along the longitudinal axis of the strip52or blank53, thereby permitting variation of the channel length for production of plates10having lengths within a predetermined range.

Each stamping operation using an axially movable channel-forming die80produces a channel segment having a length which is equal to or less than the total length of the channel28. For example, where the desired plate length is at the lower limit of the predetermined range, the channel28is preferably formed by one stamping operation using an axially movable channel-forming die80, wherein the length of the channel segment produced by the axially movable channel-forming die80is equal to the total length of the channel28.

On the other hand, where the desired plate length is above the lower limit of the predetermined range, the channel28will be formed by two or more stamping operations, at least one of which involves the use of a movable channel-forming die80. In this case, the length of the channel segment produced by the axially movable channel-forming die80will be less than the total length of the channel28. It will be appreciated that the two or more stamping operations could be performed by a single axially movable channel-forming die80, by two or more axially-movable channel forming dies80, or by an axially movable channel-forming die80in combination with a stationary channel-forming die.

In the particular method illustrated byFIGS. 14 to 22, the desired length of channel28is greater than the lower limit of the predetermined range, such that multiple stamping operations are required to form channel28. In this preferred embodiment, at least one of the stamping operations is performed by an axially movable channel-forming die80. This preferred method is now described in detail below.

The method illustrated inFIGS. 14 to 21begins with a blank53which has a width and length substantially the same as that of plate10as described above. As inFIG. 4, the blank53has an elongate central portion12located between a pair of end portions14, with the approximate boundaries between central portion12and end portions14being indicated by dotted lines16. The blank53is fed to an apparatus78comprising one or more axially movable channel-forming dies80, each of which comprises an upper die portion82and a lower die portion84.

As shown inFIGS. 16 and 17, the upper and lower die portions82and84are closed on the blank53to form a first channel portion28ahaving a proximal end portion86aand a distal end portion88a, shown inFIG. 14. The distal end portion88aterminates at or near the boundary16between the central portion12and one of the end portions14of the blank53.

Following formation of the first channel portion28a, the die portions82and84are opened as inFIG. 18. As shown inFIGS. 16 to 21, the opposite ends90,92of upper die portion82are rounded or tapered. This provides the proximal and distal end portions86a,88aof first channel portion28awith gradual terminations98a,100awhich may either be rounded or tapered, thereby avoiding damage to the blank53. In the drawings, the terminations98aand100aare shown as being rounded and are exaggerated so as to be clearly visible.

The next step in the method comprises formation of a second channel portion28bwhich, as shown inFIG. 15, comprises a proximal end portion86band a distal end portion88b, with the distal end portion88bterminating at or near the boundary16between the central portion12and one of the end portions14of the blank53. It can be seen fromFIG. 15that the proximal end portion86aof the first channel portion28aand the proximal end portion86bof the second channel portion28boverlap one another by an amount A, and that the distal end portions88aand88bare spaced from one another along the longitudinal axis by an amount which is preferably equal to the desired length of channel28.

The second stamping operation may preferably be performed by the same die80which performed the first stamping operation illustrated inFIGS. 16 to 18. In this case, the blank53preferably remains stationary during the formation of channel28, while the single channel-forming die80is displaced axially between the first and second stamping operations.

In the alternative, as shown inFIGS. 19 to 22, the first and second stamping operations may be performed by different channel-forming dies80. Although the dies80may be axially aligned relative to one another, they are shown inFIG. 22as being located at different stamping stations which are transversely spaced from one another such that the blank53must be moved transversely between the first and second stamping operations.

Although dies80are described above as being axially movable, it will be appreciated that one of the dies80used to form the first channel portion28aand the second channel portion28bcould be stationary with respect to the longitudinal axis of blank53.

The upper die portion82of channel-forming die80used in the second stamping operation shown inFIG. 19also has rounded or tapered ends90,92so as to provide the second channel portion28bwith a gradual termination100bat the distal end portion88b. Due to the overlap of the proximal end portions86aand86b, no gradual termination98bwill be seen at the proximal end portion86bof the second channel portion28b. Nor is the terminal end portion98aof the first channel portion28avisible after the second stamping operation. Rather, the proximal end portions86aand86bwill blend smoothly together to form a channel28of substantially uniform cross section.

As mentioned above, at least one of the channel-forming dies80is movable along the longitudinal axis so as to vary the area of overlap A. In order to ensure that the channel28is of constant cross section, it is necessary that the proximal end portions86aand86boverlap to an extent sufficient that the gradual terminations98aand98bare not present in the channel28. In most preferred embodiments of the invention, at least about 1 inch of overlap will be required to ensure that the channel28is of constant cross-section.

Following the channel stamping operations shown inFIGS. 14 to 21, the formation of plate10is completed by formation of the raised bosses32as described above with reference toFIGS. 6 to 10. As shown inFIG. 22, the bosses may be formed simultaneously by axially-aligned boss-forming dies81, both of which are preferably movable relative to the longitudinal axis. It will, however, be appreciated that the boss-forming dies81may be transversely spaced from one another and that the formation of each of the bosses32will typically require multiple stamping operations performed by multiple pairs of boss-forming dies81.

Another preferred variation of the method according to the invention is illustrated inFIGS. 23 to 32. In this variation of the method, a blank53is provided as in the previous embodiments having a width and length substantially the same as that of plate10, and having an elongate central portion12located between a pair of end portions14, with the approximate boundaries between central portion12and end portions14being indicated by dotted lines16. The blank53is fed to an apparatus102comprising a channel-forming die104having an upper die portion106and a lower die portion108. In this embodiment, a first channel portion110is formed having end portions112and114. The first channel portion110has a length which is somewhat less than the length of the channel28, such that at least one of its end portions is spaced from the approximate boundary16between the central portion12and the end portions14of the blank53. In the preferred embodiment shown in the drawings, both end portions112,114of the channel portion110are spaced from lines16.

The channel-forming die104may either be movable along the longitudinal axis or may be stationary. In the preferred embodiment shown inFIGS. 25 to 27, the channel-forming die104is stationary. If desired, the stationary channel die104may be replaced by die(s)80as described above such that the first channel portion110is formed in two separate stamping operations.

As in the previously described embodiment, the upper die portion106of channel-forming die104preferably has opposite ends116,118which are rounded or tapered. As shown inFIG. 23, the curvature of the upper die portion106provides the end portions112,114of the first channel portion110with gradual terminations120,122, thereby avoiding damage to the blank53. As in the embodiment described above, the curvature of ends116,118is exaggerated in the drawings.

The next step in the method, illustrated inFIGS. 24,28and29, comprises formation of a second channel portion124and a first one of the raised bosses32, the channel portion124and the first boss32being formed together by stamping the blank53with a combined die126having an upper die portion128and a lower die portion130. The upper and lower die portions128,130have boss-forming portions132,134for forming the boss, and also have channel-forming portions136,138for forming the second channel portion124. The terminal end140of the channel-forming portion136of the upper die portion128is preferably smoothly rounded or tapered to blend the first and second channel portions110,124.

As shown inFIG. 24, the end portion112of the first channel portion110and the second channel portion124overlap one another by an amount B which is variable depending on the desired length of the plate10. Preferably, the combined die126is movable along the longitudinal axis to vary the amount of overlap B and thereby vary the length of the plate10. In order to ensure that the channel28is of a substantially uniform cross section, the amount of overlap is sufficient to ensure that rounded terminations of the first and second channel portions110,124are not present in the channel. Preferably, as mentioned above, the amount of overlap B is at least about 1 inch.

As shown inFIGS. 6 to 10, it will be appreciated that more than one operation is typically required to form the bosses32. In the preferred embodiment using combined die126, at least one of the boss forming operations will be performed by a combined die126, with one or more of the boss-forming operations optionally being performed by die(s) which have only a boss-forming portion.

The partially finished plate10shown inFIG. 24is then subjected to a third stamping operation, shown inFIG. 30, in which a third channel portion144and a second boss32′ are formed together by stamping the partially finished plate10with a combined die126′ which is preferably an identical mirror image of combined die126. Combined die126′ has an upper die portion128′ with a boss-forming portion132′ and a channel-forming portion136′, and has a lower die portion130′ with a boss-forming portion134′ and a channel-forming portion138′. As shown inFIG. 31, the end portion114of the first channel portion110overlaps the third channel portion144by an amount C which is variable depending on the desired length of the plate10, and is preferably at least about 1 inch. Preferably, the combined die126′ is movable along the longitudinal axis to vary the amount of overlap C and thereby vary the length of the plate10.

FIG. 32illustrates the sequence of steps which may be followed in the method described above with reference toFIGS. 23 to 31. In the embodiment illustrated inFIG. 32, the blank53is fed transversely to a channel-forming die104and then to axially-aligned combined dies126and126′. It will, however, be appreciated that the boss-forming dies are not necessarily axially aligned with one another.

Although the invention has been described in relation to certain preferred embodiments, it is not limited thereto. Rather, the invention includes all embodiments which may fall within the scope of the following claims.