Patent Publication Number: US-2021170534-A1

Title: Manufacturing method for a titanium heat exchanger

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of the French patent application No. 1913817 filed on Dec. 5, 2019, the entire disclosures of which are incorporated herein by way of reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a manufacturing method for a heat exchanger. 
     BACKGROUND OF THE INVENTION 
     Heat exchangers are used to exchange calories between a hot fluid and a cold fluid such as a heat-transfer fluid. For this purpose, the heat exchanger takes the form of a plate traversed by a network of channels through which one of the fluids flows, while the other fluid is in contact with the surface of the plate. 
     Such a plate is usually made of stainless steel or graphite. 
     Although easy to make and efficient, such exchangers are relatively heavy. Such conditions may apply when the heat exchanger is installed in a fuel cell using dihydrogen and dioxygen. 
     SUMMARY OF THE INVENTION 
     One objective of the present invention is to propose a manufacturing method for a heat exchanger using titanium strips to provide a more lightweight heat exchanger with performance levels that are at least equivalent to the heat exchangers in the prior art. Furthermore, the methods proposed enable a heat exchanger to be obtained simply and quickly. 
     For this purpose, a manufacturing method for a plate with channels is proposed, the manufacturing method including:
         a superposition step during which two strips are superposed on one another,   a welding step during which the two strips are welded together along weld seams,   a blocking step during which the zones between the first strip and the second strip, where the zones between the weld seams open out at one of the edges of the first strip and of the second strip, are blocked,   a pressurization step during which a compressed fluid is injected via another edge of the first strip and of the second strip, where the zones between the weld seams open out between the first strip and the second strip, to expand the strips, and   an opening step during which the zones blocked during the blocking step are opened.       

     The invention also proposes a manufacturing method for a plate with channels, the manufacturing method including:
         a first positioning step during which a second strip is positioned on a first strip,   a first welding step during which the edges of the two strips are welded together to form a closed volume,   a pressurization step during which a compressed fluid is injected into the closed volume to inflate the closed volume,   a second positioning step during which the inflated strips are positioned between a mold and a counter-mold, in which the mold has welding elements and negative forms, and in which the counter-mold has welding elements that are aligned with the welding elements of the mold and negative forms that are aligned with the negative forms of the mold,   a clamping step during which the mold and the counter-mold are brought together so that the two strips are in contact along the welding elements and deformed in the negative forms, and   a second welding step during which the welding elements are activated to weld the two strips together along the weld seams.       

     Each of the two manufacturing methods proposed herein enables the titanium strips to be welded together and shaped by pressurization. 
     According to a specific embodiment, the superposition step comprises successively a first positioning step during which the first strip is positioned on a base, a second positioning step during which the second strip is positioned on the first strip, and a covering step during which supporting parts that together form a welding channel are arranged on the second strip and the welding step involves moving a welding unit along the welding channel to weld the two strips together along the weld seams. 
     Advantageously, the manufacturing method includes a depositing step, between the first positioning step and the second positioning step, during which beads of a thermal insulator are deposited on the first strip, and the second positioning step involves positioning the second strip on the beads. 
     Advantageously, the manufacturing method involves a positioning step, between the blocking step and the pressurization step, during which the first welded strip and the second welded strip are positioned between two dies, each of which has negative forms corresponding to the imprints of the channels to be formed. 
     According to a specific embodiment, the superposition step comprises successively a first positioning step during which the first strip is positioned on a mold, a second positioning step during which the second strip is positioned on the first strip, and a covering step during which a counter-mold is positioned on the second strip, in which the mold and the counter-mold have a plurality of holes, and the welding step involves inserting needles into the holes of the mold and counter-needles into the holes of the counter-mold and powering the needles and the counter-needles using a voltage generator to weld the two strips together along the weld seams, and in which the mold and the counter-mold have negative forms between the holes corresponding to the imprints of the channels to be formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aforementioned and other features of the present invention are set out more clearly in the description given below of an example embodiment, said description being provided with reference to the attached drawings, in which: 
         FIG. 1  is a cross-section view of a plate of a heat exchanger obtained using a manufacturing method according to the invention, 
         FIG. 2  is a perspective view of a tool used as part of a manufacturing method according to a first embodiment of the invention, 
         FIG. 3  is a perspective view of a tool used as part of a manufacturing method according to a second embodiment of the invention, and 
         FIG. 4  is a cross-section view of a tool used as part of a manufacturing method according to a third embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a plate  100  that can be used in a heat exchanger and that has a first strip  102  and a second strip  104 . The two strips  102  and  104  are made of titanium or titanium alloy. 
     The two strips  102  and  104  are attached to one another. 
     Each strip  102 ,  104  has deformations  106 ,  108 , in this case elliptical arcs. Each deformation  106  of the first strip  102  faces a deformation  108  of the second strip  104  to form a channel  150  therebetween that can be used to channel a fluid, in particular a heat-transfer fluid, when the plate  100  is used in a heat exchanger. 
     The shape of the deformations  106 ,  108  can vary and, for example, be trapezoidal, omega-shaped, circular or triangular. 
     The plate  100  is then placed between a supply system that feeds the plate  100  with the heat-transfer fluid, and a recovery system that recovers the heat-transfer fluid coming out of the plate  100 . The fluid continuity between the supply system and the plate  100  occurs at a first edge of the plate  100  and the fluid continuity between the plate  100  and the recovery system occurs at a second edge of the plate  100 , i.e., the channels  150  are open at this first edge and at this second edge to enable flow of the heat-transfer fluid. 
     The two strips  102  and  104  are fastened to one another by spot welds  110  made between two neighboring deformations  106 ,  108 . 
     Making such a plate  100  from titanium provides a more lightweight heat exchanger that is equally efficient, in particular when used in a cooling system of a fuel cell. 
       FIG. 2  shows a tool  200  used to shape two strips  102  and  104  of titanium or titanium alloy into the plate  100  as part of a method according to a first embodiment of the invention. For the sake of clarity in the figures, the second strip  104  is partially cut-away. 
     The tool  200  has a base  202  and a welding tool  204 . The welding tool  204  in this case includes supporting parts  206   a - b  delimiting a welding channel  208  therebetween and a welding unit  210  that moves along the welding channel  208 , for example using a moving carriage. 
     The welding unit  210  is for example a laser emitter used for laser welding, but any other technique can be used such as electron-beam welding, electric resistance welding, friction stir welding or diffusion welding. 
     Once a weld seam has been formed, the supporting parts  206   a - b  and the welding unit  210  are moved to form a new weld seam. 
     The two strips  102  and  104  are arranged on top of one another and between the base  202  and the welding tool  204 , and more specifically in this case between the base  202  and the supporting parts  206   a - b.    
     Once the welding unit  210  has completed all of the weld seams, the zones between the weld seams, i.e. zones in which the two strips  102  and  104  are not welded together, are deformed and will ultimately form the channels  150  of the plate  100 . 
     As mentioned above, some channels  150  enable flow of the heat-transfer fluid penetrating the plate  100  or coming out of the plate  100  and these channels  150  open out respectively at a first edge  50  of the plate  100  and at a second edge  52  of the plate  100 , which are respectively the first edges of the first strip  102  and of the second strip  104 , and at the second edges of the first strip  102  and of the second strip  104 . 
     The zones between the weld seams are used to create these channels  150  that open out at the edges  50  and  52  and therefore extend respectively as far as the first edge  50  of the plate  100  and as far as the second edge  52  of the plate  100 . 
     In order to form the channels  150 , a pressurized fluid is injected between the strips  102  and  104  into the zones between the weld seams, and the two strips  102  and  104  are then separated from one another in these zones to form the channels  150 . In order to inject the pressurized fluid, the zones between the first strip  102  and the second strip  104  at one of the edges  50 ,  52  of the first strip  102  and of the second strip  104 , along which the zones between the weld seams open at one of the ends thereof, need to be blocked. The pressurized fluid is then injected via the other edge  52 ,  50  of the first strip  102  and of the second strip  104 , along which the zones between the weld seams open at the other ends thereof. 
     To ensure that the channels  150  are properly formed, before injection of the pressurized fluid, the first strip  102  and the second strip  104  are positioned between two dies, in which each die has negative forms corresponding to the imprints of the channels  150  to be formed. Thus, during injection of the compressed fluid, the strips  102  and  104  are separated from one another to fit the negative forms, thereby forming the channels  150 . The negative forms are made on the faces of the dies arranged against the strips  102  and  104 . 
     The previously blocked zones are then opened to enable the fluid to flow into the channels  150  of the plate  100 . 
     A manufacturing method for a plate  100  of a heat exchanger according to the first embodiment comprises:
         a first positioning step during which a first strip  102  is positioned on the base  202 ,   a second positioning step during which a second strip  104  is positioned on the first strip  102 ,   a covering step during which the supporting parts  206   a - b  are positioned on the second strip  104 ,   a welding step during which the welding unit  210  is moved along the welding channel  208  to weld the two strips  102  and  104  together along weld seams,   a blocking step during which the zones between the first strip  102  and the second strip  104 , where the zones between the weld seams open out at one of the edges  50 ,  52  of the first strip  102  and of the second strip  104 , are blocked,   a third positioning step during which the first welded strip  102  and the second welded strip  104  are positioned between two dies, each having negative forms,   a pressurization step during which the compressed fluid is injected via another edge  52 ,  50  of the first strip  102  and of the second strip  104 , where the zones between the weld seams open out between the first strip  102  and the second strip  104 , to expand the strips  102  and  104  into the negative forms, and   an opening step during which the zones blocked during the blocking step are opened.       

     The welding step is repeated for each weld seam following movement of the supporting parts  204   a - b  to obtain the desired layout of the channels  150 . Such a method is relatively simple and rapid to implement. 
     The blocking step can be carried out during the welding step. 
     To improve the precision of the welds, i.e., to prevent the two strips  102  and  104  from being welded together over too large a surface, beads  212  of an electrical and thermal insulator are deposited between the two strips  102  and  104  at the locations where no weld is to be provided between the two strips  102  and  104 , i.e., in the zone between the weld seams. The beads  212  are, for example, made of ceramic powder. 
     The zones where the beads  212  are deposited ultimately become the channels  150  of the plate  100 . 
     The beads  212  extend up to the first edge  50  of the plate  100  and up to the second edge  52  of the plate  100  as for the zones between the weld seams. 
     The manufacturing method then includes a depositing step, between the first positioning step and the second positioning step, during which beads  212  of an insulator are deposited on the first strip  102  and in which the beads  212  extend between two edges of the first strip  102 , and the second positioning step then involves positioning the second strip  104  on the beads  212  and in which the beads  212  extend between two edges of the second strip  104 . 
     If necessary, the insulator beads  212  can be removed by injecting an appropriate fluid into the channels  150 . 
       FIG. 3  shows a tool  300  used to shape two strips  102  and  104  made of titanium or titanium alloy into the plate  100  as part of a method according to a second embodiment of the invention. 
     The tool  300  comprises a mold  302  forming a base in this case, a counter-mold  303  that is positioned above the mold  302 , and a welding tool  304 . 
     The two strips  102  and  104  are arranged between the mold  302  and the counter-mold  303 . 
     The mold  302  and the counter-mold  303  include a plurality of holes  306   a - b , and the axes of the holes  306   a - b  are perpendicular to the planes of the strips  102  and  104 . 
     The welding tool  304  has a plurality of needles  307   a  in which each needle  307   a  is inserted into a hole  306   a  of the mold  302  and a plurality of counter-needles  307   b  in which each counter-needle  307   b  is inserted into a hole  306   b  of the counter-mold  303 . 
     The needles  307   a  can be arranged to face the counter-needles  307   b . It is nonetheless possible for the needles  307   a  to be staggered in relation to the counter-needles  307   b.    
     The welding tool  304  also includes a voltage generator that powers the needles  307   a  and the counter-needles  307   b  to generate a welding arc between the strips  102  and  104  and each needle  307   a  or each counter-needle  307   b.    
     In the embodiment of the invention shown in  FIG. 3 , the welding tool  304  has a row of needles  307   a  and a row of counter-needles  307   b , although more rows of needles  307   a  and counter-needles  307   b  can be provided, and the desired number of needles  307   a  and counter-needles  307   b  can be electrically powered. 
     In the embodiment shown in  FIG. 3 , the holes  306   a  of the mold  302  are offset linearly in relation to one another by a step P and the holes  306   b  of the counter-mold  303  are also offset linearly in relation to one another by the same step P, and the holes  306   a  of the mold  302  and the holes  306   b  of the counter-mold  303  are offset linearly in relation to one another by a half-step P such that a hole  306   b  of the counter-mold  303  is equidistant from two consecutive holes  306   a  of the mold  302  and vice versa. The step P extends parallel to the direction of the weld seams to be made. 
     A spot weld is made at each needle  307   a  and each counter-needle  307   b  and it is possible to make a succession of spot welds that will ultimately form the weld seams by successively moving the needles  307   a  and the counter-needles  307   b . The offsetting of the needles  307   a  and of the counter-needles  307   b  makes it possible to make a weld on the side of the first strip  102 , then on the side of the second strip  104 . 
     The weld seam is formed by a succession of spot welds made alternately by the needles  307   a  and the counter-needles  307   b.    
     Once the welding tool  304  has completed all of the weld seams, the zones between the weld seams, i.e., the zones in which the two strips  102  and  104  are not welded together, are deformed and will ultimately form the channels  150  of the plate  100 . 
     As in the first embodiment, the zones between the weld seams are used to create these channels  150  that open out at the edges of the strips  102  and  104  and therefore extend respectively as far as the first edge of the plate  100  and as far as the second edge of the plate  100 . 
     In order to form the channels  150 , a pressurized fluid is injected between the strips  102  and  104  into the zones between the weld seams, and the two strips  102  and  104  are then separated from one another in these zones to form the channels  150 . In order to inject the pressurized fluid, the zones between the first strip  102  and the second strip  104  at one of the edges of the first strip  102  and of the second strip  104 , along which the zones between the weld seams open at one of the ends thereof, need to be blocked. The pressurized fluid is then injected via the other edge of the first strip  102  and of the second strip  104  along which the zones between the weld seams open at the other ends thereof. 
     In order to correctly form the channels  150 , the mold  302  and the counter-mold  303  have negative forms  308   a - b  between the holes  306   a - b  corresponding to the imprints of the channels  150  to be formed. Thus, during injection of the compressed fluid, the strips  102  and  104  are separated from one another to fit the negative forms  308   a - b , thereby forming the channels  150 . The negative forms  308   a - b  are made on the faces of the mold  302  and of the counter-mold  303  arranged against the strips  102  and  104 . 
     The previously blocked zones are then opened to enable the fluid to flow into the channels  150  of the plate  100 . 
     A manufacturing method for a plate  100  of a heat exchanger according to a first embodiment comprises:
         a first positioning step during which a first strip  102  is positioned on the mold  302 ,   a second positioning step during which a second strip  104  is positioned on the first strip  102 ,   a covering step during which the counter-mold  303  is positioned on the second strip  104 ,   a welding step during which the needles  307   a  are inserted into the holes  306   a  of the mold  302  and the counter-needles  307   b  are inserted into the holes  306   b  of the counter-mold  303 , and the needles  307   a  and the counter-needles  307   b  are powered using the voltage generator to weld the two strips  102 ,  104  together along the weld seams,   a blocking step during which the zones between the first strip  102  and the second strip  104 , where the zones between the weld seams open out at one of the edges of the first strip  102  and of the second strip  104 , are blocked,   a pressurization step during which a compressed fluid is injected via another edge of the first strip  102  and of the second strip  104 , where the zones between the weld seams open out between the first strip  102  and the second strip  104 , to expand the strips  102  and  104  into the negative forms, and   an opening step during which the zones blocked during the blocking step are opened.       

     The welding step is repeated for each weld seam following movement of the needles  307   a  and the counter-needles  307   b  or by successive activation of several rows of needles  307   a  and of counter-needles  307   b.    
     The manufacturing method common to the first embodiment in  FIG. 2  and to the second embodiment in  FIG. 3  comprises successively:
         a superposition step during which the two strips  102 ,  104  are superposed on one another,   a welding step during which the two strips  102  and  104  are welded together along weld seams,   a blocking step during which the zones between the first strip  102  and the second strip  104 , where the zones between the weld seams open out at one of the edges  50 ,  52  of the first strip  102  and of the second strip  104 , are blocked,   a pressurization step during which a compressed fluid is injected via another edge  52 ,  50  of the first strip  102  and of the second strip  104 , where the zones between the weld seams open out between the first strip  102  and the second strip  104 , to expand the strips  102 ,  104 , and   an opening step during which the zones blocked during the blocking step are opened.       

     In the first embodiment, the superposition step comprises successively the first positioning step during which a first strip  102  is positioned on the base  202 , the second positioning step during which a second strip  104  is positioned on the first strip  102 , and the covering step during which the supporting parts  206   a - b  are arranged on the second strip  104 . The welding step then comprises a movement of the welding unit  210  along the welding channel  208  to weld the two strips  102  and  104  together along the weld seams. 
     In the second embodiment, the superposition step comprises successively the first positioning step during which a first strip  102  is positioned on the mold  302 , the second positioning step during which a second strip  104  is positioned on the first strip  102 , and the covering step during which the counter-mold  303  is positioned on the second strip  104 . 
       FIG. 4  shows a tool  400  used to shape two strips  102  and  104  made of titanium or titanium alloy into the plate  100  as part of a method according to a third embodiment of the invention. 
     The tool  400  comprises a mold  402  forming a base in this case, a counter-mold  403  that is positioned above the mold  402 , and a welding tool  404 . 
     The two strips  102  and  104  are arranged between the mold  402  and the counter-mold  403 . 
     The mold  402  and the counter-mold  403  have a plurality of welding elements  406 , such as resistive heating elements, which are aligned in several rows, and the welding elements  406  of the mold  402  and of the counter-mold  403  are aligned, in this case vertically. 
     The welding tool  404  has a plurality of welding elements  406  distributed in rows on the mold  402  and the counter-mold  403  and a current generator that powers the welding elements  406  to create an electrical arc that generates a temperature increase that welds the strips  102  and  104  together. 
     A weld seam is made at each row of welding elements  406 . 
     The mold  402  and the counter-mold  403  also have negative forms  408   a - b  corresponding to the imprints of the channels  150  to be formed. 
     The welding elements  406  and the negative forms  408   a - b  are made on the faces of the mold  402  and of the counter-mold  403  arranged against the strips  102  and  104 . 
     The manufacturing principle of the plate  100  involves welding all of the edges of the two strips  102  and  104  together in order to create a closed volume therein. A pressurized fluid is then injected into this closed volume, for example through a pipe  409  opening into the closed volume. The mold  402  and the counter-mold  403  are then brought together to force contact between the two strips  102  and  104  between the welding elements  406 . During this step, the pipe  409  is blocked to prevent the pressurized fluid from leaking out and at the same time, by maintaining the volume of the pressurized fluid in the closed volume, the strips  102  and  104  are deformed into the negative forms  408   a - b  in order to form the channels  150 . The welding elements  406  are then activated to weld the two strips  102  and  104  along the weld seams. The ends of the channels  150  through which the heat-transfer fluid flows are then opened, for example by cutting the edges of the strips  102  and  104 . 
     Once the welding tool  404  has completed all of the weld seams, the zones between the weld seams, i.e., the zones in which the two strips  102  and  104  are not welded together and have therefore been deformed, form the channels  150  of the plate  100 . 
     After the ends of the channels  150  have been opened, the zones between the weld seams open out at the edges of the strips  102  and  104  and therefore extend respectively as far as the first edge of the plate  100  and as far as the second edge of the plate  100 . 
     A manufacturing method for a plate  100  of a heat exchanger according to a third embodiment comprises successively:
         a first positioning step during which the second strip  104  is positioned on the first strip  102 ,   a first welding step during which the edges of the two strips  102  and  104  are welded together to form a closed volume,   a pressurization step during which a compressed fluid is injected into the closed volume to inflate the closed volume,   a second positioning step during which the inflated strips  102 ,  104  are positioned between a mold  402  and a counter-mold  403  in which the mold  402  has welding elements  406  and negative forms  408   a , and in which the counter-mold  403  has welding elements  406  that are aligned with the welding elements  406  of the mold  402  and negative forms  408   b  that are aligned with the negative forms  408   a  of the mold  402 ,   a clamping step during which the mold  402  and the counter-mold  403  are brought together so that the two strips  102  and  104  are in contact along the welding elements  406  and deformed in the negative forms  408   a - b , and   a second welding step during which the welding elements  406  are activated to weld the two strips  102 ,  104  together along the weld seams.       

     The pressurized fluid can, for example, be air, oil or any other appropriate fluid. 
     Such heat exchangers  100  can be stacked to fasten the deformations  106 ,  108  of a heat exchanger  100  and to bring same into contact with the deformations  108 ,  106  of another heat exchanger  100  arranged on top in order to create open channels that are delimited by the deformations  106  and  108  of the two heat exchangers  100  and the welded zones, i.e. the zones between the channels  150 . Thus, in the context of a fuel cell, a coolant liquid can flow through the channels  150  to provide the heat exchange function, while air and hydrogen can flow through the open channels thus formed. 
     While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.