Method of making an automotive evaporator

Abstract: A method for making a plate-tube heat exchanger 10 is disclosed. The method includes the steps of forming a generally planar plate blank 36 from a deformable sheet of material, forming an aperture 38 at one end of the plate blank and forming a plurality of generally elongate bead preforms 40 in a predetermined configuration by drawing the material from the bottom surface of the plate blank towards the top surface. Next, a plurality of individual beads 34 are formed from each of the plurality of bead preforms by reverse drawing the bead preforms in a direction from the top surface of the plate towards the bottom surface of the plate. The method of the present invention concludes by forming the finish edges 46 of the plate.

Description: The present invention relates to a method for manufacturing a plate for a plate-tube type heat exchanger, as indicated in the preamble of claim 1. Plate-tube heat exchangers are well known in the art. In these types of heat exchangers, a plurality of elongated plates are joined together, such as through a lamination process to define a plurality of passageways for the movement of a fluid therethrough. Each of the passageways is formed by the inwardly facing surfaces of a pair of joined plates. The interior surfaces of the joined plates generally define a central fluid conducting section. The passageways are interconnected so that a fluid may flow through the plurality of joined plates forming the heat exchanger. As is also known in the art, conductive fin strips are located between outwardly facing surfaces of the pairs of joined plates. Heat exchangers of this type have particular utility as evaporators for air conditioning systems of motor vehicles, and one such heat exchanger is described in U.S. Patent No. 5,125,453, assigned to the assignees of the present application. Typically, the plates used in heat exchangers such as described in the '453 patent are formed by stamping or pressing the plate configuration from a sheet of deformable material, such as steel or aluminium. As shown in the '453 patent, the plates include a plurality of beads which act to disrupt the flow of fluid between pairs cf plates. The beads are formed in a single drawing process, wherein each of the beads are formed in one operation. Although adequate in most applications, it has been determined that drawing the beads in a single operation can cause microcracking around the sharp corners of the beads. These cracks result in leakage of the plates and ultimately in reduced effectiveness of the heat exchanger. Therefore, it would be desirable to form the plates so that cracking at the beads does not occur. US Patent No. 3,258,832 (nearest state of the art) describes a method of making a heat exchanger having opposite sides for admitting and discharging a first fluid such as air, said method comprising forming alternate wide and narrow portions along a length of sheet metal, the said forming including holding peripheral margins of each of said wide portions of said sheet in a given plane and simultaneously pressing the metal within the interior contour of said margins to form ridges protruding from one side of said sheet and plane, forming large width openings in each wide portion, with each large width opening surrounded by one of said ridges, forming small width openings in each of the narrow portions, folding said sheet in zigzag formation into a stack of said wide portions while confining the bending as incurred in the folding to the said narrow portions, forcing the adjacent facing surfaces of said wide portions together into contact, metal fusing the said adjacent facing surfaces of said wide portions together so that said large width openings are in registry to determine a passage for a second fluid such as oil through each of said wide portions, and removing at least some of said narrow portions of said sheet at one side of the stack to accommodate the flow of said first fluid. According to the present invention, there is provided a method of making a heat exchanger plate of the kind having an end portion including apertures for transporting a heat exchange medium therethrough, the plate being configured to be joined to a second plate in face-to-face contact to form a fluid passageway for the heat exchange medium to flow therethrough, the method comprising the steps of: providing a sheet of deformable material; forming a generally planar plate blank from the deformable sheet of material, the plate blank defining a top surface, a bottom surface, a first end and a second end; forming an aperture at one end of the plate blank; characterised by forming a plurality of generally elongate bead preforms in a predetermined configuration by drawing the material from the bottom surface of the plate blank towards the top surface, the bead preforms projecting from the plane of the plate blank by a predetermined height; forming a plurality of individual beads in each of the plurality of bead preforms by reverse drawing the bead preforms in a direction from the top surface of the plate towards the bottom surface of the plate; and forming the finish edges of the plate. It is an advantage of the present invention that it provides a method of making the heat exchanger plates which reduces cracking and leakage around the beads. It is a further advantage of the present invention that it provides a method of making a heat exchanger plate which reduces the likelihood of leakage resulting from the manufacturing process. The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a heat exchanger; Figure 2 is a top plan view of the heat exchanger of Figure 1; Figure 3 is a plan view of a finished plate member; Figures 4-7 show the progressive stages in the formation of a plate for the heat exchanger in accord with the principles of the present invention; and Figure 8 is a schematic representation of a manufacturing tool used in the production of the plate member according to the principles of the present invention. Referring now to the drawings, Figures 1 and 2 show a plate-tube heat exchanger, generally designated by the numeral 10, in the form of an evaporator particularly adapted for use in an automobile air conditioning system. The heat exchanger 10 comprises a stack of formed, elongated plates 12, pairs of which are joined together in face-to-face relationship so that adjacent pairs form tubes to provide alternate passageways for the flow of refrigerant therebetween as will be described further below. The plates are joined by brazing. Heat transfer fins 14 are positioned between joined pairs of plates 12 to provide increased heat transfer area as is well known in the art. The joined plate pairs and fin assemblies are contained within endsheets 16. The heat exchanger 10 includes an inlet port 20 and an outlet port 22 formed within a header 18 at either one or both ends of the heat exchanger 10. The header is in direct communication with the tube passageways between the joined pairs of plates 12 as will become apparent from the following description. The plates 12 have aligned apertures at the ends thereof providing communication between inlet and outlet ports 20, 22, respectively, of header 18. However, as is well known in the art, each of the plates can include apertures at either one or both ends thereof and the inlet and outlet ports 20, 22 can be located at opposite ends of the heat exchanger as is well known in the art. In the heat exchanger Figure 1, refrigerant is directed into the inlet port 20, passed through the pair plurality of joined plates 12 in a known manner. The refrigerant then exits through outlet port 22 to complete the cooling cycle. As shown in Figure 3, each of the plate members 12 includes a top surface 24, a bottom surface, a pair of end portions 28 and a generally longitudinal intermediate portion 30 therebetween. As shown in Figure 3, a pair of apertures 32 are formed at one of the end portions 28. Alternatively, as is well know in the art, apertures can be formed at both ends of the plate. The apertures are aligned when the heat exchanger is assembled to provide for a fluid conduit for the heat exchanger fluid to pass therethrough. Each of the intermediate portions 30 of the plate member 12 includes a plurality of beads 34 which, as is well known in the art, provide a circuitous path for the fluid to pass through the plate tube 12 to increase the turbulence of the fluid and provide for better heat transfer characteristics. Figures 4-7 show the steps in manufacturing the plate members 12. As shown in Figure 4, the plate members 12 are formed from a sheet of deformable material. The material can be an aluminium material coated with an aluminium brazing alloy as is known in the art. A sheet of material can either be of a predetermined length with a predetermined number of plate members 12 therein or may be formed as a continuous strip of material which is cut at a predetermined number of plates to form a heat exchanger of predetermined size. The plate members 12 are stamped using pneumatic and hydraulic gauges in a die as is well known in the art. As shown in Figure 4, a plate member blank 36 is first formed in the stamping process. The blank 36 includes generally the dimensions of the final plate member. After the blank 36 is formed, a cup-shaped aperture 38 is formed in one end of the blank. As described above, these cup-shaped apertures 38 become connected together in the final assembly to form the header 18 for the fluid entering and exiting the evaporator as described above. It should be understood that an additional aperture can be formed on the opposite end of the plate as well. Referring now to Figure 5, after the apertures are formed, a plurality of bead preforms 40 are drawn next. The bead preforms 40 are drawn from the bottom surface of the plate toward the top surface using a conventional drawing technique. The bead preforms 40 are drawn to the finish height of the beads on the plate 36. Selected bead preforms may be drawn slightly lower than others to reduce bowing of the plate member 36. In the preferred embodiment, the majority of bead preforms 40 are drawn to a height of 0.127 cms (0.050 inches), while certain other preforms 40 are drawn to 0.2286 cms (0.090 inches). It was necessary to draw the majority of the bead preforms 40 to 0.127 cms (0.050 inches) to reduce bowing of the plate member 36. As shown in Figure 6, after the bead preforms 40 are drawn, the individual beads 34 are formed in each of the preforms. This is done by a reverse drawing process wherein a die contacts the top surface of the bead preforms 40 and pushes the preforms 40 toward the bottom surface of the plate until each of the individual beads are formed to the design height (as schematically illustrated in Figure 8). This process leaves a coined oblong-shaped slot 42 around each grouping of beads. By utilising the two-step drawing process, very sharp radii of the beads can be formed without cracking and ultimately without leaking. Furthermore, at this stage in the manufacturing process, a longitudinal rib 44 may be formed at approximately the centreline of the plate member 36. The rib 44 divides the plate into two fluid flow sections. The rib is formed to one-half the height of the beads since ribs on mating plates must also join. As shown in Figure 7, the manufacturing of the plate member 12 is completed when the finish edges 46 of the plate are formed and the apertures 38 are formed into the final cup-shaped apertures 32. As is known in the art, the edges 46 provide mating surfaces for joining adjacent plate members together. Figure 8 shows a tool 50 for forming the plate members of the present invention. The plate members 12 are stamped using pneumatic and hydraulic gauges in a die 52 either manually controlled as is known in the art or controlled by a PLC\PLS or other computerised means known in the die pressing art. The patterns to be embossed on the plate member are formed on the dies such that when the plate proceeds through the progressive stages in the die, the patterns are formed according to the steps described above.

Claims: A method of making a heat exchanger plate (12) of the kind having an end portion including apertures for transporting a heat exchange medium therethrough, the plate (12) being configured to be joined to a second plate in face-to-face contact to form a fluid passageway for the heat exchange medium to flow therethrough, the method comprising the steps of: providing a sheet of deformable material; forming a generally planar plate blank (36) from the deformable sheet of material, the plate blank defining a top surface, a bottom surface, a first end and a second end; forming apertures (38) at one end of the plate blank; forming a plurality of generally elongate bead preforms (40) in a predetermined configuration by drawing the material from the bottom surface of the plate blank (36) towards the top surface, the bead preforms (40) projecting from the plane of the plate blank by a predetermined height; characterised by forming a plurality of individual beads (34) in each of the plurality of bead preforms (40) by reverse drawing the bead preforms in a direction from the top surface of the plate towards the bottom surface of the plate; and forming the finish edges (46) of the plate. A method according to Claim 1, wherein the step of forming a plurality of individual beads includes forming three beads (34) per bead preform (40). A method according to Claim 1 or 2, wherein the step of forming a plurality of individual beads includes forming a generally oblong-shaped groove (42) at the base of the bead preform (40). A method according to any one of Claims 1 to 3, wherein each of the forming steps is performed at successive locations in a progressive die. A method according to any one of the preceding Claims further including the step of forming a generally longitudinal rib (44) along a longitudinal centreline of the plate (12), the height of the rib being approximately one-half the height of the beads. A method according to any one of the preceding Claims, wherein the step of forming apertures (38) at one end of the plate blank (12) further includes the step of forming an aperture at both ends of the plate blank. A method of making an evaporator core for use in an automotive vehicle comprising the steps of: forming a plurality of plate members (12) by a method as claimed in any one of the preceding claims; joining a pair of plate members (12) together in face-to-face abutting relationship to form a plate tube; interweaving fin members (14) between adjacent plate tubes to form an assembled core; and brazing the assembled core at a predetermined temperature for a predetermined time.

Inventors: BERTRAND DAVID WILLIAM, FRAZIER KATHLEEN LOUISE, WISE KEVIN BENNETT, BERTRAND, DAVID WILLIAM, FRAZIER, KATHLEEN LOUISE, WISE, KEVIN BENNETT
Applicants: FORD MOTOR CO, FORD MOTOR COMPANY
Application year: 1996
Main classification: B21D53
IPC codes: F28D1, F28F3, B21D22, B21D53