KR20110069843A - Method of forming aluminium heat exchangers header tanks - Google Patents

Abstract

The present invention provides a method for manufacturing a heat exchanger header tank, comprising: providing a tube having a core made of AA3XXX aluminum alloy; Optionally preheating the tube; Inserting the tube into a forming tool having a forming cavity having the shape of a final header tank; Plugging both ends of the tube; Heating the tube to a forming temperature when the tube is not sufficiently preheated and applying internal pressure to the tube using a gas to allow the tube to conform to the shape of the tool cavity to obtain a final header tank; Removing the header tank from the tool; And cooling the header tank; relates to a method for manufacturing a heat exchanger header tank comprising. This method allows for the efficient manufacture of unusually shaped header tanks made of AA3XXX aluminum alloy. The invention also relates to a method for manufacturing a heat exchanger, wherein the header tank is connected to a plurality of tubes and a corrugated fin inserted between the tubes and subsequently to a method for producing a heat exchanger for brazing bonding the fins to the tube. .

Description

METHOD OF FORMING ALUMINUM HEAT EXCHANGER HEADER TANK {METHOD OF FORMING ALUMINIUM HEAT EXCHANGERS HEADER TANKS}

The present invention relates to a header tank, also referred to as a manifold tank, for use in automotive or stationary aluminum heat exchangers that are brazed and joined in an almost arbitrary tank shape and a method for producing the header tank. The present invention also relates to a heat exchanger comprising a molded header tank and a method for producing the heat exchanger.

Today's automotive engineers face increasing challenges in fitting all underhood parts (or engine room parts) in an ideal way. Engines are becoming more powerful, and a growing number of different parts are fitted to support the engine and provide passengers with ever-increasing levels of driving, stability and ride comfort. This results in a lack of available underhood space. Heat exchangers are almost conventionally rectangular in shape, which is a limitation for automotive engineers in properly placing the heat exchanger assembly in the vehicle. Many of the limitations regarding the geometry of heat exchangers stem from the economic feasibility of manufacturing header plates and tanks for making heat exchangers of unusual or special shape. Such headers and tanks provide heat exchangers that are too expensive by current manufacturing methods.

In addition, the increase in underhood components for safety, ride comfort and performance undesirably makes the front end of the vehicle heavier than the rear end. In ordinary passenger cars, heat exchangers such as a charge air cooler (CAC), a condenser, a radiator, and an EGR cooler need to be located close to the front of the vehicle in order to easily achieve sufficient heat exchange performance. The present invention facilitates weight reduction of such components while at the same time reducing costs and increasing geometric flexibility for package construction without sacrificing performance.

The most commonly used method of manufacturing heat exchanger header tanks is to provide a flat rolled brazing sheet, and to form the flat rolled brazing sheet to produce a tab for crimping the plastic tank, a flow tube used for circulating cooling fluid. The slot for insertion and the header having the final shape of the molded header are to be made. This is usually done by cutting the flat rolled sheet to the correct dimensions, punching the sides to make rectangular edges (for the tabs) of the sheet, and deep drawing the sheet pieces to form the header plate, and finally the flow tube / fin package It is performed by punching out the slot to be inserted. Then, the conventional brazing joint is started. After brazing bonding, the clad on the header surface melts and flows into the header tube joint to create fillets of the correct dimensions and shapes. The tank is then crimped in place.

In the case of radiators, heaters and charge air coolers (CACs), which are usually made of aluminum, the tank is usually made of polymer. Another technique conventionally used to mold header tanks is hydroforming.

The manufacturing methods described above are expensive and require very tight control with regard to the lubrication of the tool geometry and tool / sheet contact. The manufacturing methods described above also require an investment in the control of manpower placement, floor space and mechanism configuration, along with disposal of lubrication residues and control of cleaning and disposal of metal scrap by punching at the manufacturing site, which adds cost. Let's do it. In addition, since deep drawing is performed at room temperature (room temperature), it is generally limited to using cold tool steel, which is difficult and expensive to machine with strict tolerances.

The manufacture of plastic tanks by injection molding is a fairly slow and expensive method, requiring a large investment in machinery construction, tool operation and control. The tank is a multifunctional part of the heat exchanger and is built with fasteners and for example an easy-to-access assembly position for the tank-mounted oil cooler and sensing equipment. In addition, since the plastic material is considerably less rigid than aluminum, the wall thickness of the tank is thick, and the tank is made with an integrated external reinforcement framework to achieve sufficiently large torsional rigidity. Thus, the tank is weighted even though it is made using a low density material. Whisker reinforcement or fiber reinforcement may be used to significantly increase the stiffness, but incurs a significant cost increase.

In the case of a charge air cooler (CAC), its operating temperature may exceed the temperature at which the plastic material loses too much strength for use. Thus, tanks are generally made of aluminum today. In most cases, such tanks are manufactured using die casting techniques, which typically limit the tank wall thickness to a range above 1.5 mm, which adds weight to the heat exchanger. In addition, the cast aluminum is not easy to crimp on the header, so a common joining method is melt welding by MIG welding or TIG welding. Tanks and joining methods of this type usually provide a rigid assembly. However, such welding is expensive and time consuming, especially since the tank is made to have a very large thickness where such welding takes place and the header plate also needs to be thickened to accommodate a successful weld joint. Add significant weight.

Thus, there is a need for an effective and flexible method for manufacturing header tanks.

The present invention relates to a header tank made of AA3XXX aluminum alloy.

Alloy-based AA3XXX, commonly used in heat exchanger header tanks, is difficult to form into the desired shape by the methods conventionally used to make header tanks. This alloy does not have the moldability required for further shape shaping of the header tank at room temperature under casting and rolling conditions.

Previous methods have not been able to meet the long felt requirements required for header tanks that can be brazed and can be molded into complex shapes. According to the invention, a method for the production of such a header tank is provided by the steps described in the appended claims.

Elongation at break in excess of 20% is essential for successful high quality molding. In order to obtain very good formability, the core ingot of clad brazing sheet material is exposed to high temperature homogenisation treatment in the state of the art process. Homogenization treatments provide microstructures which, when precisely carried out, increase the formability of alloy strips after hot and cold rolling and annealing treatments. In this homogenization process, most of the manganese present in the alloy is precipitated to form large dispersoid particles, which lose some of the strength that can be provided by manganese in solid solution. Corrosion resistance of AA3XXX alloys may also be negatively affected by the homogenization treatment. Homogenization and annealing treatments also incur additional costs for the material compared to only preheating before hot rolling. Therefore, it is preferable to avoid homogenization treatment and annealing treatment for the alloy to be used for the header tank of the heat exchanger.

In order to obtain a high elongation in the material delivery state, the material is supplied in a fully softened O-tempering state or sometimes in an H112 tempering state, ie an annealing state. This also adds to the heat exchanger material cost. By manufacturing the heat exchanger header tank by the method of the present invention, the alloy of the tube does not need to be homogenized and enables efficient molding of the unhomogenized aluminum alloy tube. In addition, the tube blank does not need to be annealed prior to molding, which makes the method of the present invention more cost effective.

The present invention provides a method for manufacturing a heat exchanger header tank, comprising: providing a tube having a core made of AA3XXX aluminum alloy; Optionally preheating the tube; Inserting the tube into a forming tool having a forming cavity having the shape of a final header tank; Plugging both ends of the tube; Heating the tube to a forming temperature when the tube is not sufficiently preheated and applying internal pressure to the tube using a gas to allow the tube to conform to the shape of the tool cavity to obtain a final header tank; Removing the header tank from the tool; And cooling the header tank; provides a method for manufacturing a heat exchanger header tank. This method makes it possible to efficiently manufacture a header tank made of AA3XXX aluminum alloy.

By using a material for the tube that is not homogenized, improved corrosion resistance and mechanical properties can be obtained. Unannealed tubes contribute to cost savings and reduced environmental burden. Thus, the non-homogenized AA3XXX alloy header tanks produced by the process of the present invention will have higher strength and improved corrosion resistance compared to deep drawing processed header tanks made of the same material but homogenized AA3XXX alloy.

The tube core may have at least one clad made of an aluminum alloy to improve brazing bondability. To facilitate the fabrication of the heat exchanger, the slots or connectors of the tubes may be formed in the shaped header tanks following the molding.

It may be desirable for the gas pressure used in the molding process to be higher than 85 bar to achieve efficient molding of the tube corresponding to the forming cavity of the tool.

If necessary, axial pressure may be applied to both ends of the tube during the forming process of the tube to feed material into the forming cavity during the forming process of the tube.

Further, to facilitate assembly of the heat exchanger, connectors, screws or anchors may be formed at the ends of the tubes during the shaping of the tubes.

Pressures in excess of 200 bar may be required depending on the shape of the tank and the thickness of the aluminum blank.

The tube to be molded into the header tank can be made by welding the rolled aluminum alloy blank to form the tube. By doing so, the tube is effectively provided. In particular, it is advantageous to produce a tube from rolled brazed bonded clad aluminum blank, since it is an efficient way of obtaining a brazed bonded clad tube. Brazing bonded clad tube is very expensive and extremely difficult to extrude.

Optionally, the tube can be made of extruded aluminum alloy, which is advantageous in some cases, especially when no brazing joint cladding is provided in the tube.

The present invention also provides a heat exchanger header tank which is shaped by the hot metal gas forming.

The invention also provides a heat exchanger comprising a header tank when the heat exchanger is not rectangular in shape.

The invention also provides a method for manufacturing a heat exchanger, wherein the header tank is connected to a plurality of tubes and a corrugated fin inserted between the tubes, and subsequently to a method for producing a heat exchanger for brazing bonding the fins to the tube. .

Hot metal gas forming enables the construction of almost any shape aluminum header tank made of AA3XXX alloy for heat exchangers.

The header tank according to the invention for such a heat exchanger can be optimized for low weight and low cost compared to other competing technologies.

The exclusion of plastic tanks makes material recycling easier. The cross-sectional geometry of the tank can vary within greater limits than other competing aluminum forming techniques such as, for example, hydroforming or deep drawing. Tensile tests conducted showed that the moldability of the header tank material increased significantly as the forming temperature increased, which was greater than 100% elongation at break when the temperature increased to 400 ° C. compared to 20-30% at room temperature. It can be increased.

The geometry of the header tank manufactured by this invention is not limited to manufacturing a rectangular heat exchanger, A non-traditional shape is also possible similarly. In particular, a non-rectangular heat exchanger can be formed with great flexibility in shape.

The header tanks produced by the present invention provide much higher material yields than the deep drawing or hydroforming techniques used today.

The header tank according to the present invention facilitates the economic manufacture of heat exchangers that enable automotive engineers to more efficiently package the underhood compartment and at the same time open up the possibility of optimizing heat exchange performance.

The header tanks produced by the present invention can be made using materials having higher strength and higher corrosion resistance, which materials can be produced by more environmentally friendly processes involving less thermodynamic work compared to other competing technologies. Can be prepared.

Embodiments of the present invention will be readily understood from the following description with reference to the accompanying drawings, which are briefly described below. Embodiments of the present invention are described by way of example and are not limited by the accompanying drawings.
1 is a view showing a heat exchanger header tank according to an embodiment of the present invention.
FIG. 2 is a view illustrating a 90 ° rotation of the heat exchanger header tank of FIG. 1.
3 is a view showing an example of the selection of the tube cross-sectional shape of the header tank according to the present invention.
4 is a schematic representation of a non-rectangular heat exchanger comprising a header tank made in accordance with the present invention.
5 is a side view of the heat exchanger according to the invention with the header tank curved across the longitudinal axis.

The header tank of the present invention comprises the following steps: i) fabricating a brazed bonded sheet according to standard industry specifications, ii) welding and possibly bending a tube made of a brazed bonded sheet, iii) designed according to the header tank product. Hot metal gas forming the tube in the tool, iv) fabricating a slot for the flow tube and making a connector to the rest of the heat exchanger system.

The brazing bond sheet is made of a core material to which the clad can be attached to one or both surfaces of the sheet. The core material is selected from the AA3XXX-based having a melting temperature in excess of 610 ° C, such as AA3003 or AA3005, for example. Brazing joint cladding is generally selected from low temperature melting hypoeutectic AA4XXX alloys such as AA4343 and AA4045.

In addition, a clad of more than one material, so-called multiple clads, may be attached to one or both surfaces of the sheet. In addition, clads made of electrochemically balanced materials can be attached, particularly on tube strips for radiators and heaters as well as other heat exchangers, to contribute to the core in corrosive environments. Thus, the core material may have a clad attached to one or both surfaces of the sheet or no clad attached to any surface. The clad may be attached as a single layer or a bilayer on one or both surfaces of the sheet, and the cladding may be applied with the brazing joint to reduce the braze joint-core interaction by cold melt brazing bonding or contributing cladding or by diffusion, for example. It may consist of clad joints interposed between the cores.

The clad is attached to the core by hot rolling followed by cold rolling and heat treatment necessary to achieve the correct intermediate and final tempering treatment before forming the slits to the correct width. Fabrications made of brazing bond sheets can then be brazed using controlled atmosphere brazing (CAB) or vacuum brazing bonds.

For products that are not intended to be brazed (by CAB), 6XXX or 5XXX alloys are commonly used. These alloys are used in products where high strength is required, such as in detail products. 6XXX or 5XXX alloys gain their strength through high Mg content. CAB-brazing bonding of these alloys is difficult due to the reaction between magnesium and flux.

For radiator manufacturers using controlled atmosphere brazing joints (CAB), two major problems have arisen with previously available header core materials: too low mechanical strength and too low corrosion resistance. AA6063, a heat treatable alloy with an Mg content of approximately 0.7 wt-%, is not considered brazable by the CAB process. AA6060 containing approximately 0.4-0.5 wt-% Mg requires more flux, special flux and special flux application techniques, and in some cases the strength after brazing bonding is not sufficient, but brazing bonding is possible. .

In AlMgSi alloys, small Mg ₂ Si precipitates are formed over time, causing an increase in strength. Thus, a simple solution of increasing strength will appear to increase the content of Mg and Si, allowing more Mg ₂ Si to be formed. However, because Mg reacts with the flux during the brazing process, which limits the amount of Mg, alloys with Mg in excess of 0.4% are difficult to effectively braze with CAB. In addition, the aforementioned AA6060 and AA6063 generally exhibit low through corrosion resistance due to, for example, intergranular corrosion and the like.

A 3XXX alloy with approximately up to 0.4% Mg may be brazed to the CAB. By the method of the present invention, the difficulty of forming the 3XXX alloy into the desired shape is overcome. Thus, the method of the present invention makes it possible to select a 3XXX alloy for the header tank, which results in the header tank being brazed to the CAB in later stages.

According to the invention, one of the intermediate products in the manufacture of the header tank is a tube. In order to be able to fabricate a tube from a clad bonded sheet with or without a clad attached, it is necessary to fabricate a welded tube from a clad bonded sheet with or without a clad attached. The actual welding method may be induction welding, MIG welding, TIG welding, friction stir welding or other suitable welding method.

The tube may have a circular, elliptical, square, rectangular, triangular or other suitable symmetrical or asymmetrical cross-sectional geometry. The tube can be manufactured with constant or variable cross-sectional geometry and dimensions along its length, depending on customer requirements. Although not always necessary, it is advantageous to select a cross section to avoid excessive strain demands in subsequent processes. In addition, when the tube is welded so that the cross-sectional geometry is constant along the length of the tube, the material yield in the welding operation preceding the length cutting operation is theoretically 100%.

Heat exchangers used in the automotive industry generally have a rectangular shape. This results in a limitation with respect to the proper location of the heat exchanger assembly in the vehicle. In some cases, a round, curved or stepped shape, or an unusual shape heat exchanger uses the available underhood space for assembly into the available underhood space or in the most optimal way to optimize heat exchange performance. It can be ideal for doing this.

In such a case, it would be desirable to provide a heat exchanger with a shape that fits into the available space in the vehicle or to the desired flow pattern. Such heat exchangers require a custom header tank. The method of the present invention allows shaping of a header tank of any desired shape in three dimensions. Contemplated shapes are, for example, ring-shaped, S-shaped, L-shaped or C-shaped. The header tank may be curved or bent along its longitudinal axis and / or across the longitudinal axis. The flow tubes are attached in line along the length of the header tank, which means that the entire heat exchanger will take a cross-sectional shape corresponding to the shape of the header tank.

Thus, there may be a need to be non-rectangular, such as a circular heat exchanger, for reasons of underhood package construction, heat exchange performance or simple product customization. This need can thus be met by bending a weld tube made of clad attachment brazing sheets to form with a suitable radius of curvature. Optionally, an S-shaped, trapezoidal, or unusual shape header tank may be required.

When a bent or curved tank is to be produced, the tube can be bent into a suitable preliminary shape prior to hot gas forming. The bending of the tube can be made using any bending method suitable for the particular shape to be produced. Bending can be undertaken at ambient or elevated temperatures to meet the requirements for the particular shape required for the final header tank.

Tubes welded and bent according to the customer's requirements are optionally heated using suitable tools or heated tools, such as furnaces, flames or induction machines, for example. Induction heating and flame heating have the advantage that heat input can be made locally in the selected region of the tube. This can be employed as a means of changing the mechanical properties in selected areas where the material temperature is known to have a decisive effect on properties such as yield stress, ultimate tensile stress, elongation at break and formability. Depending on the alloy type, tempering treatment, sheet thickness and deformation required to fabricate the header tank, the desired molding temperature can vary between 250 ° C and 550 ° C.

The tube is placed into the forming tool, such that the inner surface of the tool corresponds to the outer geometry of the final header tank. The tool may be cold (eg room temperature), in which case the tube must be preheated, but it is preferred that the tool is heated to a suitable elevated temperature prior to or during the molding process. The choice of tool and tube temperature is determined by the mechanical and molding properties of the tube material and the final geometry of the header tank.

Next, both ends of the tube are blocked, and the tube is connected to the high pressure gas system. During the molding process, the tube is at a temperature between 250 ° C and 550 ° C. This molding temperature can be achieved by preheating the tube to this temperature before inserting the tube into the molding cavity, preheating the tool before inserting the tube into the tool, or heating the tool during the molding process, for example by induction heating. Can be. The pressure of the gas is increased inside the tube and corresponds to the increasing pressure due to deformation. The pressure is increased until the tube deforms to the surface of the tool. The actual final pressure and gas pressure increase rate are determined, among other things, by the mechanical properties of the tube alloy at that temperature, the tube wall thickness, the final header tank shape and the amount of deformation required for the tube to achieve the desired shape.

After the molding process, the high pressure gas can be vented and the product formed is removed from the tool. The gas can be air, nitrogen, an inert gas or any other suitable gaseous material. The pressure during the molding process is much lower than the pressure employed for example in hydroforming and the like. The upper limit sufficient to mold the aluminum alloy material into a heat exchanger of the desired shape is approximately 250 bar. Due to the limited pressure during the forming process of the tank, the forming tool used for producing the header tank according to the present invention may be made of a material different from that used for the tool used in the conventional forming method. After molding, the molded product can be cooled in air or quenched in water.

It is also possible to feed the material into the tool by applying axial pressure to the tube ends during the forming process. This may be advantageous to obtain small tube wall thickness changes after molding, or to avoid very demanding tube-shaped tube breaks that require large local deformations, for example, near sharp curvatures or corners.

To avoid sticking of the tube on the tool surface, it may be necessary to apply a release agent or a hot lubricant. The application of the release agent or hot lubricant may be done on the tube or on the tool surface, may be applied before each new tube is molded, or in the form of a coating, it does not have to be re-applied so often.

There are several ways to create the slots required for the insertion of tubes, connectors and fasteners. One method is to process hot gas-formed products by punching multiple or all slots individually or in one punch. The holes and slots may be formed by applying any other suitable technique to a milled or drilled or hot gas molded article. Optionally, the hole is a later stage of the hot gas forming process when the final shape of the tube is obtained and hot gas pressure can provide support within the tube to prevent the tube shape from collapse as a result of the punching operation. Can be punched out. The fasteners may be attached to the hot gas formed article by any suitable method such as, for example, rivet fastening, brazing joining, welding or adhesive joining. The choice of fastening method depends on customer requirements, allowed costs, performance and whether the fastening should be made before or after brazing joining. The header tank may be formed with indents to facilitate forming slots in the header tank, an example of which is shown in FIG.

In order to provide gas entering the tube during the hot gas forming process, at least one plug (tubing member) at the end of the tube has an opening attached to the gas system. Before the tank is used in the heat exchanger, the opening must be closed. This can be done in several ways. First, open tube ends can be plugged by attaching inlet and outlet connectors for heat exchanger media that are liquid or gaseous. Second, the open tube end can be closed by a seal that can be brazed, welded or glue bonded or attached by any other suitable method. Optionally, the ends may be blocked by squeezing, and the remaining gaps and gaps may be filled with metal or polymer filler to ensure a leak-free closure. Application of such sealants is accomplished using any suitable method.

In order to facilitate the connection of the pipe or hose, it is conceivable to form a screw on the end of the tube into which the pipe can be screwed. Optionally, an anchor can be formed for attachment of the hose by the clamp.

desirable Example  Explanation

For easier understanding of the invention, examples of how to practice the invention are disclosed.

A 3 mm thick sheet of aluminum AA3003 clad with AA4343 is welded to form a 40 mm diameter tube. The tube is pre-bended into a Y-shaped shape and pushed into a tool preheated up to 500 ° C. of similar shape. The tool is lubricated with a solid lubricant that can withstand molding temperatures without disassembly. Both ends of the tube are plugged and a force is applied by a hydraulic cylinder to prevent the two tool parts from separating. Gas is applied into the tube through one of the plugs at both ends of the tube and the pressure rises from 0 bar to 200 bar. The pressure is released after a few seconds at maximum pressure, the shaped tube is removed from the tool and cooled by spraying water. Slots are punched out at the point where the connector is needed.

The tube now has the final form of a header tank with preformed slots and bulges. Heat exchanger fins and flow tubes can now be assembled into a tank and brazed to form a heat exchanger.

Claims (13)

A method for manufacturing a heat exchanger header tank,
a) providing a tube having a core made of AA3XXX aluminum alloy;
b) optionally preheating the tube;
c) inserting the tube into a forming tool having a forming cavity having the shape of the final header tank;
d) plugging both ends of the tube;
e) heating the tube to the forming temperature if the tube is not sufficiently preheated and applying internal pressure to the tube using a gas to allow the tube to conform to the shape of the tool cavity to obtain a final header tank;
f) removing the header tank from the tool; And
g) cooling the header tank; and a method for manufacturing a heat exchanger header tank. The method of claim 1 wherein the material used for the tube is not homogenized. The method of claim 1, wherein the tube is not annealed. 3. The method of claim 2, wherein the tube core has at least one clad of aluminum alloy. The method according to any one of claims 1 to 4, wherein a slot or a connector for the tube is formed in the molded header tank during or after the molding process. Way. 6. A method according to any one of the preceding claims, wherein the gas pressure used is higher than 85 bar. 7. A method according to any one of the preceding claims, wherein axial pressure is applied to both ends of the tube during the forming process of the tube. 8. A method according to any one of the preceding claims, wherein a screw or anchor is formed on the end of the tube during the forming of the tube. 9. A method according to any one of the preceding claims, characterized in that a tube made from the blank welded in step a) is provided. Heat exchanger header tank formed by the method according to any one of claims 1 to 9. Heat exchanger comprising a heat exchanger header tank according to claim 10. The heat exchanger according to claim 11, wherein the heat exchanger is in a shape other than a rectangular shape. As a method for manufacturing a heat exchanger,
Manufacturing a header tank by the method according to any one of claims 1 to 12;
Providing an opening for the flow tube in the header tank;
Connecting a plurality of flow tubes to the header tank at the openings;
Inserting a fin between the flow tubes; And
Brazing bonding the fins to the flow tube.

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