Welding of electric vehicle batteries

Abstract

An electron beam welding apparatus is provided that includes an electron beam gun (50) associated with a welding chamber (54) configured to weld a battery array (33) to a busbar (32) and beam adjusters (56, 58) operative in response to a controller (60) to modify beam characteristics and a position of an electron beam (52) generated by the electron beam gun (50), at least two sub-chambers (70, 72) are disposed on opposite sides of the welding chamber (54), all chambers being evacuable to be under vacuum, a beam detector (61) is disposed proximate the welding chamber (54) to generate data relating to the beam characteristics and position, and the controller (60) is configured to synchronously control the beam adjusters (56, 58) in response to data from the beam detector (61) to generate a consistent weld penetration depth of a weld formed between the busbar (32) and the battery array (33) regardless of the incidence angle of the electron beam. An associated welding method is also provided.

Description

[Technical field]

[0001] FIELD OF THEINVENTION This invention relates to the welding of electric vehicle batteries, and in particular to electron beam welding of batteries containing cylindrical cells. [Background technology]

[0002] 2. Background of the Invention Electric vehicle production is expanding worldwide, but a bottleneck in the production of these vehicles is the rate at which batteries can be produced. Batteries require good electrical connections with low electrical resistance to maximize electrical efficiency, so welding of connectors is necessary. Welding often requires joining dissimilar metals and requires that heat input to the battery be minimized at all times to prevent damage, as some battery materials are highly flammable.

[0003] Welding of connectors to such vehicle batteries is typically done using a laser. The laser is deflected from a single point source to weld an array of battery cells to the connector. Mechanical manipulation of prisms is used to change the beam direction, but this limits the welding speed. The long focal range and large deflection angle reduce the precision of the weld and also introduce astigmatism into the laser beam, causing variation in weld quality across the battery.

[0004] Given that many electrical components associated with batteries are made of aluminum or aluminum alloys, which oxidize during welding, laser welding must be performed under expensive shielding gases such as argon. Laser welding is also unable to weld certain metals due to reflectivity issues, which limits the metals that can be used in battery manufacturing. Summary of the Invention [Means for solving the problem]

[0005] Summary of the Invention According to one aspect of the present invention, an electron beam welding apparatus is provided that includes an electron beam gun associated with a welding chamber configured to weld a battery array to a busbar, and a beam adjustment device responsive to a controller to modify beam characteristics and a position of an electron beam generated by the electron beam gun, at least two sub-chambers are disposed on opposite sides of the welding chamber, all chambers are evacuable to be under vacuum, a beam detector is disposed proximate the welding chamber to generate data regarding the beam characteristics and position, and the controller is configured to synchronously control the beam adjustment device responsive to data from the beam detector to create a consistent weld penetration depth of the weld formed between the busbar and the battery array regardless of the incidence angle of the electron beam. Thus, the weld depth can be controlled and excessive penetration into the cells that may result in combustion can be avoided. Welding in a vacuum also ensures that minimal combustion occurs.

[0006] The beam conditioning devices are typically electromagnetic coils configured to achieve high speed deflection, dynamic focus, and dynamic astigmatism control of the electron beam.

[0007] Preferably, the welding chamber is separable from each sub-chamber by a sealable door to allow independent evacuation of each chamber. This may desirably be accomplished by the sealable door being a foldable door pivotally movable from the opening between adjacent chambers to a side wall of the sub-chamber.

[0008] According to another aspect of the present invention, there is provided an electron beam welding apparatus comprising: an electron beam gun associated with a welding chamber configured to weld a battery array to a busbar; and a beam adjustment device operative in response to a controller to modify beam characteristics and a position of the electron beam generated by the electron beam gun; at least two sub-chambers disposed on opposite sides of the welding chamber, all of the chambers being evacuable to be under vacuum; the welding chamber being separable from each sub-chamber by a sealable door to enable independent evacuation of the welding chamber and each of the sub-chambers; and at least one of the sealable doors being a foldable door pivotally movable from an opening between the welding chamber and the sub-chambers to a side wall of the sub-chamber.

[0009] For both aspects of the invention, the apparatus may further comprise transport means associated with the chambers for transporting the battery arrays and bus bars between the chambers, thereby allowing automation of the flow of the bus bars and battery arrays through the welding chambers.

[0010] The transport means may comprise conveyor means comprising three substantially adjacent portions, one portion disposed in each chamber, and may additionally or alternatively comprise a pressing element.

[0011] The apparatus may further comprise a linear series of multiple sub-chambers to ensure that a good vacuum can be maintained within the welding chamber even when the busbar and battery array enter the welding chamber.

[0012] According to a third aspect of the present invention there is provided a method of electron beam welding a vehicle battery, the method comprising: (i) placing the battery array and bus bars in a welding chamber of an electron beam gun; (ii) positioning a beam detector proximate the battery array and the busbar; (iii) generating an electron beam to weld the battery array to the busbar at a plurality of locations; and (iii) transmitting data from the beam detector to a controller for synchronously controlling a beam adjuster in response to the data to form a consistent weld penetration depth of a weld formed between the bus bar and the battery array regardless of an incidence angle of the electron beam; Includes.

[0013] The method may further include forming a plurality of linear welds between the busbar and the battery array, which provides a larger contact surface area and a more robust weld than spot welds.

[0014] The cell array and bus bars are preferably placed in a pre-chamber prior to entering the welding chamber, and the pre-chamber and welding chamber are evacuated before the array is moved under vacuum into the welding chamber.

[0015] The cell array and busbars may be transported between the chambers using a conveyor means that comprises three substantially adjacent sections, one section being placed in each chamber.

[0016] Preferably, the battery array is an array of cylindrical cells. The invention will now be described, by way of example only, with reference to the following drawings, in which: [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram of a portion of a vehicle battery. [Diagram 2] FIG. 1 is a schematic diagram of prior art laser welding. [Diagram 3] FIG. 1 is a schematic diagram of electron beam welding of a vehicle battery according to the present invention. [Figure 4] FIG. 2 is a schematic diagram of a load chamber apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] explanation FIG. 1 shows an electrical storage device or battery 10 typically used in electric vehicles, which is cylindrical and comprises an array of individual power cells 12, e.g., lithium-ion or nickel-metal hydride cells. Each battery 10 typically consists of several hundred cylindrical cells 12 arranged in a grid arrangement. A battery busbar 14 is used to connect the individual cells 12 together in the array. The bar 14 is typically welded to the top surface of each cell 12 using laser welding, where the laser is deflected to a welding position on the top of each cell 12 using a prism so as to weld the connection tab 16 associated with each cell 12 to the busbar 14 using an 8 mm circular weld. The busbar 14 has further welds comprising a row of spot welds that form connections to the cells 12.

[0019] A schematic diagram to illustrate prior art laser welding is shown in Figure 2. A laser 20 generates a laser beam 22 that is focused using a lens 24 and deflected using a motorized deflection prism 26 to different welding locations associated with an array of cells 30 that require welding to a busbar 32. Typically, a battery cell array 33 is placed over an area of ​​about 500 mm x 500 mm. When the welding area 34 is directly under the laser 20, the laser beam diameter 36 is circular. If the beam 22 impinges on the welding area 36, ​​38 at an angle, the cross section 40, 42 of the beam is distorted and exhibits astigmatism, resulting in an oval cross section instead of a circular one.

[0020] The mechanical manipulation of the laser prism 26 to deflect the beam 22 limits the maximum possible welding speed and long focal ranges and large deflection angles, impairs precision, and introduces astigmatism into the laser beam, thus causing variations in weld quality across the array 33. The reflectivity of the beam 22 prevents certain metals from being welded using this method. In the case of aluminum or aluminum alloys, which oxidize during welding, the weld must be performed under an expensive shielding gas such as argon.

[0021] The use of electron beam (EB) welding instead of laser beam welding overcomes many of the problems associated with laser beam welding of bus bars associated with cylindrical batteries with an array of cylindrical cells. Figure 3 shows an EB welding setup for welding bus bars and other connectors to an array 33 of battery cells. An electron gun 50 generates an electron beam 52, shown in three separate positions within a vacuum chamber 54, which is rapidly deflected to achieve welding using dynamic focusing, and in response to a controller 60, stigmator coils 56 and deflection coils 58 adjust the position of the beam 52 as well as properties such as beam width and power / penetration.

[0022] An array 33 of cells 30 requiring welding to a busbar 32 is placed in a main vacuum chamber 54 connected to the gun 50. During operation, a beam probe 61, such as a pinhole probe, detects the profile 62 of the beam 52 and instantaneously sends feedback data to a controller 60, which adjusts a power supply 64 to vary the power to the coils 56, 58 to adjust the beam profile almost instantaneously. This synchronous control of the generated beam in response to the detected beam ensures a consistent circular cross-sectional beam profile regardless of the angle of incidence of the beam 52 on the weld area, as shown by way of example with three positions 52, 52', 52'' and corresponding profiles 62, 62' and 62'', which remain circular regardless of the angle of incidence of the beam 52 on the bar 32.

[0023] Since this deflection system has no physical moving parts and the mass of the electrons is negligibly low, the only limiting factor to the deflection speed is the inductance of the deflection coil 58. The deflection coil winding and power amplifier configuration can achieve deflection speeds in excess of 15 times that achievable by current laser prism systems.

[0024] The fast deflection of the beam 52, the dynamic focus and the dynamic astigmatism correction coils are controlled synchronously. Refocusing is easily performed at high speed by the rapidly adjustable dynamic focusing coils 56, which adjust the convergence angle in synchronism with the deflection control of the coils 58 to maintain a constant welding spot diameter as the deflection system produces changes in working distance. To overcome astigmatism problems caused by the deflected electron beam landing on a surface that is not perpendicular to its direction of travel, the astigmatism correction coil assembly 56 can also be controlled synchronously to keep the beam shape the same at the welding point by reshaping the beam in the column inversely so that the beam is exactly where it is when it lands on the surface. The beam probe 61 and associated controller 60 can be used to calibrate the focusing and astigmatism correction at each welding point.

[0025] Instead of circular spot welds, the EB beam machine, including the gun 50, coils 56, 58, and associated controller 60, can be configured to create elongated linear welds to improve the robustness of the welded connection between the busbar 32 and each cell. In particular, linear welds with lengths greater than twice the diameter of the circular cross-section beam are created to weld each tab 16 to the busbar 14. Thus, linear welds are created to a certain penetration depth, and weld lengths greater than 10 mm, typically in the range of 10 to 20 mm, can be created as needed. Because spot welds are prone to failure over time or in response to excessive vibration, creating linear welds provides a larger contact area between the tabs 16 and the busbar 14, improving connectivity and improving the robustness of the weld. Desirably, the EB machine is configured to use linear welds instead of spot welds, such that spot welds are not used to connect the array to the busbar.

[0026] EB welding allows for precise control of penetration depth with feedback from the beam probe, thereby reducing the risk of penetration into the cell itself, which could cause a fire. If penetration into the cell does occur during welding, the vacuum in chamber 54 acts to suppress combustion without the need for shielding gases required for laser welding. Because welding in a vacuum reduces weld porosity, the final weld quality is superior to that of laser welding.

[0027] EB welding can weld dissimilar metals without the reflectivity issues encountered with laser welding. Automakers are not limited in their choice of materials due to the welding process and due to the lack of reflectivity, and improved control of beam size and power results in more uniform welds across each cell.

[0028] The loading vacuum chambers 70, 72 are located on either side of the chamber 54. This allows for rapid throughput of arrays into the chamber 54. Thus, as another array is loaded into the pre-chamber 70, welding takes place in the chamber 54. The pre-chamber 70 is then rapidly pumped down to a suitable vacuum level for welding using pumps and valves 71, and as welding is finished in the main welding chamber 54, the next array is ready to enter under vacuum, while the just-welded array leaves the main chamber 54 and enters the secondary chamber 72, which is also under vacuum. Welding is then started again in the chamber 54, the next array enters the pre-chamber 70 for pumping down to vacuum, and the secondary chamber 72 is returned to atmosphere to remove the welded array, and then, once empty, is rapidly evacuated again to vacuum, ready to receive the next welded array from the chamber 54. Typically, a baffle system is provided between the chambers to allow selective entry or exit of the next array. Pumps and valves 73 act to maintain the vacuum in the chamber 54, with a similar set of valves and pumps to achieve vacuum in the secondary chamber 72.

[0029] Such a load-lock system of chambers with a configuration of sealable doors and movable tools to pass the array between the chambers ensures that the central main welding chamber 54 is kept at an adequate vacuum while the unloading / loading chambers 70, 72 are vented. Figure 3 shows a linear configuration with three chambers for loading, welding, and unloading using a push system to move the array between two chambers at a time with seals and sliding doors to isolate which chamber is being evacuated or pumped at a given time. Typically, it takes about four seconds to weld a 13x13 array of cells, so the speed of throughput from the pre- and secondary chambers is necessary to ensure the most productive throughput. To further improve the speed of throughput and reduce the pump-down time of the system, additional chambers can be added to the transfer line to ensure that the vacuum in the main chamber 54 remains approximately constant.

[0030] Folding chamber interface doors can be used in place of sliding doors, see Figure 4, which shows chambers 54, 70, and 72 viewed from above. Door 80 is movable along inner rails to move between a closed position A which seals the opening between chambers 54 and 72, and pivotably moves through an intermediate position B to reach position C relative to the side wall to allow free movement of the array between the chambers.

[0031] Table 1 shows a comparison of welding speeds between EB and laser achieving a weld time of 4.3 seconds for an array of 13 x 13 cells compared to a time of 71 seconds for laser welding. Weld times are for 8 mm circular welds for similar comparison.

[0032] [Table 1]

Claims

1. 1. An electron beam welding apparatus comprising: an electron beam gun associated with a welding chamber configured to weld a battery array to a bus bar; and a beam adjustment device operative in response to a controller to modify beam characteristics and a position of an electron beam generated by the electron beam gun, wherein at least two sub-chambers are disposed on opposite sides of the welding chamber, all chambers being evacuable to be under vacuum; a beam detector disposed proximate to the welding chamber to generate data regarding beam characteristics and position; and wherein the controller is configured to synchronously control the beam adjustment devices in response to data from the beam detector to generate a consistent weld penetration depth of a weld formed between the bus bar and the battery array regardless of an incidence angle of the electron beam.

2. 10. The electron beam welding apparatus of claim 1, wherein the welding chamber is separable from each sub-chamber by a sealable door to allow independent evacuation of each chamber.

3. 3. The electron beam welding apparatus of claim 2, wherein the sealable door is a foldable door pivotable from an opening between the welding chamber and a sub-chamber to a side wall of the sub-chamber.

4. 1. An electron beam welding apparatus comprising: an electron beam gun associated with a welding chamber configured to weld a battery array to a bus bar; and a beam adjustment device operative in response to a controller to change beam characteristics and a position of an electron beam generated by the electron beam gun, wherein at least two sub-chambers are disposed on opposite sides of the welding chamber, all of the chambers being evacuable to be under vacuum, the welding chamber being separable from each sub-chamber by a sealable door to enable independent evacuation of the welding chamber and each of the sub-chambers, at least one of the sealable doors being a foldable door pivotally movable from an opening between the welding chamber and a sub-chamber to a side wall of the sub-chamber.

5. 5. The electron beam welding apparatus of claim 1, further comprising a transport means associated with the chambers for transporting battery arrays and bus bars between the chambers.

6. 6. The electron beam welding apparatus of claim 5, wherein said transport means comprises a conveyor means having three substantially adjacent portions, one portion disposed within each chamber.

7. Electron beam welding apparatus according to claim 5, wherein the conveying means comprises a pressing element.

8. 5. The electron beam welding apparatus of claim 1, further comprising a linear series of a plurality of sub-chambers.

9. 1. A method for electron beam welding a vehicle battery, comprising: (i) placing the battery array and bus bars in a welding chamber of an electron beam gun; 、 (ii) positioning a beam detector proximate the battery array and the busbar; and (iii) emitting an electron beam to weld the battery array to the bus bar at a plurality of locations; To make it live, (iii) sending data from the beam detector to a controller for synchronously controlling a beam adjustment device in response to the data to form a consistent weld penetration depth of a weld formed between the bus bar and the battery array regardless of an incidence angle of the electron beam; A method comprising:

10. 10. The method of electron beam welding a vehicle battery of claim 9, further comprising forming a plurality of linear welds between said busbar and said battery array.

11. 11. The method of electron beam welding a vehicle battery according to claim 9 or 10, further comprising placing the cell array and the bus bars in a pre-chamber and evacuating the pre-chamber and the welding chamber before moving the array under vacuum into the welding chamber.

12. 11. The method of electron beam welding vehicle batteries according to any one of claims 9 to 10, further comprising transporting the battery array and bus bars between said chambers using a conveyor means, the battery array and bus bars comprising three substantially adjacent sections, one section being disposed in each chamber.

13. The method for electron beam welding a vehicle battery according to any one of claims 9 to 10, wherein the battery array is an array of cylindrical cells.

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