Manufacturing method for electric vehicle battery cases

Abstract

This invention provides a method for manufacturing an electric vehicle battery case that can increase the area in which battery cells can be mounted while ensuring watertightness. [Solution] The present invention relates to a method for manufacturing an electric vehicle battery case body 1 comprising a tray 3 having an outward-facing flange 3c at the upper end of a rectangular bottomed frame having a peripheral wall 3a and a bottom plate 3b, and a reinforcement 5 disposed inside the tray 3, comprising a tray manufacturing step for manufacturing the tray 3, a reinforcement manufacturing step for manufacturing the reinforcement 5, and a reinforcement mounting step for attaching the reinforcement 5 to the tray 3, wherein the tray manufacturing step comprises a blank manufacturing step for manufacturing a blank 7 having notches 6 at the four corners of a steel plate, a bending forming step for forming a peripheral wall 3a and an outward-facing flange 3c from the blank 7 by bending with a bending radius of 1 mm or less, and a welding step for butt welding adjacent peripheral walls 3a and outward-facing flanges 3c at the four corners formed by bending.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a battery case main body of an electric vehicle that houses battery cells and the like.

Background Art

[0002] In recent years, particularly in the automobile industry, replacement of engine-powered vehicles with electric vehicles has been progressing due to environmental issues. Electric vehicles are provided with large battery assemblies such as large battery cases and battery packs arranged in the floor portion.

[0003] Since lithium-based materials are often used for the battery cells installed in the battery case, there is a risk of ignition if the cells are damaged and leak liquid, so watertightness that prevents liquid from leaking from the inside to the outside is important. In addition, if water enters the case from the outside, the battery cells will short-circuit, so watertightness against the outside is also important.

[0004] Such methods for manufacturing a battery case are disclosed in, for example, Patent Documents 1 and 2. In the methods for manufacturing a battery case of Patent Documents 1 and 2, frame members constituting the battery case main body are joined to each other by arc welding to form a frame-shaped portion, and the frame-shaped portion is further joined to a floor-shaped portion by arc welding (see

[0037] of Patent Document 1, and

[0024] to

[0027] of Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] For electric vehicles, where a long driving range is required, a larger battery cell capacity is advantageous. Therefore, a smaller radius (R) in both the plan view (the radius of the corners when viewed from above) and the cross-sectional radius (the radius where the vertical walls and bottom connect in the cross-section) of the battery case is advantageous because it increases the area where battery cells can be installed. However, drawing is difficult when reducing the radius (R).

[0007] In this regard, as disclosed in Patent Documents 1 and 2, there is a method of reducing the radius by joining plates or extruded materials with arc welding, but this has disadvantages because long weld lengths can lead to welding defects, making it impossible to maintain watertightness, and also increase manufacturing costs. In other words, in the inventions disclosed in Patent Documents 1 and 2, each component is joined by a very long continuous weld, and since arc welding is specified as the method of continuous welding, welding defects are likely to occur. Furthermore, there are concerns that not only will the watertightness required for the battery case not be guaranteed, but the welding length will be equal to the length of the battery case, which will increase manufacturing costs.

[0008] Furthermore, in the case disclosed in Patent Document 2, the triple corner where the joints between adjacent frame members and the joints with the floor-like section overlap is not welded (see Figure 3 in Patent Document 2), raising concerns about significantly poor watertightness.

[0009] This invention was made to solve the aforementioned problems, and aims to provide a method for manufacturing an electric vehicle battery case that can increase the area in which battery cells can be mounted while ensuring watertightness. [Means for solving the problem]

[0010] (1) A method for manufacturing an electric vehicle battery case body according to the present invention comprises a tray having an outward-facing flange at the upper end of a rectangular bottomed frame having peripheral walls and a bottom plate, and a reinforcement disposed inside the tray so as to extend in the longitudinal direction of the vehicle body to ensure the rigidity of the tray, The process comprises a tray manufacturing step for manufacturing the tray, a reinforcement manufacturing step for manufacturing the reinforcement, and a reinforcement mounting step for attaching the reinforcement to the tray. The tray manufacturing process is characterized by comprising: a blank manufacturing step of producing a blank having notches at the four corners of a steel plate; a bending forming step of forming the peripheral wall and the outward-facing flange of the blank by bending with a bending radius of 1 mm or less; and a welding step of butt welding the bent peripheral wall and the outward-facing flange at the four adjacent corners.

[0011] (2) The invention described in (1) above is further characterized in that, after the welding process, a brazing process is added to braze the corners of the tray that are surrounded by the bottom plate and the peripheral wall at the four corners.

[0012] (3) In addition, in the case described in (1) or (2) above, the reinforcement is such that when the vehicle body is divided into three parts in the longitudinal direction, front, middle and rear, the front and rear parts are at a height greater than or equal to the peripheral wall of the tray, and the middle part is lower than the peripheral wall of the tray, and the reinforcement manufacturing process is characterized in that the reinforcement is manufactured by bending and punching with a bending radius of 1 mm or less.

[0013] (4) In addition, in the case described in (1) or (2) above, the reinforcement is such that when the vehicle body is divided into three parts in the longitudinal direction, front, middle and rear, the front and rear parts are at a height greater than or equal to the peripheral wall of the tray, and the middle part is lower than the peripheral wall of the tray, and the reinforcement manufacturing process is characterized in that the reinforcement is manufactured by bonding three plates together.

[0014] (5) In addition, in any of the above (1) to (4), the blank manufacturing process is characterized by comprising a steel plate joining process in which multiple steel plates are butt-welded together to form a single steel plate.

[0015] (6) Further, in the device according to any one of the above (1) to (5), the material of the battery case main body is a steel sheet with a strength class of 340 MPa or higher.

Effects of the Invention

[0016] According to the method for manufacturing a battery case main body of the present invention, since bending forming is the main process, a drawing die as required in drawing forming is not needed, which is economical, and flexible design adapted to the battery capacity is possible. In addition, the welding length can be made as short as possible, and the watertightness problem caused by welding defects can be avoided. Furthermore, by performing bending forming with a bending radius of 1 mm or less, the capacity of the tray is increased, and the mounting amount of battery cells can be increased.

Brief Description of the Drawings

[0017] [Figure 1] It is a perspective view of an example of the battery case main body targeted by the present invention. [Figure 2] It is a front view of the battery case main body of Figure 1. [Figure 3] It is a perspective view of the fin reinforcement installed inside the battery case main body of Figure 1. [Figure 4] It is a side view of the reinforcement of Figure 3. [Figure 5] They are the A-A' cross-sectional view (Figure 5(a)) and the B-B' cross-sectional view (Figure 5(b)) taken along the arrows in Figure 4. [Figure 6] It is an explanatory diagram of the steps of the method for manufacturing a battery case main body according to the embodiment of the present invention. [Figure 7] It is an explanatory diagram of the blank manufacturing process according to the embodiment of the present invention (Part 1). [Figure 8] It is an explanatory diagram of the blank manufacturing process according to the embodiment of the present invention (Part 2). [Figure 9] It is an explanatory diagram of the reinforcement manufacturing process according to the embodiment of the present invention. [Figure 10]This is an explanatory diagram of the reinforcement mounting process according to an embodiment of the present invention. [Figure 11] This is an explanatory diagram of another embodiment of the blank manufacturing process according to the present invention. [Figure 12] This is an explanatory diagram of another embodiment of the reinforcement manufacturing process according to the present invention. [Figure 13] This figure shows the appearance of the inventive example in the embodiment. [Figure 14] This figure shows the appearance of the comparative example in the example. [Figure 15] This is a contour plot of the analysis results in the example (Example of Invention). [Figure 16] This is a contour plot of the analysis results in the example (comparative example). [Modes for carrying out the invention]

[0018] This embodiment is a method for manufacturing an electric vehicle battery case body (hereinafter simply referred to as "battery case body") comprising a tray having an outward-facing flange at the upper end of a rectangular bottomed frame, and a reinforcement disposed inside the tray. Before describing the manufacturing method, the shape of the battery case body targeted by this embodiment will be explained based on Figures 1 to 5.

[0019] As shown in Figure 1, the battery case body 1 includes a tray 3 on which battery cells (not shown) are mounted, and a reinforcement 5 disposed inside the tray 3.

[0020] <Tray> The tray 3 consists of a rectangular bottomed frame having a peripheral wall 3a and a bottom plate 3b, and an outward-facing flange 3c is provided around the entire circumference of the upper end of the peripheral wall 3a. The outward-facing flange 3c is for attaching a cover (not shown).

[0021] The angle between the bottom plate 3b and the peripheral wall 3a in tray 3 is approximately 120°. Furthermore, at the corners of tray 3, the angle between adjacent peripheral walls 3a is approximately 90°. As will be described later, the peripheral walls 3a and corners of the tray 3 in this embodiment are formed by bending steel plates, but the bending radius is set to 1 mm or less, thereby increasing the internal volume of the tray 3.

[0022] Tray 3 is made of steel plate with a material strength of 340 MPa or higher. By setting the material strength of tray 3 in this way, rigidity against external impacts is ensured.

[0023] <Reinforce> The reinforcement 5 is arranged within the tray 3 so as to extend in the longitudinal direction of the vehicle body, and is intended to ensure the rigidity of the tray 3. In this embodiment, three reinforcement 5 are provided. The material strength of Reinforce 5 can be lower than that of Tray 3; anything above 270 MPa is acceptable.

[0024] As shown in Figure 3, the reinforcement 5 consists of three parts in the longitudinal direction of the vehicle body: a front section 5a, a middle section 5b, and a rear section 5c, with the middle section 5b occupying more than one-third of the total length. In this embodiment, the length of the middle section 5b accounts for approximately 65% ​​of the total length.

[0025] Furthermore, the height of the middle section 5b is 5 mm or more, and is 20% or less of the height of the peripheral wall 3a of the tray 3. On the other hand, the heights of the front section 5a and the rear section 5c are greater than or equal to the peripheral wall 3a of the tray 3, as shown in Figure 2.

[0026] The reason the height of the middle section 5b is lower than that of the front section 5a and rear section 5c is that structural members such as cross members are positioned above the middle section 5b, and these structural members contribute to rigidity, so there is less need to ensure rigidity with reinforcement 5 in that area. Furthermore, although the middle section 5b has a cutout shape due to its low height, there are no rigidity issues because the front section 5a and rear section 5c can contact the battery case lid (not shown). By setting the height of the central section 5b to 20% or less of the peripheral wall 3a, the weight of the tray 3 can be reduced without affecting its rigidity. The height of the central section 5b is set to 5 mm or more in order to maintain its shape as a component.

[0027] The reason why the heights of the front 5a and rear 5c are set to be greater than or equal to the height of the peripheral wall 3a of the tray 3 is that if the heights of the front 5a and rear 5c are less than or equal to the height of the peripheral wall of the tray 3, the effect of rigidity improvement by the reinforcement 5 cannot be sufficiently obtained. Furthermore, since the lid member (not shown) has a predetermined height that protrudes upward, and the battery system extends up to that height, it is preferable that the heights of the front 5a and rear 5c also extend up to that height. As shown in Figures 3 and 4, the front section 5a has a shape that is cut out towards the front, which helps to reduce weight.

[0028] As described above, by designing the Reinforce 5 so that the height of the middle section 5b is lower than that of the front section 5a and rear section 5c, and the middle section 5b accounts for more than one-third of the total length, weight reduction is achieved while ensuring the necessary rigidity. By making the Reinforce 5 lighter, Tray 3 can be made of iron, which is heavier but thinner than aluminum, thereby increasing its internal capacity and the number of battery cells that can be installed.

[0029] The rear end of the rear portion 5c is provided with a rear end flange 5d for joining with the tray 3, and the rear end flange 5d is joined to the peripheral wall 3a of the tray 3. On the other hand, the front part 5a does not have a flange, and a gap is provided between the peripheral wall 3a and the front end of the front part 5a, through which cooling pipes for cooling the battery cells are passed. Alternatively, a front end flange may be provided on the front part 5a instead of the rear part 5c, or flanges may be provided on both the rear part 5c and the front part 5a. However, if flanges are provided on both sides, a method will be required to run the cooling pipes across the reinforcement 5.

[0030] Furthermore, a bottom flange 5e is provided along the entire length of the joint between the tray 3 and the bottom plate 3b in the reinforcement 5. When the battery case body 1 is mounted on the vehicle, it will bend and deform due to vibrations during driving. In this case, providing a bottom flange 5e on the bottom plate of the reinforcement 5, which is located far from the neutral axis, is effective in increasing the second moment of area and thereby increasing rigidity.

[0031] The reinforcement 5 is joined to the tray 3 by adhesive or spot welding the rear flange 5d and bottom flange 5e to the tray 3.

[0032] As described above, the battery case body 1 of this embodiment achieves weight reduction while ensuring the rigidity required for a battery case by shaping the reinforcement 5 such that the height of the middle section 5b is lower than that of the front section 5a and rear section 5c, and the lower-height middle section 5b accounts for more than one-third of the total length. If Reinforce 5 can be made lighter, it will be possible to use a high-strength and heavy material for, for example, the case tray 3, while keeping the overall assembly weight about the same as before, and improving only the rigidity. This point is demonstrated in the examples described later.

[0033] Next, we will explain the manufacturing method of the battery case body 1 as described above. As shown in Figure 6, the manufacturing method for the battery case body 1 includes a tray manufacturing step for manufacturing the tray 3, a reinforcement manufacturing step for manufacturing the reinforcement 5, and a reinforcement mounting step for attaching the reinforcement 5 to the tray 3. The following describes each step in detail.

[0034] <Tray manufacturing process> The tray manufacturing process includes a blank manufacturing process for creating blanks, a bending process for bending the blanks, and a welding process for welding the necessary parts after bending.

[0035] 《Blank Manufacturing Process》 The blank manufacturing process is a process of manufacturing a blank 7 having notches 6 at the four corners of a steel plate, as shown in Figure 7, for example. The notched portion 6 is the part that closes and becomes a corner when the blank 7 is bent. Multiple screw holes 8 are provided in the portion that becomes the outward-facing flange 3c after bending for joining with the lid member.

[0036] 《Bending and forming process》 The bending process involves bending the blank 7 along the dotted line shown in Figure 7 with a bending radius of 1 mm (R1) or less to form the peripheral wall 3a and the outward flange 3c. Furthermore, because the bending radius is small, it is preferable to set relief holes at the corners, and in this case, brazing during the welding process is preferable.

[0037] In this invention, since bending is used, a die for deep drawing is not required, making it economical. Furthermore, the height can be freely changed according to the battery capacity, allowing for flexible design.

[0038] Furthermore, by manufacturing primarily through bending from a single blank 7, the welding length can be kept to a minimum, thus avoiding watertightness problems caused by welding defects. Furthermore, by bending the tray 3 with a bending radius of 1 mm or less, the capacity of the tray 3 can be increased, allowing for a greater number of battery cells to be mounted.

[0039] Welding Process The welding process involves butt welding the adjacent periphery walls 3a and outward-facing flanges 3c at the four corners that have been bent and formed. Welding is performed using methods such as laser welding and arc welding (e.g., TIG welding). As mentioned above, relief holes are sometimes set at the corners due to the small bending radius, but since these relief holes need to be closed in the finished product, it is desirable to braze the corners of the tray 3, enclosed by the bottom plate 3b and the peripheral wall 3a, after TIG welding to ensure watertightness (see Figure 8). Generally, brazing is not used in such areas, but it is suitable for sealing holes because it does not melt the base material much, resulting in good molten metal flow.

[0040] <Reinforce Manufacturing Process> As described above, the shape of the reinforcement 5 in this embodiment is such that the front part 5a and the rear part 5c are at a height greater than or equal to the peripheral wall 3a of the tray 3, and the middle part 5b is lower than the peripheral wall 3a of the tray 3. As shown in Figure 9(a), the reinforcement 5 can be manufactured by punching the blank 7, and then bending it to a bending radius of 1 mm or less, as shown in Figure 9(b). However, it is also possible to laser blank the unnecessary portion in the central part 5b after bending the blank 7.

[0041] <Reinforcement Installation Process> The reinforcement installation process involves attaching the reinforcement 5 to the tray 3, by joining the flanges 5d and 5e, which are provided at the lower and rear ends, to the tray 3, for example, by spot welding with a joining interval of 60 mm (see Figure 10). Furthermore, a spacing of 20 mm or less between the spot dots is preferable because it increases rigidity.

[0042] According to the manufacturing method for the battery case body described above, since it mainly involves bending, it does not require a die for deep drawing as is done in the case of deep drawing, making it economical and allowing for flexible design to match the battery capacity. Furthermore, the welding length can be made as short as possible, thus avoiding watertightness problems caused by welding defects. Furthermore, by bending the tray 3 with a bending radius of 1 mm or less, the capacity of the tray 3 is increased, allowing for a greater number of battery cells to be mounted.

[0043] Furthermore, in the blank manufacturing process of the tray described above, a single sheet of steel was used. However, battery cases are often 1500mm or wider, and it is difficult to manufacture wide blanks using high-strength materials or stainless steel. In such cases, blank 7 is manufactured using a tailored weld blank (TWB). For example, as shown in Figure 11(a), two pieces of stainless steel material, each 1220 mm wide and 1860 mm long, are prepared, with the longer side sheared to improve the accuracy of the TWB end. Then, as shown in Figure 11(b), the longer sides of the two stainless steel pieces are joined together as the TWB line. After joining, cuts may be made to align the ends after the TWB. This produces a board measuring 1860 mm in width and 2440 mm in length, which can then be transformed into tray 3 shown in Figure 11(c) using the tray manufacturing process described above.

[0044] Furthermore, while the reinforcement manufacturing process described above involved a combination of bending and blanking, the reinforcement manufacturing process of the present invention is not limited to this, and can also be manufactured by laminating three plates together. In the example shown in Figure 12, a plate material 5g having a bottom flange 5e and a rear end flange 5d as shown in Figures 12(a) and 12(c) is bonded to both sides of the core material 5f shown in Figure 12(b) using, for example, an adhesive. To reduce weight, the core material 5f has been cut away in the areas indicated by the shaded lines in the diagram, creating a hollowed-out surface. Alternatively, the core material 5f and the plate material 5g may be joined by arc welding around the perimeter of the core material 5f. In the example shown in Figure 12, the rigidity is higher than that shown in Figure 9, but there is a slight increase in weight.

[0045] Furthermore, the reinforcement 5 to be placed in tray 3 is not limited to the three mentioned above; it may also be two or four. In any case, it is desirable to arrange the reinforcement 5 so that the area of ​​tray 3 is equally divided.

[0046] Furthermore, although Figure 1 shows that the peripheral wall 3a of the tray 3 slopes upward from the bottom plate 3b so as to spread outward, the battery case body 1 according to the present invention is not limited to this, and the peripheral wall 3a may rise perpendicularly from the bottom plate 3b. [Examples]

[0047] To evaluate the performance of the battery body manufactured according to the present invention, a displacement analysis using FEM was performed, which is described below. Figure 13 shows the battery case body 1 manufactured according to the example invention, and Figure 14 shows a comparative example. In both the inventive example and the comparative example, the battery cell and the cell cooling system are built into the battery case body 1.

[0048] In the example of the invention, as shown in Figure 13, three reinforcements 5 are installed on a tray 3 with an inclined wall. Tray 3 is made of iron, has a thickness of 2.0 mm, and weighs 50.6 kg. Reinforce 5 has the same shape as described in the above embodiment, is made of iron, has a thickness of 2.0 mm, and weighs 3.54 kg / piece × 3 = 10.62 kg. For the displacement analysis, with Reinforce 5 installed on Tray 3, and electrical components and resin placed on top, the total weight was 481.3 kg.

[0049] As shown in Figure 14, the comparative example battery case body 11 has three reinforcements 15 installed on the inclined wall tray 13, similar to the example of the invention. Tray 13 is made from drawn aluminum, has a thickness of 3.26 mm, and weighs 28.3 kg. Furthermore, the Reinforce 15 is made of resin, has a thickness of 6.0 mm, and weighs 6.97 kg / piece × 3 = 20.91 kg. Similar to the example of the invention, with the reinforcement 15 installed on tray 13, electrical components and resin were placed on top, resulting in a total weight of 468.6 kg.

[0050] Comparing the thickness of the trays in the inventive example and the comparative example, the thickness of tray 3 in the inventive example is 2.0 mm, while the thickness of tray 13 in the comparative example is 3.26 mm. The inventive example is approximately 60% thinner than the comparative example, representing a significant reduction in thickness. Furthermore, comparing the thickness of the reinforcement in the inventive example and the comparative example, the reinforcement in the inventive example has a thickness of 2.0 mm, while the reinforcement 15 in the comparative example has a thickness of 6.0 mm. This shows that the inventive example is about one-third the thickness of the comparative example, representing a significant reduction in thickness. Regarding the volume occupied by the reinforcement placed within the tray, the inventive example occupies 1%, while the comparative example occupies 2%, demonstrating an improvement in the amount of battery cells that can be installed.

[0051] In this example, the use of iron for the tray and reinforcement increases the total weight by 481.3 kg - 468.6 kg = 12.7 kg. However, this increase is only about 2.7%, demonstrating a significant cost-saving effect compared to using expensive aluminum.

[0052] The load constraint conditions for the displacement analysis used to evaluate stiffness are as follows: The constraint condition was to restrain the bolt fastening portion of the outward-facing flange on the battery case lid to the vehicle body. Furthermore, under load conditions, the weight of the battery cell, equivalent to 294 kg, was applied as a distributed load to the underside of the battery cell.

[0053] Contour diagrams showing the deformation of the battery case are shown in Figure 15 (Example of Invention) and Figure 16 (Comparative Example). In both cases, the internal components of the battery are tightly bonded with resin, and the entire assembly deforms as a single unit. As shown in Figure 15, the deflection of the inventive example was 0.1193 mm. On the other hand, as shown in Figure 16, the deflection of the comparative example was 0.1318 mm. Thus, it can be seen that the rigidity of the inventive example is improved by 9.5% [(0.1318 - 0.1193) / 0.1318 = 0.095] compared to the comparative example. In other words, while the total weight of the invention has increased by 2.7%, the rigidity has improved by 9.5%. The small increase in total weight is largely due to the shape of the reinforcement. In addition, the volume occupied by the reinforcement has been halved, which contributes to an increase in the number of battery cells that can be installed.

[0054] Regarding the example invention, a similar simulation was performed for a configuration in which the reinforcement was the same as described above, but the thickness of the iron tray was 1.7 mm. The tray weight in this embodiment is 43.0 kg, and the increase in the total weight of the invention is 473.7 kg - 468.6 kg = 5.1 kg, achieving cost reduction with an increase of only about 1%. Furthermore, since the thickness of the reinforcement is 2.0 mm as described above, the volume occupied by the reinforcement is 1% in the inventive example, while it is 2% in the comparative example, demonstrating the effect of improving the amount of battery cells that can be mounted. In this case, a displacement analysis similar to the one described above was performed, resulting in a 0.3% improvement in stiffness. Thus, by using a steel tray with a thickness of 1.7 mm, the effects of improved rigidity, reduced cost, and increased battery cell capacity are achieved with almost no increase in weight.

[0055] As described above, it has been demonstrated that the present invention allows for an increase in the area where battery cells can be mounted, because the volume occupied by the reinforcement is small and rigidity can be ensured. Furthermore, since the tray and reinforcement can be made of iron, which has a material cost of about 15% of that of aluminum, the cost reduction effect is also significant. [Explanation of Symbols]

[0056] 1. Battery case body 3 trays 3a Peripheral wall 3b Bottom plate 3c Outward flange 5 Reinforce 5a front 5b Chubu 5c Rear 5d Rear end flange 5e Bottom flange 5f core material 5g plate material 6 Notch 7 Blank 8 screw holes 9 spot hits 11. Battery case body (comparative example) 13 Trays (Comparative Example) 15. Reinforcement (Comparative Example)

Claims

1. A method for manufacturing a battery case body for an electric vehicle, comprising: a tray having an outward-facing flange at the upper end of a rectangular bottomed frame having peripheral walls and a bottom plate; and a reinforcement disposed inside the tray so as to extend in the longitudinal direction of the vehicle body to ensure the rigidity of the tray, The process comprises a tray manufacturing step for manufacturing the tray, a reinforcement manufacturing step for manufacturing the reinforcement, and a reinforcement mounting step for attaching the reinforcement to the tray. The tray manufacturing process is characterized by comprising: a blank manufacturing step of producing a blank having notches at the four corners of a steel plate; a bending forming step of forming the peripheral wall and the outward flange of the blank by bending with a bending radius of 1 mm or less; and a welding step of butt welding the bent peripheral wall and the outward flange at the four adjacent corners.

2. The method for manufacturing a battery case body for an electric vehicle according to claim 1, further comprising a brazing step of brazing the corners of the tray, which are surrounded by the bottom plate and the peripheral wall, after the welding step.

3. The method for manufacturing a battery case body for an electric vehicle according to claim 1 or 2, wherein when the vehicle body is divided into three parts in the longitudinal direction, front, middle, and rear, the front and rear parts are at a height greater than or equal to the peripheral wall of the tray, and the middle part is lower than the peripheral wall of the tray, and the manufacturing process of the reinforcement is characterized in that the reinforcement is manufactured by bending and punching with a bending radius of 1 mm or less.

4. The method for manufacturing a battery case body for an electric vehicle according to claim 1 or 2, wherein when the vehicle body is divided into three parts in the longitudinal direction, front, middle, and rear, the front and rear parts are at a height greater than or equal to the peripheral wall of the tray, and the middle part is lower than the peripheral wall of the tray, and the manufacturing process of the reinforcement is to manufacture the reinforcement by bonding three plates together.

5. The method for manufacturing a battery case body for an electric vehicle according to claim 1 or 2, characterized in that the blank manufacturing step includes a steel plate joining step in which multiple steel plates are butted together and welded to form a single steel plate.

6. A method for manufacturing a battery case body for an electric vehicle according to claim 1 or 2, characterized in that the material strength of the battery case body is a steel plate of 340 MPa class or higher.

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