Welding a frame of a traction battery for an electric vehicle

Abstract

A battery frame for an electric vehicle has a first and second frame parts 60, 62 having respective first and second exterior surfaces 64, 68; and respective first and second abutment surfaces 66, 70. First exterior surfaces 64, 68 are at an angle (e.g. a 90° right angle) to their respective abutment surfaces 66, 70. At least one frame part 60 has an indentation 72 which can form a canal or trough 74 between the frame parts 60, 62. A weld 76 can be formed in the canal 74, between the frame parts 60, 62. The weld 76 can be sub-flush (not level) or coplanar (not proud) with the exterior surfaces 64, 68. A third frame part 80 can be laid flush to the exterior surfaces 64, 68, without needing to dress (e.g. grind) sub flush weld 76; before welding frame parts 60, 62 and 80 together using weld 82.

Description

TECHNICAL FIELD The present disclosure relates to welding a frame of a traction battery for an electric vehicle. Aspects of the invention relate to a welding system for the method of welding, a frame of a traction battery for an electric vehicle, an electric vehicle comprising the frame. BACKGROUND It is known to provide butt welds at joints between frame parts of a fabricated perimeter frame for traction battery enclosures for electric vehicles. Typically, the butt welds sit proud of exterior surfaces of the frame parts, even if a weld prep is present. The proud welds need to be dressed to be flush with the exterior surfaces of the frame parts, before a subsequent frame part, such as a base plate, can be welded over the top of the frame parts, to provide a watertight seal. A CNC (computer numerical control) grinding operation or manual techniques can be used to achieve this dressing. The grinding operation has high capital expenditure and processing costs, whereas the manual techniques may have high variability and low dimensional control. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION According to an aspect there is provided a method of welding a frame of a traction battery for an electric vehicle, the method comprising: providing a first frame part comprising a first exterior surface and a first abutment surface at an angle to the first exterior surface; providing a second frame part comprising a second exterior surface and a second abutment surface at an angle to the second exterior surface; providing an indentation in at least one of the first and second frame parts, the indentation extending from both the respective exterior surface and abutment surface of the frame part and being elongate extending along the respective exterior surface of the frame part; abutting the first abutment surface of the first frame part against the second abutment surface of the second frame part such that the indentation forms a canal between the first and second frame parts, and forming a weld in the canal between the first and second frame parts, wherein the weld is any of subflush, coplanar with respect to the first exterior surface of the first frame part and the second exterior surface of the second frame part. According to an aspect there is provided a method of welding a frame of a traction battery for an electric vehicle, the method comprising: providing a first frame part comprising a first exterior surface and a first abutment surface at an angle to the first exterior surface; providing a second frame part comprising a second exterior surface and a second abutment surface at an angle to the second exterior surface; providing an indentation in at least one of the first and second frame parts, the indentation extending from both the respective exterior surface and abutment surface of the frame part and being elongate extending along the respective exterior surface of the frame part; abutting the first abutment surface of the first frame part against the second abutment surface of the second frame part such that the indentation forms a canal between the first and second frame parts, and forming a weld in the canal between the first and second frame parts, wherein the weld is subflush with respect to the first exterior surface of the first frame part and the second exterior surface of the second frame part. The method of welding the frame providing the subflush or coplanar weld between the first and second frame parts removes the need for a grinding step to remove a weld which sits proud with respect to the first exterior surface of the first frame part and the second exterior surface of the second frame part. This makes the welding method quicker and line time production quicker. The first and second frame parts may form a side portion of the frame for the traction battery. The first and second abutment surfaces may be at an angle to the respective first and second exterior surfaces in the range 85° to 95°, for example in the range 89 to 91 °, for example 90 \ The first and second abutment surfaces may be interior abutment surfaces. Abutting the first abutment surface of the first frame part against the second abutment surface of the second frame part may be such that the first exterior surface of the first frame part is coplanar with the second exterior surface of the second frame part. This simplifies positioning of a further frame part on the first and second frame parts. Abutting the first abutment surface of the first frame part against the second abutment surface of the second frame part may be such that no gap is present between the first and second abutment surfaces. This reduces variability of the volume of the canal formed between the first and second frame parts. The indentation may be provided in at least one of the first and second frame parts such that it has a cross-sectional height and a cross-sectional width which are tuned to complement a thickness of portions of the frame part adjacent the indentation. This promotes good weld penetration and reduces weld burn through risk. The indentation may be provided in at least one of the first and second frame parts by machining the frame part. Machining the frame part may take place at a child part level (i.e. the machining of that subcomponent of the overall frame). Machining the frame part may take place whilst other features are being machined in the frame part. This facilitates manufacture of the frame part. The indentation may be provided in at least one of the first and second frame parts such that the canal has a cross-sectional shape comprising any of a trapezoidal cross-sectional shape, a triangular cross-sectional shape, a V-shaped cross-sectional shape, a U-shaped cross-sectional shape, a rectangular cross-sectional shape, a square cross-sectional shape, a quarter circle cross-sectional shape, a semicircular cross-sectional shape. The indentation provided in at least one of the first and second frame parts may have dimensions having maximum and minimum tolerances. The maximum and minimum tolerances of the dimensions of the indentation may be controlled in manufacture of the indentation. The maximum and minimum tolerances of the dimensions of the indentation may be controlled in manufacture such that the canal has a pre-determined maximum volume and a pre-determined minimum volume. This allows control of size of the weld in the canal. The maximum and minimum tolerances may be linked to primary locators of the frame parts, used to holding the frame parts within a fixture ready for welding, rather than a local datum. This controls the position of the indentation and therefore the canal relative to the first and second frame parts and results in better alignment of the canal for welding. An exterior surface of the subflush weld may be recessed with respect the first exterior surface of the first frame part and the second exterior surface of the second frame part. The exterior surface of the subflush weld may be sunken with respect to the first exterior surface of the first frame part and the second exterior surface of the second frame part. The exterior surface of the subflush weld is therefore not flush, or level, with the first exterior surface of the first frame part and the second exterior surface of the second frame part, but is subflush with respect to the first and second exterior surfaces. The exterior surface of the subflush weld may have a flat profile or a convex profile. One or more parameters of forming of the weld in the canal may be controlled to form the subflush weld between the first and second frame parts. One or more parameters of positioning of filler material within the canal may be controlled to form the subflush weld between the first and second frame parts. Controlling one or more parameters of positioning of the filler material within the canal may comprise controlling an amount of filler material positioned within the canal. Controlling an amount of filler material positioned within the canal may comprise providing an amount of filler material within the canal which is less than a pre-determined volume of the canal. Controlling an amount of filler material positioned within the canal may comprise providing an amount of filler material within the canal which is less than a pre-determined maximum volume of the canal such that the weld is subflush by at least 1,5mm. Controlling the amount of filler material facilitates achievement of a subflush weld. One or more parameters of heating of filler material within the canal may be controlled to form the subflush / coplanar weld between the first and second frame parts. Controlling one or more parameters of heating of the filler material within the canal may comprise controlling one or more parameters of a welding torch for heating the filler material within the canal. Controlling one or more parameters of the welding torch may comprise adjusting the one or more parameters to contain the filler material within the canal. This achieves a subflush weld. Controlling one or more parameters of the welding torch may comprise controlling any of arc voltage, arc length, current, pulse frequency, duty cycle. Controlling one or more parameters of the welding torch may comprise controlling travel speed of the torch along the canal. The travel speed is selected such that the amount of filler material deposited into the canal does not exceed a size of the canal, thus forming a subflush weld along the canal. Controlling one or more parameters of the welding torch may comprise controlling positioning of the welding torch with respect to the canal. Controlling positioning of the welding torch with respect to the canal may comprise controlling any of torch angle, torch target and torch beam cone width. The torch angle may be controlled to be 35° with respect to the canal. The torch target may be controlled to be a root of the canal. The torch beam cone width may be controlled to be a width of the canal plus a tolerance of the width of the canal. These facilitates achievement of a subflush weld. Controlling one or more parameters of forming of the weld in the canal may comprise selection of any of pulse frequency, duty cycle of the welding torch and controlling of feeding of filler material into the canal to control a surface contour of the subflush / coplanar weld between the first and second frame parts. The surface contour may be a surface flatness. The method of welding the frame may further comprise: providing a third frame part; placing the third frame part over a portion of the first exterior surface of the first frame part and the second exterior surface of the second frame part, such that an edge of the third frame part abuts the first and second exterior surfaces, and forming a further weld between the edge of the third frame part and the first and second exterior surfaces which further weld intersects and seals the subflush weld in the canal between the first and second frame parts. The third frame part may be a base plate of the frame. The subflush weld between the first and second frame parts allows the third frame part to be laid flush to the first and second exterior surfaces of the first and second frame parts. The further weld intersects the subflush weld and fills in a subflush recess of the subflush weld to provide a seal between the third frame part and the first and second exterior surfaces of the first and second frame parts. Providing a consistent subflush weld between the first and second frame parts allows the placing and welding of the third frame part without the need to dress the weld between the first and second frame parts. This saves considerable costs and time in the manufacture of the frame. According to an aspect there is provided a frame of a traction battery for an electric vehicle, the frame comprising: a first frame part comprising a first exterior surface and a first abutment surface at an angle to the first exterior surface; a second frame part comprising a second exterior surface and a second abutment surface at an angle to the second exterior surface; an indentation in at least one of the first and second frame parts, the indentation extending from both the respective exterior surface and abutment surface of the frame part and being elongate extending along the respective exterior surface of the frame part; wherein the first abutment surface of the first frame part is abutted against the second abutment surface of the second frame part such that the elongate indentation forms a canal between the first and second frame parts, and a weld in the canal between the first and second frame parts, wherein the weld is subflush with respect to the first exterior surface of the first frame part and the second exterior surface of the second frame part. According to an aspect there is provided an electric vehicle comprising any frame disclosed herein. According to an aspect there is provided a welding system for the method of welding the frame as disclosed herein, the welding system comprising: a control system having one or more processors collectively configured to control one or more parameters of forming the subflush weld between the first and second frame parts of the frame. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a flowchart of a method of welding a frame of a traction battery for an electric vehicle according to embodiments of the invention; Figure 2 shows a cross sectional schematic representation of first and second frame parts of a frame of a traction battery for an electric vehicle; Figure 3 shows a further cross sectional schematic representation of the firstand second frame parts of Figure 2 illustrating a weld between the frame parts according to embodiments of the invention; Figure 4 shows a further cross sectional schematic representation of the firstand second frame parts of Figure 3 illustrating forming the weld between the frame parts according to embodiments of the invention, and Figure 5 shows a cross sectional schematic representation of the first and second frame parts of Figure 2 illustrating a third frame part according to embodiments of the invention. DETAILED DESCRIPTION A method of welding a frame of a traction battery for an electric vehicle in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 1. With reference to Figure 1, the method comprises step 10 of providing a first frame part comprising a first exterior surface and a first abutment surface at an angle to the first exterior surface, step 20 of providing a second frame part comprising a second exterior surface and a second abutment surface at an angle to the second exterior surface and step 30 of providing an indentation in at least one of the first and second frame parts, the indentation extending from both the respective exterior surface and abutment surface of the frame part and being elongate extending along the respective exterior surface of the frame part. In step 40, the first abutment surface of the first frame part is abutted against the second abutment surface of the second frame part such that the elongate indentation forms a canal between the first and second frame parts. In step 50, a weld is formed in the canal between the first and second frame parts, wherein the weld is subflush with respect to the first exterior surface of the first frame part and the second exterior surface of the second frame part. A frame of a traction battery for an electric vehicle in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures 2 to 5. Figure 2 illustrates a cross sectional schematic representation of first and second frame parts 60,62 of a frame 58 of a traction battery for an electric vehicle. The first and second frame parts 60, 62 may form a side portion of the frame of the traction battery. The first frame part 60 comprises a first exterior surface 64 and a first abutment surface 66 at an angle to the first exterior surface 64. The second frame part 62 comprises a second exterior surface 68 and a second abutment surface 70 at an angle to the second exterior surface 68. The first and second abutment surfaces 66, 70 are interior abutment surfaces. The first and second abutment surfaces 66, 70 are at an angle to the respective first and second exterior surfaces 64, 68 in the range 85° to 95°, for example in the range 89° to 91 °, for example 90°. An indentation 72 is provided in the first frame part 60. It will be appreciated that the indentation could be provided in the second frame part 62 or in both the first and second frame parts. The indentation 72 extends from both the first exterior surface 64 and the first abutment surface 66 of the first frame part 60. The indentation 72 is elongate and extends along both the first exterior surface 64 and the first abutment surface 66 of the first frame part 60. The indentation 72 is provided in the first frame part 60 by machining this frame part at a child part level. Machining the frame part may take place whilst other features are being machined in the frame part. This facilitates manufacture of the frame part. The indentation 72 is provided in the first frame part 60 such that it has a cross-sectional height and a cross-sectional width which are tuned to compliment a thickness of portions of the frame part adjacent the indentation 72. This promotes good weld penetration and reduces weld burn through risk. The indentation 72 provided in the first frame part 60 has dimensions having maximum and minimum tolerances, controlled in manufacture of the indentation 72. For example, the first and second exterior surfaces 64, 68 of the frame parts 60, 62 may be cast / extruded and dimensions controlled to + / -0.25 mm, machined surfaces of the indentation 72 may be controlled to + / -0.1 mm and machined angles of the indentation may be controlled to + / -1 degree. The maximum and minimum tolerances may be linked to primary locators of the frame parts 60, 62, rather than a local datum. The primary locators are used to holding the frame parts 60, 62 within a fixture ready for welding. The locators typically comprise a hole and slot, into which a set of pins can be inserted. This locates the frame part consistently in the fixture to a known datum. The primary locators are usually positioned to span at least two-thirds of the frame part's longest length. Thus use of primary locators controls the position of the indentation 72 relative to the first and second frame parts 60, 62 and results in better alignment of the indentation / canal for welding. As shown in Figure 2, the first abutment surface 66 of the first frame part 60 is abutted against the second abutment surface 70 of the second frame part 62 such that the elongate indentation 72 forms a canal 74 between the first and second frame parts 60, 62. Abutting the first and second abutment surfaces 66, 70 is such that the first exterior surface 64 of the first frame part 60 is coplanar with the second exterior surface 68 of the second frame part 62. This simplifies positioning of a further frame part on the first and second frame parts, 60, 62. Abutting the first and second abutment surfaces 66, 70 is also such that no, or minimal, gap is present between the first and second abutment surfaces. This reduces variability of the volume of the canal formed between the first and second frame parts 60, 62. The indentation 72 is provided in the first frame part 60 such that the canal has a cross-sectional shape comprising a trapezoidal cross-sectional shape. It will be appreciated that the canal could have other cross-sectional shapes, for example a triangular cross-sectional shape, a V-shaped cross-sectional shape, a U-shaped cross-sectional shape, a rectangular cross-sectional shape, a square cross-sectional shape, a quarter circle cross-sectional shape, a semicircular cross-sectional shape. The maximum and minimum tolerances of the dimensions of the indentation 72 are controlled in manufacture such that the canal 74 has a pre-determined maximum volume and a pre-determined minimum volume. This allows control of size of the weld in the canal 74. Referring to Figure 3, a weld 76 is formed in the canal 74 between the first and second frame parts 60, 62. In this embodiment, the weld is subflush with respect to the first exterior surface 64 of the first frame part 60 and the second exterior surface 68 of the second frame part 62. An exterior surface of the subflush weld is recessed with respect the first exterior surface 64 of the first frame part 60 and the second exterior surface 68 of the second frame part 62. The exterior surface of the subflush weld is sunken with respect to the first exterior surface 64 of the first frame part 60 and the second exterior surface 68 of the second frame part 62. The exterior surface of the subflush weld is not flush, or level, with the first exterior surface 64 of the first frame part 60 and the second exterior surface 68 of the second frame part 62. The exterior surface of the subflush weld may have a flat profile or a convex profile. It will be understood, however, that the weld could be coplanar with respect to the first exterior surface 64 of the first frame part 60 and the second exterior surface 68 of the second frame part 62. One or more parameters of forming of the weld 76 in the canal 74 are controlled to form the subflush weld 76 between the first and second frame parts 60, 62. One or more parameters of positioning of filler material within the canal 74 is controlled to form the subflush weld 76. For example, controlling one or more parameters of positioning of the filler material within the canal 74 comprises controlling an amount of filler material positioned within the canal 74. Due to maximum and minimum tolerances of the dimensions of the indentation 72, the canal 74 has a predetermined maximum volume and a pre-determined minimum volume. An amount of filler material can be provided within the canal 74 which is less than the pre-determined minimum volume of the canal 74, resulting in the subflush weld 76. An amount of filler material can be provided within the canal 74 which is less than the pre-determined maximum volume of the canal 74 such that the weld 76 is subflush by 1.5 mm below the exterior surfaces 64, 68. Additionally or alternatively, one or more parameters of heating of filler material within the canal 74 are controlled to form the subflush weld 76 between the first and second frame parts 60, 62. Referring to Figure 4, forming the weld 76 in the canal 74 between the first and second frame parts 60, 62 is illustrated. A welding torch 78 is used to heat the filler material within the canal 74 to form the subflush weld 76. Controlling one or more parameters of the welding torch 78 comprises adjusting the one or more parameters to contain the filler material within the canal 74. For example, controlling one or more parameters of the welding torch 78 may comprise controlling any of arc voltage, arc length, current, pulse frequency, duty cycle. In this embodiment, controlling one or more parameters of the welding torch 78 may further comprise controlling travel speed of the torch 78 along the canal 74. In this embodiment, controlling one or more parameters of the welding torch 78 further comprises controlling positioning of the welding torch 78 with respect to the canal 74. This comprises controlling torch angle, torch target and torch beam cone width. The torch angle may be controlled to be 35° with respect to the canal 74. The torch target may be controlled to be a root of the canal 74. The torch beam cone width may be controlled to be a width of the canal 74 plus a tolerance of the width of the canal 74. Controlling one or more parameters of forming of the weld 76 in the canal 74 may comprise selection of any of pulse frequency, duty cycle of the welding torch 78 and feeding of filler material into the canal 74 to control a surface contour, comprising surface flatness, of the subflush weld 76 between the first and second frame parts 60, 62. Referring to Figure 5, a third frame part 80 is provided for the frame 58. In this embodiment, the third frame part 80 is a base plate of the frame 58. The third frame part 80 is placed over a portion of the first exterior surface 64 of the first frame part 60 and the second exterior surface 68 of the second frame part 62, such that an edge of the third frame part 80 abuts the first and second exterior surfaces 64, 68. A further weld 82 is formed between the edge of the third frame part 80 and the first and second exterior surfaces 64, 68, which further weld intersects and seals the subflush weld 76 in the canal 74 between the first and second frame parts 60, 62. The subflush weld 76 between the first and second frame parts 60, 62 allows the third frame part 80 to be laid flush to the first and second exterior surfaces 64, 68 of the first and second frame parts 60, 62. The further weld 82 intersects the subflush weld 76 and fills in a subflush recess to provide a seal between the third frame part 80 and the first and second exterior surfaces 64, 68 of the first and second frame parts 60, 62. Providing a consistent subflush weld 76 between the first and second frame parts 60, 62 allows the placing and welding of the third frame part 80 without the need to dress the weld 76 between the first and second frame parts 60, 62, for example it removes the need for a grinding step to remove part of the weld which sits proud with respect to the first exterior surface 64 of the first frame part 60 and the second exterior surface 68 of the second frame part 62. This saves considerable costs, energy consumption and time in the manufacture of the frame. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. A method of welding a frame of a traction battery for an electric vehicle, the method comprising: providing a first frame part comprising a first exterior surface and a first abutment surface at an angle to the first exterior surface;providing a second frame part comprising a second exterior surface and a second abutment surface at an angle to the second exterior surface;providing an indentation in at least one of the first and second frame parts, the indentation extending from both the respective exterior surface and abutment surface of the frame part and being elongate extending along the respective exterior surface of the frame part;abutting the first abutment surface of the first frame part against the second abutment surface of the second frame part such that the indentation forms a canal between the first and second frame parts, andforming a weld in the canal between the first and second frame parts, wherein the weld is subflush with respect to the first exterior surface of the first frame part and the second exterior surface of the second frame part.

2. A method of welding according to claim 1, in which the first and second abutment surfaces are interior abutment surfaces.

3. A method of welding according to claim 1 or claim 2, in which abutting the first abutment surface of the first frame part against the second abutment surface of the second frame part is such that the first exterior surface of the first frame part is coplanar with the second exterior surface of the second frame part.

4. A method of welding according to any preceding claim, in which the indentation is provided in at least one of the first and second frame parts such that the canal has a cross-sectional shape comprising any of a trapezoidal cross-sectional shape, a triangular cross-sectional shape, a V-shaped cross-sectional shape, a U-shaped cross-sectional shape, a rectangular cross-sectional shape, a square cross-sectional shape, a quarter circle cross-sectional shape, a semicircular cross-sectional shape.

5. A method of welding according to any preceding claim, in which one or more parameters of forming of the weld in the canal are controlled to form the subflush weld between the first and second frame parts.

6. A method of welding according to claim 5, in which one or more parameters of positioning of filler material within the canal are controlled to form the subflush weld between the first and second frame parts.

7. A method of welding according to claim 6, in which controlling one or more parameters of positioningof the filler material within the canal comprises controlling an amount of filler material positioned within the canal to be less than a pre-determined volume of the canal.

8. A method of welding according to any of claims 5 to 7, in which one or more parameters of heating of filler material within the canal are controlled to form the subflush weld between the first and second frame parts.

9. A method of welding according to claim 8, in which controlling one or more parameters of heating ofthe filler material within the canal comprises controlling one or more parameters of a welding torch for heating the filler material within the canal to contain the filler material within the canal.

10. A method of welding according to 9, in which controlling one or more parameters of the welding torch comprises controlling travel speed of the welding torch along the canal.

11. A method of welding according to claim 8 or claim 9, in which controlling one or more parameters of the welding torch comprises controlling positioning of the welding torch with respect to the canal.

12. A method of welding of any preceding claim, further comprising:providing a third frame part;placing the third frame part over a portion of the first exterior surface of the first frame part and the second exterior surface of the second frame part, such that an edge of the third frame part abuts the first and second exterior surfaces, andforming a further weld between the edge of the third frame part and the first and second exterior surfaces which further weld intersects and seals the subflush weld in the canal between the first and second frame parts.

13. A frame of a traction battery for an electric vehicle, the frame comprising:a first frame part comprising a first exterior surface and a first abutment surface at an angle to the first exterior surface;a second frame part comprising a second exterior surface and a second abutment surface at an angle to the second exterior surface;an indentation in at least one of the first and second frame parts, the indentation extending from both the respective exterior surface and abutment surface of the frame part and being elongate extending along the respective exterior surface of the frame part;wherein the first abutment surface of the first frame part is abutted against the second abutment surface of the second frame part such that the indentation forms a canal between the first and second frame parts, anda weld in the canal between the first and second frame parts, wherein the weld is subflush with respect to the first exterior surface of the first frame part and the second exterior surface of the second frame part.

14. An electric vehicle comprising the frame of claim 13.

15. A welding system for use in the method of welding of any of claims 1 to 12, the welding system 5 comprising: a control system having one or more processors collectively configured to control one or more parameters of forming the subflush weld between the first and second frame parts of the frame.13

Images