GB2640514A

GB2640514A - A method of forming a thermoplastic assembly

Info

Publication number: GB2640514A
Application number: GB2405630.1A
Authority: GB
Inventors: Santoni Claudio; Sordon Alessandro
Original assignee: Silverstone Performance Technologies Ltd
Current assignee: Silverstone Performance Technologies Ltd
Priority date: 2024-04-22
Filing date: 2024-04-22
Publication date: 2025-10-29
Also published as: GB202405630D0; WO2025223944A1

Abstract

A method of forming an assembly, for example a battery enclosure or tray for an electric vehicle, comprises providing a plurality of separate thermoplastic parts 3, 7; heating one or more of the parts along at least one or more joining surfaces; arranging the parts in at least two separate overmoulding tools 11, 13, 21; closing the at least two overmoulding tools and thereby pressing the parts together at the one or more joining surfaces to weld the parts together; and overmoulding an assembly structure onto the parts using the at least two overmoulding tools. Heating may be provided by infra-red or ultraviolet radiation. The parts and overmoulded material may comprise a fibre-reinforced thermoplastic part, including glass fibres, carbon fibres and/or aramid fibres. Overmoulding may include injecting material into spaces 30, 31, 38 to encapsulate one or more of the parts, moulding a bridging surface or ribs or encapsulating a region surrounding the weld. One or more attachment devices may be provided, such as a threaded hole 8 for receiving a machine screw or bolt. An assembly is also provided.

Description

A METHOD OF FORMING A THERMOPLASTIC ASSEMBLY FIELD OF THE INVENTION

The invention relates to methods of forming assemblies using thermoplastic parts. In particular, the invention relates to methods particularly suited to forming assemblies for automotive vehicles in which a plurality of thermoplastic parts, typically thermoplastic composites, are joined together to form a structural assembly.

BACKGROUND

Thermoplastic parts can be highly structurally efficient, or, in other words, have a good strength-to-weight ratio, that makes their usage desirable in many different scenarios. However, forming complex thermoplastic assemblies often involves having to either sacrifice some strength of the assembly in order to have an assembly that can be conveniently manufactured, or accept a more difficult manufacture process with multiple laborious assembly steps. For example, fibre-reinforced thermoplastic can be injection moulded into complex assemblies in a single step. However, a fibre-reinforced thermoplastic that can be injection moulded is structurally weaker than, for example, a continuous fibre thermoplastic, which cannot be injection moulded. These stronger thermoplastic parts that cannot be injection moulded often require laborious assembly and joining of simple constituent parts into a more complex assembly. Similarly, injection moulding in a single step limits the shapes that can be formed to those that are capable of being demoulded, limiting the available shapes for the assembly, It is desirable to provide a method that is able to produce more complex assemblies that benefit from the enhanced strength possible when forming an assembly using multiple less complex thermoplastic parts, but that nonetheless is convenient to manufacture.

SUMMARY OF INVENTION

In accordance with a first aspect of the invention, there is provided a method of forming an assembly using thermoplastic parts, the method comprising: providing a plurality of separate thermoplastic parts; heating one or more of the thermoplastic parts along at least one or more joining surfaces of the thermoplastic parts; arranging the plurality of thermoplastic parts in at least two separate overmoulding tools; closing the at least two overmoulding tools and thereby pressing the thermoplastic parts together at the one or more joining surfaces to weld thermoplastic parts together; and overmoulding an assembly structure onto the thermoplastic parts using the at least two overmoulding tools.

The present method provides the advantages of improved strength made possible by an assembly of multiple separate thermoplastic parts; but reduces manufacturing burden by using overmoulding tools to simultaneously weld the thermoplastic parts together and overmould them with additional thermoplastic material. Not only does this overmoulding process reduce manufacture burden by integrating the joining of the parts into the overmoulding process, but it provides the final product with all of the complexity normally achievable with injection moulding processes. Not only this, but this method also provides the advantage that the separate thermoplastic parts can conform to the overmoulding tool geometry better than a pre-formed assembly due to the fact that they are individually loaded/mounted onto the tool before being joined together. In total, this method allows for strong and complex thermoplastic parts while mitigating the manufacturing burden that comes from forming the part of multiple separate thermoplastic parts joined together Preferably, the method comprises heating at least two of the thermoplastic parts along at least respective joining surfaces, and closing the at least two overmoulding tools and thereby pressing said thermoplastic parts together at their respective joining surfaces to weld thermoplastic parts together. In other words, the heated joining surface of one thermoplastic part is pressed against the heated joining surface of another thermoplastic part to effect the welding. While it is preferred that both thermoplastic parts are heated in this way before being pressed together at their respective joining surfaces, in some embodiments it is possible to heat only one of the two thermoplastic parts. Heating of the second thermoplastic part to effectively weld the parts together may be achieved through heat transfer from the first thermoplastic part and/or through pressure, particularly if one of the thermoplastic parts has a shape defining an energy director that will readily deform under the applied pressure.

The present method may be used to join separate thermoplastic parts together in any configuration. However, one particularly preferred arrangement comprises providing one primary thermoplastic part and providing a plurality of secondary thermoplastic parts, arranging the primary thermoplastic part in a first of the at least two separate overmoulding tools and arranging the plurality of secondary thermoplastic parts in one or more other of the at least two overmoulding tools, closing the at least two overmoulding tools and thereby pressing each secondary thermoplastic part together with the primary thermoplastic part at respective one or more joining surfaces. The primary thermoplastic part will typically be larger than each of the plurality of secondary thermoplastic parts. The primary thermoplastic part acts as the structural base of the assembly to which the other parts are joined. This allows all welding to be performed in one pressing action.

In particularly preferred embodiments, heating one or more of the thermoplastic parts is performed before the respective thermoplastic part has been arranged in one of the overmoulding tools. It has been found to be more convenient to heat the thermoplastic parts before arranging them in the overmoulding tools so that the overmoulding tool does not need to be held inactive while the parts are heated. In this way, production output can be increased for each overmoulding tool.

However, it would also be possible to heat one or more of the thermoplastic parts only after they have been arranged in one of the overmoulding tools. In some embodiments, it may be possible to heat the thermoplastic parts while they are being pressed together by the overmoulding tools, although this is less preferred.

Heating the one or more of the thermoplastic parts preferably comprises heating using infra-red or ultraviolet radiation. However, any means of heating the thermoplastic parts may be used. Other methods could include contact heating or induction heating. The optimal heating method will be application specific. Infrared and UV heating can be more flexible, for example, a radiation source can be mounted at the end of a robot and can be regulated more effectively, but these can be more expensive.

As indicated above, the present method comprises heating one or more of the thermoplastic parts along at least one or more joining surfaces. While it is possible to heat only predefined regions of the thermoplastic parts, preferably, the method involves heating substantially the whole of one or more of the thermoplastic parts, preferably heating substantially the whole of each of the thermoplastic parts. This has been found to improve the bond between the overmoulded thermoplastic material and the thermoplastic parts.

It should be noted that heating one or more of the thermoplastic parts along at least one or more joining surfaces of the thermoplastic parts typically comprises heating the joining surfaces of the thermoplastic parts to above the glass transition temperature of the respective thermoplastic part, preferably heating the joining surfaces of the thermoplastic parts to at least the melting temperature of the respective thermoplastic part. The combination of this heat and pressure by pressing the overmoulding tools together effects a strong weld between the thermoplastic parts. Additionally, the pressure with which the overmoulded material is injected contributes to the welding of thermoplastic parts.

Any type of thermoplastic part may be used in the present method. However, preferably one or more of the thermoplastic parts comprises a reinforced thermoplastic part. For example, they may be provided with additional layers or other reinforcing elements to strengthen the thermoplastic part. While this is desirable, the present method may still be useful for non-reinforced thermoplastic parts. In particular, an assembly formed of several thermoplastic parts joined together and overmoulded onto may enable shapes to be formed that could not be formed in a single overmoulding process, which may include shapes that are inherently stronger or have other advantages.

In particularly preferable examples, one or more of the thermoplastic parts comprises a thermoplastic composite part. Particularly preferably, one or more of the thermoplastic parts comprises a fibre-reinforced thermoplastic part, preferably fibre-reinforced polypropylene. Whereas fibres of a certain length can often be injection moulded, the present method may be used for long fibres that present challenges associated with their length, orientation and flowability during a moulding process. Therefore, preferably, one or more of the thermoplastic parts comprises fibres having a length of at least 20 mm, preferably at least 50 mm, more preferably at least 100 mm, most preferably at least 200 mm. Indeed, the present method is particularly suited to thermoplastic parts made with continuous fibres. In this context, one or more of the thermoplastic parts may comprise continuous fibres extending along at least 50% of the length of the thermoplastic part along the direction of the continuous fibres, preferably along 70%, more preferably along 80%, more preferably along 90% of the length of the thermoplastic part along the direction of the continuous fibres, wherein more preferably the continuous fibres extend along substantially the entire length of the thermoplastic part along the direction of the continuous fibres. The continuous fibres could extend along any direction of the thermoplastic parts, but preferably, the continuous fibres extend along the longest dimension of the thermoplastic part.

Thus, preferably, one or more of the thermoplastic parts comprises continuous fibres extending along at least 50% of a longest dimension of the thermoplastic part, preferably along 70%, more preferably along 80%, more preferably along 90% of the longest dimension of the thermoplastic part, most preferably along substantially the entire length of the thermoplastic part along the longest dimension of the thermoplastic part. The fibres may comprise glass fibres, carbon fibres and/or aramid fibres.

In order to enhance the weldability of the thermoplastic parts, preferably each thermoplastic part comprises the same thermoplastic material or the same major component thermoplastic material, preferably polypropylene.

As mentioned above, the present method involves overmoulding an assembly structure using the overmoulding tool. This can be done while the thermoplastic parts are being pressed together using the overmoulding tools.

When overmoulding the assembly structure, any overmoulding material may be used; however, preferably this comprises overmoulding an assembly structure using a thermoplastic material. Preferably, the overmoulded thermoplastic material comprises the same thermoplastic material or the same major component thermoplastic material as one or more of the thermoplastic parts.

Preferably, the method comprises overmoulding an assembly structure using a fibre-reinforced thermoplastic material. However, overmoulding materials without fibres can also be used. Preferably, the fibres of the overmoulded thermoplastic material are shorter than any fibres of the thermoplastic parts. In this way, long fibres suited for strength but less suited to intricate moulded shapes may be used in the thermoplastic parts, whereas shorter fibres better suited to intricate moulded shapes are used during overmoulding. Preferably, the overmoulded fibre-reinforced thermoplastic material comprises fibres having a length of at least 1 mm, preferably at least 5 mm, more preferably at least 10 mm, most preferably at least 20 mm.

While it is possible that the overmoulding may be performed substantially on only one of the thermoplastic parts, preferably the method comprises overmoulding parts of the assembly structure onto a plurality, preferably each, of the thermoplastic parts. In this way, each of the thermoplastic parts is contributing to the strength of different parts of the overmoulded assembly.

In some embodiments, overmoulding an assembly structure onto the thermoplastic parts comprises substantially encapsulating one or more of the thermoplastic parts in the overmoulded material. In this way, the thermoplastic part acts as a strengthening core of the assembly, but the surface structures of the assembly may be formed with more complex surface features by the overmoulded material.

In other embodiments, overmoulding an assembly structure onto the thermoplastic parts comprises overmoulding a bridging surface extending between at least two of the thermoplastic parts. In particular, the thermoplastic parts, even once welded together, may exhibit edges or surfaces that are not joined together, or visible welded joints. These locations may be susceptible to damage, for example, and so the overmoulded material preferably defines a bridging surface extending between at least two of the thermoplastic parts. For example, the overmoulded material may extend between two unconnected edges of the thermoplastic parts, e.g. to form one continuous surface. In another embodiment, overmoulding an assembly structure onto the thermoplastic parts comprises substantially encapsulating a region surrounding the weld between the thermoplastic parts. By encapsulating the weld, i.e. the region in which the thermoplastic parts were together at their one or more joining surfaces, this weak point of the structure is supported and protected, improving the strength of the assembly.

To further reduce manufacturing complexity of the final product into which the assembly is to be incorporated, preferably the method further comprises providing one or more attachment devices for receiving a mechanical fastener and overmoulding the assembly structure onto the one or more attachment devices.

These attachment devices in this context are often referred to as "inserts". It is common to use these attachment devices to provide a reinforced location for attaching secondary components using mechanical fasteners. These inserts are commonly solid pieces of metal or polymer with a hole for receiving the mechanical fastener. These inserts act to provide a robust member that directly engages with the mechanical fastener and act to distribute any forces transmitted through the mechanical fastener over a larger area formed by the interface between the insert and the assembly. As indicated above, preferably the one or more attachment devices each has a threaded hole, either a blind hole or a through hole, for receiving a machine screw or bolt. By overmoulding the assembly structure onto the one or more attachment devices, the attachment devices may be at least partially embedded in the assembly structure. In other embodiments, one or more attachment devices could be co-moulded with the assembly structure. Providing attachment devices in the assembly structure as part of the overmoulding process avoids the need for incorporation of the attachment devices in a post-moulding machine process.

In principle, the present method may be used for forming any assembly comprising a plurality of separate thermoplastic pads. However, the present method is of particular use in the automotive industry. In some embodiments, the method is a method of manufacturing all or part of an automotive vehicle and the assembly is an assembly of the automotive vehicle. The assembly may define all or part of a vehicle frame, a vehicle monocoque, a vehicle semi-monocoque, vehicle bodywork and/or vehicle trim. However, in particularly preferable embodiments, the assembly defines all or part of a battery enclosure for an electric vehicle, preferably a tray for a battery enclosure of an electric vehicle. Battery enclosures on the one hand require complex shapes for securely housing an array of battery modules and associated hardware, but on the other hand must be strong enough to protect the enclosed battery from impact during a crash. Therefore, a battery enclosure is an example of a part of an automotive vehicle that sees significant benefit from the present method.

In embodiments in which the assembly defines all or part of a battery enclosure, preferably one or more of the plurality of thermoplastic parts at least partially define one or more of a base of the battery enclosure and one or more sidewalls of the battery enclosure, wherein preferably the plurality of thermoplastic pads at least partially define at least the base of the battery enclosure and two opposing sidewalls of the battery enclosure. The base and the sidewalls are areas of the battery enclosure that benefit the most from reinforcement. The base of the enclosure is subject impacts from below, such as objects thrown up from the road, while the sidewalls are typically those parts that are most directly affected by side impacts of the vehicle.

Again, in embodiments in which the assembly defines all or part of a battery enclosure, preferably the assembly structure comprises one or more overmoulded ribs extending between opposing sidewalls of the tray. These ribs are commonly used to separate individual battery modules within the battery enclosure and also to transmit forces between the sidewalls in order to protect the enclosed batteries. Another example of an overmoulded assembly structure is a floor of the battery enclosure, which may be defined by an array of walls perpendicular to a base of the tray, preferably defining an array of open cells. Such an intricate structure may be used to space the battery modules from the base of the enclosure to protect from damage without significantly adding to the weight of the battery enclosure. This array of walls is an example of a complex structure that can very practically be formed by moulding techniques.

In accordance with a second aspect of the invention, there is provided an assembly comprising: a plurality of thermoplastic parts joined together by a weld joint; and an assembly structure overmoulded onto the thermoplastic parts.

This assembly corresponds to an assembly manufactured in accordance with the method of the first aspect of the invention. It will be appreciated that all of the above preferred features may be implemented in this assembly according to the second aspect of the invention.

Preferably the assembly comprises a primary thermoplastic part and a plurality of secondary thermoplastic parts, each secondary thermoplastic parts being joined to the primary thermoplastic part by a respective weld joint.

Typically one or more of the thermoplastic parts comprises a reinforced thermoplastic part. Preferably one or more of the thermoplastic parts comprises a thermoplastic composite part. Preferably one or more of the thermoplastic parts comprises a fibre-reinforced thermoplastic part, preferably fibre-reinforced polypropylene. Preferably, one or more of the thermoplastic parts comprises fibres having a length of at least 20 mm, preferably at least 50 mm, more preferably at least 100 mm, most preferably at least 200 mm. Preferably, one or more of the thermoplastic parts comprises continuous fibres extending along at least 50% of the length of the thermoplastic part along the direction of the continuous fibres, preferably along 70%, more preferably along 80%, more preferably along 90% of the length of the thermoplastic part along the direction of the continuous fibres, wherein more preferably the continuous fibres extend along substantially the entire length of the thermoplastic part along the direction of the continuous fibres. Alternatively, one or more of the thermoplastic parts comprises continuous fibres extending along at least 50% of a longest dimension of the thermoplastic part, preferably along 70%, more preferably along 80%, more preferably along 90% of the longest dimension of the thermoplastic part, most preferably along substantially the entire length of the thermoplastic part along the longest dimension of the thermoplastic part. The fibres may comprise glass fibres, carbon fibres and/or aramid fibres.

In some embodiments, each thermoplastic part comprises the same thermoplastic material or the same major component thermoplastic material, preferably polypropylene.

Typically, the assembly structure comprises a thermoplastic material. Preferably, the thermoplastic material of the assembly structure comprises the same thermoplastic material or the same major component thermoplastic material as one or more of the thermoplastic parts. Preferably, the thermoplastic material of the assembly structure comprises a fibre-reinforced thermoplastic material. Preferably, the fibres of the assembly structure thermoplastic material are shorter than any fibres of the thermoplastic parts. Preferably, the fibres of the assembly structure thermoplastic material have a length of at least 1 mm, preferably at least 5 mm, more preferably at least 10 mm, most preferably at least 20 mm.

In some embodiments, the assembly structure comprises parts overmoulded onto each of the thermoplastic parts. Preferably, the assembly structure substantially encapsulates one or more of the thermoplastic parts. In some embodiments, the assembly structure comprises a bridging surface extending between at least two of the thermoplastic parts. Preferably, the assembly structure substantially encapsulates a region surrounding the weld joint between the thermoplastic parts.

Some embodiments further comprise one or more attachment devices for receiving a mechanical fastener at least partially embedded in the assembly structure, wherein preferably the one or more attachment devices each has a threaded hole for receiving a machine screw or bolt.

Preferably, the assembly is an assembly for an automotive vehicle. The assembly may define all or part of a vehicle frame, a vehicle monocoque, a vehicle semimonocoque, vehicle bodywork and/or vehicle trim. However, in particularly preferable embodiments, the assembly defines all or part of a battery enclosure for an electric vehicle, preferably a tray for a battery enclosure of an electric vehicle. Preferably, one or more of the plurality of thermoplastic parts define one or more of a base of the battery enclosure and one or more sidewalls of the battery enclosure, wherein preferably the plurality of thermoplastic parts define at least the base of the battery enclosure and two opposing sidewalls of the battery enclosure. In some embodiments, the assembly structure comprises one or more overmoulded ribs extending between opposing sidewalls of the tray. In other embodiments, the assembly structure comprises a floor of the battery enclosure defined by an array of walls perpendicular to a base of the battery enclosure, preferably defining an array of open cells.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a flow diagram illustrating a method according to a first embodiment of the invention; Figure 2 is a schematic perspective view of a plurality of reinforced thermoplastic parts used to form an assembly; Figure 3 is a schematic exploded perspective view of the reinforced thermoplastic parts of Figure 2; Figure 4 is a schematic perspective view of a plurality of the reinforced thermoplastic parts of Figures 2 and 3 loaded into an upper overmoulding tool; Figures 5A and 5B are schematic cross-sectional views through part of the upper overmoulding tool of Figure 4 in an open and closed arrangement respectively; Figure 6 is a schematic perspective view of the upper overmoulding tool of Figure 4 in opposition with a lower overmoulding tool; Figure 7 is a schematic cross-section through the lower overmoulding tool of Figure 6 illustrating the reinforced thermoplastic part loaded therein; Figure 8 is a schematic perspective view showing the upper and lower overmoulding tools of Figures 4 and 5 in a closed arrangement; Figure 9 is a schematic cross-section through the closed overmoulding tools of Figure 8 showing the welding together of the reinforced thermoplastic parts; Figure 10 is a schematic perspective view of a final assembly produced according to the first embodiment of the invention; and Figure 11 shows a variant of Figure 9 in which the overmoulding tools additionally overmould around attachment devices.

DETAILED DESCRIPTION

An assembly and its method of manufacture according to the invention will now be described in detail with reference to Figures 1 to 10.

In a first step of the method S100, a plurality of separate reinforced thermoplastic parts are provided. These reinforced thermoplastic parts 1-7 are shown in Figures 2 and 3, with Figure 2 showing them in their intended position in the final assembly and Figure 3 being an exploded view more clearly showing the separate parts. In the method of this embodiment, the assembly being formed is a tray for a battery enclosure of an electric vehicle. The tray is generally rectangular in plan view. Accordingly, the reinforced thermoplastic parts include a front transverse sidewall 1, a first longitudinal sidewall 2 and a second longitudinal sidewall 3, a rear transverse sidewall 6, first and second central transverse parts 4, 5, and a base plate 7. Each of the sidewalls 1, 2, 3, 6 and central transverse pads 4, 5 are to be arranged over the base plate 7. The front sidewall 1 is to be arranged along a front edge of the base plate 7, the first and second longitudinal sidewalls 2, 3 are to be arranged along opposing longitudinal edges of the base plate 7, and the rear transverse sidewall 6 is to be arranged along a rear edge of the base plate 7 so as to oppose the front transverse sidewall 1. The central transverse parts 4, 5 are arranged parallel to the front and rear transverse sidewalls 1, 6, and are each about halfway between the front and rear transverse sidewalls. The central transverse pad 4 is arranged to extend perpendicularly from the second longitudinal sidewall 3 towards the centre of the tray, and the central transverse pad 5 is arranged to extend perpendicularly from the first longitudinal sidewall 2 towards the centre of the tray. A small gap is left between the central transverse parts 4, 5 at the centre of the tray to allow for connections to be made between the front and rear halves of the tray, defined by the central transverse pads 4, 5.

The shape of each individual reinforced thermoplastic part can be seen more clearly in Figure 3. The base plate 7 is a substantially flat rectangular plate. The base plate 7 has a flat central region 7a and shallow raised lip 7b, 7c along each of its longitudinal edges.

The front sidewall 1 has a vertical wall la arranged to extend perpendicularly away from the base plate 7, and flat base portion lb extending perpendicularly away from the vertical wall la towards the centre of the base plate 7 and configured to engage the front edge of the central region 7a of the base plate 7. The upper edge of the vertical wall 1a has a small projection lc extending perpendicularly away from vertical wall and away from the centre of the base plate 7 so that it extends in the opposite direction to the flat base portion 1 b. This small projection is provided along the upper edge of the wall, except for in a central region of the front sidewall part 1.

The rear sidewall 6 has substantially the same shape as the front sidewall 1, with a vertical wall 6a, flat base portion 6b, and upper projection 6c and is arranged in mirrored relationship with the front sidewall 1 along the rear edge of the central region 7a of the base plate 7. The rear sidewall 6 differs from the front sidewall 1 in that it is provided with a narrow central notch 6d provided through the base portion 6b and the lower half of the vertical wall 6a to allow connections to be made through the rear wall of the final assembly.

The first longitudinal sidewall 2 also has a vertical wall 2a arranged to extend perpendicularly away from the base plate and a flat base portion 2b extending perpendicularly away from the vertical wall 2a away from the centre of the base plate 7 and configured to engage the base plate 7 along the shallow raised lip 7c. The first longitudinal sidewall 2 also has a small projection 2c extending perpendicularly away from the vertical wall 2a and away from centre of the base plate 7 so that it extends in the same direction as the flat base portion 2b.

The second longitudinal sidewall 3 has the same shape as the first longitudinal sidewall 2, comprising a vertical wall 3a, flat base portion 3b and a small projection 3c. The second longitudinal sidewall 3 is arranged in mirrored relationship with the first longitudinal sidewall 2 and extends along the shallow raised lip 7b.

The central transverse parts 4, 5 each have the same shape, comprising an elongate flat base portion 4b, 5b, configured to engage the base plate 7and opposing vertical wall portions 4a, 4c, 5a, 5c extending away from the flat base portion 4b, 5b. Each central transverse part 4, 5 thereby has a generally U-shaped profile in cross-section.

Each of these reinforced thermoplastic parts 1-7 is formed of fibre-reinforced polypropylene. In particular, each reinforced thermoplastic part 1-7 comprises continuous carbon fibres extending along substantially the full length of the part. For the base plate, the continuous carbon fibres extend along the longitudinal direction of the base plate, i.e. parallel to the longitudinal sidewalls 2, 3. For the first and second longitudinal sidewalls 2, 3, the continuous carbon fibres likewise extend along the longitudinal direction of the tray, which corresponds to the long direction of the longitudinal sidewalls 2, 3. For each of the front and rear transverse sidewalls and the central transverse parts 4, 5, the continuous carbon fibres extend along the transverse direction of the tray, which corresponds to the long direction of those parts. The reinforced thermoplastic parts 1-7 may be manufactured by providing continuous fibre preforms in respective moulds before injecting the polypropylene matrix to form the part.

With the reinforced thermoplastic parts 1-7 provided, in step S200, each of these parts is heated with infrared or UV radiation. In this embodiment, the whole of each reinforced thermoplastic part 1-7 is heated by bathing the whole part in infrared or UV radiation. However, in other embodiments, targeted areas of the reinforced thermoplastic parts 1-7 may be heated. In particular, the important areas that must be heated are the lower faces of the base portions lb, 2b, 3b, 4b, 5b, 6b of each of the sidewall and central transverse parts 1-6, and the corresponding regions of the upper surface of the base plate 7. The parts are heated so that at least the lower faces of the base portions 1 b, 2b, 3b, 4b, 5b, 6b are above the polymer melting point.

In step S300, each of the heated reinforced thermoplastic parts 1-7 is arranged in a set of overmoulding tools. This comprises firstly loading the sidewall and central transverse parts 1-6 in an upper overmoulding tool 10, as shown in Figure 4. The upper overmoulding tool 10 comprises a main body tool part 11 and first and second side tool parts 12, 13. With the first and second side tool parts 12, 13 removed from the main body tool part 11, the first longitudinal sidewall part 2 may be arranged on the first side tool part 12, which may then be closed with the main body tool part 11 so as to hold the first longitudinal sidewall part 2 in its own channel in the upper tool so that its base portion 2b is exposed and faces away from the upper overmoulding tool 10. Likewise, the second longitudinal sidewall part 3 may be arranged on the second side tool part 13, which may then be closed with the main body tool part 11 so as to hold the second longitudinal sidewall part 3 in its own channel in the upper tool so that its base portion 3b is exposed and faces away from the upper overmoulding tool 10. In some embodiments, the front and rear sidewalls 1, 6 and the central transverse parts 4, 5, may be inserted into the main body tool part 11 of the upper overmoulding tool 10 along a direction perpendicular to the main body tool part 11 so that the lower face of their base portions 3b, 4b, 5b, 6b are exposed and face away from the upper overmoulding tool 10. This limits the shape of the resulting moulded structures to those that can be demoulded along the direction perpendicular to the main body tool part. In other embodiments, front and rear sections of upper tool may be provided by separate front and rear side tool parts that can be separated in a similar manner to the first and second side tool parts. This would allow the front and rear sidewalls 1, 6 to be arranged on the front and rear side tool parts, which would then be closed against the main body tool part to hold the front and rear sidewalls 1, 6 in respective channels, in a similar manner to that shown and described for the longitudinal sidewall parts 2, 3. This allows more shapes to be formed by the front and rear sidewalls, as it allows demoulding to be performed by removing the front and rear side tool parts.

Figures 5A and 5B show cross-sections through a portion of the upper sealing tool 10, showing the second side tool part 13 spaced away from the main body tool part 11 in Figure 5A and closed to the main body tool part in Figure 5B. As illustrated here, the main body tool part 11 and second side tool part 13 have complementary shapes, such that the second longitudinal sidewall part 3 may be placed on the second side tool part 13 and such that when the second side tool part 13 is moved along the direction perpendicular to the length of the second longitudinal sidewall part 3, it closes against the main body tool part 11. In this closed arrangement, a lower face of the base portion 3b is exposed and faces away from the upper tool 10. The lower face 3d is highlighted in Figure 5B, as this corresponds to one of the joining surfaces described above, which is to be pressed against the base plate to form a weld joint.

The overmoulding tool generally defines spaces 30 within the tool that will form the overmoulded assembly structure. Whereas Figure 4 does not show the spaces 30 within the tool that will form the overmoulded assembly structure, Figures 5A and 5B show a set of these spaces for defining features of the overmoulded assembly structure. This includes a space 32 defined generally between the main body tool part 11 and the second side tool part 13 that surrounds the second longitudinal sidewall part 3 so that the second longitudinal sidewall part 3 is to be encapsulated in the overmoulded material. These Figures also show openings 31 into the main body tool part 11 that will form vertical walls in an overmoulded floor structure that will be described later. While Figures 5A and 5B show the interaction between the main body tool part 11 and the second side tool part 13, it will be appreciated that the main body tool part 11 interacts similarly with the first side tool part 12 on the opposite side.

Step S300 also includes arranging the base plate 7 in the lower overmoulding tool 20, which comprises only a unitary lower overmoulding tool part 21 that has a complementary shape the base plate 7, i.e. being generally flat except for raised regions that match the shallow lip portions 7b, 7c. Figure 6 shows the lower overmoulding tool 20 opposite the upper overmoulding tool in an open configuration. Figure 7 shows a cross-section through the lower overmoulding tool part 21 loaded with the base plate 7. In Figure 7 an upper face 7d of the shallow lip portion 7b is highlighted, as this corresponds to one of the joining surfaces described above, which is to be pressed against the lower face 3d of the base portion 3b of the second longitudinal sidewall part 3 to form a weld joint.

In step S400, the lower overmoulding tool 20 is closed with the upper overmoulding tool 10, as shown in Figure 8, by moving the lower overmoulding tool 20 along a direction perpendicular to the plane of the base plate 7. This closing of the overmoulding tools presses the reinforced thermoplastic parts together. In particular, this presses the base portions 1b, 2b, 3b, 4b, 5b, 6b of each of the sidewall and central transverse parts 1-6 against corresponding areas of the base plate 7. Because the reinforced thermoplastic parts 1-7 were heated in step S200 and are now being pressed together, the raised temperature and pressure is sufficient to weld each of the each of the sidewall and central transverse parts 1-6 to the base plate 7.

Figure 9 is a cross-section through the same parts of the tools shown in Figures 5A, 5B and 7, but now showing the tools in the closed position, as shown in Figure 8. This Figure clearly shows the pressing together of the the lower face 3d of the base portion 3b of the second longitudinal sidewall part 3 with the upper face 7d of the shallow lip portion 7b of the base plate 7 to form a weld joint at those two faces. The spaces 30 defined by the overmoulding tools can also be seen in these Figures. As indicated above, the spaces in the overmoulding tools include a space 32 that substantially surrounds the second longitudinal sidewall part 3 so as to substantially encapsulate this in overmoulded material. This encapsulation of the second longitudinal sidewall part 3 also substantially encapsulates the welded joint formed between the lower face 3d of the base portion 3b and the upper face 7d of the shallow lip portion 7b and provides overmoulded material that bridges across between the inner face of the vertical wall 3a and the upper face of the base plate 7, as well as material that encapsulates the outer edge of the base portion 3b and the outer edge along the shallow lip portion 7b. It should be noted that parts of the upper overmoulding tool 10 may need to engage with the second longitudinal sidewall part 3 so as to press the second longitudinal sidewall part 3 against the base plate, and so the second longitudinal sidewall pad 3 may not be completely surrounded by spaces 30 in the overmoulding tools. For example, the upper overmoulding tool may be configured to engage the upper surface of the base portion 3b at opposing ends of the second longitudinal sidewall part 3 along its length direction in order to press the second longitudinal sidewall pad 3 against the base plate 7.

With the overmoulding tools closed and defining spaces 30 within the tools, in step S500 overmoulding material is injected into the tools in order to overmould an assembly structure onto the reinforced thermoplastic pads. In this embodiment, the overmoulding material is a fibre-reinforced polypropylene having carbon fibres of length approximately 5 mm.

Figure 10 shows the final assembly 100 after removal from the overmoulding tools 10, 20. The assembly here is a tray for a battery enclosure of an electric vehicle. The generally structure of the tray is defined by the reinforced thermoplastic parts 1-7, as described above with reference to Figures 2 and 3. Figure 10 additionally shows the assembly structure 130 that has been overmoulded onto the reinforced thermoplastic parts.

The overmoulded assembly structure 130 includes an array of vertical walls 131 defined by the spaces 31 of the overmoulding tools. This array of vertical walls 131 defines an array of open hexagonal cells having a honeycomb-like structure extending across the upper face of the central portion 7a of the base plate 7. These open hexagonal cells provide a floor of the tray on which battery modules may sit so that they are lifted off the base plate 7.

The overmoulded assembly structure 130 also includes overmoulded material substantially encapsulating the sidewall pads 1, 2, 3, 6 and defining a continuous sidewall 132 of the tray. This continuous sidewall 132 includes corner portions 137, which bridge between the edges of the longitudinal sidewalls 2, 3, and the transverse sidewalls 1, 6. The overmoulding material also includes encapsulating material 133 extending over the upper face of the base portion 2b, 3b of the longitudinal sidewalls 2, 3, and around the longitudinal edges of the base portion 2b, 3b and the lip portions 7b, 7c of the base plate 7 to encapsulate the weld joint.

Additionally, the overmoulded assembly structure 130 includes encapsulating portions 134, 135 that substantially encapsulate the first and second central transverse pads 4, 5. These encapsulating portions 134, 135 meet the encapsulating material forming the sidewalls 132 along the longitudinal side of the tray and so bridge between the longitudinal sidewalls 2, 3 and the first and second central transverse parts 4, 5. Although not shown in Figure 10, the overmoulded material may additionally extend between the first and second central transverse parts 4, 5 to form a reinforced central cross member that may effectively transmit impact forces between the sidewalls to protect the battery modules provided in the tray.

Finally, the overmoulded assembly structure 130 includes a plurality of transverse ribs 136. These transverse ribs are formed only by overmoulded material and extend between the opposing overmoulded sidewalls 132 encapsulating the reinforced thermoplastic longitudinal sidewalls 2, 3. These ribs 136 further help to transmit impact forces between the opposing overmoulded sidewalls 132 to shield the contents of the tray from impact, and also separate battery modules from one another within the battery tray.

The battery tray shown in Figure 10 will generally be closed by a lid provided over the tray, which may be secured by nuts and bolts to the upper peripheral flange provided by the overmoulded sidewalls 132, for example. Generally, attachment devices or "inserts" must be provided in the overmoulded thermoplastic prevent the mechanical fasteners from damaging the thermoplastic material. While these inserts could be provided by machine processes performed after removal of the tray from the overmoulding tool, it is preferred that the inserts be incorporated into the overmoulded material as part of the overmoulding process. Figure 11 illustrates a way that these inserts may be incorporated into the overmoulded material.

Figure 11 shows the same cross-section as Figure 9 but differs therefrom in that it shows the arrangement of an insert 8 in the upper overmoulding tool 10. In particular, the second side tool part 13 is shown to have been provided with a recess 38 for receiving an insert. This recess is arranged so that it is formed adjacent to the edge of the projection 3c extending perpendicularly away from the vertical wall 3a of the longitudinal sidewall part 3. The recess extends vertically, substantially parallel to the vertical wall 3a, and holds an insert 8 so that its threaded hole extends substantially vertically. Space is provided around the insert 8 by the recess 38 while the opening into the threaded hole of the insert is closed by the main body part 11 of the upper overmoulding tool. In this way, when the overmoulded material is injected into the space 30 inside the overmoulding tools 10, 20, the overmoulded material surrounds the vertical sides of the insert, embedding the insert in the overmoulded sidewall 132 and holding the insert in a fixed position relative to the longitudinal sidewall part 3. It will be appreciated that an array of such inserts 8 are provided in corresponding recesses along the first and second side tool parts 12, 13 in order to provided an array of inserts along the longitudinal overmoulded sidewalls 132. Inserts could also be provided along the transverse overmoulded sidewalls 132.

While the inserts here have been described as being arranged in the overmoulded sidewalls 132, it would also be possible to provide the inserts overmoulded into the encapsulating portions 134, 135 that substantially encapsulate the first and second central transverse parts 4, 5, or into the upper edges of the overmoulded ribs 136 by providing corresponding recesses in the appropriate areas of the upper overmoulding tool 10 for receiving the inserts 8 and for overmoulding material around those inserts.

Claims

CLAIMS1. A method of forming an assembly using thermoplastic parts, the method comprising: providing a plurality of separate thermoplastic parts; heating one or more of the thermoplastic parts along at least one or more joining surfaces of the thermoplastic parts; arranging the plurality of thermoplastic parts in at least two separate overmoulding tools; closing the at least two overmoulding tools and thereby pressing the thermoplastic parts together at the one or more joining surfaces to weld thermoplastic parts together; and overmoulding an assembly structure onto the thermoplastic parts using the at least two overmoulding tools.
2. A method according to claim 1, comprising heating at least two of the thermoplastic parts along at least respective joining surfaces, and closing the at least two overmoulding tools and thereby pressing said thermoplastic parts together at their respective joining surfaces to weld thermoplastic parts together
3. A method according to claim 1 or claim 2, comprising providing one primary thermoplastic part and providing a plurality of secondary thermoplastic parts, arranging the primary thermoplastic part in a first of the at least two separate overmoulding tools and arranging the plurality of secondary thermoplastic parts in one or more other of the at least two overmoulding tools, closing the at least two overmoulding tools and thereby pressing each secondary thermoplastic part together with the primary thermoplastic part at respective one or more joining surfaces.
4. A method according to any of the preceding claims, wherein heating one or more of the thermoplastic parts is performed before the respective thermoplastic part has been arranged in one of the overmoulding tools.
5. A method according to any of the preceding claims, comprising heating one or more of the thermoplastic parts using infra-red or ultraviolet radiation.
6. A method according to any of the preceding claims, comprising heating substantially the whole of one or more of the thermoplastic parts.
7. A method according to any of the preceding claims, wherein one or more of the thermoplastic parts comprises a reinforced thermoplastic part.
8. A method according to any of the preceding claims, wherein one or more of the thermoplastic parts comprises a thermoplastic composite part.
9. A method according to any of the preceding claims, wherein one or more of the thermoplastic parts comprises a fibre-reinforced thermoplastic part, preferably fibre-reinforced polypropylene.
10. A method according to claim 9, wherein one or more of the thermoplastic parts comprises fibres having a length of at least 20 mm, preferably at least 50 mm, more preferably at least 100 mm, most preferably at least 200 mm.
11. A method according to claim 9 or claim 10, wherein one or more of the thermoplastic parts comprises continuous fibres extending along at least 50% of the length of the thermoplastic part along the direction of the continuous fibres, preferably along 70%, more preferably along 80%, more preferably along 90% of the length of the thermoplastic part along the direction of the continuous fibres, wherein more preferably the continuous fibres extend along substantially the entire length of the thermoplastic part along the direction of the continuous fibres.
12. A method according to any of claims 9 to 11, wherein the fibres comprise glass fibres, carbon fibres and/or aramid fibres.
13. A method according to any of the preceding claims, wherein each thermoplastic part comprises the same thermoplastic material or the same major component thermoplastic material, preferably polypropylene.
14. A method according to any of the preceding claims, comprising overmoulding an assembly structure using a thermoplastic material.
15. A method according to claim 14, wherein the overmoulded thermoplastic material comprises the same thermoplastic material or the same major component thermoplastic material as one or more of the thermoplastic parts.
16. A method according to claim 14 or claim 15, comprising overmoulding an assembly structure using a fibre-reinforced thermoplastic material.
17. A method according to claim 16, wherein the overmoulded fibre-reinforced thermoplastic material comprises fibres having a length of at least 1 mm, preferably at least 5 mm, more preferably at least 10 mm, most preferably at least 20 mm.
18. A method according to any of the preceding claims, comprising overmoulding parts of the assembly structure onto a plurality of the thermoplastic parts.
19. A method according to any of the preceding claims, wherein overmoulding an assembly structure onto the thermoplastic parts comprises substantially encapsulating one or more of the thermoplastic parts.
20. A method according to any of the preceding claims, wherein overmoulding an assembly structure onto the thermoplastic parts comprises overmoulding a bridging surface extending between at least two of the thermoplastic parts.
21. A method according to any of the preceding claims, wherein overmoulding an assembly structure onto the thermoplastic parts comprises substantially encapsulating a region surrounding the weld between the thermoplastic parts.
22. A method according to any of the preceding claims, further comprising providing one or more attachment devices for receiving a mechanical fastener and overmoulding the assembly structure onto the one or more attachment devices, wherein preferably the one or more attachment devices each has a threaded hole for receiving a machine screw or bolt.
23. A method according to any of the preceding claims, wherein the assembly defines all or part of a battery enclosure for an electric vehicle, preferably a tray for a battery enclosure of an electric vehicle.
24. A method according to claim 23, wherein one or more of the plurality of thermoplastic parts at least partially define one or more of a base of the battery enclosure and one or more sidewalls of the battery enclosure, wherein preferably the plurality of thermoplastic parts at least partially define at least the base of the battery enclosure and two opposing sidewalls of the battery enclosure.
25. A method according to claim 23 or claim 24, wherein the assembly structure comprises one or more overmoulded ribs extending between opposing sidewalls of the tray.
26. A method according to any of claims 23 to 25, wherein the assembly structure comprises a floor of the battery enclosure defined by an array of walls perpendicular to a base of the battery enclosure, preferably defining an array of open cells.
27. An assembly comprising: a plurality of thermoplastic parts joined together by a weld joint; and an assembly structure overmoulded onto the thermoplastic parts.
28. An assembly according to claim 27, manufactured using a method according to any of claims 1 to 26.