STRUCTURES FORMED THEREBY

The present invention relates to methods of forming bonded structures. It also relates to bonded structures, vehicles including such bonded structures and methods of manufacturing vehicles such as automotive vehicles, land vehicles and motor cars. The invention may also be applied in fields outside the automotive arena.

A known method of forming a bonded structure comprises providing a substrate, applying adhesive to the substrate, and then moving a second substrate into contact with the adhesive in order to bond the substrates together. A problem with this method is that with complex joint geometries, it is often difficult to control the amount of adhesive to be used and adhesive wastage may occur when adhesive may be squeezed from between the substrates. The process can also be time consuming, costly and a potential bottleneck in a production line.

The present invention aims to alleviate at least to a certain extent at least one of the problems of the prior art, or to provide a useful or improved bonding method and bonded structure.

According to a first aspect of the present invention, there is provided a method of forming a bonded structure comprising:

providing a first substrate and a second substrate;

providing a containment means at least partially around a region between the first and second substrate; and

adding a first adhesive into the said region bounded by the first, the second substrate and the containment means.

By the provision of a containment means, the first adhesive is contained or restrained to a defined region between the first and second substrate. This avoids leakage of the first adhesive. This also reduces the need to clean the bonded structure after the first adhesive has cured. In addition, the method avoids the wasting of adhesive and its associated cost and thereby optimises the use of materials. The containment of the first adhesive can also serve to facilitate handling of the bonded structure, and improve cleanliness and efficiency in the manufacturing environment.

By using the method of the present invention, the quantity and location of the first adhesive can be controlled in the bonded structure. This helps to ensure the reproducibility of the bonded structure and accuracy in the addition of the first adhesive. As such, the reliability or repeatability, for example, in terms of the strength of the resultant bond or structural integrity of bonded structures produced by the method can be improved. The engineering robustness of structures formed using the method can therefore be improved.

The containment means is preferably disposed between the first and second substrate. The first adhesive may preferably bond the first and second substrate together to form the bonded structure.

The substrate material may be a metal alloy, for example aluminium alloy or an anodised aluminium material, a composite material such as a material comprising fibres and resin or a laminated composite or plastics material. The substrate materials are preferably fully or substantially fully cured before the provision of the containment means or the addition of the adhesive into the region between the substrates. The first or second substrates materials may be formed of multiple parts. Additional substrates may be provided which bound the said region.

Preferably, the containment means provides a seal which extends, preferably fully, between the first substrate and the second substrate. Preferably, the containment means is a separate part, i.e. not formed integrally with the first and second substrate materials. The containment means may provide a fully enclosed region between the first and second substrate materials. Whether the containment means extends fully between the two substrates will be dependent on the nature of the first adhesive, for example its viscosity and the arrangement of the containment means may be advantageously chosen depending on the bonded structure and the adhesive being employed. Preferably, the containment means is provided on a surface of the first and/or second substrate. The containment means may be provided on a surface of either of the substrate materials, preferably the surfaces facing the region in which the adhesive is to be added or injected. Alternatively, the containment means may be provided as two parts, one part being provided on the surface of one substrate and the other part being provided on the surface of the other substrate. The containment means may be formed of a flexible material which can form or adapt to undulations or imperfections in the substrate materials. Advantageously, therefore, the containment means can take up tolerances or variations in the spacing between the substrates.

The containment means may be formed or applied with any suitable cross section, for example, substantially circular, square or with one or more stepped edges. The containment means may be provided as discrete blobs of material. Preferably, the containment means extends fully around the said region. Preferably, the containment means extends around the perimeter of one or more of the first and second substrates. In this way a fully enclosed region is provided between the first and the second substrate materials into which the adhesive may be added. This advantageously may prevent the ingress of water or other environmental pollutants into the structure and thereby may reduce the likelihood of corrosion in the completed structure.

An aperture may be provided in one or both of the substrates to be bonded, through which an adhesive injector in the form of a nozzle may be inserted. A vent hole may also be provided. The vent hole may be provided spaced from the aperture in the substrate. The vent hole could also be provided in the containment means such that air may flow through the vent hole, but the adhesive, due to its greater viscosity may not. Preferably, the containment means is adhered to a least one of the first or second substrates. The containment means may be formed of a separate part, for example formed of any suitable material such as plastics or metal. The containment means may be provided with an adhesive to adhere the containment means to one of the first or second substrates to maintain the containment means in position while the adhesive is added.

Preferably, the containment means comprises a second adhesive. The second adhesive may be applied to one of the substrates before the addition of the first adhesive such that the second adhesive may be allowed to at least partially cure before the addition of the first adhesive. The second adhesive may be formed of the same adhesive as the first adhesive. The second adhesive may be of greater or higher viscosity in an uncured state than the first adhesive in its uncured or cured state. The second adhesive may have a greater or higher yield stress in an uncured state that the first adhesive in its uncured state or cured state.

Preferably, the second adhesive is configured to cure faster than the first adhesive. In this way, the first adhesive may be added directly after the provision or application of the containment means.

The containment means may be applied around the perimeter or edge of the first and or second substrate. Alternatively, a defined geometry may be formed by the containment to provide one or more regions of predefined shape or area, depending on the bond properties required, into which the first adhesive may be added.

Preferably, the first and second substrates are held in spaced relationship while the first adhesive is added. Preferably, this holding of the substrates or parts may be by the use of rivets or other fixing means or may be by the use of a jig or a robot/automated handling means.

Preferably, the substrates are arranged in position after the containment means has been provided or applied to one of the first or second substrates. As an alternative, the containment means may be applied or provided after the substrates have been arranged in position.

Preferably, the first substrate and/or second substrate have/has a substantially flat or planar surface facing the region in which the first adhesive is added. The surfaces may be substantially parallel. The first adhesive may be injected until it completely fills the region or volume bounded by the first and second substrate and containment means. The spacing between the substrates may be chosen depending on, for example, the performance or strength desired in the bonded structure and the first adhesive material. The spacing may be constant or may vary. The spacing or gap may be constant or vary between about 1 mm to 10mm or so wide, 2 to 8mm, 4 to 6mm or between 0.05 and 3mm.

Preferably, one or both of the substrates may include an aperture through which an adhesive may be added or injected into the said region. Preferably, the first adhesive may be applied at a pressure of between 3 to 6 bar.

Preferably, the first and second substrates may be held in position until the first adhesive has cured. Alternatively, the substrates may be held in position until the second adhesive cures. Mechanical fixings may be used to hold the substrates in position.

The containment means may be provided around a perimeter of the first and/or second substrate or spaced from the perimeter of the first and/or second substrate.

Preferably, the containment means engages with the first and/or second substrate by relative movement between the substrates in a direction substantially perpendicular to a surface of the first and/or second substrate. This advantageously provides a forced seal between the substrates and the containment means.

Preferably, the containment means engages with the first and/or second substrate by relative movement between the substrates in a direction substantially parallel to a surface of the first and/or second substrate. Because the substrates may be brought into engagement with the containment means in varying ways, the method may be applied to different applications and handling methods.

Preferably, the containment means is configured to deform upon addition of the first adhesive. Preferably, the containment means deforms as a result of pressure of the addition of the first adhesive. The containment means may remain flexible, pliable and/or deformable upon addition of the first adhesive.

Preferably, the containment means deforms due to fluid movement or pressure build- up within the said region.

Preferably, the containment means is formed as a plastics material. Preferably, the containment means is provided with an adhesive to join or adhere it to one or more of the first or second substrates.

Preferably, the containment means is formed as a tape or strip of material. Preferably, the tape or strip is provided with an adhesive surface in order to adhere the containment means to one or both of the first and second substrates. Preferably, the strip of material is formed as a strip of folded membrane. The fold opening is preferably orientated to face the region in which the first adhesive is applied.

Preferably, the containment means is electrically conductive. In this way the containment means can provide a grounding connection between the first and second substrates.

Preferably, the containment means is formed of a material which is more flexible than the first adhesive once the first adhesive has cured. Preferably, the containment means, when it comprises a second adhesive, is more flexible when than the first adhesive when both the first and second adhesives are cured. In this way, stress concentrations in the bonded structure in the region of the containment means is reduced.

Preferably, the containments means may be applied or provided to at least one of the substrates before, simultaneously with or after the first adhesive portion.

Preferably, the containment means has extent perpendicular to the surface of the substrate to which it is provided, applied or adhered. Preferably, the first adhesive is injected into the region between the first and second substrates. Preferably, the first adhesive and second adhesive or containment means have different chemical compositions to one another. According to a further aspect of the invention, there is provided a bonded structure formed in accordance with the first aspect of the invention.

According to a further aspect of the invention, there is provided an automotive structure which consists of or includes as a part thereof a bonded structure formed in accordance with the first aspect of the invention.

Preferably, the automotive structure comprises an automotive bodyshell assembly, box section, chassis assembly, structural assembly, pillar, post or crash load absorption structure, or a panel structure, such as a door, roof, tonneau bow member, wing, fender, trunk/boot lid, hood/bonnet structure, ducting e.g. a cooling duct, container, e.g. a fuel tank, or an aerodynamic wing, diffuser, spoiler or air dam. The method is also applicable to bonded structures in other technical areas, such as aerospace. According to a further aspect of the invention, there is provided an automotive vehicle or a land vehicle, such as a motor car, which includes a structure according to any other aspect of the invention.

According to a further aspect of the invention, there is provided a method of manufacturing an automotive vehicle or a land vehicle, such as a motor car, which includes the step of forming a bonded structure in accordance with any other aspect of the invention.

The present invention may be carried out in various ways and a number of preferred embodiments of forming bonded structures in accordance with the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figures 1 a and 1 b show substrates before and after being brought into sealing contact with containment means, here in the form of an adhesive;

Figure 2a shows substrates in spaced relationship before engagement with the containment means, here in the form of an adhesive;

Figure 2b shows the two substrates in sealing engagement with the containment means with an adhesive being injected between the two substrates;

Figures 3a and 3b show substrates being slid towards one another to engage with containment means, here in the form of an adhesive;

Figure 4 shows adhesive present between two substrates and a corresponding diagram showing the stress concentration in relation to the distance along the joint;

Figures 5a and 5b show an alternative containment means, in the form of a folded strip of material;

Figures 6a and 6b show the moulded containment means, here in the form of a strip of material before and after injection of adhesive between the two substrates.

In Figure 1 a, a lowermost substrate 1 is shown. The lowermost substrate 1 may be formed of a material such as aluminium alloy, anodised aluminium material, or a composite material such as a material comprising fibres and resin or a laminated composite or plastic material.

On one surface 1 a of the lowermost substrate 1 , a containment means is applied. In the example shown, the containment means is provided as a strip of adhesive applied and adhered to a surface 1 a of a lowermost substrate 1.

The adhesive is shown schematically in the form of a strip of material 3a, 3b with a rectangular cross section. However, the adhesive may be applied in blobs or as a continuous bead along the surface of the lowermost substrate 1 with any desired cross-section such as circular or square or with a stepped edge.

As shown in Figure 1 a, the containment means in the form of the adhesive is provided in strips 3a, 3b which are spaced on the surface 1 a of the lowermost substrate 1 in order to provide an enclosed region 9 there between. An uppermost substrate 2, which in Figure 1 a is shown as a planar sheet, is brought towards the lowermost substrate 1 in a direction substantially perpendicular to the surfaces 1 a, 2a of the lowermost substrate 1 and uppermost substrate 2. The uppermost substrate 2 may be formed of materials similar to or different to the lowermost substrate 1 .

As shown in Figure 1 b, as the uppermost substrate 2 is brought into engagement the containment means 3a, 3b, the uppermost substrate 2 engages and is forced into, i.e. embeds, in the adhesive 3a, 3b.

When the uppermost substrate 2 and the lowermost substrate 1 are brought into a proximate arrangement in which the uppermost substrate 2 engages with the containment means 3a, 3b, an enclosed region 9 is formed or bound between the two substrates. The spacing between the uppermost substrate 2 and the lowermost substrate 1 may be chosen depending on the joint gap required, but may typically be between 0.05mm and 3mm.

The containment means, here in the form of the adhesive strips 3a, 3b, is applied to the lowermost substrate. The adhesive adheres to the surface 1 a of the lowermost substrate 1. The adhesive extends perpendicular to the substrate surface and is compliant and is deformable and will take up variations in surface quality and tolerances of the surface 1 a of the lowermost substrate 1 . In Figure 2a, a variation of the containment means of Figures 1 a and 1 b is shown wherein the adhesive strip is formed with a stepped edge on its edge facing the uppermost substrate 2. This stepped edged facilitates the matching or joining of the uppermost substrate 2 which is then brought in proximate arrangement with the lowermost substrate 1 , for example by using automated handling means. In Figure 2a, it can be seen that the uppermost substrate 2 is provided with a substrate aperture 7 through which an adhesive injector 4 can be inserted such that the outlet of an injector nozzle 6 may be located within the region 9 bounded by the lowermost substrate 1 and the uppermost substrate 2. As shown in Figure 2b, the uppermost substrate has been forced into engagement with the containment means 3b, such that a closed region 9 is formed or bound between the uppermost substrate 2 and the lowermost substrate 1 .

In order to maintain the uppermost substrate 2 and the lowermost substrate 1 in a spaced relationship, a jig or other holding means may be used. Alternatively, the uppermost substrate and the lowermost substrate may be held in spaced relationship using a robot or other automated handling means.

In Figure 2b, an adhesive 5 has been injected through the adhesive injector 4 and out through the injector nozzle 6 into the region 9 between the lowermost substrate 1 and the uppermost substrate 2. Before it cures or sets, the adhesive is fluid and flows within the region 9 towards the containment means 3b. The containment means 3b therefore serves as a barrier and contains the adhesive within the region 9.

In order to facilitate the flow of the adhesive within the region 9, a bleed-hole may be provided (not shown in the Figures) to allow air trapped within the region 9 to be expelled as the adhesive 5 is injected.

The material used for the containment means 3a, 3b may be the same adhesive material as the adhesive injected between the uppermost substrate 2 and the lowermost substrate 1 . If the same adhesive is used, typically the adhesive for the containment means 3a, 3b would be allowed to cure at least partially before the adhesive is injected through the adhesive injector 4.

Alternatively, the adhesive used for the containment means 3a, 3b may be a material or an adhesive which has a faster curing rate than the adhesive which is injected through the adhesive injector. If the containment means is a solid material such as a plastics material, it need only be adhered to one of the substrate surfaces. In this way, the steps of the method for producing the bonded structure may be carried out in rapid succession. The adhesive material which is injected through the adhesive injector and also the adhesive which is used for the containment means may be any type of suitable adhesive or other adhesive material, such as a epoxy resins, acrylics, methyl evaporates or other types of contact adhesive.

The containment means may be applied to the substrates using automated means, for example, a robot, or alternatively may be manually applied.

In Figures 3a and 3b an alternative procedure and arrangement is shown for producing the seal between the uppermost substrate 2 and the lowermost substrate 1. In Figure 3a, the lowermost substrate 1 is provided with a containment means in the form of adhesive strip 3b applied to its uppermost surface 1 a.

The uppermost substrate 2 has an adhesive strip 3a to provide the containment means. The lowermost substrate 1 and the uppermost substrate 2 are brought into engagement via the containment means 3a, 3b, by sliding the uppermost substrate 2 and the lowermost substrate 1 relative to one another in a direction substantially parallel to the surfaces 1 a, 2a of the lowermost substrate 1 and the uppermost substrate 2 respectively.

The material used for the containment means 3a, 3b may be a material which cures to form a substantially rigid adhesive connection between the lowermost substrate 2 and the uppermost substrate 1 . Alternatively, the material of the containment means 3b may be a material or an adhesive which is relatively flexible in its cured state relative to the material of the substrates. In this way, the material exhibits improved toughness and energy absorption properties than the adhesive which is injected into the region 9 between the substrate. With such an arrangement, the containment means not only provides a way to prevent leakage of the adhesive which is injected between the substrates 1 , 2 but this also then serves as a stress reducer along the joint edges of the substrates thereby improving overall joint performance.

In Figure 4, a chart is shown in which the relationship between stress concentration and distance along the joint is shown for a convention bonded joint relative to the joint of the present invention. The line 10 shows the stress variation in a conventional bonded joint and line 1 1 shows the stress variation in the proposed bonded joint of the present invention. The containment means may be provided in any desired shape and can be applied as a bead or tape along the edge between the lowermost substrate 1 and the uppermost substrate 2. The containment means may be any suitable material such as plastics or metal and is chosen depending on the application. Because the containment means, for example an adhesive material, which is applied to the substrates is deformable, or flexible in nature, it can deform to take account of rough bond surfaces on the substrate, or variations or imperfections in the spacing between the substrates. Furthermore, because the containment means is flexible and deformable, the containment means can deform or adapt to deformations in the substrate surfaces during curing. The containment means can also act as a local means of fixing between the substrates before and during the cure of the adhesive which is injected into the region 9 between the substrates 1 , 2.

The material of the containment means may be chosen such that it does not irritate skin, for example by being formed of a high molecular weight material. The containment means can therefore provide a useful environmental barrier to the adhesive which is injected between the substrates 1 , 2 into the region 9. In this way, the bonded substrate is more readily handled.

The use of the containment means also serves to reduce leakage of adhesive which is injected into the region 9 between the substrates and thereby reduces the need to clean the parts after the bond has been made. Once cured, the containment means can also serve as an environmental barrier to the ingress of environmental pollutants/contaminants such as water which could corrode or otherwise affect the integrity of the bond structure. The use of the containment means serves to avoid smearing of adhesive which can result in conventional methods for forming bonded structures. The amount of first adhesive can be more effectively controlled using the method of the present invention. In addition, in the manufacture of components the bond structure can be more reliably and repeatably formed in each component.

Figures 5a and 5b show an alternative containment means. In Figure 5a, the containment means is provided as a folded strip which extends along the edge of the surface 1 a of the lowermost substrate 1 . Corresponding containment means 8b is provided spaced from the containment means 8a to provide a region 9 therebetween.

As a result of the injection of adhesive into the region 9 between the substrate 1 , 2, the folded strips 8a, 8b are forced into engagement with the adjacent substrate surface, here the surface 2a of the uppermost substrate 2.

In Figure 6a, the uppermost substrate is shown provided with an aperture through which an adhesive injector 4 may be inserted with an injector nozzle 7 which extends into the region 9 between the lowermost substrate 1 and the uppermost substrate 2. The containment means 8b, here in the form of a folded strip 8b, may be provided as a metallic strip of material. The metallic strip may be adhered to the uppermost surface 1 a of the lowermost substrate 1 using an adhesive. The fold opening 12 of the containment means 8b faces towards the innermost section of the region 9 between the substrates 1 , 2.

In Figure 6b, as the fluid adhesive 5 is injected into the region 9 between the lowermost substrate 1 and the uppermost substrate 2, the flow of fluid, here air and/or adhesive 5 causes the folded seal to be deformed in order that it engages with the uppermost substrate 2.

The strip material may be formed as a folded membrane and could be formed to be electrically conductive in order to provide grounding across the joints with the lowermost substrate 1 and the uppermost substrate 2. In particular, the containment means 8a, 8b may be provided as a single sided metallic tape.

In the case of the containment means being provided in the form of an adhesive material, the adhesive may have superior ultimate tensile strength, Young's modulus, yield strength, compressive strength, impact strength, fracture toughness, fatigue cycling performance, vibration resistance, and/or vibration damping, chemical resistance, temperature resistance and/or thermal shock resistance than the adhesive which is injected into the region 9 between the lowermost substrate 1 and uppermost substrate 2.

Once the adhesive which has been injected between the first and second substrates has cured, it is possible that the containment means may be configured to be removed. Alternatively, the containment means may form part of the final bonded structure.

The method may be applied to and bonded structure may be part of a motor vehicle construction, for example box structures. The method may also be applied in other technical areas.

Although in the embodiment shown, the substrates are shown as planar materials, the invention is applicable to substrates of varying geometries, forms and materials. It is envisaged that the skilled person in the art may make various changes to the embodiments specifically described above without departing from the scope of the invention.