METHOD AND SYSTEM FOR JOINING METAL COMPONENTS BY OVERMOLDING

FIELD OF THE INVENTION

[0001] The present invention relates to a method and system for joining metal components by overmolding. More specifically, the present invention relates to a method and system for joining two or more metal components by overmolding a portion of the metal components to form a structural and sealed connection between the metal components.

BACKGROUND OF THE INVENTION

[0002] It is known to make assemblies of metal components by riveting, through- bolting, welding or otherwise joining two or more metal components together to obtain the desired assembly. For example, gas tanks for vehicles are often formed from two stamped metal components which are joined together to form the hollow tank by riveting or welding.

[0003] While joining techniques such as riveting and through-bolting are widely employed, they can suffer from disadvantages. For example, if the joint between the metal components needs to be liquid-proof or airtight, such as with a gas tank, it is often required that a gasket or other resilient sealing member first be positioned between the components before the rivets or through bolts are fastened. [0004] A welded joint can often provide a sealed, structural joint without the need for a gasket, however welding can only be performed on particular metals, or combinations of metal, and is labor and/or time intensive to perform. For example, it is not possible to weld zinc die cast components, etc. Also, welding generally requires that the components to be joined have similar gauges. Further, the inevitable heating of the metal components when welding can damage treatments of the components, such as anticorrosion layers and/or hardening treatments, etc.

[0005] It is known to join and/or seal plastic components by overmolding additional plastic material onto the plastic components to form a structural and sealed seam. However, to date, it has not been possible to overmold metal joints onto metal components.

SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a novel method and system for joining metal components by overmolding which obviates or mitigates at least one disadvantage of the prior art.

[0007] According to a first aspect of the present invention, there is provided a method of joining at least two metal components into an assembly, comprising the steps of: forming a first metal component including a joining feature; forming a second component including a joining feature; loading the first metal component and the second metal component into a joining die, the first and second metal components being loaded into the joining die such that their respective joining features are in proximity to one another and are located in a joint cavity; and injecting a thixotropic material into the joint cavity of the joining die about the joining features of the first and second metal components to form a structural joint between the first and second metal components.

[0008] The present invention provides a novel system and method for joining metal components to form assemblies, the components having a metal joint overmolded onto them. The metal joint is overmolded from a thixotropic alloy, such as a magnesium- based alloy, which is injected into a joint cavity in a joining die into which the components to be joined are loaded. The joint is formed over and/or through flanges or other features provided on the components and results in a structural joint which can also be liquid and/or air tight. The system and method permit the joining of components formed of different materials, formed by different processes and./or formed of different gauge materials.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:

Figure 1 shows a portion of a perspective cross section of an assembly of components to be joined in accordance with the present invention;

Figure 2 shows a portion of a joining die into which the assembly of Figure 1 has been placed;

Figure 3 shows the joining die of Figure 2 after a joint has been overmolded on the components in accordance with the present invention;

Figure 4 shows one arrangement for providing a thixotropic material to the joining die of Figure 2;

Figure 5 shows an alternative arrangement for providing a thixotropic material to the joining die of Figure 2;

Figure 6 shows an alternative flange structure for the components of Figure 1 onto which a joint can be overmolded in accordance with the present invention;

Figure 7 shows a portion of a perspective cross section of the resulting joint molded onto the components of Figure 6; and

Figure 8 shows a cross section through a portion of an assembly of components to be joined in accordance with the present invention wherein the components include a flash inhibiting feature.

DETAILED DESCRIPTION OF THE INVENTION

[0010] A portion of an assembly of metal components to be joined is indicated generally at 20 in Figure 1. As shown assembly 20 comprises a lower component 24 which is generally dish-shaped and which includes a flange 28 about its outer periphery. Assembly 20 further includes an upper component 32 which is also generally dish-shaped and which also includes a flange 36 about its periphery. [0011] Lower component 24 and upper component 32 can be formed in any appropriate manner as will occur to those of skill in the art. For example, either or both of lower component 24 and upper component 32 can be formed by stamping, bending, molding, casting, etc. and the present invention is not limited to use with components manufactured by any particular process. In fact, one of the perceived advantages of the present invention is that the present invention can be used to join components manufactured with different processes. For example, upper component 32 can be formed by metal stamping while lower component 24 can be formed by die-casting. Further, the joined components of the present invention need not be formed of the same material and this permits, for example, a steel component to be joined with an aluminum component.

[0012] Flanges 28 and 36 preferably include joining features, such as through holes 40, which facilitate in forming a joint between the components of assembly 20, as described below.

[0013] As shown in Figure 2, components 24 and 32 are placed in a joining die 44 which, in the illustrated embodiment, comprises a bottom die half 48 and a top die half 52. Components 24 and 32 can be placed into position for joining and then placed into die 44 or lower component 24 can be loaded into lower die half 48 and upper component 32 can be loaded into upper die half 52 and die 44 can then be closed, bringing components 24 and 32 into position for joining.

[0014] As shown in the Figure, preferably, the cavities in each of lower die half 48 and upper die half 52 are sized and shaped such that a gap 56 is provided between die halves 48 and 52 and their respectively loaded components 24 and 32 so that the clamp force exerted on die 44 during the below-described molding operation is applied to the area of die halves 48 and 52 adjacent flanges 28 and 36 to be joined. When die 44 is closed, a joint cavity 60 is formed about the periphery of flanges 28 and 36 and any joining features, such as holes 40.

[0015] The present inventors have discovered that, by employing a thixotropic molding process, a structural joint can be formed in cavity 60 about flanges 26 and 36. In a presently preferred embodiment of the invention, a thixotropic magnesium-based alloy is injected into cavity 60 to form joint 64, as illustrated in Figure 3. While the present invention is not limited to use with any particular magnesium-based alloy, nor to the use of magnesium based alloys, examples of suitable alloys can include AZ91 D, AM60B, AM50A, AM-Lite™ (produced by Advanced Magnesium Technologies), etc. [0016] As shown in Figure 3, when flanges 28 and 36 include joining features, such as holes 40, joint 64 fills these features to achieve a better joint. [0017] Figure 4 shows one possible configuration for die 44 for forming joint 64. In the illustrated embodiment, die 44 (which has been omitted from the Figure for clarity) is provided with an inlet 68 for receiving a pressurized shot of the thixotropic material for forming joint 64 and that material is conveyed to cavity 60 via a pair of hot runners 72 and 76. Figure 5 shows another possible configuration for die 44 for forming joint 64 of larger assemblies 20. In this embodiment, two inlets 68a and 68b are provided, each

supplying a portion of cavity 60 via a respective pair of hot runners 72a, 72b and 76a, 76b.

[0018] Figure 6 shows another possible configuration for a joining feature, such as hole 40. In this example, in addition to the passage of hole 40 extending between flanges 28 and 36, an edge passage 84 is provided which extends between hole 40 and the outer periphery of flange 28. Edge passage assists in the filing of hole 40, or other joining feature, with the thixotropic material of joint 64 and can mitigate the effects of the two melt fronts, of the thixotropic material entering hole 40 from the top and bottom, resulting in a structurally stronger joint 64, as shown in Figure 7. [0019] Depending upon the size of assembly 20 on which joint 64 is to be formed, the injection pressure of the thixotropic material to form joint 64 may be significant. In such a case, to inhibit the formation of flash on the inner peripheral edge of flanges 28 and 36 a correspondingly high clamp pressure will be required. If the required clamp pressure is otherwise excessive, requiring an oversized clamp, assembly 20 can be designed with one or more flash inhibiting structures to mitigate the probability of flash formation. Figure 8 shows one contemplated example of such a flash inhibiting structure 88 which can be employed with the present invention. [0020] Specifically, as shown in Figure 8, each of flanges 28 and 36 are formed with a complementary and inter-engaging set of ridges which form flash inhibiting structure 88 when component 24 is assembled with component 32. As will be apparent, flash inhibiting structure 88 inhibits the ingress of the thixotropic material from which joint 64 is molded from the outer to inner peripheries of flanges 28 and 36. [0021] While the discussion above shows flanges 28 and 36 extending continuously around components 24 and 36 respectively, the present invention is not so limited and a wide variety and arrangement of flanges, or other provided features, about components to be joined is contemplated. For example, one or both components to be joined can be provided with a set of radially extending tabs, rather than a continuous flange. Further, a wide variety of joining features can be employed to augment joint 64. As discussed above, these joining features can include holes 40 and/or passages, but can also include bosses or other features which joint 64 can positively engage to augment the strength of the resulting joint.

[0022] The present invention provides a novel system and method for joining metal components to form assemblies, the components having a metal joint overmolded onto them. The metal joint is overmolded from a thixotropic alloy, such as a magnesium- based alloy, which is injected into a joint cavity in a joining die into which the components to be joined are loaded. The joint is formed over and/or through flanges or other features provided on the components and results in a structural joint which can also be liquid and/or air tight. The system and method permit the joining of components formed of different materials, formed by different processes and./or formed of different gauge materials.

[0023] The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.