INTERFACE SUSPENSION FOR ALLOY BASED LASER WELDING

BACKGROLMD ART

1. Field of the Invention

[0001] The invention relates generally to a laser welded joint. More particularly, the invention relates to a suspension applied to a welded joint to facilitate the welding thereof.

2. Description of the Related Art

[0002] Welding is the process of using heat to join two components together. In some instances, pressure is used in the process, hi other methods, a third material is used. The process of welding components together is a very effective process when assembling structures because the resulting union of the parts is as strong or stronger than it would have been using other means to fasten the parts together.

[0003] Another reason why parts are welded together as opposed to other means is due to the aesthetic result of welding. When finished, the parts joined together often look like a single part. This provides a look that is pleasing, hi some instances, this enhanced look can also be useful in a functional sense. This is true when fluids flow past the joined parts and the finished composite part does not create turbulences or flow disruptions at the weld position.

[0004] When the parts being welded are galvanized steel, there is a potential for poor weld quality if the source of heat is elevated rapidly and concentrated in a specific area. This typically occurs when a laser or electron beam is used in the welding process to heat the metals. The poor welding results occur because a laser weld occurs rapidly and the vaporization of certain materials in the weld area are trapped within the molten material created by the laser beam, hi these situations, the zinc material used in the galvanization of the metal has a lower melting point resulting the rapid vaporization of that metal while continued energy is being impinged upon the metal to melt the steel or iron.

[0005] United States Patent 3,969,604 discloses a method for joining galvanized steel metal through a welding process wherein a flux material is deposited on the area in which the welding is to occur. This flux material is characterized by a melting temperature that is

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substantially the same or higher than the steel parts. When the flux material is placed in the weld location, a high energy density beam, e.g., a laser beam, impinges the area allowing the welding process to occur while preventing vapor created by the melting of the zinc to be trapped within the welding materials allowing for a smoother finish.

[0006] United States Patent 6,479,168 discloses a method for laser lap welding a pair of metal members together, hi particular, the welded joint includes two galvanized sheets of metal that are coated with zinc. A metal foil is placed between the two galvanized sheets of metal. The copper metal foil is a sheet of copper having a thickness of 0.0035 to 0.0045 inches thick. Copper is used in the foil because its melting point allows it to react with the zinc coating on the galvanized steel sheets to reduce the volatility during the weld process. This method is, however, cumbersome in that copper metal foil is difficult to apply and maintain in the specific area that is to be welded, hi addition, much of the copper is not used and, therefore, wasted during the laser welding process.

[0007] hi addition to these two methods for applying an intermediate material between two sheets of metal to be laser welded, there is a third that uses a copper powder mixed with an oil. The copper powder/oil mixture is applied to the area that needs to be welded. This method of introducing an intermediate material to facilitate the welding of two galvanized sheets of metal is cumbersome for several reasons. First, it is difficult to control the application of an oil on a sheet of galvanized metal when the surface to which the oil is being applied is not horizontal. Much of the oil and copper powder run off. Another disadvantage of the oil/copper powder combination is the size of the particulate is so small that it does not create a gap between the two sheets of metal being welded. Powder is defined as being less than 40 microns, hi addition, particulate that makes up a powder has no defined shape because the powder is created in a pulverization process. Some of the particles are flakes and others are multifaceted. Any type of consistency in separation, if separation were possible, would not be consistent. Because the oil and copper powder are so small and fluid, the two sheets of galvanized steel may be too close together to facilitate a proper, non-violent weld.

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SUMMARY QF THE INVENTION

[0008] An interface suspension is disclosed for facilitating the laser welding of a first metal having a first zinc coating and a second metal having a second zinc coating. The interface suspension includes a petrolatum base. The interface suspension also includes a plurality of metal spherules suspended in the petrolatum base. The interface suspension melts when the laser welding occurs and allows the plurality of metal spherules to absorb vapors released by the first and second zinc coatings when the first and second zinc coatings boil.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein:

[0010] Figure 1 is a cross-sectional side view of two galvanized metal sheets at a beginning stage of the laser welding process; and

[0011] Figure.2 is a cross-sectional side view of the two sheets of galvanized metal during the final stages of laser welding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0012] The invention is an interface suspension 10. The interface suspension 10 is used to facilitate laser welding of a first metal 12 having a first zinc coating 14 to a second metal 16 having a second zinc coating 18. In the embodiment shown, the first metal 12 and the second metal 16 are steel sheet metal that are coated with zinc on both sides. It should be appreciated by those skilled in the art that the first 12 and second 16 metal pieces may be other forms of metal fabricated from metal others than steel and may only be partially coated with zinc. The zinc coatings 14, 18 are used to inhibit corrosion of the base component, i.e., the first 12 and second 16 metals. This combination of a zinc coated steel piece of steel is commonly referred to as galvanized steel.

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[0013] Due to the low melting and boiling points of zinc, the zinc in the first 14 and second 18 coatings is vaporized quickly when subjected to laser welding procedures. The vapors created at the weld position are trapped in the molten metal that is creating the weld. The trapped zinc vapors increase the porosity of the weld line.

[0014] The interface suspension 10 creates a controlled gap between the first 14 and second 18 zinc coatings. The gap 20 provides a sufficient space for the molten metals and the vaporized zinc to interact. The interface suspension 10 includes a petrolatum base 22 and a plurality of metal spherules 24. The metal spherules 24 are suspended in the petrolatum base 22 such that the interface suspension 10 melts when laser welding to allow the plurality of metal spherules 24 to absorb vapors released by the first 14 and second 18 zinc coatings when they are boiling.

[0015] Figure 1 illustrates an example of how a laser weld occurs when using two sheets of galvanized metal 12, 16. In this example, a clamping pressure is applied adjacent the weld position. The clamping pressure, graphically illustrated by blocks 26, 28 force the first metal 12 and the second metal 16 together minimizing the amount of interface suspension 10 therebetween to approximately the same distance as the diameter of the spherules 24. In this example, the first metal 12 extends laterally over a surface area different than the second metal 16. An opportunity for the first 12 and second 16 metals to be coaxial is also contemplated, hi addition, it should be noted that one of the pressure blocks 28 extends out beyond a peripheral edge of the second metal 16. This is shown by way of example and the applied pressure may also be applied fully within the periphery of either the first 12 or second 16 metals.

[0016] A laser beam, graphically represented at 30, impinges on one of the first 12 and second 16 metals. The laser beam 30 is directed to a position exposed adjacent the pressure blocks 26, 28 because that is the location that the first 12 and second 16 metals are at their proper separation distance equal to the desired gap 20.

[0017] Referring to Figure 2, the laser beam 30 has impinged enough energy upon the first 12 and second 16 metals such that a molten pool of metal 32 extends between the first 12 and second 16 metals. The molten pool of metal 32 includes traces of zinc 34 therein. Within

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the gap 20, the metal spherules 24 and the zinc coatings 14, 18 combine or fuse together to form a secondary metal alloy 36. The secondary metal is a combination of the molten spherules 38 and the boiling zinc. By selecting a material for the spherules 24 that has a melting point similar to that of the zinc coatings 14, 18, the secondary metal alloy 36 is able to be created through fusion preventing the boiling and vaporized zinc from interfering with the smooth laser welding of the first 12 and second 16 metals.

[0018] The plurality of metal spherules 24 define diameters in the range between 40 microns and 250 microns. This range is the ideal range to define the gap 20 and by utilizing spherules 24 of this size ensures the gap 20 is at a preferred distance.

[0019] The metal spherules 24 may be fabricated from any metal suitable for melting at a temperature that is similar to the boiling point of zinc, 907° Celsius. Examples of metals that have melting points similar to the boiling point of zinc include copper, silver and nickel. To ensure the best creation of the secondary metal alloy 36, the purity level of the metal spherules 24 is greater than 99%. In the example where copper is used for the plurality of spherules 24, the secondary metal alloy 36 is brass, a combination of copper and zinc.

[0020] The petrolatum base 22 is within the range of 50% and 90% of the weight of the interface suspension 10. Therefore, the metal spherules comprise the remaining 50% to 10% by weight of the interface suspension 10. hi one example, the petrolatum base 22 is 80% of the interface suspension with the plurality of metal spherules comprising the remaining 20%. The petrolatum base 22 is a petrolatum USP gel/grease with a viscosity or consistency (USP) between 100 and 300. In addition, the petrolatum base 22 is defined by having a melting point between the range of 122° F and 160° F.

[0021] Because the petrolatum base 22 has a thick consistency, once the plurality of spherules 24 are mixed into the petrolatum base 22, there is no need to remix the interface suspension 10 to maintain the proper consistency of the interface suspension 10 prior to its usage in a laser welding process. The interface suspension 10 may be packaged in a standard, open ended style container of various capacities, i.e., 55, 10 and 5 gallon barrels or drums. These containers (not shown) will be sealed, capped and labeled according to the Petrolatum

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International Transportation Regulations. The interface suspension 10 is fabricated through a mixing procedure which minimizes or prevents the entrapment of ambient gases therein.

[0022] Prior to the actual welding of the two metals 12, 16, the interface suspension 10 is applied to one of the first 12 and second 16 metals. Because the interface suspension 10 utilizes a petrolatum base 22, the interface suspension 10 adheres to the surface of the metal 12, 16 to which it is applied. The interface suspension 10 will remain in place as long as the temperature does not reach the melting point of the petrolatum base 22, namely a temperature within the previously mentioned range of 122° F and 140° F.

[0023] The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.

[0024] Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.

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