Method and apparatus for welding to laminated metal

The present invention relates to a method for welding a fastener or other component to a laminated metal panel.

It is known in modern automobile manufacture to employ laminated metal, particularly laminated steel, in the forming of components such as oil pans, rocker covers, wheelhouse inners and front-dash structures. Laminated metal is comprised of two sheets of metal, such as steel, aluminum or magnesium, with a layer of polymer interposed there between. Laminated metal is known to provide a good combination of vibration damping properties and high strength-to-weight ratios and is accordingly of interest to the exacting performance demands of the automobile industry.

It is known to weld fasteners and other components to the laminated metal by conventional welding processes such as projection resistance welding. However, in such processes, the fastener is welded to only the outer layer of metal of the laminated metal, rather than to both layers of metal. In addition, the use of electric resistance welding is complicated by the fact that the layer of polymer acts as a dielectric to retard to flow of welding current through the laminated metal.

A method is provided for the projection electric resistance welding of a component to a laminated metal member. The laminated metal member is comprised of top and bottom metal sheets adhered together by a polymer layer provided between the top and bottom metal sheets. A plurality of projections is provided on the component and the projections extend toward the top metal sheet of the laminated metal. Force is applied to the component and the projections have a pointed shape so that the projections pierce through the top metal sheet and contact the bottom metal sheet. Weld current is then applied to flow through the projections so that the projections are electric resistance welded to both the top and bottom metal sheets.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is an elevation view of a fastener resting upon a sheet of laminated metal;

FIG. 2 is an elevation view having parts broken away and in section showing the laminated metal supported by a back-up electrode and a movable electrode forcing sharp projections formed on the fastener to pierce through the top layer of sheet metal and polymer and into contact with the bottom layer of sheet metal; and,

FIG. 3 is an elevation view having parts broken away and in section showing the fastener welded to the laminated metal.

The following description of certain exemplary embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or uses.

Referring to FIG. 1 , a component 10 , more particularly a bolt 12 . Bolt 12 includes a threaded shank 14 and a head 16 that is to be welded to a sheet of laminated metal 20 . The sheet of laminated metal 20 includes a top layer 22 of sheet metal, a bottom layer 24 of sheet metal and a middle layer of polymer 26 that binds the top layers 22 and the bottom layer 24 .

As seen in FIG. 1 , projections 28 , 30 and 32 are provided on the head 16 on the side thereof opposite to the threaded shank 14 . The projections may be cold headed during the conventional manufacture of the treaded shank 14 , or otherwise formed thereon as convenient to the bolt manufacturing process.

The projections are sharpened or pointed at their tips to enable the projections to pierce through the laminated metal 20 as will be described in particular hereinafter.

FIG. 2 shows the laminated metal 20 supported by a backup electrode 36 that engages with the bottom layer 24 of sheet metal. A welding electrode 38 is seated over top the bolt 12 and has a bore 40 that receives the threaded shank 14 and an end face 44 that engages with the head 16 of the bolt 12 . The welding electrode 38 is mounted on a press or hydraulic cylinder. As seen in FIG. 2 , force is applied to the electrode 38 in the direction of arrows “F” and causes the bolt 12 to be forcibly advanced toward the laminated metal 20 so that the pointed projections 28 , 30 and 32 are caused to pierce through the top layer 22 , and through the polymer layer 26 . The length of the projections is such that the projections 28 , 30 , and 32 also pierce into the bottom layer 24 , or at least come into close contact or near close contact with the bottom layer 24 . Thus, although the presence of the layer 26 would normally prevent the flow of electrical current between the top and metal sheets 22 and 24 , the projections 28 , 30 and 32 will provide a path for flow of electrical current.

A welder 50 is connected to the weld electrode 38 by a cable 52 and to the back up weld electrode 36 by a cable 54 . After the projections of the bolt 12 have pierced though the laminated metal 20 as shown in FIG. 2 , weld current is applied to the weld electrode 38 and back up electrode 36 , so that the weld current passes through the head 16 and its projections 28 , 30 and 32 to the laminated metal top layer 22 and bottom layer 24 . This induces electrical resistance heating and welding so that welds 56 , 58 and 60 are formed as shown in FIG. 3 .

It will be appreciated that the welds 56 , 58 and 60 reach between the bolt head 16 and both metal layers of the laminated metal. Thus when either axial force or torque is applied to the bolt 12 during its eventual use in an automobile or other products, the bolt 12 will have the advantage of being fixedly attached to both layers of the laminated metal 20 .

The foregoing description of the invention is merely exemplary in nature and, thus, variations thereof are intended to be within the scope of the invention. For example, although the drawing shows the component 10 as being a bolt 12 , the component could be a rivet, a threaded nut, or some other type of fastener. Alternatively the component could be a mounting bracket or other component that is to be welded directly to the laminated metal 20 rather than being attached to the laminated metal by a fastener such a the bolt 12 .

Although the example shown herein has three projections 28 , 30 and 32 , it will be appreciated that any number of projections can be employed, depending upon how many welds are desired. In addition, the length of the projections can vary, provided however that the projections assure the formation of the weld nugget to fuse with the bottom layer 24 of the laminated metal 20 .