Method and apparatus for clinching metal sheets

#The present invention relates to a method and apparatus for clinching metal sheets together for assembling automotive vehicle structures.

#It is known that the manufacture of automotive vehicles often requires that metal sheets be attached to each other to form automotive vehicle structures. Clinching is one potential method of attaching such sheets. Clinching typically requires steps of stamping or otherwise cold forming corresponding indentations in at least two stacked metal sheets for frictionally or otherwise mechanically interlocking the sheets to each other. During conventional clinching processes, the metal sheets may require fairly substantial deformation of the sheets to form proper indentations. Such deformation can be particularly difficult to achieve in high strength metal sheets, which tend to be more brittle than certain lower strength metals, or require expensive heat treatment for relieving internal stresses. Therefore, there is a need for improved clinching techniques, apparatuses or both, for achieving high integrity attachment of metal sheets, particularly, sheets formed of advanced or high strength metals such as aluminum, magnesium, high strength steel and the like.

#The present invention meets these needs by providing an improved method of clinching a first metal sheet to a second metal sheet, with particular utility in the formation of components for an automotive vehicle. The method involves clinching at least two sheets of metal with a punch and die assembly during or after contacting electrodes with the metal sheet for locally heating the metal sheet at the clinching locations. More specifically, the method includes a step of stacking a first metal sheet on a second metal sheet. Each of the sheets includes a first side and a second side and at least a portion of the second side of the first sheet is in overlapping contact with at least a portion of the first side of the second sheet for forming an overlapped region. Once the sheets are stacked, the first and second metal sheets are placed between a punch assembly and a die assembly. The punch assembly includes a punch surrounded by a first electrode, wherein the first electrode is adapted for contacting the first sheet. The die assembly includes a die surrounded by a second electrode, wherein the second electrode is adapted for contacting the second sheet. The first and second electrodes are each connected to an electrical energy source. Upon contacting the first and second electrodes with the metal sheets, the electrical energy source is capable of inducing an electrical current that flows between the first and second electrodes and the first and second metal sheets to elevate the temperature of the overlapped region of the first sheet and the second sheet. Mating indentations are punched within the overlapped region for additionally securing the first sheet to the second sheet. During formation of the indentations, an outer periphery of one of the indentations at least partially bonded to an inner periphery of another of the indentations. Additionally, the clinching die provides force to clinch the inner periphery onto the outer periphery.

#These and other aspects and advantages of the present invention will become apparent upon reading the following detailed description in combination with the accompanying drawings, in which:

#FIG. 1 is a sectional view of a clinching apparatus prior to clinching a pair of stacked metal sheets to each other;

#FIG. 2 is a sectional view of the clinching apparatus of FIG. 1 during clinching of the pair of stacked metal sheets to each other;

#Referring to FIGS. 1 and 2, a first metal sheet 10 is clinched to a second metal sheet 12 by a clinching apparatus 14. The clinching apparatus 14 includes a punch assembly 16 for stamping generally cup-shaped or generally cylindrical mating indentations 18, 20 into the metal sheets 10, 12 and a die assembly 22 for supporting the metal sheets 10, 12 and for assisting in the stamping or forming of the indentations 18, 20.

#The punch assembly 16 includes a generally elongated metal stripper 24 having an opening 26 extending down a length of the stripper 24. An elongated cylindrical steel punch 28 of the assembly 16 is received in the opening 26 and the punch 28 is moveable along a length of the opening 26 between at least a first position, as shown in FIG. 1, and a second position, as shown in FIG. 2. The punch 28 may be moved hydraulically, mechanically, electrically, pneumatically or otherwise. Preferably, the punch assembly 16 also includes a spring 30 attached to the stripper 24, the punch 28 or both that is biased against the motion of the punch 28 from its first to its second position for assisting in retracting the punch 28 after clinching as further described below.

#A copper electrode 34 of the punch assembly 16 is generally annular and surrounds at least a portion of the stripper 24 and the hole 26 through which the punch 28 moves. A generally annular insulator 36 of the punch assembly 16 is disposed between the stripper 24 and the electrode 34 to electrically separate the electrode 34 from the stripper 24 and the punch 28. The insulator 36 may be formed of an insulative material such as a plastic, polymer, ceramic, or the like. In one preferred embodiment, the insulator 36 is a laminate formed with a fabric or paper molded with a synthetic resin.