Method of forming a grounding point on an aluminum member

Abstract

A method of providing an electrical grounding point on an aluminum structural member of a motor vehicle. The member is hydro-formed to produce a closed cross-section, after which a hole surrounded by a flange is formed in a wall of the member. The flange is generally the shape of a truncated cone and extends toward an interior of the member. A self-tapping fastener having a grounding lead attached thereto is driven into the hole to cut threads into the flange and secure the grounding lead to the member. The self-tapping fastener allows the grounding connection to be achieved without any access to the hollow interior of the member as would otherwise be required.

Claims

1. A method of securing a grounding lead to an aluminum member comprising: hydro-forming the member to a closed cross-section; forming an unthreaded hole in a wall of the member, the hole surrounded by a truncated-conical flange extending toward an interior of the member; connecting the grounding lead to a self-tapping fastener; and driving the self-tapping fastener into the hole to cut threads into the flange and urge the grounding lead into contact with the member.

2. The method of claim 1, wherein the hole and flange are formed while the member is retained in a hydro-forming die set.

3. The method of claim 1, wherein the hole and flange are formed in a post-hydro-forming machining step.

4. The method of claim 1, wherein the hole and flange are formed by flow drilling.

5. The method of claim 1, wherein the grounding lead comprises a conductor terminated by an eyelet and the step of connecting the grounding lead to the fastener comprises passing the fastener through the eyelet.

6. The method of claim 1, wherein a thickness of the flange has a maximum at a root of the flange and the thickness decreases towards a distal end of the flange.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention described herein are recited with particularity in the appended claims. However, other features will become more apparent, and the embodiments may be best understood by referring to the following detailed description in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a partial perspective view of an aluminum structural member having a closed cross-section and a grounding lead attached thereto by a grounding bolt;

(3) FIG. 2 is a cross-section taken along line 2-2 of FIG. 2;

(4) FIG. 3 is an enlarged cross-section taken through the frame member prior to insertion of the bolt;

(5) FIG. 4 is a cross-section view taken through with a self-tapping fastener installed in the hole;

(6) FIG. 5 is a simplified, schematic view of a frame member held by a flow-drilling fixture;

(7) FIGS. 6A-6C are simplified schematic views of a flow-drilling bit process;

(8) FIG. 7 is a general schematic view of a member after forming in a hydro-forming die set; and

(9) FIG. 8 is a detail view of FIG. 7 showing a flow drilling bit 40 forming a hole and flange in the member.

DETAILED DESCRIPTION

(10) The illustrated embodiments are disclosed with reference to the drawings. However, it is to be understood that the disclosed embodiments are intended to be merely examples that may be embodied in various and alternative forms. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed are not to be interpreted as limiting, but as a representative basis for teaching one skilled in the art how to practice the disclosed concepts.

(11) In FIG. 1, an aluminum member 10 is a structural component used in the manufacture of a motor vehicle. Member 10 may, for example, be a component of the frame, bed, or cab structure of a pick-up truck. An electrical grounding point for an electrical component or circuit (not shown) of the vehicle is provided on the member 10 by securing a grounding lead 12 to the member by a self-tapping fastener 14. In the disclosed embodiment, grounding lead 12 comprises a conductor 12a which terminates in an eyelet 12b, and the fastener 14 passes through the eyelet. The end of the conductor 12a distal from eyelet 12b is attached to an electrical component or circuit being grounded (not shown). Conductor 12a may comprise a wire, cable, or strap as is well known in the art.

(12) Grounding eyelet 12b may have an anti-rotation tab 12c formed integrally therewith, the tab engaging a corresponding notch, depression, or hole 16 in the member 10 when the eyelet is clamped against the member by the fastener 14.

(13) As best seen in FIG. 2, member 10 has a closed cross-sectional shape such as may be formed in a hydro-forming process, as is well known in the art. In the disclosed embodiment, member 10 is generally rectangular in cross-section. This is by way of example only, as the present method is applicable to a member of any hollow or closed shape. The term “closed cross-section” as used herein refers to a hollow shape such that access the hollow interior of the member is largely blocked. The term does not negate the possibility that the member may have holes, slots, windows, or other openings in one or more of its walls, as may be necessary for reasons of proper design function and/or fabrication of the member.

(14) As is apparent from FIG. 2, there is no opening in the wall 10b opposite from fastener 14 that would allow access to the rear/interior side of wall 10a by a tool (not shown) required to weld or otherwise secure a nut to the wall 10a and/or to permit a nut to be threaded into engagement with the bolt.

(15) Referring now to FIG. 3, an enlarged cross-section of a portion of member 10 illustrates a hole 20 formed in wall 10a of the member 10 prior to receiving a self-tapping fastener. An annular flange 24 surrounds the hole 20 and projects from the rear side r of the wall 10a into the hollow interior of the member. The flange 24 has a truncated cone-shaped cross-section, with a maximum thickness t.sub.max at its root (the end of the flange adjacent to wall 10a) and gradually decreasing in thickness toward the end of the flange distal from the wall 10a. The flange 24 is formed by material of wall 10a that is displaced inwardly as hole 20 is formed. The inner surfaces of hole 20 and flange 24 are of a constant diameter and are substantially smooth (not threaded). The maximum flange thickness t.sub.max is substantially smaller than the thickness t.sub.w of wall 10a.

(16) As seen in FIG. 4, self-tapping fastener 14 is driven into hole 20 from the exterior of member 10, cutting threads into the inner surface of the hole 20 and flange 24 as it is driven so that the fastener engages the wall and flange to hold the eyelet 12b in contact with the front surface f of wall 10a. The axial length l of flange 24 provides additional thread engagement length to that available solely from wall thickness t.sub.w, thereby providing more secure mechanical connection and better electrical continuity (due to the increased contact surface area) between the fastener and the member 10.

(17) The hole 20 and flange 24 may be formed while member 10 is still retained in the hydro-forming die cavity, or in a separate machining step or steps performed after the member 10 is removed from the hydro-forming dies. Hydro-piercing and flow drilling (also known as thermal friction drilling and flow punch forming) are believed to be appropriate processes. Preferably, the process used to form hole 20 and flange 24 does not produce any chips or slugs that separate from the member 10.

(18) FIG. 5 is a simplified, schematic depiction of a hollow frame member 100 secured in a machining fixture 102, after it has been removed from the hydro-forming dies (not shown). A dual-bit flow-drill press 104 is positioned to form two closely-adjacent grounding holes.

(19) FIGS. 6A-6C show (in simplified, schematic form) a flow-drilling bit 106 in the process of forming a hole with inward-projecting flange 124 in member 100.

(20) FIGS. 7 and 8 are simplified schematic depictions of hydro-forming die set comprising an upper die 32, a lower die 34, a first end plug 36, and a second end plug 38. Member 10 is shown contained in the die cavity after having been hydro-formed. A flow drill bit 40 is shown inserted through a pilot shaft in upper die 32. The flow drill bit 40 is rotated and advanced by a drill press (not shown) to form a hole in the wall of the member.

(21) The disclosed method eliminates the requirement to form an access hole in the wall of the member opposite from the grounding point, as is necessary when a captive nut retains the grounding fastener. It also eliminates the need to form threads in the aluminum member prior to insertion of the fastener, which reduces fabrication cost and complexity and also reduces the likelihood of cross-threading and/or thread damage when the fastener is inserted.

(22) The embodiments described above are specific examples that do not describe all possible forms of the disclosure. The features of the illustrated embodiments may be combined to form further embodiments of the disclosed concepts. The words used in the specification are words of description rather than limitation. The scope of the following claims is broader than the specifically disclosed embodiments and also includes modifications of the illustrated embodiments.