Patent Application
20060067806
The present invention relates to fasteners and more specifically to fasteners formed by staking, such as studs and rivets.
Staked fasteners, such as studs and rivets, are a well-known fastening technology. Studs are typically used to secure a body, such as a circuit board, to a foundation. Rivets, on the other hand, are typically used to fasten two bodies, such as sheet materials, together at an overlapping seam. For either a stud or a rivet, fastening is accomplished by the creation of a head on a shank. In the case of a stud having two ends, a head is formed on one end of the shank with the other end fixed to the foundation with the body therebetween. In the case of a rivet, heads are formed on both ends of the shank with the bodies therebetween.
A staked fastener can be made from many materials, such as steel, aluminum and plastic. Where weight is a concern, such as in an airplane, helicopter, or spacecraft, materials with high strength-to-weight ratios, such as plastic, are preferred. Unfortunately, plastic rivets simply do not have the ultimate strength of rivets made from other materials. As a result, plastic rivets, though desirable for many applications, cannot be practicably used, or in some cases used at all.
There have been many advances in the plastic rivet. From an initial beginning when plastic rivets were simply all plastic, such as a thermoplastic (e.g., polyetheretherketone (more commonly known as “PEEK”)), newer composite plastic rivets have some type of reinforcement added to the plastic. For example, many composite plastic rivets are reinforced with fibers, such as carbon or glass.
Rivets are typically formed in a two step process. First, an initial head is formed with a shank extending therefrom. Generally, the initial head is formed in a factory setting by a machine, by molding or staking an end of a rod, which tends to make a high quality initial head with a properly contoured contact surface (the surface of the head that will abut the body). Also, additional fabrication of the initial head, such as cleanup of the contact surface, can be performed relatively easily.
Then in an application, a second head is formed in situate on the end of the shank. More specifically, when a rivet is used in an application, such as connecting two bodies, a hole is made in each of the two bodies. The diameter of the holes is sized such that when the holes are aligned with each other the shank can pass through, but the initial head can not pass through the first hole that the shank passed through. The second head is then formed on the other end of the shank, thereby securing the two bodies together.
Unlike the initial head, the second head is formed at the job site, typically using a hand held tool, thus the conditions are not as controlled as those during the formation of the initial head. Additionally, cleanup of its contact surface is impossible, as it is abutting the body. As a result, the precision of the contact surface of the second head is generally not to the level of that of the contact surface of the initial head. This discrepancy results in a second head with less strength than the initial head.
More specifically, many processes used on plastic rivets to form the second head create voids in the contact surface of the rivet head. As a result, the head has a local weakness at its parameter edge. If pressure is applied thereto, it will cause a local failure of the head. These local failures result in “play” between the rivet and body, thereby creating the unacceptable amount of movement between the head and the shaft, causing the rivet to fail.
What is needed in the art is a staked fastener head and way to make the head such that the resulting rivet, or stud, is stronger than it otherwise would be.
This invention is a unified multi-part head and a method for making it for a staked fastener, such as a rivet. In an exemplary embodiment of a rivet employing the unified multi-part head, a shank with two ends has an initial head formed at one end. Proximate the other end is at least one fiber embedded in the shank. In an application, the shank is passed through a body and a unified multi-part head is formed by staking the shank's other end, thereby trapping the body between the heads. In forming the unified multi-part head, a first member is created from a clinch portion of the shank (which has at least a portion of the at least one fiber therein), and a supplemental member placed proximate the first member such that the supplemental member is trapped during staking between the forming first member and the body. Additional sufficient energy is applied during staking such that at least one of the at least one fibers will become a shared fiber (a fiber having one segment embedded in the supplemental member and another segment embedded in the first member).
These and other features, aspects, and advantages of embodiments of the present invention will become apparent with reference to the following description in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.
Referring to
The grip member 24 and the clinch portion 28 are separate segments of a shank 30, which extends outwardly from the initial head 16. In the embodiment depicted in
Referring to the series of Figures that comprise
A supplemental member 40 is collocated with the clinch portion 28 of the shank 30 proximate the second body 14. Further discussion of the supplemental member 40 is presented below.
Continuing with
As shown in the expanded view of
As shown in
The staking procedure imparts to at least one of the at least one fibers 38 and the supplemental member 40 sufficient energy such that a portion of those fibers cross the boundary and become embedded in the supplemental member 40. As a result, at least one of the at least one fibers 38 will become a shared fiber 45. The shared fiber 45 being a fiber that is simultaneously embedded in the first member 26 and the supplemental member 40. In other words, the shared fiber 45 will have a segment embedded in the first member 26 and a segment embedded the in supplemental member 40. As shown in
The staking method employed depends upon the materials selected for the clinch portion 28 and the supplemental member 40. For example, where the clinch portion 28 and the supplemental member 40 are plastic, such methods as ultrasonic and/or induction could be used.
The staking procedure to create a shared fiber 45, however, is different than conventional procedures. In a standard ultrasonic procedure, the staking procedure is controlled by the distance ds the staking tool must travel to accomplish the formation of the relevant head. More specifically, sufficient energy is applied to the clinch portion 30 via the staking tool to cause the clinch portion to flow thereby allowing the staking tool to act on the clinch portion to travel the distance ds to deform the clinch portion into a desired head shape. Once the desired head shape is accomplished, i.e., the travel distance ds has been accomplished, the energy is removed, but the staking tool is held in position for some hold time. The hold time allows the head, which is under the staking tool and still fluid enough to flow, to cool sufficiently so that the staking tool can be removed without the clinch portion further flowing. In the procedure of the invention, there is fixer step in the staking procedure that occurs after the travel distance ds has been accomplished prior to the hold. In the fixer step, energy is still applied, generally at the level previously used, to the pre-head (the head as it exists immediately after the travel distance ds has been reached). The fixer step adds additional energy to the pre-head to create the shared fiber 45, thereby converting the pre-head to a unified multi-part head 20. The amount of energy is application dependent depending on such factors as the materials used in the pre-head and their associated masses. Depending upon the degree of additional energy added during the fixer step and the materials used, the supplemental member 40 and the first member 26 may merely be welded to each other or may form a coherent mass.
If induction staking is used, materials that generate heat when exposed to induction energy would most likely have to be present in the clinch portion 30, but could be present elsewhere, such as in the supplemental member 40.
The supplemental member 40 can be of almost any shape, such as a rectangular solid (
The supplemental member 40 should have a sufficient initial volume V1, V2, V3, V4 to permit it to at least fill the void 44. The supplemental member 40 may have a greater volume than that necessary to fill the void 44 that will simply flow out during the staking operation. As those skilled in the art will appreciate, some material of the first member 16 may also flow out from under the staking tool as it travels the distance ds, causing a decrease in the density of the first member 16. Therefore, the volume V1, V2, V3, V4 of the supplemental member 40 may be sufficiently increased above that required to fill the void 44 to compensate for this loss in density.
As depicted in
Referring to
The keyed structure may also have the additional feature of a non-rotational cross-sectional shape such that in cooperation with the cross-sectional shape of the hole the supplemental material will not rotate within the hole defined by the body, or bodies. For example referring to
The supplemental member 40 may also be graduated. Referring to
The supplemental member 40 may also be designed to engage the clinch portion. Engagement could be by friction or mechanical fastener. As shown in
Referring to
While the results of a hemispherical shaped head for a staking tool have been previously depicted, other shapes can be used.
Materials for the rivet 10 and supplemental member 40 are a matter of design choice. Typical plastics, which include thermoplastics, such as PEEK or polyetherimide (more commonly known as PEI), are particularly well suited for the invention. As discussed above, staking may cause a weld to occur between the material of the rivet 10 and the supplemental member 40 and even between the rivet and/or the supplemental member and the second body 14.
As those skilled in the art will appreciate, the strength of the weld or whether a coherent mass is formed between the first member 26 and supplemental member 40 is, among other things, dependent upon the materials from which the rivet and supplemental member are made. If the rivet and supplemental member are made from compatible or the same material, the weld could be stronger and the coherent mass more uniform than it might otherwise be.
Any fibers can be embedded into the plastic of the rivet 10 or supplemental member 40. Fibers are also a matter of design choice and may include carbon or glass. Carbon fibers are particularly strong and lightweight.
The at least one fiber 38 in the shank 30 has been depicted in
Referring to
Referring to
While there has been illustrated and described what is at present considered to be preferred and alternative embodiments of the claimed invention, it will be appreciated that numerous changes and modifications are likely to occur to those skilled in the art. For example, while the unified multi-part head has been shown for a rivet, it is equally applicable for use with a stud. In addition, the unified multi-part head could be used for both heads of a rivet. Also, the use of the singular should be interpreted to mean at least one unless the specification makes such expressly clear. It is intended in the appended claims to cover all those changes and modifications that fall within the spirit and scope of the claimed invention.
