Patent Grant
7077755
1) Field of the Invention
The present invention relates to the manufacture of articles such as fasteners and, more particularly, relates to an apparatus and method for reducing the grain size of materials through an angular extrusion process and forming the articles therefrom.
2) Description of Related Art
Articles such as fasteners, clips, brackets and the like that are used in the aerospace industry, where weight and strength are of critical concern, typically are subjected to repeated cycles of shear, compressive, and/or tensile stresses over the life of the articles. As a result, the articles must exhibit good mechanical strength and fatigue resistance and preferably not be unduly heavy. In addition, because the articles may be exposed to the ambient environment, including moisture and temperature fluctuations, the articles must have good corrosion resistance and resistance to thermal stresses.
To address the strength and weight requirements, some articles such as rivets are typically formed of materials having high strength-to-weight ratios, such as aluminum and aluminum alloys that are hardened by cold working or precipitation hardening. Advantageously, a number of high strength aluminum alloys are available that are lightweight, and also have relatively high fatigue and corrosion resistance. A variety of heat treatments can be performed to achieve the desired properties of the materials. For example, heat treatments for rivets, including quenching, solution treating/annealing, and precipitation-hardening aging are discussed in U.S. Pat. No. 6,403,230 to Keener. Such heat treatments can be performed during or after the manufacture of the rivets. Often, multiple heat treatments are performed during manufacture to offset cold working effects that result during the formation of the rivets. For example, heat treatments such as annealing can be used to increase the formability of the material during manufacture. Following the formation of the articles, the desired mechanical properties of the articles can be achieved by other heat treatments, such as precipitation hardening or aging. Unfortunately, the various heat treatments required during such a manufacturing process are time consuming and increase the cost of the finished articles. Additionally, if the heat treatments are conducted improperly, undesirable mechanical properties can result in the articles.
Thus, there exists a need for an improved apparatus and method for manufacturing articles having favorable mechanical properties such as strength, toughness, formability, and resistance to fatigue, corrosion, and thermal stresses. Preferably, the method should reduce the amount of heat treating that is required during manufacture. Additionally, the method should be cost effective and compatible with materials that have high strength-to-weight ratios.
The present invention provides apparatuses and methods for manufacturing blanks and articles using angular extrusion to refine the grain structure thereof and imparting favorable mechanical properties such as strength, toughness, formability, and resistance to fatigue, corrosion, and thermal stresses. The methods can be used to manufacture articles such as rivets cost-effectively from materials with high strength-to-weight ratios such as aluminum, titanium, and alloys thereof.
According to one embodiment, the present invention provides an apparatus for extruding a workpiece to form a structural member having a refined, or “ultra-fine,” grain structure. The apparatus includes first and second rotatable rollers configured to form a nip therebetween. One or both of the rollers are rotated by an actuator to advance a workpiece through the nip and into a die. The die defines an extrusion passage with first and second portions. The first portion at least partially defines a first cross-sectional shape that corresponds in shape to the workpiece, and one or both of the portions define a second cross-sectional shape that is imparted to the workpiece to form the blank. For example, the first and second cross-sectional shapes of the die can be rectangular and circular, respectively, so that a rectangular workpiece is extruded to form a cylindrical blank. The second portion defines an extrusion angle relative to the first portion so that the workpiece is angularly extruded through the passage. The extrusion angle can be between about 45 and 135 degrees, for example, about 90 degrees. The cross-sectional area of the second portion of the passage can be about equal to the cross-sectional area of the first portion of the passage, each cross sectional area being measured in a plane normal to the direction of motion of the workpiece in the respective portion.
According to another embodiment, the present invention provides a method of manufacturing an article having a refined grain structure and articles formed thereby. The method includes extruding the workpiece through the first and second extrusion passage portions so that a grain size of at least a portion of the workpiece is refined and the workpiece is extruded to form a blank. A cross-sectional shape of the workpiece can also be changed, for example, from rectangular to circular. At least a portion of the blank is then formed into the article, such as by extruding the blank through a die or stamping the blank with a punch. For example, the blank can be used to form a rivet having a cylindrical shank with a head at one end and a second end adapted to be upset to form a second head. The blank or the article can also be heat treated.
The foregoing and other advantages and features of the invention, and the manner in which the same are accomplished, will become more readily apparent upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings, which illustrate preferred and exemplary embodiments, and which are not necessarily drawn to scale, wherein:
The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
Referring now to the drawings, and in particular to
The rollers 12, 14 can be formed of metal such as tool steel or other hard and wear resistant metallic materials. The rollers 12, 14 can be arranged in a generally parallel configuration, and rotatably mounted on shafts. One or more actuators 18 can be connected to the rollers 12, 14 to rotate the rollers 12, 14 and move the workpiece 40 through the passage 22 of the die 20. The actuators 18 can be connected to both rollers 12, 14, or only of the rollers 12, 14, as shown in
The die 20, which can also be formed of tool steel or other hard and wear resistant metallic materials, can be shaped to at least partially receive the rollers 12, 14, as shown in
Alternatively, the workpiece 40 can define other shapes, such as a square or circular bar, sheet, foil, or the like. The workpiece 40 can be selected from a variety of materials such as aluminum, aluminum alloys, titanium, titanium alloys, and other metallic materials for which improved material properties can be achieved through angular extrusion.
The passage 22 defines first and second extrusion passage portions 28, 30, which define an extrusion angle A therebetween. The die 20 can be a single monolithic device, as shown in
The cross-sectional areas of the first and second extrusion passage portions 28, 30 can be the same or different. According to one embodiment of the invention, the cross-sectional area of the second portion 30 of the passage 22, measured in a plane normal to the direction of motion of the workpiece 40 through the second portion 30, is about equal to the cross-sectional area of the first portion 28 of the passage 22, measured in a plane normal to the direction of motion of the workpiece 40 through the first portion 28 of the passage 22. Accordingly, the cross-sectional size of the workpiece 40 is not substantially increased or decreased due to the extrusion angle A, and the speed of the workpiece 40 through the passage 22 is about equal as the workpiece 40 enters the extrusion angle A from the first portion 28 of the passage 22 and emerges from the extrusion angle A into the second portion 30. Alternatively, the cross-sectional sizes of the first and second portions 28, 30 of the passage 22 can be dissimilar proximate to the extrusion angle A, for example, so that the cross-sectional size of the workpiece 40 is reduced in the extrusion angle A and moves at a faster speed as it emerges from the extrusion angle A or so that the cross-sectional size of the workpiece 40 is enlarged in the extrusion angle A and the workpiece 40 moves at a faster speed as it enters the extrusion angle A.
The shape of the portions 28, 30 proximate to the extrusion angle A can also be similar or dissimilar. According to one embodiment of the present invention shown in
The process of angular extrusion, sometimes referred to as “equal angle extrusion” in the art, mixes the material of the workpiece 40, thereby cold working the workpiece 40 and refining the grain structure by reducing the grain size of the material of the workpiece 40. While not intending to be bound by any particular theory of operation, it is believed that the material is plasticized as it passes through the shear plane at the angle A in the passage 22 and reconsolidates with a refined, or smaller, grain structure achieved through uniform cold-working and characterized by grains of reduced size that become homogenous throughout the workpiece 40. Upon cooling, the refined grain structure of the blank 42 imparts improved material characteristics such as improved strength, toughness, ductility, fatigue resistance, and corrosion resistance so that the material will resist the formation and propagation of cracks. It is believed that the refined grain structure formed according to the present invention is more formable or ductile than the unrefined grain structure or coarse-grained material of conventional materials that are used to form articles such as rivets, since the former has a finer grain having a greater total grain boundary area to impede dislocation motion.
Thus, improved material properties can be achieved by the inventive process delineated herein, which can be used in addition to, or in lieu of, thermal or heat treatment processes used in the manufacture of articles. For example, metallic fasteners, such as the rivet 50 of
The blank 42 of
The rivets 50 are formed of a metal or metal alloy such that the rivets 50 have an ultra-fine grain structure, and preferably a refined grain structure with a grain size of less than about 0.0004 inches (approximately 10 microns), for example, a refined grain structure with a grain size ranging in order of magnitude from approximately 0.0001 to approximately 0.0003 inches (approximately 2.5 to 7.5 microns) and having equiaxed shape.
The blank 42 and/or the articles formed from the blank 42 can also be heat treated. According to one embodiment of the present invention, the rivets 50 are heat treated according to a predetermined heat treatment schedule by heating the rivets 50 to one or more heat treatment temperatures, maintaining those temperatures, and subsequently cooling. For example, rivets formed of 7050 aluminum alloy can be heated in a furnace from an ambient temperature to a first heat treatment temperature of about 250° F., held at that temperature for a duration of about 4–6 hours, further heated to a second heat treatment temperature of about 355° F., held at that temperature for a duration of about 8–12 hours, and thereafter cooled by ambient air to the ambient room temperature. Heat treatments are described in U.S. Pat. Nos. 6,403,230; 6,221,177; 5,922,472; 5,858,133; and 5,614,037 to Keener, each of which is assigned to the assignee of the present invention and the entirety of each of which is incorporated herein by reference.
Referring now to
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
This application is a divisional of U.S. application Ser. No. 10/331,672, now U.S. Pat. No. 6,912,885, filed Dec. 30, 2002, which is hereby incorporated herein in its entirety by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 20050193793 A1 | Sep 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10331672 | Dec 2002 | US |
| Child | 11114457 | US |
