The present invention relates to apparatus, methods for producing plastically deformed sheets, especially metallic sheets and plastically deformed sheets produced by the disclosed method. More particularly, the invention relates to apparatus and methods of producing sheets of fine-grained alloys, especially fine-grained aluminum alloys.
Superplastic forming is emerging as an industrial process for making hard-to form aluminum sheet metal parts. The use of superplastic forming in commercial production of metallic sheet parts, especially aluminum sheets, should provide desirable improvements in both cost and efficiency. However, superplastic forming processes generally require the use of fine-grain sheet alloys, typically those having grain size of less than 10 microns. These fine-grain sheet alloys have traditionally been produced by imparting heavy cold plastic deformation to sheet metal through massive cold rolling reduction achieved in multiple rolling mill passes. A major concern for commercializing superplastic forming is that the process is inherently slow resulting in very long part forming times compared to the room temperature stamping process. High-rate superplastic forming has been demonstrated in many alloys, but requires the use of sheet metal having an ultra-fine grain microstructure, generally less than 1 to 2 microns. However, current industrial sheet metal processing done in traditional rolling mills has generally been unable to produce an ultra-fine microstructure.
Severe plastic deformation, through confined shear deformation, has been shown to produce ultra-fine grain size in aluminum alloys. Severe plastic deformation is usually achieved through procedures such as equal-channel angular pressing and high-pressure torsion. However, to date, neither of these procedures has been available for use in the processing of continuous metal strips or metal sheet stock.
A process known as continuous confined strip shearing has been proposed to address the disadvantages of equal-channel angular pressing. In this process, the friction forces from a feeding roll acting on an aluminum sheet or strip propel the sheet or strip along an upper die into a deformation zone having an angled channel. However, high friction forces acting from the upper die on the metal sheet and the deformation resistance in the deformation zone impede or stop the motion of the sheet. As a result, the sheet may slip and slide on the feeding roll, causing process instabilities and interruptions. Aluminum may also adhere to the surfaces that the sheet contacts, resulting in challenges for high-volume production processes.
Disclosed is an apparatus for plastically deforming a work piece in the form of a sheet, comprising at least two cylindrical guide rolls rotatable in a first direction, each of said cylindrical guide rolls having an outer circumference; a bendable strip having a portion of at least one surface in communication with a portion of the outer circumference of each of the at least two guide rollers, said bendable strip being capable of motion around the at least two guide rollers in the first direction and exerting a force upon a work piece, a first cylindrical feeding roll rotatable in a second direction opposite to the first direction, said first cylindrical feeding roll having an outer circumference, a plastic deformation passage having a first surface and a second surface, at least a portion of the first surface being defined by a portion of the bendable strip, and at least a portion of the second surface being defined by the outer circumference of the first cylindrical feeding roll, wherein one or both of the bendable strip and the cylindrical feeding roll, when in motion, propel the work piece through the plastic deformation passage wherein it is plastically deformed.
Also disclosed is a method of plastically deforming a work piece, comprising providing an apparatus comprising, at least two cylindrical guide rolls rotatable in a first direction, each of said cylindrical guide rolls having an outer circumference; a bendable strip having at least one surface in communication with a portion of the outer circumference of each of the at least two guide rollers, said bendable strip being capable of movement with the at least two guide rollers in the first direction and exerting a force upon a work piece, a cylindrical feeding roll rotatable in a second direction opposite to the first direction, said cylindrical feeding roll having an outer circumference, a plastic deformation passage having an first surface and a second surface, at least a portion of the first surface being defined by the bendable strip, and at least a portion of the second surface being defined by the outer circumference of the first cylindrical feeding roll, rotating the at least two cylindrically guide rolls in a first direction and the cylindrical feeding roll in a second direction, propelling a work piece into the plastic deformation passage by the rotation of one or both of the bendable strip or the feeding roll, plastically deforming the work piece in the plastic deformation passage, and removing a plastically deformed work piece from the plastic deformation passage.
Also disclosed is an apparatus for plastic deforming a metallic sheet, comprising at least two cylindrical guide rolls rotatable in a first direction, each of said cylindrical guide rolls having an outer circumference; a bendable strip having at least one surface in communication with a portion of the outer circumference of each of the at least two guide rollers, said bendable strip having a tension force to facilitate movement of the bendable strip with the at least two guide rollers in the first direction, a first cylindrical feeding roll rotatable in a second direction opposite to the first direction, said first cylindrical feeding roll having an outer circumference, a plastic deformation passage having a first surface, a second surface, and a channel, at least a portion of said first surface being defined by the bendable strip, and at least a portion of said second surface being defined by the outer circumference of the first cylindrical feeding roll, said channel being defined by an upper and lower die, said upper die being in communication with a portion of the bendable strip positioned between the at least two cylindrical guide rolls and said lower die being in communication with the outer circumference of the feeding roll, wherein the bendable strip exerts a force on a metallic sheet and one or both of the bendable strip or the cylindrical feeding roll when under motion propel the metallic sheet into the plastic deformation passage.
The above described apparatus and other features are exemplified by the following figures and detailed description.
Referring now to the figures, which are meant to be exemplary embodiments, and wherein the like elements are numbered alike.
According to the current invention, an apparatus and method are proposed in which a plastically deformable work piece in the form of a sheet is extruded in as continuous a manner as possible in a rolling mill type apparatus. The apparatus may be referred to herein as a rolling extrusion mill and the method of using the apparatus as a rolling extrusion process.
The apparatus disclosed herein imparts plastic deformation to plastically deformable work pieces, especially those in the form of sheets or strips. In one embodiment, the apparatus for plastically deforming a work piece comprises at least two cylindrical guide rolls rotatable in a first direction, each of said cylindrical guide rolls having an outer circumference; a bendable strip having at least one surface in communication with a portion of the outer circumference of each of the at least two guide rollers, said bendable strip being capable of motion or rotation around the at least two guide rollers in the first direction, a first cylindrical feeding roll rotatable in a second direction opposite to the first direction, said first cylindrical feeding roll having an outer circumference, a plastic deformation passage having an first surface and a second surface, at least a portion of said first surface being defined by a portion of the bendable strip and at least a portion of said second surface being defined by a portion of the outer circumference of the first cylindrical feeding roll, wherein the bendable strip exerts a force on an inserted work piece and one or both of the bendable strip or cylindrical guide roll propel a work piece into the plastic deformation passage. A plastically deformed work piece is pushed out the plastic deformation passage by the propelled work piece.
Plastic deformation as used herein is defined as a permanent deformation that does not recover upon removal of the deforming force.
Referring to
Cylindrical guide rolls 12 and 14 may be made of high strength steel, cemented carbides or any other material with a sufficient compressive strength and wear resistance so as to undergo only elastic deformations during the operation of the apparatus. Also, the rollers may be coated with a protective wear resistant coating. Illustrative examples of such protective coatings include ceramic coatings such as titanium nitride, tungsten carbide, chromium nitride, and the like.
Additional guide rollers may be used in addition to the at least two required guide rollers 12 and 14. Each additional cylindrical guide roll must rotate in the same direction as that of the at least two cylindrical guide rolls 12 and 14.
The apparatus 10 further comprises a bendable strip or chain 20 that is sufficiently flexible so as to be pliant and capable of bending and following the outer circumference of the at least two cylindrical guide rolls 12 and 14 and the feeding roll 40 in an arcuate curve. In one exemplary embodiment, the flexible strip 20 will be a continuous loop or belt. The term ‘bendable strip’ as used herein may be used interchangeably with ‘belt’, ‘chain’ and the like.
In general, bendable strip or chain 20 may be made of metal, plastic, rubber, or mixtures thereof. Illustrative examples of suitable metals include low-alloyed steel, high strength steel and the like. In one embodiment, the bendable strip may be made of a mixture of materials. For example, a bendable strip 20 may have a composite construction having a first layer that comprises inner surface 20 that is made of rubber or a rubber like material, while a layer made of a metal such as steel provides outer surface 24. In one exemplary embodiment, the bendable strip 20 will be made of low-alloyed steel.
The bendable strip 20 as shown in
However, it is possible for the bendable strip 20 used in other embodiments of the apparatus 10 to be non-continuous. For example, non-continuous bendable strips 20 may be particularly suitable for smaller applications such as those encountered in laboratory settings and smaller scale up models of apparatus 10.
Illustrative examples of suitable bendable strips 20, whether continuous or not, include bendable strips, belts and chains having inner and outer surfaces that may have structures thereon or be smooth, textured, rough or a combination thereof. One illustrative embodiment is shown in
In another embodiment as shown in
It will be appreciated that the embodiments shown in
In one particularly exemplary embodiment, the bendable strip 20 will be made of steel having a surface roughness pattern on outer surface 24 and will be an infinite continuous loop that does not have a beginning or an end.
The bendable strip 20 has a tension force to facilitate the rotation of the bendable strip 20 with the first and second guide rolls 12 and 14 in the first direction. In one exemplary embodiment, this tension force results from the placement of the bendable strip 20 of a particular length in the form of an infinite loop around the guide rolls 12 and 14, and applying equal but opposite forces on the rolls. Such equal but opposite forces may be applied via the use of tensioners, springs, hydraulic mechanisms and the like as known to those of skill in the art. In another embodiment, the bendable strip 20 of a finite length (non continuous) can be held in tension and propelled between the rolls by interlocking of first structures, such as teeth, on the circumference of the guide rolls and second structures, such as chain links or teeth, on the inner surface of the bendable strip 20.
Returning to
Cylindrical feeding roll 40 may be made of materials such as are described above with respect to guide rolls 12 and 14. In one exemplary embodiment, the cylindrical feeding roll 40 will be made of steel.
The outer circumference 42 of feeding roll 40 may also possess various structural features designed to increase the friction between outer circumference 42 and work piece 18. Illustrative examples of such structural features include barreling, crowning, profiling and surface roughness patterns 30 as discussed above and as illustrated in
The rolling mill apparatus 10 also includes a plastic deformation passage 44 for plastically deforming the work piece 18. In the case of metallic work pieces 18, such plastic deformation will generate new crystallographic dislocations, which, upon annealing, will generate new desirable grain structure with small grain size.
The plastic deformation passage 44 in
In the embodiment shown in
Work or energy is imparted to the deformable work piece 18 when it is propelled through the plastic deformation passage 44 as a result of the motion, movement or rotation of bendable strip 20 and feeding roll 40. This work or energy also depends on the configuration, dimensions, height, etc of the plastic deformation passage. The plastic deformation passage 44 will exert forces upon the work piece 18 as it passes through the length 50 of the passage 44. As a result, the work piece 18 is plastically deformed when it exits the plastic deformation passage 44 as plastically deformed work piece 19.
In the embodiment shown in
In this embodiment, the plastic deformation passage 44 has a height that is the same throughout the length 50 of the passage 44. The plastic deformation passage 44 shown in
It will be appreciated that while the passage 44 must exert plastic deformation forces upon the work piece 18, not all the forces exerted upon the work piece 18 over the entire length 50 of the passage 44 need to be plastically deforming forces. That is, some of the forces exerted upon the work piece 18 may only elastically deform the work piece 18. For example, in
In another exemplary embodiment, the configuration of plastic deformation passage 44 is such that the height of the plastic deformation passage 44 may decrease over the length 50 to a height that is less than the thickness of the work piece 18 to be deformed. This is illustrated in the embodiment of
Returning to the embodiment shown in
Alternatively, if the direction of cylindrical guide rolls 12 and 14 was clockwise, that portion of bendable strip 20 in cooperation with the outer circumference 16 of guide roll 14 would push deformable work piece 18 toward plastic deformation passage 44 while that portion of bendable strip 20 in cooperation with the outer circumference 16 of cylindrical guide roll 12 would pull the work piece away from and out of plastic deformation passage 44. It will be appreciated that in this case, the work piece being pulled out would be a plastically deformed work piece 19.
The rotation of the cylindrical feeding roll 40 in a direction opposite to that of the at least two guide rolls 12 and 14 acts to propel the work piece 18 through the plastic deformation passage 44 in the direction of rotation of the feeding roll 40.
During the operation of the rolling mill apparatus 10, the feeding roll 40 rotates with a constant surface velocity V. The guide rolls 12 and 14 rotate and supply the bendable strip 20 with substantially the same or slightly higher velocity V. As illustrated in
Due to friction between the deformable work piece 18 and the bendable strip 20 and the feeding roll 40, the former is clamped by the bendable strip 20 and the feeding roll 40 so that it enters the plastic deformation passage 44.
In all those embodiments where the feeding roll 40 acts to propel the deformable work piece 18, the friction between the feeding roll 40 and the deformable work piece 18 also propels the latter further along the plastic deformation passage 44. The tension force in the bendable strip 20 acts to compress the deformable work piece 18 between the bendable strip 20 and the outer circumference 42 of feeding roll 40 and facilitates the transmission of friction forces to the deformable work piece 18. The resultant friction forces from the bendable strip 20 and feeding roll 40 act on the deformable work piece 18 and force the deformable work piece 18 to enter the plastic deformation passage 44. When the deformable sheet reaches end of the plastic deformation passage in
Deformable work piece 18 may be in the form of a sheet or strip. In one exemplary embodiment, the deformable work piece 18 will be a sheet. “Sheet” as used herein refers to a long piece of deformable material having a first dimension such as thickness, a second dimension such as width and a third dimension such as length, wherein the second dimension is at least 5 times the first dimension. In one exemplary embodiment, the second dimension will be at least 500 times the first dimension, while in another exemplary embodiment the second dimension will be at least 1000 times the first dimension. In addition, in one embodiment, the third dimension will be at least 1000 times the first dimension. In another exemplary embodiment, the third dimension will be at least 2000 times the first dimension. In one exemplary embodiment, the third dimension will be infinite or continuous such as when the sheet is in the form of a roll of sheet metal.
Illustrative examples of suitable sheets include those having a first dimension of less than about 10 mm, a second dimension greater than about 50 mm, and a third dimension greater than about 200 mm. Other suitable examples include sheets having a first dimension of from about 1 to 5 mm, a second dimension of from about 1 to 2 meters, and a third dimension of from about 500 to 1000 meters. In one exemplary embodiment, suitable sheets are those having a first dimension of from about 2 to 3 mm, a second dimension of from about 1.2 to 1.7 meters and a third dimension of more than about 1000 meters.
In another exemplary embodiment, the deformable work piece 18 will be as continuous as possible, i.e., without any breaks or interruptions. In another exemplary embodiment the deformable work piece 18 will be a continuous sheet.
Deformable work piece 18 may comprise one or more deformable materials. For example, in one exemplary embodiment, the deformable work piece may comprise a mixture of two or more deformable materials. In another exemplary embodiment, the deformable work piece 18 may be comprised of two or more deformable layers, such as a laminate. In such a case any of the deformable layers may comprise a mixture of two or more deformable materials.
Examples of illustrative deformable materials include deformable metals such as aluminum, magnesium, titanium, iron and their alloys, and mixtures thereof. Examples of suitable aluminum alloys include AA 5083 and AA6061.
In one exemplary embodiment, the work piece 18 will be a sheet of aluminum alloy.
Another embodiment of the disclosed apparatus 10 is illustrated in
In this exemplary embodiment, the one or more guide shoes 58 have holes 60 through which lubricants may be supplied to decrease friction between the shoes 58 and the bendable strip 20. Suitable lubricants include oils, supplied through the holes 60 under high pressure. Another example of lubricants may be solid lubricants that fill in the holes 60 before the apparatus is used.
The shoe guide 58 as illustrated in the embodiment of
The exemplary embodiment of
In this case, the plastic deformation passage 44 begins at the point 73a at which the deformable work piece 18 is first compressed between the feeding roll 40 and the bendable strip 20. At this point, bendable strip 20 has an arcuate shape corresponding to the arcuate shape of the outer circumference 42 of feeding roll 40. The plastic deformation passage ends at the point 73b where the deformed work piece 19 exits the angled channel 68.
Turning briefly now to
It will be appreciated that in yet another exemplary embodiment, the plastic deformation passage 44 may include a combination of the narrowing extrusion channel 90 shown in
In another embodiment of the apparatus set forth in
Returning to the apparatus 10 shown in
The upper die 64 maybe in communication with that portion of the bendable strip 20 that is in communication with one of the cylindrical rollers 12 or 14.
If one or more back-up rollers 62 are employed, the preferable back-up roller configuration is such that they exert a self-equilibrating system of forces on the feeding and guiding rollers as illustrated by
In this exemplary embodiment as shown in
The tension rollers 56 and back up rollers 62 will generally be made of materials as described above with respect to guide rollers 12 and 14 and feeding roll 40. Similarly, tension rollers 56 may be barreled, crowned or otherwise profiled to guide the bendable strip. Also, in each pair of contacting rollers only one may be barreled while the other one may be conforming to the first one.
During the operation of the proposed rolling mill 10 of
Due to friction between the bendable strip 20 and the deformable work piece 18, the latter is drawn in between the bendable strip 20 and the feeding roll 40. In one exemplary embodiment, the pressure between the first guiding roll 12 and the feeding roll 40 may deform the deformable work piece 18 and decrease its thickness. The friction between the feeding roll 40 and the deformable work piece 18 propels the later further along the length 73 of plastic deformation passage 44 such that it forms an arcuate shape with respect to the shape of feeding roll 40. The guide shoe 58 compresses the deformable work piece 18 between the bendable strip 20 and the feeding roller 40 and facilitates the transmission of friction forces to the deformable work piece 18. The friction forces from the bendable strip 20 and feeding roll 40 act on the deformable work piece 18 in the same direction (shown with arrows 74 in
Thus, in the proposed method of plastically deforming a work piece 18 as described above, a deformable work piece 18 is pushed and pulled into the plastic deformation passage 44 by the action of bendable strip 20. The work piece 18 is then propelled along the length 73 of plastic deformation passage 44 into pre-channel 76 and angled channel 68 by friction from the feeding roll 40 and from the bendable strip 20.
To increase the durability of the bendable strip 20, it is proposed in one exemplary embodiment to operate it at a stress level below its endurance limit, ōE. The largest stress ō in the bendable strip 20 is a combination of the bending stress and the tensile stress: ō=ōB+ōT<ōE. The bending stress, ōB can be found as: ōB=Et/d, where E is the Young's elastic modulus of the bendable strip material, t is the bendable strip thickness and d is the diameter of the smallest of the rollers. The tensile stress ōT depends on the placement of the tension roll 56 vis-à-vis the rest of the rolling mill and on the magnitude of the tension force as displayed by force vectors 57a or 57b.
The disclosed method of plastic deforming a work piece such as a sheet may be repeated a number of times. That is, the deformed work piece 19 extruded by the apparatus 10 may be reintroduced in the apparatus 10 one or more times. Thus a plastically deformed work piece 19 may be capable of additional deformation and may be used as deformable work piece 18. Repeated cycles of rolling and extruding the deformable work piece results in substantial plastic deformation that acts as a driving force for material recrystallization and refinement of grain structure. It will be appreciated that increasing the number of cycles of rolling and extrusion in the apparatus of the invention will result in increasingly fine-grained sheet metal.
In the above formula, T1 is the tangential force acting on the deformable work piece 18 on coming in contact with the feeding roll 81 and T2 is the tangential force acting on the deformable work piece 18 on separating from the feeding roll 40, α is the wrap angle around the feeding rolls 81 and 40, and μ is the combined friction coefficient due to friction forces acting on the deformable work piece 18 from the bendable strip 20 and feeding rolls 40 and 81.
Turning now to
Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to a particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
This application is a divisional of U.S. Ser. No. 10/763,666 filed Jan. 23, 2004, now U.S. Pat. No. 7,293,445 and also claims priority of U.S. Provisional Application No. 60/478,672 filed Jun. 13, 2003 and assigned to the assignee of the present invention.
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Number | Date | Country | |
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20080028814 A1 | Feb 2008 | US |
Number | Date | Country | |
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60478672 | Jun 2003 | US |
Number | Date | Country | |
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Parent | 10763666 | Jan 2004 | US |
Child | 11871292 | US |