Patent Publication Number: US-2018029097-A1

Title: Hydrostatic cyclic expansion extrusion process for producing ultrafine-grained rods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority from Iran Patent Application Serial Number 139550140003008482, filed on Oct. 5, 2016, and entitled “HYDROSTATIC CYCLIC EXPANSION EXTRUSION (HCEE) PROCESS FOR PRODUCING UFG HIGH STRENGTH LONG RODS,” which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Ultrafine-grained and nanostructured materials are materials that possess particularly high strength. Structures made of ultrafine-grained and nanostructured materials are often suitable for making lighter and at the same time energy efficient vehicles, airplanes, and other machinery. A variety of methods have been developed to produce ultrafine-grained (UFG) materials. For example, processing through the use of various metalworking techniques such as severe plastic deformation (SPD) can apply strain to produce ultrafine grained and nanostructured materials. In some cases, SPD may be understood as a process in which high strain is applied without any significant change in the dimensions of a workpiece. 
     SUMMARY 
     This summary is intended to provide an overview of the subject matter of this patent, and is not intended to identify essential elements or key elements of the subject matter, nor is it intended to be used to determine the scope of the claimed implementations. The proper scope of this patent may be ascertained from the claims set forth below in view of the detailed description below and the drawings. 
     In one aspect, the present disclosure is directed to a method of producing ultrafine grain materials that includes positioning a workpiece in a die channel, the die channel being formed in a die assembly, pouring lubricant into a first end of the die channel, thereby substantially surrounding the workpiece with the lubricant, and moving a first punch toward the workpiece and thereby pushing the workpiece toward a second end of the die channel. 
     The above general aspect may include one or more of the following features. For example, the method can further include inserting a first seal into the first end of the die channel, thereby sealing the lubricant in the die channel. The method can also include a step of inserting the first punch into the first end of the die channel, as well as inserting a second punch into the second end of the die channel. In some cases, the method can include rotating the die assembly approximately 180 degrees to complete a first pass, and/or pouring additional lubricant into the second end of the die channel during a second pass. In addition, in some implementations, the method includes inserting a second seal into the second end of the die channel during the second pass, and/or inserting the first punch into the second end of the die channel. In another example, the method can include removing the second punch from the die assembly, and/or removing the first seal from the die assembly. 
     In another aspect, the present disclosure is directed to a die assembly for production of ultrafine-grain materials that includes a first die segment including a first die portion joined to a first panel portion and a second die segment including second die portion joined to a second panel portion. In addition, the first die segment is removably attached to the second die segment. 
     The above general aspect may include one or more of the following features. For example, the die assembly can further include a first plurality of fasteners configured to attach the first die portion to the first panel portion. In another example, the first panel portion may include a gasket. In some implementations, the first die portion has a substantially cylindrical shape, and/or the second die portion has a substantially cylindrical shape. In one implementation, the first die portion and the first panel portion include a plurality of apertures for receiving the first plurality of fasteners. In addition, in some cases, the die assembly includes a set of connectors configured to removably attach the first die segment to the second die segment. In one example, a die channel extends from the first die segment to the second die segment. In some implementations, the die channel includes an expansion section and an extrusion section, and a lubricant may fill or be disposed within the die channel, the lubricant being configured to substantially surround an entire exterior surface of a workpiece disposed in the die channel. Furthermore, the die assembly can be configured to apply hydrostatic pressure to a workpiece. In one implementation, a second plurality of fasteners may be configured to attach the second die portion to the second panel portion. 
     Other systems, methods, features and advantages of the implementations will be, or will become, apparent to one of ordinary skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description and this summary, be within the scope of the implementations, and be protected by the following claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The implementations can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the implementations. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. 
         FIGS. 1A and 1B  depict an implementation of an overview and progression of a hydrostatic cyclic expansion extrusion system; 
         FIG. 2  depicts an implementation of a method of hydrostatic cyclic expansion extrusion; 
         FIG. 3  is an exploded view of an implementation of a die assembly. 
         FIG. 4  is an cross-sectional view of an implementation of the die assembly of  FIG. 3 ; 
         FIG. 5A  is a photograph of an implementation of a product formed by a hydrostatic cyclic expansion extrusion process assembly; and  FIG. 5B  shows evolution grain size from unprocessed to HCEE processed after two passes; 
         FIGS. 6  graphs presenting a hardness distribution in an annealed sample and the hydrostatic cyclic expansion extrusion process; and 
         FIG. 7  is a graph presenting stress-strain data of unprocessed and HCEE processed samples. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, various examples are presented to provide a thorough understanding of inventive concepts, and various aspects thereof that are set forth by this disclosure. However, upon reading the present disclosure, it may become apparent to persons of skill that various inventive concepts and aspects thereof may be practiced without one or more details shown in the examples. In other instances, well known procedures, operations and materials have been described at a relatively high-level, without detail, to avoid unnecessarily obscuring description of inventive concepts and aspects thereof. 
     As compared to more conventional coarse grained materials, UFG materials typically demonstrate highly improved mechanical, chemical and physical properties. In conventional Cyclic Expansion Extrusion (CEE) processes, long metal articles cannot be formed, because increased friction forces cause a fracture of the die and failure in the die. In the following disclosure, a Hydrostatic Cyclic Expansion Extrusion (HCEE) process is introduced, a process in which the limiting effects of friction is removed and workpieces of greater quality may be produced. In the HCEE process, the workpiece does not come into contact with the die and metal forming is achieved through pressurized lubricating fluid. In conventional methods, friction remains a limiting factor, making the production of long metal articles difficult or impossible. 
     Thus, an objective of the present disclosure is to present a novel process that allows for the production of workpieces without limitation on the length of the workpiece. For purposes of reference, this process will be referred to as Hydrostatic Cyclic Expansion Extrusion (HCEE). Generally, in HCEE, deformation is achieved through the application of compressed fluid, thereby reducing or eliminating friction. This reduction in friction can allow the HCEE process to be substantially independent of the length of the workpiece, making it possible to fabricate ultrafine grained materials of longer lengths. Thus the HCEE process makes the mass production of long metal UFG articles possible. 
     Referring to  FIG. 1A , a schematic view of an implementation of an HCEE system  210  is depicted. In different implementations, HCEE system  210  can include a die assembly  150 , an upper punch assembly (“upper punch”)  110 , a lower punch assembly (“lower punch”)  160 , and a lubricating fluid (“lubricant”)  130 . A workpiece  140  is shown in the system for purposes of clarity. In some implementations, a sealant or seal  120  may also be used in HCEE system  210 . 
     In different implementations, a cyclic extrusion expansion (CEE) system a die can comprise an axisymmetric barrel-like hollow, as well as one or more punches that can control or impose a flow of material. An extrusion section is placed after the part in which the sample experiences expansion. In one implementation, the force needed to extrude the material also provides the appropriate amount of back-pressure for expansion. Within the die cavity, the cylindrical material is initially expanded in diameter and then shrunk (usually returned to its original diameter) through an extrusion configuration. The material undertakes two portions of straining at expansion and extrusion. It can be understood that the HCEE process described herein can incorporate some or all features of the CEE system. 
     Referring now to  FIG. 1A , in the HCEE apparatus, it can be seen that lubricant  130  fills a space between die assembly  150  and workpiece  140 . In some implementations, lubricant  130  can be pressurized. In one implementation, a pressurized lubricating fluid covers the entire exterior of the workpiece, thereby minimizing friction. By substantially or entirely surrounding the workpiece with a lubricant, as shown in  FIG. 1A , the process remains independent of the length of the workpiece as the effect of friction is reduced or eliminated. Thus, workpieces of virtually any length can be fabricated. As an example, a magnified view of a portion of workpiece  140  is provided, which identifies an expanded portion with a first diameter  180  and an extruded portion with a second diameter  190 , where second diameter  190  is smaller than first diameter  180 . In other words, the region in which the diameter begins to expand toward a center of the die channel provides an expansion section  102 , and a second section from the center of the die channel toward a narrowing region of the die channel provides an extrusion section  104 . In addition, as generally represented by an angle  170 , it can be seen that the curvature of the workpiece changes as it passes through the expansion section of the die assembly. 
     Referring now to both  FIGS. 1A and 1B , an implementation of a method of utilizing the HCEE system is described. In  FIG. 1B , a schematic view of the method is depicted. As shown in  FIG. 1B , in a first stage  210 , the primary punch or upper punch  110  descends and/or moves in a direction toward workpiece  140  that is placed in the apparatus. Initially, the exit (e.g., the lower end of the “barrel” or channel) can be blocked by a second punch or lower punch  160 . Lower punch  160  can act as a backing plate in one implementation. This arrangement can allow pressure associated with the primary punch cause a radial flow of the material until the material is pressed against the inner walls of the channel. In other words, the material may expand and take on the shape of the channel, as shown in a second stage  220 . As depicted in both first stage  210  and second stage  220 , lubricant  130  substantially surrounds workpiece  140  throughout the process, reducing or eliminating friction between the workpiece and the inner surface of the channel and improving the efficient passage of the material through the system. In some implementations, the workpiece can expand against the pressurized lubricating fluid that surrounds the workpiece during first stage  210  and/or second stage  220 . 
     In a third stage  230 , lower punch  160  that had blocked the exit (associated with a second end  280  disposed toward the lower end of the die assembly) is removed, whereby the necessary back-pressure for expansion of the workpiece is provided by the subsequent extrusion that occurs after the expansion. Upper punch  160  moves further inward or downward through a first end  270 , pushing the material such that it flows through the die cavity or die channel, and moving the workpiece material downward to its end point. At this point, the workpiece has gone through one pass of the HCEE process. If desired, additional passes can be performed, as represented by a fourth stage  240 , where the apparatus (including workpiece  140 ) can be rotated approximately 180 degrees, such that first end  270  is now disposed toward the lower end of the die assembly and second end  280  is now disposed toward the upper end of the die assembly. After the assembly has been rotated, additional lubricant  230  is poured into the die, and another seal  220  can be added therein. The upper punch  160  can then be inserted or entered through the opposite opening (what had been the end associated with the exit), pressing the workpiece in a direction opposite to the previous direction. The additional lubricant ensures that friction continues to be minimized during the procedure. The apparatus can be rotated and the process can be performed any number of times until the workpiece is in the desired condition. In some cases it is necessary to remove the previous seal before refilling or pouring additional lubricant into the cavity. 
     In  FIG. 2 , a flow chart is presented in which an implementation of an HCEE method is provided. As shown in  FIG. 2 , a first step  201  can involve positioning a workpiece in a die channel, where the die channel is formed in a die assembly. In a second step  202 , lubricant is poured into the die channel via the first or upper end, such that the lubricant substantially surrounds the workpiece. The first punch assembly can be inserted into the first end of the die channel. A lower or second punch assembly or backplate can also be positioned within the lower end of the die channel (a second end that is disposed opposite to the first end that served as an entryway for the lubricant). In an optional third step  203 , a seal is inserted above the lubricant via the first end of the die channel, sealing the lubricant inside of the die channel. In a fourth step  204 , an upper or first punch assembly descends toward the workpiece, pushing down against both the workpiece and the lubricant fluid, and causing the workpiece to move in a direction associated with the second end of the die channel. In some implementations, the upper punch assembly presses against the seal, which in turn exerts pressure on the lubricant fluid and the workpiece below. In a fifth step  205 , the lower punch is removed after the deformation of the workpiece by (for example) the chamber die, and the upper punch pushes further downward, moving the workpiece toward an endpoint associated with the lower or second end of the die assembly. In an optional sixth step  206 , the apparatus can be rotated 180 degrees, and additional lubricant as well as a second seal can be inserted into the die channel via the second end (now associated with an upper end of the die assembly), allowing the process to be repeated if desired in another pass. Thus, the first punch is inserted into the second end of the die channel during the second pass, while the second punch is inserted into the first end of the die channel during the second pass. It should be understood that in some implementations, the first seal or the second seal can be removed as needed to allow for the addition of lubricant during each pass, and then replaced to form a seal again. 
     In order to provide greater detail to the reader, an exploded view of an implementation of a die assembly for use in the HCEE system is presented next in  FIG. 3 . In different implementations, die assembly  150  can comprise a plurality of components that are attached, connected or joined together. A first component comprising a first die portion  410  is configured to be attached to a second component comprising a first panel portion  420 . In addition, a third component comprising a second die portion  430  is configured to be attached to a fourth component comprising a second panel portion  440 . First die portion  410  and second die portion  430  can comprise a substantially cylindrical three-dimensional shape in some implementations. In one implementation first die portion  410  and/or second die portion  430  include a substantially round or circular cross-sectional shape. In addition, first panel portion  420  and/or second panel portion  440  can comprise generally flat or relatively thin segments with a cross-sectional shape and size similar to the cross-sectional shape and size of first die portion  410  and/or second die portion  430 . In some implementations, first panel portion  420  and/or second panel portion  440  comprise gaskets. 
     In different implementations, one or both set of components (i.e., first die portion  410  with first panel portion  420 , and second die portion  430  with second panel portion  440 ) are securely fitted together as shown in  FIG. 3  by a plurality of fasteners  460  (for example, screws, threaded fasteners, or other connectors etc.) that are inserted into openings or apertures formed in each component. In one implementation, four fasteners are used to join together each of the two sets of components, and each of the first die portion  410 , second die portion  430 , first panel portion  420 , and second panel portion  440  include a plurality of apertures that are aligned with the apertures of a neighboring component, and the apertures are configured to receive fasteners. Thus, it can be understood that in one implementation, a first plurality of fasteners are configured to attach or join together first die portion  410  with first panel portion  420  and a second plurality of fasteners are configured to attach or join together second die portion  430  with second panel portion  440 . 
     In addition, the four components are aligned and connected as shown in  FIG. 3  by insertion of a plurality of elongated connectors  450 . In some implementations, there are two to eight elongated connectors. In  FIG. 3 , there are four elongated connectors, which are configured to extend through regions of first die portion  410 , first panel portion  420 , second die portion  430 , and second panel portion  440  and securely join the assembly together. A substantially continuous and hollow cavity or die channel is formed as the four components are linked together, extending through the first die segment and the second die segment. In different implementations, the die assembly is designed as comprising two main segments (i.e., first segment  470  and second segment  480 ) that can be readily separated and re-connected, facilitating the removal of the workpiece upon completion of the process. In other words, portions of the die assembly may be removably attached to one another. For purposes of this disclosure, the term “removably attached” or “removably inserted” shall refer to the joining of two components or a component and an element in a manner such that the two components are secured together, but may be readily detached from one another. Examples of removable attachment mechanisms may include hook and loop fasteners, friction fit connections, interference fit connections, threaded connectors, cam-locking connectors, compression of one material with another, and other such readily detachable connectors. 
     For purposes of clarity, a cross-sectional view of die assembly  150  is also provided in  FIG. 4 . As noted above, it can be seen that a substantially continuous and hollow cavity or die channel  510  is formed as the four components are linked together. It can be understood that, in one implementation, the material of the workpiece is expanded in the middle segment, and then it is extruded to regain its initial diameter. As a result of this severe deformation, as well as the strain imposed on the workpiece, the microstructure of the workpiece changes and an ultrafine-grained and/or nanostructured material can formed. The application of hydrostatic pressure allows long UFG materials to be fabricated, and improves the properties of the finished product. 
     For purposes of illustration,  FIG. 5A  includes a photograph of an implementation of a product formed by a hydrostatic cyclic expansion extrusion process. In one study, an aluminum alloy  1050  was used. After being processed in the HCEE apparatus, the aluminum alloy workpiece was ultrafine-grained. In addition,  FIG. 5B  depicts an OM micrograph of an annealed aluminum AL  1050  microstructure and TEM micrograph of the two cycles hydrostatic cyclic expansion extrusion processed sample. 
     Referring to  FIG. 6 , a graph presenting a hardness distribution in an annealed sample and first pass of an implementation of the hydrostatic cyclic expansion extrusion process is provided. 
     In addition,  FIG. 7  is a graph presenting stress-strain data of unprocessed and HCEE processed samples. In this case an annealed microstructured aluminium workpiece formed through a HCEE process was tested. It can be seen that the final strength of the product increased by approximately  220  percent in the first pass of the HCEE process. As the number of passes the workpiece is exposed to increases, the strength of the workpiece increases as well, as reflected by the curve associated with the second pass. 
     Thus, as presented herein, the HCEE process can provide for the fabrication of ultrafine-grained and/or nanostructured bulk articles in long lengths. Testing of the process has shown that articles comprising materials that have low formability in room temperature such as magnesium can be produced. Furthermore, it should be understood that in addition to the production of UFG long length rods at ambient temperature, the disclosed HCEE process and apparatus can be used at high temperature for materials that are not prone to deformation at room (or ambient) temperatures, such as magnesium and titanium, and other materials that deform only at relatively higher temperatures. 
     The inclusion of a layer of lubricating fluid provides the system with substantially reduced friction of the die as a result of the separation of the workpiece and the inner surface of the cavity. The production of long materials with a favorable strength-weight ratio offer many advantages to the automotive and aerospace industry. With the elimination of the effects of friction in the disclosed HCEE process, the mass production of long metal articles of ultrafine grained and nanostructured materials become possible. 
     While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that the teachings may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all applications, modifications and variations that fall within the true scope of the present teachings. 
     Unless otherwise stated, all measurements, values, ratings, positions, magnitudes, sizes, and other specifications that are set forth in this specification, including in the claims that follow, are approximate, not exact. They are intended to have a reasonable range that is consistent with the functions to which they relate and with what is customary in the art to which they pertain. 
     The scope of protection is limited solely by the claims that now follow. That scope is intended and should be interpreted to be as broad as is consistent with the ordinary meaning of the language that is used in the claims when interpreted in light of this specification and the prosecution history that follows and to encompass all structural and functional equivalents. Notwithstanding, none of the claims are intended to embrace subject matter that fails to satisfy the requirement of Sections  101 ,  102 , or  103  of the Patent Act, nor should they be interpreted in such a way. Any unintended embracement of such subject matter is hereby disclaimed. 
     Except as stated immediately above, nothing that has been stated or illustrated is intended or should be interpreted to cause a dedication of any component, step, feature, object, benefit, advantage, or equivalent to the public, regardless of whether it is or is not recited in the claims. 
     It will be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. Relational terms such as first and second and the like may be used solely to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “a” or “an” does not, without further constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
     The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various implementations. This is for purposes of streamlining the disclosure, and is not to be interpreted as reflecting an intention that the claimed implementations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed implementation. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter. 
     While various implementations have been described, the description is intended to be exemplary, rather than limiting and it will be apparent to those of ordinary skill in the art that many more implementations and implementations are possible that are within the scope of the implementations. Although many possible combinations of features are shown in the accompanying figures and discussed in this detailed description, many other combinations of the disclosed features are possible. Any feature of any implementation may be used in combination with or substituted for any other feature or element in any other implementation unless specifically restricted. Therefore, it will be understood that any of the features shown and/or discussed in the present disclosure may be implemented together in any suitable combination. Accordingly, the implementations are not to be restricted except in light of the attached claims and their equivalents. Also, various modifications and changes may be made within the scope of the attached claims.