Patent Application
20140283574
The present invention relates generally to extrusion processing and extrusion tools. More particularly, the invention relates to a shear-assisted extrusion system and process for production of extrusion structures including high-performance extrusion structures.
Extrusion is a process in which a billet or block of material composed of metals, polymers, ceramics, or foodstuffs is forced through an extrusion die with a ram tool that transmits an extrusion force to the billet that plasticizes the material. The plasticized material is then extruded through the orifice of an extrusion die that forms an extrusion product (extrudate). The resulting extrusion product has a cross-sectional area or profile that is typically smaller than that of the original billet. In conventional extrusion, only the linear or axial motion of the ram plasticizes and extrudes the billet material. Extrusion processes fall under two general categories: (i) direct extrusion, and (ii) indirect extrusion. In direct extrusion, the extrusion die and a solid ram are positioned on opposite ends of the billet. In indirect extrusion, the extrusion die is attached to a hollow ram on the same side of the billet. A mandrel may be attached to the hollow ram during extrusion of the billet material to produce hollow extrudates. Problems with extrusion processing are well known in the art. Conventional extrusion requires high extrusion pressures on the order of 400 MPa or higher. In addition, non-uniform deformation of extrudates is common, which yields extrusion products with structural and physical property variations in both the longitudinal and transverse directions. Further, microstructure refinement is often inconsistent and typically insufficient so mechanical properties vary widely. And, while processes like mechanical alloying, rapid solidification, friction stir processing, equal channel angular extrusion, twist extrusion, waffle pattern rolling, non-axis symmetric rolling, and other processes have been used to make high performance materials, such processes are not presently cost-effective for commercial production. Accordingly, new extrusion processing tools and processes are needed that overcome conventional force requirements and other limitations of conventional extrusion processing. The present invention addresses these needs. The purpose of the foregoing abstract is to enable the United States Patent and Trademark Office and the public generally, especially scientists, engineers, and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The abstract is neither intended to define the invention of the application, which is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way.
The present invention includes an extrusion assembly and process for production of high-performance extrusion structures and extrusion products. The extrusion assembly may include a shear tool with an extrusion die of a selected shape. The shear tool is configured to apply a rotational shear (shearing) force and an axial extrusion pressure to the face of a billet material at the shear tool/billet interface positioned within the die chamber of the extrusion assembly that plastically deforms the billet material. The billet may include various selected materials including, but not limited to, e.g., metals, metal alloys, cast solids, powders, and non-solids. The extrusion die may be positioned at the billet end of the shear tool and may include an orifice with a selected shape and selected dimensions. The extrusion die may extrude the plasticized billet material along the length of the inner bore of the shear tool in response to the axial extrusion pressure applied to the face of the billet yielding extrusion structures and products with selected shapes including complex shapes with selected dimensions. The inner bore of the shear tool may include selected dimensions. The shear tool forms extrusion structures and products at an axial extrusion pressure significantly lower than required for extrusion structures without the shearing force applied. The extrusion die may extrude the plasticized billet material along the length of the inner bore of the shear tool in response to the axial extrusion pressure applied to the face of the billet material.
The present invention also includes a shear-assisted extrusion process that produces extrusion structures including high-performance extrusion structures. The process may include applying a rotational shearing force and an axial extrusion force to the face of the billet material at the shear tool/billet interface to plasticize the billet material. The shearing force may be applied at the shear tool/billet interface by rotation of the shear tool at a selected rotation speed relative to a stationary billet, or by rotation of the billet relative to a stationary shear tool, and/or by rotation of the shear tool at a rotation speed that is different relative to the rotation of the billet, or vice versa. The plasticized material may be extruded the through an orifice of an extrusion die positioned on the billet side of the shear tool. The orifice of the extrusion die may include various selected shape that yield extrusion structures with selected shapes. Rotational shear force values are not limited. Shear forces are selected that reduce the axial extrusion pressures needed to plasticize billet materials. The extrusion assembly extrudes the billet material at an axial extrusion force less than that required for extrusions performed without the rotational shearing force applied by the shear tool and/or the billet at the shear tool/billet interface.
In some applications, the billet may be a pierced cast billet, a pre-drilled cast billet, a solid cast billet, or loose powder billets.
Extrusion structures may be hollow or solid. The extrusion assembly may include a mandrel that inserts into the inner bore of the shear tool to a selected depth. In some applications, the mandrel may be introduced through the center of the billet and into the inner bore through an orifice of the extrusion die positioned at the billet end or other end of the shear tool. The mandrel may include a width dimension that is less than the dimension of the orifice of the extrusion die that forms a separation gap between the surface of the mandrel and the inner wall of the extrusion die when the mandrel is inserted. During extrusion, the separation gap allows plasticized materials to flow past the mandrel along the length of the inner wall of the extrusion die and into the inner bore of the shear tool that yields hollow extrusion structures with selected shapes. The extrusion die determines the wall thickness of hollow extrusion structures produced during extrusion.
Shapes are not limited. In various applications, extrusion structures may be hollow tubular structures with selected uniform or non-uniform inner dimensions and selected uniform or non-uniform wall thicknesses. In various applications, extrusion structures may be solid extrusion structures with selected uniform or non-uniform cross-sections. No limitations are intended.
In some applications, the mandrel may be a fixed mandrel or a floating mandrel. In some applications, the extrusion die may be a bridge extrusion die. However, mandrels and extrusion dies are not limited thereto.
The shear tool may include one or more surface features positioned at the billet end of the shear tool that engage the face of the billet material to facilitate shear-assisted extrusion and flow of plasticized materials during operation. Features may include, but are not limited to, e.g., scrolls, flutes, vanes, or other features including combinations of these features.
In some applications, the extrusion assembly may include a heating device such as an external heating device or an embedded heating device and/or a cooling device positioned to heat or cool the billet material positioned within the die chamber, respectively. Billet materials may also be heated using the frictional heat generated from the plastically deformed billet materials.
Extrusion temperatures are not limited. In some applications, extrusion of the plasticized billet material may be performed at a temperature selected between about −196° C. and about 0° C. In some applications, extrusion of the plasticized billet material may be performed at a temperature selected between about 0° C. and about 1000° C., or greater.
Shearing forces applied by the present invention may be obtained by rotating the billet while keeping the shear tool stationary, by rotating the shear tool while keeping the billet material stationary, or by rotating the shear tool at a rotational speed different than the rotational speed of the billet material or vice versa.
In some applications, applying the rotational shear force and extruding the plasticized billet material may be performed simultaneously. In some applications, applying the rotational shear force and extruding the plasticized billet material may be performed independently from the other step.
In some applications, axial extrusion pressures required for extrusion may be reduced by at least a factor of about 16 times compared to extrusion operations performed without the rotational shearing force. In some applications, the axial extrusion pressure is at or below about 50 MPa. In some applications, the axial extrusion pressure is at or below about 25 MPa. However, axial pressures are not limited.
Feed rates for the billet are not limited. In some applications, feed rates may be between about 0.15 inches (0.38 cm) per minute and about 1.18 inches (3.0 cm) per minute.
Rotational speeds are not limited. In various applications, rotation may be performed at a rotation speed between about 500 revolutions-per-minute (rpm) and about 1000 rpm. In some applications, rotation may be performed at a rotation speed up to about 1000 rpm. In some applications, rotation speed may be between about 10 rpm and about 1000 rpm.
Shear-assisted extrusion processing of the present invention can refine the microstructure of billet materials including cast billet materials and powdered billet materials, or other processed materials. For example, billets containing coarse matrix grains and second-phase intermetallic particles with sizes up to a millimeter (1000 microns) may be refined in a single process step to yield smaller grains and particles. In some applications, the process refines the microstructure to yield fine matrix grains and second-phase intermetallic particles with a size less than or equal to about 10 microns. In some applications, the process yields very (ultra) fine matrix grains and second-phase intermetallic particles with a size less than or equal to about 1 micron or finer. In some applications, the process yields grains with a size less than about 100 nanometers or finer. However, no limitations are intended. In some applications, the present invention alters the morphology of second-phase particles in the starting billet material from an aspect ratio above about 2 to an aspect ratio below about 2 following the shear-assisted extrusion processing. In some applications, microstructure grains and particles of the original billet material are refined by at least a factor of 2 times to a size that is at least one-half that of the original billet material prior to extrusion processing or finer. Shear-assisted extrusion processing can also uniformly distribute grains and particles within the refined microstructure.
In some applications, extrusion structures are tubular extrusion structures that may be included as components of a compression device, a stent device, a bending-resistant device. Compression devices include, but are not limited to, e.g., compression bumpers or collapsible safety frames deployed in automobiles. In various applications, extrusion structures of the present invention may be incorporated as components of selected structures such as in support pillars or other structures deployed in vehicles to enhance mechanical properties, performance, or to resist bending. In some applications, extrusion structures may be included as components of a stent device.
A new shear-assisted extrusion apparatus and process are disclosed for producing high-performance extrusion structures including, e.g., hollow and solid extrusion structures. In the following description, embodiments of the present invention are shown and described that include a best mode contemplated for carrying out the invention. It will be clear from the following description that the invention is susceptible of various modifications and alternative constructions. The present invention is intended to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined in the claims. Therefore the description should be seen as illustrative and not limiting.
Extrusion assembly 100 may include a container 8 comprised of, e.g., an upper container plate 7 and a lower container plate 9. Container 8 may also be a single component. No limitations are intended. In the instant embodiment, outer (top) die ring 14 and a lower die ring (described further in reference to
Shear tool 2 may include an inner bore 4 of a selected inner dimension with orifices 5 positioned at respective ends of shear tool 2. Outer (top) die ring 14 and lower die ring (not shown) secure shear tool 2 in die chamber 10. Outer die ring 14 may be secured with locking keys (not shown) that insert into key slots 20 positioned on respective sides of shear tool 2. Position and number of key slots 20 is not limited. During operation, plasticized billet materials extrude along the length of inner bore 4 and exit from an orifice 5 of shear tool 2 as extrusion structures (extrudates) 6. Direction of release of extrudates is not limited, as detailed further herein.
In operation, shear tool 2 when introduced into chamber 10 applies a rotational shear (shearing) force 26 and an axial extrusion force 24 to the face of billet material 22 at the shear tool/billet interface within die chamber 10. Rotational shear (shearing) force 26 assists or promotes plasticization of billet material 22. In some embodiments, rotational shear (shearing) force 26 may be applied by rotating the shear tool 2 at a selected rotation speed while keeping billet 22 stationary. In some embodiments, rotational shear (shearing) force 26 may be applied by rotating the billet 22 while keeping shear tool 2 stationary. In some embodiments, rotational shear (shearing) force 26 is applied by rotating shear tool 2 and billet 22 at different rotation speeds relative to the other component or material.
Die assembly 100 may further include an optional heater/cooler 36 that couples externally to, or is embedded within, outer die ring 14 to heat or cool billet material 22 positioned within chamber 10. Heating and cooling of billet material 22 can be used to assist deformation of billet material 22, e.g., by softening the billet material in cases where the billet material shows limited initial plasticity. Heating may also be used, e.g., to lower frictional forces that assist extrusion of the plasticized billet material. All heating and cooling devices as will be selected by those of ordinary skill in the art in view of this disclosure are within the scope of the present invention. No limitations are intended.
Application of axial extrusion force 24, rotational shear force 26, and/or heat or cooling to billet material 22 plasticizes the billet material, which forms a region of plastic deformation (SPD) 34 positioned at the shear tool/billet interface. SPD region 34 is typically narrow (e.g., <300 microns) to reduce extrusion force 24 needed to extrude the plasticized billet materials.
Plasticized billet materials may enter into inner bore 4 through an orifice (not shown) positioned, e.g., at the billet end of shear tool 2. In the instant embodiment, plasticized material extrudes past mandrel 28 and flows upward to yield extrusion structures (extrudates) 6 that are hollow extrusion structures (e.g., tubes). In some embodiments, extrusion structures may include uniform inner dimensions and wall thicknesses. In some embodiments, extrusion structures may include non-uniform inner dimensions and wall thicknesses. When mandrel 28 is not employed, extrusion structures are solid structures. Solid extrusion structures may include uniform dimensions or non-uniform dimensions. In the instant embodiment, extrusion structures (extrudates) 6 may be released through another orifice 5 positioned at the top end of shear tool 2.
Billets may be in the form of solids, cast solids, blocks, semi-solids, non-solids, and/or powders. Cast billets may be cast using casting techniques known in the casting arts. Billets may be composed of, or include, any material that can be plastically deformed (plasticized) at selected temperatures. Billet materials are preferred that deliver desirable mechanical properties such as ductility, compression strength, bendability, or selected microstructural refinement, or other suitable properties to the extrusion structures or products produced. However, no limitations are intended. In various embodiments, billets may include or be constructed of various materials including selected alloys and high-performance alloys. In some embodiments, billets may employ magnesium alloys. Magnesium alloys include, but are not limited to, e.g., magnesium alloys (e.g., AZ31F); magnesium-aluminum (Mg—Al) alloys; magnesium-zinc (Mg—Zn) alloys; magnesium-zirconium (Mg—Zr) alloys; magnesium-silicon (Mg—Si) alloys (e.g., Mg-2Si; Mg-7Si); magnesium alloys that include rare-earth (RE) elements; magnesium alloys that include various non-rare-earth elements; magnesium-zinc-zirconium alloys (e.g., ZK60-T5), and combinations of these various alloys. While magnesium-based alloys are described herein due to their desirable ductility properties for compression applications, the present invention is not intended to be limited thereto. In some embodiments, billets used for extrusion may include a central bore or hollow cavity through which the mandrel may be introduced during extrusion. In some embodiments, billets may be solid billets that are pierced or predrilled prior to use.
The shear tool of the present invention may include an extrusion die that includes an inner bore with various selected shapes that delivers extrusion structures with selected shapes including complex shapes. Shapes include, but are not limited to, e.g., round, oval, circular, square, rectangular, triangular, pentagonal, hexagonal, octagonal, ellipsoidal, trapezoidal, rhombal, or combinations of these various shapes. Complex shapes include, but are not limited to, e.g., spherical, tetrahedral, pyramidal, pentagonal, pentagonal pyramidal, irregular, ortahedral, icosahedral, dedecahedral, stars, cones, boat-shape ovals, parallelograms, rounded rectangles, chevrons, round left, round right, bent arrows, arrows, double arcs, curved, obround, single-D, double-D, long-D, quad-D, letters, numerical, alpha-numerical, symmetrical shapes, non-symmetrical shapes, oblong shapes, rings, pictoral shapes, other non-standard shapes, including, e.g., embedded shapes such as, e.g., ovals within a square, squares within an oval, and like embedded shapes. All shapes as will be selected by those of ordinary skill in the art in view of the disclosure are within the scope of the present invention. No limitations are intended.
TABLE 1 lists compositions of alloy billets and process parameters employed in selected extrusion tests.
Billet feed rates are not limited. Feed rates may be selected that maximize extrusion throughput, plasticity, flow, uniformity of the extrudates, and other physical and mechanical properties. In some embodiments, feed rates for billet deformation may be greater than about 0.01 inches per minute. In some embodiments, feed rates for billet deformation may be between about 0.01 inches per minute and about 0.1 inches per minute. In some embodiments, feed rates for billet deformation may be between about 0.1 inches per minute and about 1.0 inches per minute. In some embodiments, feed rates for billet deformation may be between about 1.0 inches per minute and about 10 inches per minute.
Rotation rates for the rotatable shear tool or the billet are not limited. In some embodiments, rotation may proceed at a rate up to about 1000 revolutions-per-minute (rpm). In some embodiments, rotation speed may be between about 50 rpm and about 500 rpm. In some embodiments, the process may include rotating the ram at a rate between about 500 rpm and about 1000 rpm.
Extrusion temperatures are not limited. Temperatures may be selected that maximize shear on the face of the billet, plastic deformation of the selected billet materials, microstructure refinement, and other physical and mechanical properties. In some embodiments, extrusion may be performed at temperatures above about 100° C. In some embodiments, extrusion may be performed at temperatures between about 100° C. and about 500° C. In some embodiments, extrusion may be performed at temperatures between about 500° C. and about 1000° C. In some embodiments, extrusion may be performed at temperatures above about 1000° C. In some embodiments, extrusion may be performed at temperatures below about 100° C. In some embodiments, extrusion may be performed at temperatures between about 0° C. and about −100° C. In some embodiments, extrusion may be performed at temperatures between about −100° C. and about −196° C. (the temperature of liquid nitrogen). No limitations are intended. In other embodiments, temperatures may be selected that are identified from equilibrium phase diagrams of the selected alloys or the billet materials being processed. No limitations are intended.
TABLE 2 lists results obtained from extrusion of selected materials.
Extrusion ratio (R) may be calculated from Equation [1], as follows:
R=A
0
/A
f [1]
Here, (A0) is the initial cross sectional area of the billet, and (Af) is the final cross-sectional area of the extrusion structures following extrusion.
In some embodiments, shear-assisted extrusion of the present invention may be performed continuously to produce extrusion structures of any selected and/or extended lengths. In some embodiments, shear-assisted extrusion may be performed semi-continuously or batch-wise to produce various and/or multiple extrusion structures.
Shear-assisted extrusion processing of the present invention refines the microstructure of cast billets. For example, billets containing coarse matrix grains and second-phase intermetallic particles with sizes up to a millimeter (1000 microns) may be refined in a single process step. In some embodiments, the process yields a microstructure containing fine matrix grains and second-phase intermetallic particles with a size less than or equal to about 10 microns. In some embodiments, the process yields a microstructure containing very (ultra) fine matrix grains and second-phase intermetallic particles with a size less than or equal to about 1 micron or finer. However, no limitations are intended. For example, in some embodiments, the present invention alters the morphology of second-phase particles in the starting billet material from an aspect ratio above about 2 to an aspect ratio below about 2 following shear-assisted extrusion processing. In some embodiments, microstructure grains and particles of the original billet material are refined by at least a factor of 2 times or finer. Grains and/or particles are formed that have a size at least one-half that of grains in the original billet material prior to extrusion processing. Shear-assisted extrusion processing can further distribute grains and particles uniformly within the refined microstructure.
Extrusion structures of the present invention find application as parts, pieces, or components in various devices. In some embodiments, tubular extrusion structures of the present invention may find application as crush tubes or compression structures in front and rear bumpers of automobiles or in other compression applications. In other embodiments, extrusion structures of the present invention may be in the form of lightweight alloy tubes that find application as dissolvable stents. For example, tubes may be inexpensively produced and subsequently machined into stents. In yet other embodiments, hollow extrusion structures of the present invention may find application as bendable components, e.g., in pillar applications for use in automobiles. All applications as will be envisioned by those of ordinary skill in the art in view of the disclosure are within the scope of the present invention. No limitations are intended.
While preferred embodiments of the present invention have been shown and described, it will be apparent to those of ordinary skill in the art that many changes and modifications may be made without departing from the invention in its true scope and broader aspects. The appended claims are therefore intended to cover all such changes and modifications as fall within the spirit and scope of the invention.
This is a Non-Provisional application that claims priority from U.S. Provisional Application No. 61/804,560 filed 22 Mar. 2013, which reference is incorporated herein in its entirety.
This invention was made with Government support under Contract DE-AC05-76RLO-1830 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61804560 | Mar 2013 | US |
