1. Field
The present disclosure generally relates to the powder metallurgy, and deals more particularly with a method and die for fabricating crack-free direct consolidated powder-based metallic parts.
2. Background
Powder metal technology is sometimes used to produce near-net-shape (NNS) metallic parts, eliminating the need for metal removal processes such as machining, and thereby reducing costs. Blended, fine powder materials such as titanium alloys are compacted into the shape of a part, known as a compact. The compact is then sintered in a controlled atmosphere to bond the powder materials into a finished part. In one compaction process known as cold isostatic compaction (CIP), a flexible die is filled with metallic powder and placed in a press where it is immersed within a working medium, such as a liquid. The press compresses the liquid, causing a compaction pressure to be uniformly applied around the surface of the die. The die flexes slightly, transmitting the compaction pressure to the powder to compress and form the compact. The compact is then removed from the die and transferred to a sintering furnace where elevated temperature bonds the metallic powder particles into a solid part.
Problems may be encountered where the die includes internal die components for forming features or details of the part. For example, where the internal die components are asymmetrically shaped or arranged, the applied compaction pressure may impose unbalanced loads on the die components which cause them to bend or deform. When a compaction cycle is complete and the compaction pressure is withdrawn, the deformed die components flex back to their original shape. This flex-back of the die components may generate localized biaxial tensile forces within the powder compact, particularly near the surface. At this stage of processing, the compact is relatively fragile and has minimal fracture toughness because the powder particles in the compact are not yet metallurgically bonded together. Consequently, in some cases, the tensile forces generated by flex-back of the internal die components may cause undesired deformation of the compact, and/or localized cracking of the compact.
Accordingly, there is a need for a method and a die for making crack-free NNS powder metal parts, particularly where the die includes die components subject to unbalanced loading.
The disclosed embodiments enable crack-free fabrication of NNS parts from metallic powders that are direct consolidated using cold isostatic pressing and subsequent vacuum sintering into a solid part. Flex-back of internal die components causing residual tensile stresses in powder compacts is substantially eliminated. Reduction or elimination of biaxial tensile stresses reduces or eliminates the possibility of cracking of the powder compact. Lower tensile stresses are achieved by introducing metallic powder on both sides of internal die components used to shape metallic powder and react compaction forces.
According to one disclosed embodiment, a method is provided of fabricating a near net shape metallic part. The method comprises placing at least one die component inside a flexible container, the die component having opposite sides and a plane extending therethrough. The method further comprises filling the container with a metallic powder, including placing the metallic powder on both of the opposite sides, and compacting the metallic powder into a powder compact, including compressing the flexible container. The method also includes removing the powder compact from the container, and sintering the powder compact into a solid part. The die component may be a metal plate, and filling the container may include introducing a layer of the metallic powder into a lower interior region of the container, and placing at least one die component includes placing the metal plate on the layer of the metallic powder. Filling the container includes introducing a layer of the metallic powder into an upper interior region of the container covering the metal plate. The metallic powder may be a hydride-dehydride blended-elemental powder titanium alloy composition. Compacting the metallic powder into a powder compact is performed using cold isostatic pressing.
According to another disclosed embodiment, a method is provided of producing a crack-free metallic powder compact, comprising filling a flexible container with metallic powder, and placing at least one die component in the flexible container, including arranging the die component within the metallic powder in a manner that substantially prevents bending of the die component under load. The method further comprises compacting the metallic powder into a desired powder compact by subjecting the flexible container to a hydrostatic pressure. Arranging the die component within the metallic powder includes introducing the metallic powder on opposite sides of the die component. Arranging the die component with the metallic powder may include placing the die component between two layers of the metallic powder. Compacting the metallic powder into the desired powder compact may be performed by cold isostatic pressing. Arranging the die component may include positioning the die component symmetrically within the container.
According to another disclosed embodiment, a method is provided of producing a crack-free metallic powder compact, comprising fabricating at least one relatively stiff die component, and placing the die component in a flexible container. The method also includes introducing a layer of metallic powder into the flexible container covering the die component, and introducing a layer of relatively soft material beneath the flexible container to balance loading of the die component during compaction. The method further comprises compacting metallic powder into a powder compact by subjecting the flexible container to a hydrostatic pressure. Introducing the layer of relatively soft material may be performed by introducing metallic powder into the flexible container. Fabricating the die component may include producing a set of symmetric mirror image die features, and compacting the metallic powder may be performed by cold isostatic pressing.
According to still another disclosed embodiment, a die assembly is provided for fabricating metallic powder-based parts. The die assembly includes a container having flexible walls configured to be compressed by hydrostatic pressure, and at least one relatively stiff die component located within the container for forming features of the parts, the die component having first and second opposite sides and a plane of overall symmetry. The die assembly further comprises a layer of metallic powder on the first side of the die component, and a layer of relatively soft material on the second side of the die component for balancing loads applied to the die component resulting from compression of the container by the hydrostatic pressure. The relatively soft material may be a metallic powder, and each of the metallic powder and the relatively soft material may be a titanium powder and an alloying element powder. The die component includes a first set of elements on the first side of the die component for forming features of a first part, and a second set of elements on the second side of the die component for forming features of a second part. The first set of elements is a mirror image of the second set of elements. The first and second sets of elements are symmetric about the plane of overall symmetry.
The features, functions, and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments in which further details can be seen with reference to the following description and drawings.
The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein:
The disclosed embodiments provide a method and die assembly for fabricating crack-free, direct consolidated, near net shape (NNS) powder-based metallic parts. For example, referring to
Referring now to
In use, the die components 35 are set and arranged within the container 45, and the container 45 is filled with a desired metallic powder. The metallic powder is then tapped down and the container top wall 32 is installed. The die assembly 26 is placed in an isostatic press (not shown) in which the container hydrostatic compaction pressure is applied to all surfaces of the container 45. As mentioned above, the pressure applied to the container 45 is transmitted to the metallic powder, pressing it into a powder compact that may then be sintered into a solid part 20. Depending on the geometry of the part 20 and the location/orientation of the plane of overall symmetry 24, the pressure applied to the container 45 during the compaction process may result in unbalanced loads being applied to the plate 36 which may deform the plate 36. For example, referring to
Referring particularly to
Attention is now directed to
The embodiment of the die assembly 26 shown in
Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, automotive applications and other application where metallic parts may be used. Thus, referring now to
Each of the processes of method 62 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on.
As shown in
Systems and methods embodied herein may be employed during any one or more of the stages of the production and service method 62. For example, components or subassemblies corresponding to production process 70 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages 70 and 72, for example, by substantially expediting assembly of or reducing the cost of an aircraft 64. Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft 64 is in service, for example and without limitation, to maintenance and service 78.
As used herein, the phrase “at least one of”, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of each item in the list may be needed. For example, “at least one of item A, item B, and item C” may include, without limitation, item A, item A and item B, or item B. This example also may include item A, item B, and item C or item B and item C. The item may be a particular object, thing, or a category. In other words, at least one of means any combination items and number of items may be used from the list but not all of the items in the list are required.
The description of the different illustrative embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different illustrative embodiments may provide different advantages as compared to other illustrative embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.
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Extended European Search Report, dated Jul. 29, 2016, regarding Application No. 16158703.5, 7 pages. |
Number | Date | Country | |
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20160256927 A1 | Sep 2016 | US |