The present invention relates generally to methods and systems for machining composites, and more specifically, to methods and systems for machining composites using electroerosion.
The term “composite material” (also referred to as a “composite”) generally refers to a material made of a mechanical mixture of two or more different materials. In many cases, composites are made of materials having complementary properties, such as where a brittle, high-strength material is encapsulated in a ductile material to give the overall composite sufficient toughness for practical applications. Examples of composite materials include, for example, metal-matrix composites, where a ductile metal is reinforced with a high-strength fiber or particulate phase; concrete, where an aggregate material is bonded together with cement; and fiberglass, where a polymer material is reinforced with glass fibers.
The fabrication of components comprising composites, particularly those composites comprising a significant volume fraction of brittle materials, presents significant technical challenges. The brittle nature of the material presents problems with chipping during machining, for example, often necessitating the use of slow precision processes such as abrasive water-jet cutting and fine diamond grinding to achieve required dimensions and surface finish tolerances.
The problem of slow processing is compounded in applications where the composite component is fabricated by individually machining “blocks” of a first, brittle material to shape, followed by assembly of the blocks into a desired configuration and finally forming a composite component by bonding the blocks together using a second material. This is a common technique used, for example, in the manufacture of large magnets for medical imaging applications. In such a process, a magnetizable material, often a brittle rare earth magnetizable material, is cut by a water-jet cutting apparatus into several specifically shaped blocks that are assembled and bonded together with epoxy to form a magnetizable composite material component. The water-jet process is necessarily slow in order to avoid chipping and cracking the magnetizable material. Further, assembling the blocks requires cumbersome numbering of each block, increasing the chance of error in a final composite shape. It also introduces an irregularity in the final composite shape that is undesirable in composite parts that require a precise shape or have tight tolerances. Certain methods, such as that described in commonly assigned U.S. Pat. No. 6,518,867, allow for the assembly and bonding of the magnetizable material, that is, the formation of the composite, prior to cutting to shape. Although this significantly decreases the processing time, the cutting is still done by a relatively slow process such as water-jet.
Accordingly, it would be advantageous to have faster methods of fabricating components, especially those comprising composite materials that contain brittle materials prone to chipping, to increase productivity and yield of complex products.
The present invention addresses these and other needs by providing a method for fabricating a component including providing at least one workpiece, providing an electroerosion apparatus, and removing a portion of the workpiece by operating the electroerosion apparatus on the workpiece.
An aspect of the invention resides in a method for fabricating a magnet. The method includes providing at least one workpiece that comprises one of Samarium-Cobalt (Sm—Co) and rare earth Iron-Boron (RE-Fe—B) material. The method further comprises providing an electroerosion apparatus, and removing a portion of the workpiece by operating the electroerosion apparatus on the workpiece.
An aspect of the invention resides in a method for fabricating a magnet assembly. The method includes providing at least one workpiece comprising one of Samarium-Cobalt (Sm—Co) and rare earth Iron-Boron (RE-Fe—B) material. An electroerosion apparatus is provided for removing a portion of the at least one workpiece by operating the electroerosion apparatus on the workpiece(s) to form multiple magnet segments. The segments are then assembled to form a magnet assembly.
Another aspect of the invention resides in a method for fabricating a composite magnet, in which a workpiece having a composite material is provided. The composite material includes an epoxy resin and a magnetizable material comprising at least one of Samarium-Cobalt (Sm—Co) and rare earth Iron-Boron (RE-Fe—B) material. An electroerosion apparatus comprising an electrode tool having an abrasive material is provided, and a portion of the workpiece is removed by operating the electroerosion apparatus on the workpiece. At least a portion of the workpiece is removed by an abrasive action of the electrode tool on the workpiece.
According to a disclosed embodiment, a method for fabricating a component includes providing a (meaning at least one) workpiece. The workpiece may be the component itself or a sub-part thereof. An electroerosion apparatus comprising an electrode tool is provided and operated on the workpiece, removing a portion of the workpiece by operating the electroerosion apparatus on the workpiece.
U.S. patent application Ser. No. 10/248,214 discloses an example of the electroerosion apparatus. In general, electroerosion utilizes a rotating movement of a selectable shape, such as cylindrically shaped, or similar profiled electrode, tapered about the longitudinal axis and having a profiled tip to remove material from a workpiece. The tool-electrode, hereinafter referred to as “electrode tool”, is connected to the negative polarity of a power supply, thereby configuring the electrode tool as a cathode, while the workpiece is connected to the positive polarity, thereby configuring the workpiece as an anode. The workpiece 20 is included in the electroerosion apparatus 10. Briefly, according to the physics of electroerosion process, when the cathode tool approaches the anode workpiece surface to a small proximity gap, for example in a range of approximately 10 microns, an electrical discharge or sparking occurs under a voltage across the gap between the cathode tool and the anode workpiece. The gap, which constitutes a machining zone, is typically filled with a liquid electrolyte medium with moderate to low electrical conductivity, and the gap allows for the flow of electrolyte, which removes eroded particles from the gap besides providing a suitable medium for electrical discharge or sparking for electroerosion.
According to an embodiment, a workpiece 20 provided for fabrication includes a magnetizable material. In specific embodiments, the magnetizable material comprises Samarium-Cobalt (Sm—Co), rare earth Iron-Boron (RE-Fe—B) material, or a combination thereof. The electroerosion apparatus 10 having an electrode tool 30 removes at least a portion of the workpiece. As used herein the term “magnetizable material” will be generally understood to include permanent magnet material including rare earth materials, such as Samarium-Cobalt (Sm—Co) and rare earth Iron-Boron (RE-Fe—B) material, for example Neodymium Iron Boron (Nd—Fe—B), and soft magnetizable material, such as ferritic steels, nickel-iron alloys, iron-cobalt alloys, and combinations thereof, for example, Alnico (aluminum, nickel and cobalt alloy), among others. It will be further appreciated that this description is meant to be indicative of the general category of magnetizable materials, and not meant to be restrictive to the specific materials as discussed herein.
According to an embodiment of the fabricating method, providing at least one workpiece comprises providing multiple workpieces. The multiple workpieces are assembled to form a composite material. At least a portion of the composite material is removed by operating the electroerosion apparatus on the composite material. In specific embodiments, the assembling of multiple workpieces comprises bonding the multiple workpieces using a bonding material. The bonding material may comprise a synthetic resin and a silicone, and according to an embodiment the synthetic resin comprises an epoxy. In certain embodiments, the multiple workpieces comprise a magnetizable material, which may comprise a rare earth element for example, neodymium, samarium, among others. In specific embodiments, the magnetizable material comprises one of Samarium-Cobalt (Sm—Co) and rare earth Iron-Boron (RE-Fe—B) material.
According to another embodiment, the workpiece is a composite material. In specific embodiments, the composite material include electrically non-conductive materials, such as, for example, a silicone; a synthetic resin, for example an epoxy resin; a ceramic, for example one of oxides, borides, suicides, aluminides, hydrides, carbides, nitrides, ferrites, carbo-oxy-nitrides, boro-silicides, boro-carbides or combinations thereof; and a fiberglass, or combinations thereof.
In general, conductive materials will be understood to have electrical conductivity generally above about 0.01 Siemens/cm, and the materials with a much lower conductivity, such as that below about 0.0001 Siemens/cm, will be generally understood as non-conductive materials. In general, fabricating non-conductive materials using electroerosion presents challenges because sustenance of an arc is extremely difficult for non-conductive materials. Typically, instance of such non-conductive materials may extinguish the arc established between the workpiece and the tool, and hence, may involuntarily terminate the electroerosion process. As is appreciated, certain embodiments disclosed herein overcome the challenge of removing non-conductive material by using an abrasive action of the tool 30 having a serrated and/or abrasive working surface 12 to remove a non-conductive portion of the workpiece 20.
According to other specific embodiments, the composite material comprises intermetallic materials, such as titanium-aluminide and molybdenum-disilicide, among others. Intermetallic materials are different from metal alloys, in that the constituents of intermetallic materials are chemically associated, whereas in alloys the constituent elements are substantially physically mixed. In another embodiment, the composite material comprises a metal, and/or a metal alloys. Examples of metals include, without limitation, nickel, iron, copper, aluminum, cobalt, niobium, tantalum, molybdenum, chromium, zinc, tin, zirconium, titanium, and alloys comprising any of the foregoing. According to another embodiment, the composite material comprises printed circuit boards. Printed circuit boards have a non-conductive substrate layer over which conductive circuits, typically made of metal, are formed. Electronic components such as circuit chips may be mounted on the printed circuit board and conductively associated with the printed circuit board by metal contacts such as solder joints.
According to a specific example embodying one of the methods disclosed herein, a magnet is fabricated by providing a workpiece including one of Samarium-Cobalt (Sm—Co) and rare earth Iron-Boron (RE-Fe—B) material, or a combination thereof. The electroerosion apparatus 10 operates upon the workpiece 20, and removes at least a portion of the workpiece. The fabricated magnets so obtained, may be used for providing magnet components for medical imaging equipments, among other applications.
According to another embodiment, a magnet assembly is fabricated by providing one or multiple workpieces comprising at least one of Samarium-Cobalt (Sm—Co) and rare earth Iron-Boron (RE-Fe—B) material, and an electroerosion apparatus. The electroerosion apparatus 10 operates upon the workpiece(s), removing at least a portion of the workpiece(s), forming a number of magnet segments. The magnet segments are then assembled to form a magnet assembly.
According to an example for fabricating a composite magnet, a workpiece comprising a composite material is provided. Referring to
While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.