Patent Publication Number: US-2004052674-A1

Title: Ultrasonic powdered metal compaction

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Technical Field  
       [0002] The present invention relates generally to an apparatus for producing powdered metal cores for an ignition coil, and more particularly, to the use of ultrasonic vibrations to produce powdered metal cores for an ignition coil.  
       [0003] 2. Description of the Related Art  
       [0004] In the past, ignition coil assemblies for automobile engines were placed in the engine compartment where there was sufficient space for the coil assemblies. Long wires were used to connect the coil assemblies to the spark plug assemblies. The drawbacks to this design included power losses in the wires and the inefficient amount of space used in the engine compartment. The trend is toward smaller ignition coil assemblies that can be placed close to the spark plug assembly or integrated with it. The most efficient design for these space-saving ignition coil assemblies is a cylindrical shape. However, the current methods of making the metal core for ignition coil assemblies are not entirely successful in creating cores with a sufficient density or that do not involve expensive steps in the process. One method of creating a core is uniaxially compacting powdered iron particles into cores, the particles being encapsulated individually in polymer coatings. However, with this method, the resulting cores do not have a high enough density or a uniform sufficiently density. The core center density is inadequate to provide the core with the necessary flux carrying capacity for an ignition coil. Attempts to compact the powdered iron particles in a core in a horizontal direction to improve the density of the core results in burrs created at the parting lines, which run along the width of the core. Another method of creating a core involves the use of electromagnetic compaction whereby powdered metal particles are placed in a cylinder made of conductive material, preferably copper, and the filled cylinder is placed in an electromagnetic field ranging from about 1-200 Oersted, as seen by reference to U.S. Pat. No. 6,156,264 issued to Johnston et al. Johnston et al. disclose a system wherein the magnetic field will generate eddy currents in the cylinder, which generates a counter magnetic field, thereby creating forces on the powdered iron particles that result in compaction having a uniform, high density core. In the system of Johnston et al., the cylinder serves as a pressure-transmitting medium to the powdered particles. While this process does result in a uniform, high density core, the process is expensive and requires the use of high voltages. Therefore, there exists a need to provide an apparatus that is capable of producing powdered metal cores for ignition coils that minimizes or eliminates one or more of the above deficiencies.  
       SUMMARY OF THE INVENTION  
       [0005] It is an object of the present invention to provide a solution to one or more of the above-mentioned deficiencies. In one aspect of the invention, an apparatus is provided for making ignition coil cores using a powdered metal having magnetically-permeable material. The apparatus includes an ultrasonic tool. The ultrasonic tool includes a cavity that has a first axis. Powdered metal is placed into the cavity. The tool vibrates to provide radial compression. The apparatus also includes a first and a second ram, each located along the first axis, wherein the tool cavity is located between the rams. The rams are configured for opposing movement, each toward the tool cavity, to provide axial compression of the powdered metal placed in the cavity. The apparatus further includes a means for simultaneously controlling the radial compression provided by the ultrasonic tool and the axial compression provided by the first and second rams. In one embodiment, the rams are retractable along the first axis and radially to facilitate removal of the core.  
       [0006] In a second aspect of the invention, a method is provided for making ignition coil cores using a powdered metal having magnetically-permeable material. The method includes the steps of providing an ultrasonic tool having a cavity that is located between a first ram and second ram. The rams are configured for opposing movement toward the cavity along a first axis. The next steps involve filling the cavity with a powdered metal and moving the rams toward each other into the cavity to compress the powdered metal. Finally, simultaneously vibrating the tool while moving the rams. In one embodiment, the rams move and the tool vibrates to aid in removal of the completed core from the cavity.  
       [0007] Other objects, features, and advantages of the present invention will become apparent to one skilled in the art from the following detailed description and accompanying drawings illustrating features of the this invention by way of example, but not by way of limitation. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008]FIG. 1 is a simplified perspective view of an apparatus according to the invention.  
     [0009]FIG. 2 is a perspective view of a completed central core made using the apparatus of FIG. 1.  
     [0010]FIG. 3 is a flow chart of a method of making a central core according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0011] Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views, FIG. 1 is a simplified perspective view of an embodiment of an apparatus  10  for making a powdered metal core. Apparatus  10  includes an ultrasonic tool  12  having a cavity  14 , a first ram  16 , and a second ram  18 . Cavity  14 , first ram  16 , and second ram  18  are each located along a first axis  20 . Cavity  14  is located between first ram  16  and second ram  18 . First ram  16  and second ram  18  are configured for opposing movement via respective movement apparatus  21   a  and  21   b , each ram  16 ,  18  being capable of movement toward cavity  14 . Apparatus  10  incorporates equipment including power supplies  22 ,  24 , converters  26 ,  28 , and boosters  30 ,  32  to provide the necessary mechanical power for tool  12  to ultrasonically vibrate. Apparatus  10  also includes a means, such as a control unit  34 , to control operation of tool  12  and first ram  16  and second ram  18 .  
     [0012] Apparatus  10  is used as follows. Powdered metal is placed in cavity  14 . The powdered metal may be made up of magnetically permeable particles. Substantially pure iron may be used. Alternatively, iron alloys that include copper, nickel, zinc, cobalt, silicon or manganese may be used. Particle size may vary, and may range from about 5 to 400 micrometers. While not required, the particles may be encapsulated in a polymeric material. This encapsulation aids in removal of the completed metal core  39  from cavity  14 . The particles must, however, be coated with an electrical insulator, polymeric or otherwise. Each particle may comprise an iron or iron alloy encapsulated in a continuous shell of an amorphous thermoplastic, thermoset and/or inorganic material, each encapsulant comprising an electrical insulator. The types of powdered metal particles and coatings may comprise those as described in U.S. Pat. No. 6,156,264 granted to Johnston, et al., assigned to Delphi Technologies, Inc., hereby incorporated by reference. Without limitation, these particles may include substantially pure iron or an iron alloy. The iron alloys that may be used include, without limitation, copper, zinc, nickel, cobalt, silicon, and manganese. The thermoplastic shell may be selected from the group consisting of a polyetherimide, polyethersulfone, and polyamideimide having a heat deflection greater than about 200° C. The thermoset shell may be selected from a group consisting of but not limited to phenolics, epoxies, alkyds, polyesters or silicones. The inorganic shell may be selected from a group consisting of but not limited to silicates, metal oxides, ceramics, borides, nitrides, carbides, ferrites, or phosphates.  
     [0013] Tool  12 , ultrasonically vibrates radially in a plane substantially perpendicular to axis  20 , providing radial compression of powdered metal. It also vibrates vertically to reduce friction so less force is required from rams  16  and  18 . Tool  12  may vibrate at a preferable operating frequency of about 20 kHz and may vibrate at variable amplitudes. Power supplies  22 ,  24  coupled with power converters  26 ,  28  provide tool  12  with the mechanical power to vibrate at an ultrasonic frequency. Boosters  30 ,  32 , resonant at the operating frequency, may be used to increase the vibration amplitude, preferably to provide a 1:3 ratio amplitude gain. Power supplies  22 ,  24  are controlled by control unit  34 , which allows power supplies  22 ,  24  to operate in phase with each other. Tool  12  may comprise conventional components known to those of ordinary skill in the art. Tool  12  and power supplies  22 ,  24 , converters  26 ,  28 , and boosters  30 ,  32  may comprise commercially available components, such as a Power supplies—Branson 920 MA; Converters—Branson Model 922 JA; and Boosters—Branson part #E.O.P. 109-016-428. Tool  12  comprises an ultrasonic sonotrode.  
     [0014] Control unit  34  is configured to provide the means for simultaneously controlling the radial compression (i.e., ultrasonic tool  12 ) and the axial compression (i.e., the rams  16 ,  18  via apparatus  21   a  and  21   b ). Control unit  34  may comprise a programmed processor configured to perform the control as described herein.  
     [0015] The friction created by the radial vibrations of tool  12  between the inner surfaces  36   a ,  36   b  of tool  12  that define cavity  14  and the powdered metal placed in cavity  14  is greatest at the axial center of cavity  14 . The friction created is minimal at the axial ends  38   a ,  38   b  of cavity  14 . The friction created provides energy in the form of heat to aid in compressing powdered metal into an individual core  39 . While tool  12  vibrates, first ram  16  and second ram  18  each move toward cavity  14  along axis  20  compressing powdered metal in axial direction. A speed range may vary and may be developed on actual equipment; but slower speeds should provide a more uniform density core.  
     [0016] This combination of radial and axial compression of the powdered metal, preferably simultaneously, compresses the powdered metal to a desired density within at least 96%, more preferably 99%, of the theoretical density of the powdered metal, into a core that can be advantageously used in ignition coils. As an example, iron particles bound together with 0.5% by weight of polyetherimide (i.e., ULTEM® from the General Electric Company) has a theoretical density of 7.613 g/cc. Other encapsulated powdered metals and their theoretical densities are described in U.S. Pat. No. 5,629,092 issued to Gay et al., hereby incorporated by reference. The exact amount of force required may vary and may be experimentally determined on the equipment. One major advantage of the untrasonic energy however is that it reduces drag friction on the sides of the cavity  14  and reduces friction between the particles so the force required may be significantly lower than the 50-60 tons/in 2  normally used for non-ultrasonic presses.  
     [0017] Tool  12  is of a shape such that when powdered metal is placed in cavity  14  and compressed, the resulting shape of completed core  39  is that of a cylinder. FIG. 2 illustrates a perspective view of a completed core  39  with a cylindrical shape. Tool  12  is removable from apparatus  10  and different tools could be used in apparatus  12  to produce cores of varying diameter and length, and potentially shape. Cavity  14  of tool  12  would be the determining factor in the size of the core formed.  
     [0018] First ram  16  and second ram  18  are adjustable in terms of respective travel along axis  20  to enable apparatus  10  to make cores of varying lengths, the limit being the axial length of tool  12 . Rams  16 ,  18  are also controlled by control unit  34 , which allows rams  16 ,  18  to each move toward cavity  14  along axis  20  simultaneously to compress the powdered metal located in cavity  14 . Control unit  34  also controls the operation of power supplies  22 ,  24  (and thereby the radial, ultrasonic compression provided by tool  12 ). Control unit  34 , by controlling both power supplies  22 ,  24  and rams  16 ,  18 , controls the simultaneous axial and radial compression of the powdered metal.  
     [0019] Rams  16 ,  18  are also retractable, both along axis  20  and radially in a plane substantially perpendicular to axis  20 . The retractability aids in removal of the completed core from cavity  14 . By way of example, ram  18  may retract along axis  20  away from cavity  14 . Further, ram  18  may be configured to retract radially so that ram  18  does not impede the removal of the core from cavity  14 , inasmuch as the core is removed along axis  20 . Core removal may be aided by opposing ram  16 , which moves toward cavity  14  along axis  20 , mirroring the movement performed when compressing powdered particles. Ram  16  may push the core out of cavity  14 . Additionally, tool  12  may vibrate briefly to aid in removal of the core by loosening it within cavity  14 . Control unit  34  controls operation of tool  12  and rams  16 ,  18  during core removal.  
     [0020] Referring now to FIG. 3, a method according to the invention for making a core from powdered metal of a magnetically permeable material is provided. First, tool  12  is provided  40  that has cavity  14  of whatever desired length, diameter and shape. Then, powdered metal is placed  42  in cavity  14 . Rams  16 ,  18  then move  44  along axis  20  toward each other into cavity  14  compressing powdered metal in cavity  14 . While rams  16 ,  18  are moving  44 , tool  12  vibrates  46 , aiding in compression of powdered metal, particularly the powdered metal located in the center of cavity  14 . Ram moving step  44  and tool  12  vibrating step  46  are performed for a pre-determined amount of time, long enough to compress the powdered metal into a core with sufficient density to be used in ignition coils. Additional steps include removal of the core from the cavity as previously described above.  
     [0021] The apparatus and method of the present invention have several advantages over the known options for making powdered metal cores. First, the cores that are produced can have the desired cylindrical shape for space efficient design of ignition coil assemblies, while also having a sufficient uniform high density necessary to meet ignition coil performance requirements. Second, the apparatus used does not require use of high voltages and takes less physical space than the apparatus required for electromagnetic compression of powdered metal, making the inventive method more cost efficient. Additionally, the apparatus allows for flexibility in core sizing. Cores of different lengths and diameters can be formed because of the ease with which tool  12  and rams  16 ,  18  can be replaced or adjusted.  
     [0022] It is to be understood that the above description is merely exemplary rather than limiting in nature, the invention being limited only by the appended claims. Various modifications and changes may be made thereto by one of ordinary skill in the art which embody the principles of the invention and fall within the spirit and scope thereof.