Method for manufacturing coil-embedded dust core and coil-embedded dust core

Abstract

It is an object to provide a method for manufacturing a coil-embedded dust core with a small variation in inductance value with efficiency and the like. A step (a) of charging soft magnetic metal powder including an insulating material, composing a green body 10 , so as to cover a coil 1 , and a step (b) of compacting the soft magnetic metal powder covering the coil 1 in an axial direction of the coil 1 are included, and in the step (b), the soft magnetic metal powder is compacted while an amount of the soft metal powder charged into the part corresponding to the winding section is kept smaller than an amount of the soft magnetic metal powder charged into the other part that are not corresponding to the winding section, with an upper surface or a lower surface of the winding section as a reference. Thereby, a coil-embedded dust core with entirely uniform density can be obtained, and according to the coil-embedded dust core with entirely uniform density, a variation in inductance value is reduced and it becomes possible to obtain a predetermined inductance value with stability.

1 . A method for manufacturing a coil-embedded dust core constructed by embedding an air-core coil having a winding section and end sections led out of said winding section in a green body, comprising: 
 a step (a) of charging soft magnetic metal powder including an insulating material, composing said green body, so as to cover said air-core coil; and    a step (b) of compacting said soft magnetic metal powder covering said air-core coil in an axial direction of said air-core coil,    wherein in said step (b), said soft magnetic metal powder is compacted while an amount of said soft metal powder charged into a part corresponding to said winding section is kept smaller than an amount of said soft magnetic metal powder charged into the other part that is not corresponding to said winding section, with an upper surface or a lower surface of said winding section as a reference.    
   
   
       2 . A method for manufacturing the coil-embedded dust core according to  claim 1 , wherein said other part is a part corresponding to a hollow part of said air-core coil.  
   
   
       3 . A method for manufacturing the coil-embedded dust core according to  claim 1 , wherein in said step (b), a compression ratio of said soft magnetic metal powder in a part corresponding to the maximum number of windings out of said winding section and a compression ratio of said soft magnetic metal powder in said other part are equal.  
   
   
       4 . A method for manufacturing the coil-embedded dust core according to  claim 1 , wherein a density of said green body in the vicinity of an upper surface or a lower surface of the part corresponding to the maximum number of windings out of said winding section and a density of said green body in said other part are equal.  
   
   
       5 . A method for manufacturing a coil-embedded dust core in which an air-core coil is embedded in a green body with use of a die machine comprising a upper die set including an upper die and a top punch ascending and descending inside said upper die, and a lower die set including a lower die and a bottom punch ascending and descending inside said lower die, comprising: 
 a step (a) of charging soft magnetic metal powder including an insulation material, composing said green body, into a cavity of said lower die equipped with a tubular member, which has a top portion in substantially the same shape as the plane shape of said air-core coil, in said bottom punch to be ascendable and descendable;    a step (b) of placing said air-core coil concentrically with said tubular member in a state in which it ascends to a predetermined position, inside the cavity of said lower die with said soft magnetic metal powder being charged therein;    a step (c) of lowering said upper die to said lower die, and further charging said soft magnetic metal powder into a cavity of said upper die so as to cover said air-core coil; and    a step (d) of compacting said soft magnetic metal powder in an axial direction of said air-core coil by relatively lowering said top punch with respect to said bottom punch.    
   
   
       6 . A method for manufacturing the coil-embedded dust core according to  claim 5 , wherein 
 said air-core coil is a coil made by winding a flat conductor, including a winding section being insulation coated and end sections led out of said winding section, and    prior to said step (a), said method further comprises a step of controlling a relative position of said lower die, said bottom punch and said tubular member in a compacting direction according to thickness of said winding section of said air-core coil in the axial direction.    
   
   
       7 . A method for manufacturing the coil-embedded dust core according to  claim 5 , wherein 
 said air-core coil is a coil made by winding a flat conductor, including a winding section being insulation coated and end sections led out from said winding section, and    in said step (d), said upper die, said lower die and said tubular member relatively descend to a predetermined position with respect to said bottom punch while a state in which said end sections of said air-core coil are held between said upper die and said lower die is kept and in synchronism with the movement to relatively lower said top punch with respect to said bottom punch.    
   
   
       8 . A coil-embedded dust core comprising: 
 a green body in a rectangular parallelepiped shape having a front and back surfaces opposed to each other with a predetermine distance and a side surface formed on perimeters of said front and back surfaces; and    an air-core coil having a winding section and end sections led out from said winding section, with at least said winding section being placed in said green body,    wherein densities of said green body are equal in a part corresponding to a maximum number of windings out of said winding section and a hollow part of said air-core coil.    
   
   
       9 . A coil-embedded dust core according to  claim 8 , wherein 
 a difference in density between the part corresponding to the maximum number of windings out of said winding section and the hollow part of said air-core coil is 0.3 g/cm 3  or less.    
   
   
       10 . A coil-embedded dust core according to  claim 8 , wherein said air-core coil is constructed by a rectangular wire.  
   
   
       11 . A coil-embedded dust core according to  claim 8 , wherein part of said air-core coil functions as a terminal section.  
   
   
       12 . A coil-embedded dust core according to  claim 8 , wherein said end sections are exposed to an outside of said green body from a center of the side surface of said green body with a thickness direction of said green body as the reference.