Patent Publication Number: US-2021178489-A1

Title: Diamond-coated tool

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of application No. PCT/JP2020/007685, filed on Feb. 26, 2020, and claims the benefit of priority from Japanese Patent Application No. 2019-040859, filed on Mar. 6, 2019 and the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to a diamond-coated tool obtained by diamond-coating a tool base material. 
     In the related art, tools obtained by diamond-coating a cemented carbide insert base material are used for cutting hard materials such as ceramics, cemented carbide, and carbon fiber reinforced plastic (CFRP). Single-crystalline diamond tools or polycrystalline diamond tools are also used for cutting such hard materials, but due to their high cost, diamond-coated tools have a significant advantage in terms of cost. 
     JP H06-335806 A discloses a throw-away insert obtained by diamond-coating an insert base material. In such a throw-away insert, in order to prevent a cutting edge of a coated layer from being damaged when a coated rake face is held by a clamping means, a portion, near the cutting edge, of the rake face of the insert base material is lowered one  step relative to a center portion of the rake face. 
       FIG. 1  shows a structure of a portion around a cutting edge of a diamond-coated tool  50  known in the related art. The diamond-coated tool  50  is manufactured by diamond-coating a portion around a cutting edge  53  of a tool base material  51  made of cemented carbide and has a diamond-coated layer  52  provided on the cutting edge  53 , a rake face  54 , and a flank face  55  of the tool base material  51 . In  FIG. 1 , an X-axis direction represents a cutting thickness direction during a cutting process with the diamond-coated tool  50 , and a Y-axis direction represents a cutting direction during the cutting process. 
     When adhesion between the tool base material  51  and the diamond-coated layer  52  in the diamond-coated tool  50  is not high, and a workpiece has ultra-high hardness or a cutting force increases due to an increase in wear on the cutting edge, the diamond-coated layer  52  tends to separate off from the tool base material  51 . 
     Examples of the measures to be taken to solve this problem include adjusting the composition of the cemented carbide (for example, reducing the proportion of Co serving as a binder), and increasing the surface roughness of the base material to bring about an anchor effect, but such measures are not adequate for solving the problem, and the separation problem still remains.  
     SUMMARY 
     The present disclosure has been made in view of such circumstances, and it is therefore an object of the present disclosure to provide a structure for suppressing separation of a diamond-coated layer from a tool base material in a diamond-coated tool. 
     In order to solve the above-described problem, one aspect of the present disclosure relates to a diamond-coated tool obtained by diamond-coating a tool base material including a rake face, a flank face, and a cutting edge serving as a boundary between the rake face and the flank face. In the diamond-coated tool according to this aspect, the flank face of the tool base material includes a first flank face continuously extending to the cutting edge, a second flank face located farther away from the cutting edge than the first flank face and located outside the first flank face when viewed from an inside of the tool base material, and a flank face-side stepped portion connecting the first flank face and the second flank face. The diamond-coated layer is provided on the cutting edge, the first flank face, and the flank face-side stepped portion. 
     Another aspect of the present disclosure relates to a diamond-coated tool obtained by diamond-coating a tool base material including a rake face, a flank face, and a cutting edge serving as a boundary between the rake face and the flank face. In the diamond-coated tool according to this  aspect, the rake face of the tool base material includes a first rake face continuously extending to the cutting edge, a second rake face located farther away from the cutting edge than the first rake face and located outside the first rake face when viewed from an inside of the tool base material, and a rake face-side stepped portion connecting the first rake face and the second rake face. The diamond-coated layer is provided on the first rake face and the rake face-side stepped portion, and the rake face of the diamond-coated tool is made flat. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a structure around a cutting edge of a diamond-coated tool known in the related art; 
         FIG. 2  is a diagram showing a shape of a tool base material according to an embodiment; 
         FIG. 3  is an enlarged cross-sectional view of a flank face-side stepped portion; 
         FIG. 4  is a diagram showing a structure of a diamond-coated tool; 
         FIG. 5  is a diagram showing another example of the structure of the diamond-coated tool; and 
         FIG. 6  is a diagram showing yet another example of the structure of the diamond-coated tool.  
     
    
    
     DETAILED DESCRIPTION 
     The disclosure will now be described by reference to the preferred embodiments. This does not intend to limit the scope of the present disclosure, but to exemplify the disclosure. 
     A description will be given below of a diamond-coated tool according to the embodiment. 
       FIG. 2  shows a shape of a tool base material  1  according to the embodiment. The tool base material  1  includes a rake face  10 , a flank face  20 , and a cutting edge  2  serving as a boundary between the rake face  10  and the flank face  20 . The diamond-coated tool is manufactured by diamond-coating a portion around the cutting edge  2  of the tool base material  1 . 
     The flank face  20  of the tool base material  1  includes a first flank face  21  continuously extending to the cutting edge  2 , a second flank face  23  located farther away from the cutting edge  2  than the first flank face  21 , and a flank face-side stepped portion  22  connecting the first flank face  21  and the second flank face  23 . When viewed from the inside of the tool base material  1 , the second flank face  23  is located outside the first flank face  21 . In other words, when the first flank face  21  and the second flank face  23  are viewed in their respective orthogonal directions from the inside of the tool base material  1 , the second flank face  23  is located on a side larger in cutting part thickness than  the first flank face  21 . The first flank face  21  and the second flank face  23  may be provided as planate or flat surfaces and be approximately parallel to each other. For example, the first flank face  21  and the flank face-side stepped portion  22  may be provided by cutting out the second flank face  23  provided as a planate or flat surface extending up to the cutting edge. 
     The rake face  10  of the tool base material  1  includes a first rake face  11  continuously extending to the cutting edge  2 , a second rake face  13  located farther away from the cutting edge  2  than the first rake face  11 , and a rake face-side stepped portion  12  connecting the first rake face  11  and the second rake face  13 . When viewed from the inside of the tool base material  1 , the second rake face  13  is located outside the first rake face  11 . In other words, when the first rake face  11  and the second rake face  13  are viewed in their respective orthogonal directions from the inside of the tool base material  1 , the second rake face  13  is located on a side larger in cutting part thickness than the first rake face  11 . The first rake face  11  and the second rake face  13  may be provided as planate or flat surfaces and be approximately parallel to each other. For example, the first rake face  11  and the rake face-side stepped portion  12  may be provided by cutting out the second rake face  13  provided as a planate or flat surface extending up to the cutting edge.  
       FIG. 3  is an enlarged cross-sectional view of the flank face-side stepped portion. As shown in  FIG. 3 , a boundary P between the flank face-side stepped portion  22  and the first flank face  21  and a boundary Q between the flank face-side stepped portion  22  and the second flank face  23  are defined. An inclined surface of the flank face-side stepped portion  22  may be a plane connecting the boundary P and the boundary Q, but as shown in  FIG. 3 , the inclined surface may be located on a deep side relative to the plane connecting the boundary P and the boundary Q when viewed from the outside of the tool base material  1  (specifically, the inclined surface of the flank face-side stepped portion  22  may be concave relative to the plane connecting the boundary P and the boundary Q when viewed from the outside of the tool base material  1 ). 
     When an intersection point between an imaginary surface extending from the first flank face  21  toward the inside of the tool base material  1  and a perpendicular line drawn from the boundary Q is denoted by R, a distance W between the boundary P and the intersection point R is preferably smaller than a distance H between the boundary Q and the intersection point R. Specifically, in  FIG. 3 , it is preferable that an angle formed by a line segment PR and a line segment PQ be equal to or greater than 45 degrees. Further, when the inclined surface of the flank face-side stepped portion  22  is concave relative to the plane  connecting the boundary P and the boundary Q, it is preferable that an angle formed by the line segment PR and a tangent to the concave shape at a point near the boundary Q be approximately equal to 90 degrees. Note that a structure may be employed where the boundary P is located near the intersection point R, the angle formed by the line segment PR and the line segment PQ is approximately equal to 90 degrees, and the flank face-side stepped portion  22  is a wall surface approximately perpendicular to the first flank face  21 . 
     Note that  FIG. 3  shows the structure of the flank face-side stepped portion  22  provided on the flank face  20 , but the rake face-side stepped portion  12  provided on the rake face  10  may be the same in structure as the flank face-side stepped portion  22  shown in  FIG. 3 . 
       FIG. 4  shows a structure of a diamond-coated tool  3  obtained by diamond-coating the tool base material  1 . A diamond-coated layer  30  is provided on the cutting edge  2 , the rake face  10 , and the flank face  20  of the tool base material  1 . A cutting part  31  having a radius approximately equal to a layer thickness is provided at the cutting edge  2  of the tool base material  1 . The layer thickness of the diamond-coated layer  30  is preferably equal to or smaller than the distance H (see  FIG. 3 ). In  FIG. 4 , the X-axis direction represents a cutting thickness direction during a cutting process with the diamond-coated tool  3 , and the Y-axis direction represents a cutting direction during the  cutting process. 
     On the flank face  20 , the diamond-coated layer  30  is provided on at least the first flank face  21  and the flank face-side stepped portion  22 . Herein, providing the diamond-coated layer  30  on the first flank face  21  and the flank face-side stepped portion  22  corresponds to bringing the diamond-coated layer  30  into close contact with the first flank face  21  and the flank face-side stepped portion  22 . 
     When the cutting part  31  receives a cutting force from a workpiece during the cutting process with the diamond-coated tool  3 , the diamond-coated layer  30  provided on the flank face  20  receives a shearing load, produced by the cutting force, in the extending direction of the first flank face  21 . At this time, the flank face-side stepped portion  22  serves as a separation suppressing structure that suppresses shear separation between the first flank face  21  and the diamond-coated layer  30  caused by receiving the shearing load applied to the diamond-coated layer  30 . 
     On the rake face  10 , the diamond-coated layer  30  is provided on at least the first rake face  11  and the rake face-side stepped portion  12 . Herein, providing the diamond-coated layer  30  on the first rake face  11  and the rake face-side stepped portion  12  corresponds to bringing the diamond-coated layer  30  into close contact with the first rake face  11  and the rake face-side stepped portion  12 . 
     During the cutting process with the diamond-coated  tool  3 , the diamond-coated layer  30  provided on the rake face  10  receives a shearing load, produced by the cutting force, in the extending direction of the first rake face  11 . At this time, the rake face-side stepped portion  12  serves as a separation suppressing structure that suppresses shear separation between the first rake face  11  and the diamond-coated layer  30  caused by receiving the shearing load applied to the diamond-coated layer  30 . 
     Note that, in order to cut a high-hardness workpiece, with a cutting edge strength taken into consideration, cutting process is performed usually with a cutting thickness smaller than the thickness of the coated layer (that is, smaller than the round radius of the cutting edge of a typical coated tool). In such cutting process, an actual rake angle is often determined by the round radius of the cutting edge and the cutting thickness, but the diamond-coated tool  3  according to the embodiment may be formed such that a designed rake angle becomes a negative angle. When the designed rake angle is a positive angle (see  FIG. 1 ), the direction of the cutting force applied to the cutting part  31  and the extending direction of the rake face  10  are close to each other, so that the shearing load produced by the cutting force becomes large. On the other hand, when the designed rake angle is a negative angle, a difference between the direction of the cutting force and the extending direction of the rake face  10  becomes large, so that the shearing load  produced by the cutting force becomes small. Therefore, in the diamond-coated tool  3  according to the embodiment, setting the cutting edge angle (cutting tool angle) of the tool base material  1  equal to or greater than 90 degrees makes the designed rake angle negative to reduce the shearing load applied, in a direction parallel to the rake face  10 , between the diamond-coated layer  30  and the tool base material  1 . 
     In the diamond-coated tool  3  according to the embodiment, the separation suppressing structure is provided on at least the flank face  20 . Providing the separation suppressing structure on the flank face  20  makes it possible to suppress shear separation of the diamond-coated layer  30  on the flank face  20 . When the separation suppressing structure is provided on only the flank face  20 , it is preferable that the diamond-coated tool  3  be used such that the designed rake angle becomes a negative angle as described above. Note that the separation suppressing structure may be further provided on the rake face  10 . 
       FIG. 5  shows another example of the structure of the diamond-coated tool  3 . A diamond-coated layer  30  is provided on the cutting edge  2 , the rake face  10 , and the flank face  20  of the tool base material  1 . In  FIG. 5 , the X-axis direction represents a cutting thickness direction during the cutting process with the diamond-coated tool  3 , and the Y-axis direction represents a cutting direction  during the cutting process. 
     On the flank face  20 , the diamond-coated layer  30  is provided on the first flank face  21  and the flank face-side stepped portion  22 , but is not provided on the second flank face  23 . With reference to  FIG. 4 , when diamond-coating is applied to the second flank face  23 , a convex portion of the diamond-coated layer  30  protruding in the cutting thickness direction is formed near the boundary between the flank face-side stepped portion  22  and the second flank face  23 . This convex portion may come into contact with a finished surface of the workpiece; therefore, in the diamond-coated tool  3  shown in  FIG. 5 , no diamond-coated layer  30  is provided on the second flank face  23  to prevent the convex portion from being formed. 
     Therefore, in the manufacturing process of the diamond-coated tool  3 , before the coating process, a predetermined preprocessing may be performed to prevent the second flank face  23  from being coated with diamond. As another manufacturing procedure, after the diamond-coated layer  30  is formed on the flank face  20  by the coating process, the diamond-coated layer  30  formed on the second flank face  23  may be eliminated. In this elimination process, the diamond-coated layer  30  may be eliminated, to the extent of not coming into contact with the finished surface of the workpiece, and it is not necessary to eliminate all of the diamond-coated layer  30  formed on the second flank face  23 .  
       FIG. 6  shows yet another example of the structure of the diamond-coated tool  3 . A diamond-coated layer  30  is provided on the cutting edge  2 , the rake face  10 , and the flank face  20  of the tool base material  1 . In  FIG. 6 , the X-axis direction represents a cutting thickness direction during the cutting process with the diamond-coated tool  3 , and the Y-axis direction represents a cutting direction during the cutting process. 
     On the rake face  10 , the diamond-coated layer  30  is provided on the first rake face  11  and the rake face-side stepped portion  12 , but is not provided on the second rake face  13 . With reference to  FIG. 5 , when diamond-coating is applied to the second rake face  13 , a portion of the diamond-coated layer  30  around the rake face-side stepped portion  12  protrudes outward. This shape may hinder the outflow of chips, and therefore, in the diamond-coated tool  3  shown in  FIG. 6 , the diamond-coated layer  30  is not provided on the second rake face  13  to make the diamond-coated layer  30  on the first rake face  11  and the rake face-side stepped portion  12  flush with the second rake face  13 . Note that the structure where the diamond-coated layer  30  and the second rake face  13  are flush with each other includes a structure where the diamond-coated layer  30  and the second rake face  13  are connected, to the extent of not hindering the outflow of chips and are approximately flush with each other. 
     In the manufacturing process of the diamond-coated  tool  3 , after being formed on the rake face  10 , the diamond-coated layer  30  may be eliminated to make the rake face of the diamond-coated tool  3  flat. At this time, as shown in  FIG. 6 , all of the diamond-coated layer  30  provided on the second rake face  13  may be eliminated, but the elimination of the diamond-coated layer  30  is performed to make the rake face of the diamond-coated tool  3  flat so as not to hinder the outflow of chips; therefore, the diamond- coated layer  30  may remain on the second rake face  13 . 
     The present disclosure has been described on the basis of the embodiment. It is to be understood by those skilled in the art that the embodiment is illustrative and that various modifications are possible for a combination of components or processes, and that such modifications are also within the scope of the present disclosure. 
     An outline of aspects of the present disclosure is as follows. One aspect of the present disclosure relates to a diamond-coated tool obtained by diamond-coating a tool base material including a rake face, a flank face, and a cutting edge serving as a boundary between the rake face and the flank face. In this diamond-coated tool, the flank face of the tool base material includes a first flank face continuously extending (connected) to the cutting edge, a second flank face located farther away from the cutting edge than the first flank face and located outside the first flank face when viewed from an inside of the tool base material,  and a flank face-side stepped portion connecting the first flank face and the second flank face. The diamond-coated layer may be provided on the cutting edge, the first flank face, and the flank face-side stepped portion. 
     According to this aspect, the flank face-side stepped portion serves as a separation suppressing structure to suppress separation of the diamond-coated layer on the flank face. 
     The rake face of the tool base material includes a first rake face continuously extending (connected) to the cutting edge, a second rake face located farther away from the cutting edge than the first rake face and located outside the first rake face when viewed from the inside of the tool base material, and a rake face-side stepped portion connecting the first rake face and the second rake face. The diamond-coated layer may be provided on the first rake face and the rake face-side stepped portion. In this structure, the rake face-side stepped portion serves as a separation suppressing structure to suppress separation of the diamond-coated layer on the rake face. 
     Another aspect of the present disclosure relates to a diamond-coated tool obtained by diamond-coating a tool base material including a rake face, a flank face, and a cutting edge serving as a boundary between the rake face and the flank face. In this diamond-coated tool, the rake face of the tool base material includes a first rake face  continuously extending (connected) to the cutting edge, a second rake face located farther away from the cutting edge than the first rake face and located outside the first rake face when viewed from an inside of the tool base material, and a rake face-side stepped portion connecting the first rake face and the second rake face. The diamond-coated layer is provided on the first rake face and the rake face-side stepped portion, and the rake face of the diamond-coated tool is made flat. 
     According to this aspect, the rake face-side stepped portion serves as a separation suppressing structure to suppress separation of the diamond-coated layer on the rake face, and the rake face after the diamond-coating is made flat to allow chips to flow out smoothly. The diamond-coated layer need not be provided on the second rake face. 
     A shearing load applied to the diamond-coated layer on the rake face may be reduced by setting an angle of the cutting edge equal to or larger than 90 degrees and setting a designed rake angle to a negative angle.