JP2017109272A - Ball end mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cut a workpiece provided with a convex part such as a dental prosthesis having a large curvature radius and a fine uneven shape part by one end mill body.SOLUTION: A cutter part 3 is provided at the tip of an end mill body 1 rotated about an axis O. At the tip of the cutter part 3, a spherical bottom blade 7 having a central angle θ of less than 180° at which a rotation locus about the axis O has a center C on the axis O is formed. From the outer peripheral end P of the bottom blade 7 to a rear end side, a convex surface outer peripheral blade 8 that has a curvature radius R larger than that of the bottom blade 7 on a cross-section along the axis O and that comes into contact with the bottom blade 7 at the outer peripheral end P of the bottom blade 7 to swell to the outer peripheral side closer to the rear end, and then is recessed is formed.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a ball end mill suitable for use in cutting a dental prosthesis such as an artificial crown.

  In order to cut the surface of such a dental prosthesis, for example, Patent Documents 1 to 3 propose cutting with a CAD / CAM system using a ball end mill or a tapered ball end mill.

JP-A-8-299365 JP-A-8-299366 Japanese Patent Application Laid-Open No. 2014-068679

  By the way, in a dental prosthesis such as an artificial crown, the side surface has a convex curved surface shape with a relatively large radius of curvature, and the radius of the bottom blade at the tip of the cutting blade portion where the rotation trajectory around the axis forms a hemisphere. Although a large ball end mill can perform efficient cutting, the top surface of the dental prosthesis has a fine irregular shape. Therefore, a ball end mill with a large bottom blade radius cannot perform cutting, and the radius of the bottom blade Another small ball end mill must be prepared. On the other hand, if only the ball end mill having a small radius of the bottom blade is used, it takes a lot of time to cut the side surface of the dental prosthesis having a convex curved shape having a large curvature radius.

  In addition, cutting by the ball end mill on the side surface of such a dental prosthesis is performed by cutting the lower surface side by turning the dental prosthesis upside down after cutting the upper surface side of the side surface with the bottom blade. There is also a problem that burrs are likely to occur at the joint portion between the upper surface side and the lower surface side of the side surface.

  The present invention has been made under such a background, and a workpiece having a convex curved surface portion having a large curvature radius and a portion having a fine uneven shape, such as a dental prosthesis, is provided as one end mill body. An object of the present invention is to provide a ball end mill capable of performing cutting.

  In order to solve the above problems and achieve such an object, according to the present invention, a cutting edge is provided at the tip of the end mill body rotated around the axis, and the tip of the cutting edge is provided at the tip of the cutting edge. A spherical bottom blade whose center angle is less than 180 ° with the rotation trajectory formed around the axis being formed on the axis is formed, and the bottom blade is formed from the outer peripheral end to the rear end side of the bottom blade. A convex curved outer peripheral edge having a larger radius of curvature than the bottom edge in a cross section along the axis, which is recessed toward the inner peripheral side after being inflated toward the outer peripheral side toward the rear end side in contact with the bottom edge at the outer peripheral end of Is formed.

  In the ball end mill having such a configuration, the rotation trajectory of the cutting edge portion has a so-called oval shape, and the rotation trajectory of the bottom blade is spherical with a central angle of less than 180 ° at the tip of the cutting edge portion. That is, since this bottom blade has a substantially hemispherical rotation trajectory like the bottom ball of a normal ball end mill, by making the radius of this hemisphere relatively small, a fine uneven shape on the upper surface of the dental prosthesis is obtained. Cutting can be performed.

  On the other hand, from the front end to the rear end side of the cutting blade part, in the cross section along the axis line, the outer edge of the cutting blade part comes into contact with the outer peripheral end and bulges toward the rear end side, and then toward the inner peripheral side. An outer peripheral blade having a concave convex curve is formed, and the radius of curvature of the convex curve formed by the outer peripheral blade is set larger than the radius of the spherical surface (hemisphere) formed by the rotation locus of the bottom blade. Therefore, with this outer peripheral blade, it is possible to efficiently cut the side surface of a convex prosthesis having a large curvature radius, like a ball end mill having a large bottom blade radius. Cutting of the surface of a workpiece such as a dental prosthesis can be performed reliably and efficiently.

  In addition, since the outer peripheral blade has a convex curve shape that bulges toward the outer peripheral side as it goes toward the rear end side as described above and is recessed toward the inner peripheral side, the side surface of the convex curved surface of the dental prosthesis is cut. When performing, for example, the portion where the outer peripheral blade swells toward the outer peripheral side of the cutting blade portion from the outer peripheral end of the bottom blade toward the rear end side is made to face the upper surface side of the side surface of the dental prosthesis, and the upper surface of the side surface at this portion After the side portion is cut, the lower surface side of the side surface can be cut at the portion where the outer peripheral blade on the rear end side of the cutting edge is recessed toward the inner peripheral side. For this reason, it is possible to prevent burrs from occurring on the side surface of the dental prosthesis after processing as in the case of cutting by a conventional ball end mill.

  Here, it is desirable that the central angle of the spherical surface formed by the rotation locus of the bottom blade is 90 ° or more. If the center angle of this bottom blade whose rotation locus forms a spherical shape is smaller than 90 °, the range of the bottom blade at the tip of the cutting blade portion that cuts the upper surface of the fine uneven dental prosthesis becomes too small. This may cause difficulty in cutting the upper surface.

  In addition, it is desirable that the radius of curvature of the convex curve formed by the outer peripheral blade in the cross section along the axis is not less than three times the radius of the spherical surface formed by the rotation locus of the bottom blade. If the radius of curvature of the outer peripheral blade is less than three times the radius of the bottom blade, the radius of curvature of the outer peripheral blade becomes too small when the radius of the bottom blade is set to be relatively small as described above. There is a risk that it may be difficult to efficiently cut the side surface of the object.

  As described above, according to the present invention, it is possible to perform cutting of a workpiece having a complex uneven shape on the upper surface, such as a dental prosthesis, and having a convex surface with a large radius on one end mill body. The ball end mill can be surely and efficiently performed, and further, it is possible to prevent the occurrence of burrs in the side surface cutting, and to perform high quality cutting.

It is a perspective view which shows one Embodiment of this invention. It is a side view of embodiment shown in FIG. It is an enlarged front view of the cutting edge part in embodiment shown in FIG. It is an expanded sectional view along the axis line of the rotation locus | trajectory of the cutting blade part in embodiment shown in FIG.

  1 to 4 show an embodiment of the present invention. In the ball end mill of this embodiment, the end mill body 1 is integrally formed in a shaft shape centering on the axis O by a hard material such as cemented carbide or high-speed tool steel, and the rear end portion of the end mill body 1 (see FIG. 1 is a cylindrical shank portion 2 centered on the axis O, and a tip portion (a lower left portion in FIG. 1 and a left portion in FIG. 2) is A cutting blade portion 3 is formed, and a neck portion 4 is formed between the shank portion 2 and the cutting blade portion 3.

  The neck portion 4 includes a truncated cone-shaped tapered neck portion 4A centering on an axis O whose outer diameter gradually decreases from the shank portion 2 toward the distal end side, and further extends from the distal end of the tapered neck portion 4A to the distal end side. It is formed of a small-diameter cylindrical straight neck portion 4B centering on the axis O. In such a ball end mill, the shank portion 2 is gripped by the main spindle of the machine tool and rotated in the end mill rotation direction T around the axis O, while the cutting edge portion 3 cuts a workpiece such as a dental prosthesis. Do.

  A plurality of strips (three strips in the present embodiment) are twisted on the outer periphery of the cutting blade portion 3 around the axis O toward the opposite side to the end mill rotation direction T as it goes from the front end portion to the rear end side of the cutting blade portion 3. The discharge grooves 5 are formed at equal intervals in the circumferential direction, and these chip discharge grooves 5 reach the tip of the straight neck portion 4B of the neck portion 4 in the present embodiment. Further, a concave groove-like gash 6 is formed at the tip of these chip discharge grooves 5 so that the bottom surface of the chip discharge groove 5 facing the outer peripheral side of the end mill body 1 is cut out to the inner peripheral side. .

  Then, at the tip of the cutting edge portion 3, a spherical bottom blade 7 having a center angle θ less than 180 ° having a center C on the axis O as shown in FIG. The gash 6 is formed on the outer peripheral edge of the wall surface facing the end mill rotation direction T side. Further, on the outer periphery of the cutting edge portion 3, the outer peripheral edge P is in contact with the bottom blade 7 at the outer peripheral end P from the outer peripheral end P to the rear end side, and then swells toward the outer peripheral side toward the rear end side. A convex curved outer peripheral edge 8 having a radius of curvature larger than that of the bottom edge 7 in the cross section along the axis O that is recessed to the side is formed at the outer peripheral edge of the chip discharge groove 5. The rotation trajectories of the plurality (three) of the bottom blades 7 and the outer peripheral blades 8 formed at the outer peripheral edge portions of the respective gashes 6 and the chip discharge grooves 5 are made to coincide with each other, and the tips of the plurality of bottom blades 7 are axial lines. It crosses almost on O.

  Here, the central angle θ of the spherical surface formed by the rotation locus of the bottom blade 7 is the both ends of an arc drawn by a cross section along the axis O of the rotation locus around the axis O of the bottom blade 7 as shown in FIG. That is, it is an angle formed by two straight lines connecting the outer peripheral edge P of the bottom blade 7 and the center C of the bottom blade 7, and is 90 ° or more in this embodiment. Further, in this embodiment, the rotation trajectory of the outer peripheral blade 8 around the axis O is formed so as to form an arc that is convex toward the outer peripheral side of the cutting blade portion 3 in the cross section along the axis O. The radius R is set to be not less than three times the radius r of the arc formed by the rotation locus of the bottom blade 7 in the same cross section.

  Accordingly, the outer diameter of the cutting edge portion 3 at the position where the outer peripheral blade 8 swells most outward is larger than the outer diameter of the straight neck portion 4B of the neck portion 4. In FIG. 1 to FIG. 3, the rear end of the cutting blade 3 and the tip of the straight neck 4B of the neck 4 are connected through a step, but as shown in FIG. The convex arc formed by the rotation locus may be directly connected to the straight neck portion 4B. Furthermore, in this embodiment, as shown in FIG. 3, the groove width of the chip discharge groove 5 is larger than the thickness in the circumferential direction of the cutting edge portion 3 left between the adjacent chip discharge grooves 5. Is formed.

  When cutting the surface of the dental prosthesis such as an artificial crown as described above by the ball end mill configured as described above, when the concave and convex shape is cut on the upper surface of the dental prosthesis, the tip of the cutting edge portion 3 is used. The bottom blade 7 is used. Since the bottom blade 7 has a spherical rotation locus having a radius r smaller than the radius of curvature of the convex curve formed by the section along the axis O of the rotation locus of the outer peripheral blade 8, the radius of the normal bottom blade is Similar to a small ball end mill, it is possible to form fine irregularities on the upper surface of the dental prosthesis.

  On the other hand, when a convex curved surface having a large curvature radius is cut on the side surface of the dental prosthesis, an outer peripheral blade 8 on the outer periphery of the cutting blade portion 3 extending from the outer peripheral end P of the bottom blade 7 to the rear end side is used. Since the cross section along the axis O of the rotation locus of the outer peripheral blade 8 is a convex curve having a radius of curvature larger than the radius r of the spherical surface formed by the rotation locus of the bottom blade 7, as described above. A convex curved surface having a large radius of curvature can be efficiently formed on the side surface of the dental prosthesis. Therefore, according to the ball end mill having the above-described configuration, it is possible to perform reliable and efficient cutting on the surface of a workpiece such as a dental prosthesis by the ball end mill having one end mill body 1.

  In particular, when cutting the side surface of the dental prosthesis, for example, the outer peripheral blade 8 of the outer peripheral blade 8 swells toward the outer peripheral side of the cutting blade portion 3 from the outer peripheral end P of the bottom blade 7 toward the rear end side. After the portion is made to face the upper surface side portion of the side surface of the dental prosthesis and the upper surface side portion of the side surface is cut by this portion, the outer peripheral blade 8 on the rear end side of the cutting blade portion 3 is continuously provided as it is. Cutting on the lower surface side of the side surface can be performed by the recessed portion on the circumferential side. For this reason, it is possible to prevent the occurrence of burrs at the joint portion between the upper surface side and the lower surface side of the side surface of the dental prosthesis as in the case of cutting with a conventional ball end mill, and to perform high-quality surface cutting. Can do.

  Furthermore, in this embodiment, the central angle θ of the spherical surface formed by the rotation locus of the bottom blade 7 is 90 ° or more, and the above-described uneven shape cutting of the upper surface of the dental prosthesis can be reliably performed. . If the center angle of the bottom blade 7 is less than 90 °, the range in which the bottom blade 7 having a spherical rotation locus is formed at the tip of the cutting blade portion 3 becomes too small, that is, the rotation locus of the bottom blade 7 is the axis. It becomes a flat shape close to a plane perpendicular to O, and it may be difficult to perform uneven cutting of the upper surface that requires a certain depth.

  In the present embodiment, the radius of curvature of the convex curve formed by the outer peripheral blade 8 in the cross section along the axis O (the radius R of the convex arc) is set to be three times or more the radius r of the bottom blade 7. Cutting of the side surface of the dental prosthesis can be performed more reliably and efficiently. That is, when the radius of curvature of the outer peripheral blade 8 is less than three times the radius r of the bottom blade 7, the outer peripheral blade is set when the radius r of the bottom blade 7 is set to be relatively small in order to cut fine irregularities. The curvature radius of 8 is also reduced, and it may be difficult to efficiently perform the cutting of the convex curved side surface having a large curvature radius of the dental prosthesis.

  In this way, in the present embodiment, the convex curve formed by the cross section along the axis O of the rotation locus of the outer peripheral blade 8 is a convex arc having a radius R that is three or more times the radius r of the bottom blade 7. For example, the radius of curvature of the convex curve gradually increases from the outer peripheral edge P of the bottom blade 7 toward the rear end, and the curvature increases from the position where the outer peripheral blade 8 swells most to the outer peripheral side of the cutting edge 3 toward the rear end. An elliptical shape with a gradually decreasing radius may be used. In this case, the maximum curvature radius of the ellipse may be at least three times the radius r of the bottom blade.

  In the present embodiment, the case of cutting the surface of a dental prosthesis such as an artificial crown has been described. Of course, the ball end mill of the present invention may be used for cutting a workpiece other than the dental prosthesis. Is possible.

DESCRIPTION OF SYMBOLS 1 End mill main body 2 Shank part 3 Cutting edge part 4 Neck part 5 Chip discharge groove 6 Gash 7 Bottom blade 8 Outer peripheral edge O End mill main body 1 axis T End mill rotation direction P Outer end of bottom edge 7 C Center of spherical surface formed θ Center angle of spherical surface formed by rotation locus of bottom blade 7 r Radius of spherical surface formed by rotation locus of bottom blade 7 R Radius of curvature of convex curve formed by outer peripheral edge 8 in cross section along axis O (convex arc) Radius)

Claims (3)

  A cutting edge is provided at the tip of the end mill body that rotates about the axis, and the center angle of the rotation locus formed around the axis is 180 ° at the tip of the cutting edge. A spherical bottom blade less than the bottom blade is formed, and from the outer peripheral end to the rear end side of the bottom blade, the outer peripheral end of the bottom blade comes into contact with the bottom blade and swells toward the rear end side toward the rear end side. A ball end mill characterized in that a convex curved outer peripheral blade having a radius of curvature larger than that of the bottom blade is formed in a cross section along the axis which is recessed later on the inner peripheral side.   The ball end mill according to claim 1, wherein a central angle of a spherical surface formed by the rotation locus of the bottom blade is 90 ° or more.   The radius of curvature of the convex curve formed by the outer peripheral blade in a cross section along the axis is not less than three times the radius of the spherical surface formed by the rotation trajectory of the bottom blade. Ball end mill.

Images