JPS6363325B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ball end mill used for cutting molds, etc., and is particularly suitable for small diameter end mills by improving the cutting blade configuration. Conventionally, this type of small-diameter ball end mill has been difficult to manufacture because the small diameter of the cutting edge restricts the shape of the grinding wheel, and as a result, high sphericity cannot be achieved. In addition, due to the rigidity of the tool, it is not possible to create a large chip pocket during cutting.
The result was unsatisfactory. Furthermore, it has been difficult for the user to achieve reproducibility by re-grinding. For these reasons, there is a demand for the development of a small-diameter ball end mill that has a cutting edge configuration that facilitates cutting edge grinding and facilitates chip evacuation. The present invention has been made in view of the above points, and includes a cylindrical handle, a blade whose basic shape is a small elliptical cylinder formed at one end of the handle, and a tip of the blade. The present invention provides an improved ball end mill having a cutting edge ridge formed in the shape of a ball end mill. That is, the blade portion is arranged so as to be offset from one half of the handle portion having a circular cross section,
Moreover, one side surface on the short axis side constituting the ellipse is approximately inscribed in the axial center line of the handle when viewed from the end face direction. In addition, this blade part is set at an inclination angle θ with respect to the axial center line of the handle part, and is obliquely cut in the short axis direction by this inclination angle θ, so that the oblique surface obtained by this is seen in the vertical direction. The basic shape is a circular surface. Furthermore, in the approximately mid-plane region between the beveled start point and the end point of the blade,
It is designed to have upturned grooves. On the other hand, the cutting edge is composed of two arcuate cutting edges and one outer circumferential cutting edge.
The two arcuate cutting edge edges are formed separately on the bevel start point side and the end point side due to the existence of the cut-up groove and the uncut portion on the opposing circumferential side of the cut-up groove. Moreover, the outer circumferential cutting edge edge is formed adjacent to the arcuate cutting edge edge on the end point side due to the presence of the up-cut groove. Hereinafter, an embodiment of the ball end mill of the present invention will be described with reference to the drawings. In FIGS. 1 to 4, reference numeral 1 denotes a cylindrical handle portion, and a blade portion 2 having a basic shape of a small elliptical cylinder is attached to one end of the handle portion so as to be offset. As shown in FIG. 3, the deviation with respect to the handle 1 is such that one side of the short axis side of the ellipse is
It is substantially inscribed in the axial center line 3 of the handle 1, and the other side is substantially inscribed in the outer surface of the handle 1. In this case, the inscription on the other side surface is not inevitable because it changes depending on the required diameter of the cutting edge. Furthermore, this blade part 2 has an axis center line 3 of the handle part 1.
An inclination angle θ is set with respect to the inclination angle θ, and the inclination angle θ is used to obliquely cut in the short axis direction. As a result, the oblique surface 4 obtained has a substantially circular surface when viewed in the vertical direction. The ridge line portion formed by this circular surface is used as the ridge of the cutting edge so that it can participate in spherical cutting. This takes advantage of the fact that if a sphere is cut with a plane, a circular surface is formed, and the locus of rotation of this circular ridge line becomes a part of the sphere. In a ball end mill, since the starting point of the cutting edge must be located near the center of rotation, the angle of inclination θ is set with respect to the shaft center line 3. Moreover, regarding the ellipse used as the blade body part 2, when the radius of the sphere to be cut is R,
It is derived using the following calculation formula. Length of major axis = 2R・cosθ Length of short axis = 2R・cosθ・sinθ However, the ball end mill of the present invention
It is intended not only for hemispherical cutting, but also for subsequent shoulder cutting. Therefore, an up-cut groove 5 extending in the axial direction is formed at a substantially intermediate circumferential surface portion between the start point of the oblique cut and the end point of the cut-up, and the ridge line portion thereof is defined as an outer circumferential cutting edge ridge 6. Further, a non-cut portion 7 is formed on the opposing peripheral surface side of the cut groove 5 by providing a chamfered portion, for example. Therefore, in the ball end mill of the present invention, two arcuate cutting edge edges 8 and 9 and one outer peripheral cutting edge edge 6 are formed as the cutting edge edges. That is, the two arcuate cutting edge edges 8 and 9 are formed separately on the oblique cutting start point side and the end point side due to the existence of the up-cut groove 5 and the non-cutting portion 7, and the outer circumferential cutting edge edge 6 is Due to the presence of the cut groove 5, it is formed adjacent to the arcuate cutting edge 9 on the end point side. Therefore, as seen in FIG. 3, on the arcuate cutting edge 8 side, the convexly curved elliptical side surface becomes the rake surface, and on the arcuate cutting edge 9 side, the oblique cutting surface 4 becomes the rake surface. In addition, since the cutting of the shoulder part was taken into consideration by forming the cut-up groove 5, if the sphericity of the spherical surface to be cut is required, theoretically one side of the short axis should be placed on the center line 3. The angle of inclination θ should be set to 45°. Therefore, in this case, the length of the minor axis of the ellipse is R from the above-mentioned calculation formula, and the length of the major axis is √2R. However, since the ball end mill of the present invention is usually applied to small diameter ones, the sphericity does not matter much even if the inclination angle θ is set in the range θ=40° to 45°. In this embodiment, the handle portion 1 and the blade portion 2 are integrally formed of cemented carbide, high-speed steel, or the like. However, it is also possible to apply only the blade portion 2 made of cemented carbide. Next, cutting examples using the ball end mill of the present invention will be explained. When using the tool of the present invention, the radius R of the sphere to be cut is 3 mm, and the inclination angle θ of the blade part 2 is
is set to 40°, and the length of the major axis = 4.596 mm and the length of the minor axis = 2.954 mm using the calculation formula described above.
As shown in FIG. 4, the arcuate cutting edge edges 8 and 9 were each formed to be 1/4 circle when viewed in a direction perpendicular to the oblique surface 4. In addition, the rotation speed of the tool was set to 2000 rpm (the cutting speed was 38 m/min at the outer diameter), and the FC25
and S50C with good results.

[Table] As described above, in the present invention, the blade portion 2 exhibiting an oval shape in cross section is provided on the handle portion 1, and is beveled at an inclination angle θ, thereby forming two arcuate cutting blades. Since the ridges 8, 9 and one outer cutting edge ridge 6 are formed, the following effects are obtained. First, the cutting edge can be formed with high accuracy and easily. This is because the elliptical shape and inclination angle θ of the blade body portion 2 need only be made accurate, and no special grinding such as giving an clearance angle is required. Second, the user can easily perform re-grinding, and the reproducibility of the shape of the cutting edge can be reliably obtained. This is because this can be reproduced by grinding the oblique surface 4 having the above-mentioned inclination angle θ and by grinding the chamfered portion 7. Thirdly, the cutting action and chip evacuation are also good. This is because the arcuate cutting edges 8 and 9 are convexly curved, so the strength of the cutting edge is high, and a large inclination angle θ can be achieved. Therefore, even a small diameter ball end mill can be applied to shoulder milling.

[Brief explanation of drawings]

FIG. 1 is a front view showing an embodiment of the ball end mill of the present invention, FIG. 2 is a side view thereof, FIG. 3 is a bottom view, and FIG. 4 is a bottom view from an oblique direction. DESCRIPTION OF SYMBOLS 1... Handle part, 2... Blade body part, 3... Shaft center line, 4... Oblique cut surface, 5... Cut-up groove, 6... Outer periphery cutting edge ridge, 7... Chamfered part, 8, 9... Circular cutting edge ridge.

Claims (1)

[Claims] 1. A cylindrical handle 1, and a blade 2 whose basic shape is a small elliptical cylinder formed at one end of the handle 1.
and a cutting edge 6 formed at the tip of this blade body part 2,
8 and 9, the blade part 2 is connected to one half of the handle part 1 having a circular cross section so as to be offset from one side thereof, and furthermore, the blade part 2 is provided with a short part forming an ellipse. One side surface on the shaft side is substantially inscribed in the shaft center line 3 of the handle part 1 when viewed from the end face direction, and is obliquely cut in the short axis direction by an inclination angle θ with respect to the shaft center line 3, thereby obtaining an advantage. The beveled surface 4 has a basic circular shape when viewed in the vertical direction, and a cut-up groove 5 is provided at an approximately intermediate circumferential surface portion between the bevel start point and the cut-up end point.
The cutting edge ridges 6, 8, 9 are composed of two arcuate cutting edge ridges 8, 9 and one outer peripheral cutting edge ridge 6; is formed separately on the bevel start point side and the end point side due to the existence of the cut-up groove 5 and the uncut portion 7 on the opposite peripheral surface side of the cut-up groove 5,
Further, the ball end mill is characterized in that the outer peripheral cutting edge ridge 6 is formed adjacent to the arcuate cutting edge 9 on the end point side due to the presence of the upward cutting groove 5.